Open Shortest Path First (OSPF) is a link-state IGP developed by the OSPF working group of the IETF. OSPF version 2 is used for IPv4. OSPF refers to OSPFv2 throughout this chapter.

OSPF features

OSPF has the following features:

· Wide scope—Supports multiple network sizes and several hundred routers in an OSPF routing domain.

· Fast convergence—Advertises routing updates instantly upon network topology changes.

· Loop free—Computes routes with the SPF algorithm to avoid routing loops.

· Area-based network partition—Splits an AS into multiple areas to facilitate management. This feature reduces the LSDB size on routers to save memory and CPU resources, and reduces route updates transmitted between areas to save bandwidth.

· ECMP routing—Supports multiple equal-cost routes to a destination.

· Routing hierarchy—Supports a 4-level routing hierarchy that prioritizes routes into intra-area, inter-area, external Type-1, and external Type-2 routes.

· Authentication—Supports area- and interface-based packet authentication to ensure secure packet exchange.

· Support for multicasting—Multicasts protocol packets on some types of links to avoid impacting other devices.

OSPF packets

OSPF messages are carried directly over IP. The protocol number is 89.

OSPF uses the following packet types:

· Hello—Periodically sent to find and maintain neighbors, containing timer values, information about the DR, BDR, and known neighbors.

· Database description (DD)—Describes the digest of each LSA in the LSDB, exchanged between two routers for data synchronization.

· Link state request (LSR)—Requests needed LSAs from a neighbor. After exchanging the DD packets, the two routers know which LSAs of the neighbor are missing from their LSDBs. They then exchange LSR packets requesting the missing LSAs. LSR packets contain the digest of the missing LSAs.

· Link state update (LSU)—Transmits the requested LSAs to the neighbor.

· Link state acknowledgment (LSAck)—Acknowledges received LSU packets. It contains the headers of received LSAs (an LSAck packet can acknowledge multiple LSAs).

LSA types

OSPF advertises routing information in Link State Advertisements (LSAs). The following LSAs are commonly used:

· Router LSA—Type-1 LSA, originated by all routers and flooded throughout a single area only. This LSA describes the collected states of the router's interfaces to an area.

· Network LSA—Type-2 LSA, originated for broadcast and NBMA networks by the designated router, and flooded throughout a single area only. This LSA contains the list of routers connected to the network.

· Network Summary LSA—Type-3 LSA, originated by Area Border Routers (ABRs), and flooded throughout the LSA's associated area. Each summary-LSA describes a route to a destination outside the area, yet still inside the AS (an inter-area route).

· ASBR Summary LSA—Type-4 LSA, originated by ABRs and flooded throughout the LSA's associated area. Type 4 summary-LSAs describe routes to Autonomous System Boundary Router (ASBR).

· AS External LSA—Type-5 LSA, originated by ASBRs, and flooded throughout the AS (except stub and NSSA areas). Each AS-external-LSA describes a route to another AS.

· NSSA LSA—Type-7 LSA, as defined in RFC 1587, originated by ASBRs in NSSAs and flooded throughout a single NSSA. NSSA LSAs describe routes to other ASs.

· Opaque LSA—A proposed type of LSA. Its format consists of a standard LSA header and application specific information. Opaque LSAs are used by the OSPF protocol or by some applications to distribute information into the OSPF routing domain. The opaque LSA includes Type 9, Type 10, and Type 11. The Type 9 opaque LSA is flooded into the local subnet, the Type 10 is flooded into the local area, and the Type 11 is flooded throughout the AS.

OSPF areas

Area-based OSPF network partition

In large OSPF routing domains, SPF route computations consume too many storage and CPU resources, and enormous OSPF packets generated for route synchronization occupy excessive bandwidth.

To resolve these issues, OSPF splits an AS into multiple areas. Each area is identified by an area ID. The boundaries between areas are routers rather than links. A network segment (or a link) can only reside in one area as shown in Figure 1.

You can configure route summarization on ABRs to reduce the number of LSAs advertised to other areas and minimize the effect of topology changes.

Figure 1 Area-based OSPF network partition

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Backbone area

Each AS has a backbone area that distributes routing information between non-backbone areas. Routing information between non-backbone areas must be forwarded by the backbone area. OSPF has the following requirements:

· All non-backbone areas must maintain connectivity to the backbone area.

· The backbone area must maintain connectivity within itself.

In practice, these requirements might not be met due to lack of physical links. OSPF virtual links can solve this issue.

Virtual links

A virtual link is established between two ABRs through a non-backbone area. It must be configured on both ABRs to take effect. The non-backbone area is called a transit area.

As shown in Figure 2, Area 2 has no direct physical link to the backbone Area 0. You can configure a virtual link between the two ABRs to connect Area 2 to the backbone area.

Figure 2 Virtual link application 1

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Virtual links can also be used as redundant links. If a physical link failure breaks the internal connectivity of the backbone area, you can configure a virtual link to replace the failed physical link, as shown in Figure 3.

Figure 3 Virtual link application 2

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The virtual link between the two ABRs acts as a point-to-point connection. You can configure interface parameters, such as hello interval, on the virtual link as they are configured on a physical interface.

The two ABRs on the virtual link unicast OSPF packets to each other, and the OSPF routers in between convey these OSPF packets as normal IP packets.

Stub area and totally stub area

A stub area does not distribute Type-5 LSAs to reduce the routing table size and LSAs advertised within the area. The ABR of the stub area advertises a default route in a Type-3 LSA so that the routers in the area can reach external networks through the default route.

To further reduce the routing table size and advertised LSAs, you can configure the stub area as a totally stub area. The ABR of a totally stub area does not advertise inter-area routes or external routes. It advertises a default route in a Type-3 LSA so that the routers in the area can reach external networks through the default route.

NSSA area and totally NSSA area

An NSSA area does not import AS external LSAs (Type-5 LSAs) but can import Type-7 LSAs generated by the NSSA ASBR. The NSSA ABR translates Type-7 LSAs into Type-5 LSAs and advertises the Type-5 LSAs to other areas.

As shown in Figure 4, the OSPF AS contains Area 1, Area 2, and Area 0. The other two ASs run RIP. Area 1 is an NSSA area where the ASBR redistributes RIP routes in Type-7 LSAs into Area 1. Upon receiving the Type-7 LSAs, the NSSA ABR translates them to Type-5 LSAs, and advertises the Type-5 LSAs to Area 0.

The ASBR of Area 2 redistributes RIP routes in Type-5 LSAs into the OSPF routing domain. However, Area 1 does not receive Type-5 LSAs because it is an NSSA area.

Figure 4 NSSA area

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Router types

As shown in Figure 5, OSPF routers are classified into different types, including internal routers, ABRs, backbone routers, and ASBRs.

Figure 5 OSPF router types

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Internal router

All interfaces on an internal router belong to one OSPF area.

ABR

An ABR belongs to more than two areas, one of which must be the backbone area. ABR connects the backbone area to a non-backbone area. An ABR and the backbone area can be connected through a physical or logical link.

Backbone router

No less than one interface of a backbone router must reside in the backbone area. All ABRs and internal routers in Area 0 are backbone routers.

ASBR

An ASBR exchanges routing information with another AS. An ASBR might not reside on the border of the AS. It can be an internal router or an ABR.

Route types

OSPF prioritizes routes into the following route levels:

· Intra-area route.

· Inter-area route.

· Type-1 external route.

· Type-2 external route.

The intra-area and inter-area routes describe the network topology of the AS. The external routes describe routes to external ASs.

A Type-1 external route has high credibility. The cost of a Type-1 external route = the cost from the router to the corresponding ASBR + the cost from the ASBR to the destination of the external route.

A Type-2 external route has low credibility. OSPF considers that the cost from the ASBR to the destination of a Type-2 external route is much greater than the cost from the ASBR to an OSPF internal router. The cost of a Type-2 external route = the cost from the ASBR to the destination of the Type-2 external route. If two Type-2 routes to the same destination have the same cost, OSPF takes the cost from the router to the ASBR into consideration to determine the best route.

Router ID

A router ID uniquely identifies a router in an AS. For a router to run OSPF, it must have a router ID. You can choose to manually specify a router ID, automatically obtain a router ID, or use the global router ID for an OSPF process.

Manual configuration

When you create an OSPF process, you can manually specify a router ID. To make sure the router ID is unique in the AS, you can specify the IP address of an interface on the router as the router ID.

Automatic configuration

When you create an OSPF process, you can enable the OSPF process to automatically obtain a router ID. The OSPF process obtains a router ID in the following ways:

· During the startup of the OSPF process, the primary IPv4 address of the first interface that runs the process is specified as the router ID.

· During the reboot of the router, the primary IPv4 address of the first interface that runs the process is specified as the router ID.

· During the restart of the OSPF process, the highest primary IPv4 address of the loopback interface that runs the process is specified as the router ID. If no loopback address is available, the highest primary IPv4 address of the interface that runs the process is used, regardless of the interface state (up or down).

Using the global router ID

If you do not specify a router ID when creating an OSPF process, the global router ID is used. As a best practice, manually specify a router ID or enable the OSPF process to automatically obtain a router ID when you create the OSPF process.

Route calculation

OSPF computes routes in an area as follows:

· Each router generates LSAs based on the network topology around itself, and sends them to other routers in update packets.

· Each OSPF router collects LSAs from other routers to compose an LSDB. An LSA describes the network topology around a router, and the LSDB describes the entire network topology of the area.

· Each router transforms the LSDB to a weighted directed graph that shows the topology of the area. All the routers within the area have the same graph.

· Each router uses the SPF algorithm to compute a shortest path tree that shows the routes to the nodes in the area. The router itself is the root of the tree.

OSPF network types

OSPF classifies networks into the following types, depending on different link layer protocols:

· Broadcast—If the link layer protocol is Ethernet or FDDI, OSPF considers the network type as broadcast by default. On a broadcast network, hello, LSU, and LSAck packets are multicast to 224.0.0.5 that identifies all OSPF routers or to 224.0.0.6 that identifies the DR and BDR. DD packets and LSR packets are unicast.

· NBMA—If the link layer protocol is Frame Relay, ATM, or X.25, OSPF considers the network type as NBMA by default. OSPF packets are unicast on an NBMA network.

· P2MP—No link is P2MP type by default. P2MP must be a conversion from other network types such as NBMA. On a P2MP network, OSPF packets are multicast to 224.0.0.5.

· P2P—If the link layer protocol is PPP or HDLC, OSPF considers the network type as P2P. On a P2P network, DD packets are unicast and other OSPF packets are multicast to 224.0.0.5.

The following are the differences between NBMA and P2MP networks:

· NBMA networks are fully meshed. P2MP networks are not required to be fully meshed.

· NBMA networks require DR and BDR election. P2MP networks do not have DR or BDR.

· On an NBMA network, OSPF packets are unicast, and neighbors are manually configured. On a P2MP network, OSPF packets are multicast by default, and you can configure OSPF to unicast protocol packets.

DR and BDR

DR and BDR mechanism

On a broadcast or NBMA network, any two routers must establish an adjacency to exchange routing information with each other. If n routers are present on the network, n(n-1)/2 adjacencies are established. Any topology change on the network results in an increase in traffic for route synchronization, which consumes a large amount of system and bandwidth resources.

Using the DR and BDR mechanisms can solve this problem.

· DR—Elected to advertise routing information among other routers. If the DR fails, routers on the network must elect another DR and synchronize information with the new DR. Using this mechanism without BDR is time-consuming and is prone to route calculation errors.

· BDR—Elected along with the DR to establish adjacencies with all other routers. If the DR fails, the BDR immediately becomes the new DR, and other routers elect a new BDR.

Routers other than the DR and BDR are called DR Others. They do not establish adjacencies with one another, so the number of adjacencies is reduced.

The role of a router is subnet (or interface) specific. It might be a DR on one interface and a BDR or DR Other on another interface.

As shown in Figure 6, solid lines are Ethernet physical links, and dashed lines represent OSPF adjacencies. With the DR and BDR, only seven adjacencies are established.

Figure 6 DR and BDR in a network

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NOTE:

In OSPF, neighbor and adjacency are different concepts. After startup, OSPF sends a hello packet on each OSPF interface. A receiving router checks parameters in the packet. If the parameters match its own, the receiving router considers the sending router an OSPF neighbor. Two OSPF neighbors establish an adjacency relationship after they synchronize their LSDBs through exchange of DD packets and LSAs.

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DR and BDR election

DR election is performed on broadcast or NBMA networks but not on P2P and P2MP networks.

Routers in a broadcast or NBMA network elect the DR and BDR by router priority and ID. Routers with a router priority value higher than 0 are candidates for DR and BDR election.

The election votes are hello packets. Each router sends the DR elected by itself in a hello packet to all the other routers. If two routers on the network declare themselves as the DR, the router with the higher router priority wins. If router priorities are the same, the router with the higher router ID wins.

If a router with a higher router priority becomes active after DR and BDR election, the router cannot replace the DR or BDR until a new election is performed. Therefore, the DR of a network might not be the router with the highest priority, and the BDR might not be the router with the second highest priority.

OSPF state machines

I nterface state machine

On receipt of link state information, OSPF establishes adjacency relationships with neighboring devices, and then exchanges LSAs with them. The state of an OSPF interface indicates the role of the device in an OSPF link. Two neighboring devices can correctly form an adjacency relationship by checking the other's interface state.

The interface state machine involves the following interface states:

· Down—Initial interface state.

An OSPF interface in this state cannot be used for traffic sending or receiving.

· Loopback—The network-facing interface is looped back on the device.

A loopback interface is not available for regular data transmission. However, to obtain link quality information on the interface, you might either send ICMP ping packets to the loopback interface or have a bit error test. To meet this potential requirement, each OSPF device advertises loopback interface information in Router LSAs.

· Waiting—The device is determining the DR and BDR for the network.

When the device does not run for the DR or BDR, the interface starts a wait timer. The hello packets sent by the device does not contain any DR or BDR information unless the wait timer expires. The device cannot be elected as the DR or BDR on the network until it exits from Waiting state. The wait timer mechanism prevents unnecessary DR and BDR changes.

This interface state is supported only on NBMA networks and broadcast networks.

· Point-to-point—The interface is connected to a physical P2P network or to a virtual link.

If an interface enters this state, it attempts to establish an adjacency relationship with the neighboring device.

This interface state is supported only on P2P networks and P2MP networks.

· DR Other—The interface is connected to a broadcast or NBMA network on which another device has been elected as the DR.

A device in DR Other state is neither elected as the DR nor the BDR. When DR and BDR election is complete on the network, each DR Other device establishes adjacencies with both the DR and the BDR.

· BDR—The device is the BDR on the attached network.

As the BDR, the device establishes adjacencies with all other devices on the attached network. It will immediately become the new DR if the existing DR fails.

· DR—The device is the DR on the attached network.

As the DR, the device establishes adjacencies with all other devices on the attached network.

A number of i nput events (IE) can cause OSPF interface state changes. As shown in Figure 7, the relationships between IEs and state changes form the OSPF interface state machine.

Figure 7 OSPF interface state machine

Table 1 shows the IEs that can cause interface state changes.

Table 1 Input events

Input event	Description
IE1	InterfaceUp event: Lower-level protocols have indicated that the interface is operational.
IE2	WaitTimer event: The wait timer has expired and the device can run for the DR or the BDR.
IE3	BackupSeen event: The device has detected the existence or non-existence of a BDR on the attached network through one of the following methods: · The interface receives a hello packet from a neighbor that claims itself to be the BDR. · The interface receives a hello packet from a neighbor that claims itself to be the DR. The hello packet also indicates that there is no BDR. This event marks an end to Waiting state and indicates that the device and the neighbor can have bidirectional communication.
IE4	The interface is elected as the DR.
IE5	The interface is elected as the BDR.
IE6	The interface is neither elected as the DR nor the BDR.
IE7	NeighborChange event: A neighbor associated with the interface has a change. The DR and BDR need to be re-elected. The following neighbor changes might lead to the re-election of DR and BDR: · The device can have bidirectional communication with a neighbor. · The device no longer has bidirectional communication with a neighbor. · A neighbor claims itself as DR or BDR. The device detects this event again by examining the hello packets from the neighbor. · A neighbor no longer claims itself as DR or BDR. The device detects this event again by examining the hello packets from the neighbor. · The DR priority for a neighbor has changed. The device detects this event again by examining the hello packets from the neighbor.
IE8	UnloopInd event: Network management or l ower-level protocols has indicated that the interface is no longer looped back.
IE9	InterfaceDown event: Lower-level protocols has indicated that the interface is not operational. If this event occurs, the interface state might change to Down.
IE10	LoopInd event: Network management or lower-level protocols has indicated that the interface is looped back. If this event occurs, the interface state might change to Loopback.

N eighbor state machine

The process of OSPF adjacency establishment involves a series of neighbor state changes that transition from Down state to Full state.

The neighbor state machine involves the following neighbor states:

· Down —Initial state of a neighbor conversation.

This state indicates that the local device does not receive any hello packets from the neighbor within the neighbor dead interval. An OSPF device sends hello packets at intervals of PollInterval.

Whether an OSPF device sends hello packets to neighbors in Down state depends on its network type. The device sends hello packets to neighbors in Down state only when its network type is NBMA.

· Attempt—In this state, the local device attempts to establish neighbor relationships with the manually specified neighbors by sending hello packets at intervals of HelloInterval.

This state is valid only for the neighbors on NBMA networks.

· Init—This state indicates that the local device has received a hello packet from a neighbor before the neighbor dead interval elapses. However, the local device has not established bidirectional communication with the neighbor, because the received hello packet does not contain the OSPF device's router ID.

· 2-Way—This state indicates that the local device has established a neighbor relationship with a neighboring device. Each of the two devices has received a hello packet from another and has seen its own router ID in the received hello packet.

If the neighbor relationship between two devices does not prompt to an adjacency, the neighbor state will remain 2-Way.

DR and BDR election starts only when the neighbor state is 2-Way or greater.

· ExStart—This state indicates that the local device and the neighbor is deciding which is the master. This step is to determine the sequence number for initial DD packets. The devices can then exchange DD packets in order.

· Exchange—This state indicates that the local device is exchanging DD packets with the neighbor. The local device describes its LSDB information in DD packets and sends them to the neighbor.

· Loading—This state indicates that the local device and the neighbor are having bidirectional LSDB synchronization. They send LSRs to each other to request the most recent LSAs, and then synchronize their LSDBs through exchanges of LSUs and LSAcks.

· Full—This state indicates that the local device and the neighbor has completed bidirectional LSDB synchronization and they are fully adjacent.

As shown in Figure 8, the relationships between IEs and state changes form the OSPF neighbor state machine.

Figure 8 OSPF neighbor state machine

Table 2 shows the IEs that can cause neighbor state changes.

Table 2 Input events

Input event	Description
IE1	Start event: The OSPF device attempts to establish a neighbor relationship with the neighbor by sending hello packets at intervals of HelloInterval. This event is supported only on NBMA networks.
IE2	HelloReceived event: The OSPF device has received a hello packet from the neighbor.
IE3	2-WayReceived event: The OSPF device has received a hello packet from the neighbor and has seen its router ID in the received hello packet. The two neighboring devices have established bidirectional communication. The OSPF device then performs the following task: · If the OSPF device needs to form an adjacency with the neighbor, it changes the neighbor state to ExStart. · If the OSPF device should not form an adjacency with the neighbor, it changes the neighbor state to 2-Way.
IE4	NegotiationDone event: The OSPF device and the neighbor have completed master/secondary relationship negotiation and have determined the sequence number for initial DD packets.
IE5	ExchangeDone event: The OSPF device have exchanged DD packets with the neighbor. The OSPF device then performs the following task: · If t he LSR list is empty, the device changes the neighbor state to Full. This neighbor state indicates that bidirectional LSDB synchronization is complete and the device has established an adjacency with the neighbor. · If the LSR list is not empty, the device changes the neighbor state to Loading, and then sends LSRs to the neighbor to request missing link state information. If the OSPF device should not form an adjacency with the neighbor, it changes the neighbor state to 2-Way.
IE6	LoadingDone event: The LSR list is already empty.

OSPF GR

Graceful Restart (GR) enables a device to forward data uninterruptedly when it performs an active/standby switchover or restarts a routing protocol. When a GR-capable device restarts a routing protocol, it notifies the event to its neighbors. Those neighbors then maintain adjacencies and the routing information of the device within the specified interval. After the protocol is restarted, the device retrieves the information (topology, routing and session information) from the neighbors and restores the state before reboot. During the restart process, no route flapping occurs and no forwarding path is changed. Thus, the system can operate continuously.

OSPF GR ensures the service continuity of an OSPF-enabled router during active/standby switchover or OSPF restart.

OSPF NSR

Nonstop routing (NSR) backs up necessary OSPF information from the active process to the standby process, such as OSPF neighbor information and link state information. After an active/standby switchover, NSR can complete link state recovery and route regeneration without tearing down adjacencies or impacting forwarding services.

NSR does not require the cooperation of neighboring devices to recover routing information, and it is typically used more often than GR.

Protocols and standards

· RFC 1245, OSPF protocol analysis

· RFC 1246, Experience with the OSPF protocol

· RFC 1370, Applicability Statement for OSPF

· RFC 1403, BGP OSPF Interaction

· RFC 1745, BGP4/IDRP for IP---OSPF Interaction

· RFC 1765, OSPF Database Overflow

· RFC 1793, Extending OSPF to Support Demand Circuits

· RFC 2154, OSPF with Digital Signatures

· RFC 2328, OSPF Version 2

· RFC 3101, OSPF Not-So-Stubby Area (NSSA) Option

· RFC 3166, Request to Move RFC 1403 to Historic Status

· RFC 3509, Alternative Implementations of OSPF Area Border Routers

· RFC 4167, Graceful OSPF Restart Implementation Report

· RFC 4577, OSPF as the Provider/Customer Edge Protocol for BGP/MPLS IP Virtual Private Networks (VPNs)

· RFC 4750, OSPF Version 2 Management Information Base

· RFC 4811, OSPF Out-of-Band LSDB Resynchronization

· RFC 4812, OSPF Restart Signaling

· RFC 5088, OSPF Protocol Extensions for Path Computation Element (PCE) Discovery

· RFC 5250, The OSPF Opaque LSA Option

· RFC 5613, OSPF Link-Local Signaling

· RFC 5642, Dynamic Hostname Exchange Mechanism for OSPF

· RFC 5709, OSPFv2 HMAC-SHA Cryptographic Authentication

· RFC 5786, Advertising a Router's Local Addresses in OSPF Traffic Engineering (TE) Extensions

· RFC 6571, Loop-Free Alternate (LFA) Applicability in Service Provider (SP) Networks

· RFC 6860, Hiding Transit-Only Networks in OSPF

· RFC 6987, OSPF Stub Router Advertisement

Restrictions and guidelines: OSPF configuration

Before you configure OSPF, make a proper configuration plan to avoid incorrect settings that can result in route blocking and routing loops.

OSPF tasks at a glance

To configure OSPF, perform the following tasks:

1. Configuring basic OSPF functions

¡ Enabling an OSPF process

¡ Configuring an OSPF area

¡ Enabling OSPF

¡ (Optional.) Configuring OSPF areas

¡ Configuring a stub area

¡ Configuring an NSSA area

¡ Configuring a virtual link

2. (Optional.) Configuring OSPF network types

¡ Configuring the broadcast network type for an interface

¡ Configuring the NBMA network type for an interface

¡ Configuring the P2MP network type for an interface

¡ Configuring the P2P network type for an interface

3. (Optional.) Configuring OSPF route control

¡ Configuring OSPF inter-area route summarization

¡ Configuring redistributed route summarization

¡ Configuring received OSPF route filtering

¡ Configuring Type-3 LSA filtering

¡ Setting an OSPF cost for an interface

¡ Enabling OSPF to advertise the maximum link cost to neighbors

¡ Setting the maximum number of ECMP routes

¡ Setting OSPF preference

¡ Configuring discard routes for summary networks

¡ Redistributing routes from another routing protocol

¡ Redistributing a default route

¡ Advertising a host route

¡ Advertising OSPF link state information to BGP

¡ Configuring OSPF to advertise network performance parameters

4. (Optional.) Setting OSPF timers

¡ Configuring OSPF packet timers

¡ Setting LSA transmission delay

¡ Setting SPF calculation interval

¡ Setting the LSA arrival interval

¡ Setting the LSA update interval

¡ Setting OSPF exit overflow interval

¡ Setting the LSU transmit rate

5. (Optional.) Configuring OSPF packet parameters

¡ Disabling interfaces from receiving and sending OSPF packets

¡ Adding the interface MTU into DD packets

¡ Setting the DSCP value for outgoing OSPF packets

¡ Setting the maximum length of OSPF packets that can be sent by an interface

6. (Optional.) Controlling LSA generation, advertisement, and reception

¡ Setting the maximum number of external LSAs in LSDB

¡ Filtering outbound LSAs on an interface

¡ Filtering LSAs for the specified neighbor

¡ Configuring update suppression

7. (Optional.) Accelerating OSPF convergence speed

¡ Enabling OSPF ISPF

¡ Configuring prefix suppression

¡ Configuring prefix prioritization

¡ Configuring OSPF PIC

8. (Optional.) Configuring advanced OSPF features

¡ Configuring stub routers

¡ Configuring OSPF isolation

¡ Configuring OSPF shutdown

¡ Enabling compatibility with RFC 1583

¡ Configuring OSPF dynamic host name mappings

¡ Configuring OSPF neighbor flapping suppression

¡ Configuring the virtual system feature

9. (Optional.) Enhancing OSPF availability

¡ Configuring OSPF GR

¡ Configuring BFD for OSPF

¡ Configuring OSPF FRR

¡ Enabling OSPF to adjust the interface cost according to the link quality

10. (Optional.) Configuring OSPF security features

¡ Configuring OSPF authentication

¡ Configuring GTSM for OSPF

11. (Optional.) Configuring OSPF logging and SNMP notifications

¡ Logging neighbor state changes

¡ Configuring the OSPF logging feature

¡ Configuring OSPF network management

¡ Setting the maximum number of OSPF neighbor relationship troubleshooting entries

Configuring basic OSPF functions

Enabling an OSPF process

1. Enter system view.

system-view

2. (Optional.) Configure a global router ID.

router id router-id

By default, no global router ID is configured.

If no global router ID is configured, the highest loopback interface IP address, if any, is used as the router ID. If no loopback interface IP address is available, the highest physical interface IP address is used, regardless of the interface status (up or down).

3. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

By default, OSPF is disabled.

4. (Optional.) Configure a description for the OSPF process.

description text

By default, no description is configured for the OSPF process.

As a best practice, configure a description for each OSPF process.

Configuring an OSPF area

1. Enter system view.

system-view

2. (Optional.) Configure a global router ID.

router id router-id

By default, no global router ID is configured.

3. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

By default, OSPF is disabled.

4. (Optional.) Configure a description for the OSPF process.

description text

By default, no description is configured for the OSPF process.

As a best practice, configure a description for each OSPF process.

5. Create an OSPF area, and enter OSPF area view.

area area-id

6. (Optional.) Configure a description for the area.

description text

By default, no description is configured for the area.

As a best practice, configure a description for each OSPF area.

This configuration is available only in OSPF area view.

Enabling OSPF

About this task

To enable OSPF on a router, you must perform the following tasks:

1. Create an OSPF process.

2. Create an OSPF area for the process.

3. Specify a network in the area.

The interface attached to the network will run the OSPF process in the area. OSPF advertises the direct route of the interface.

OSPF supports multiple processes. To run multiple OSPF processes, you must specify an ID for each process. The process IDs take effect locally and has no influence on packet exchange between routers. Two routers with different process IDs can exchange packets.

You can configure an OSPF process to run in a VPN instance. An OSPF process with no VPN instance specified runs on the public network. For more information about VPN, see MPLS Configuration Guide.

Restrictions and guidelines for enabling OSPF

When you configure OSPF on an interface, follow these restrictions and guidelines:

· You can enable OSPF on the network where the interface resides or directly enable OSPF on that interface. If you configure both, the latter takes precedence.

· If the specified OSPF process and area do not exist, the operation creates an OSPF process and area for the interface. Disabling an OSPF process on an interface does not delete the OSPF process or the area.

Enabling OSPF on a network

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Enter OSPF area view.

area area-id

4. Specify a network to enable the interface attached to the network to run the OSPF process in the area.

network ip-address wildcard-mask

By default, no network is specified.

A network can be added to only one area.

This configuration is available only in OSPF area view.

Enabling OSPF on an interface

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Enable an OSPF process on the interface.

ospf process-id area area-id [ exclude-subip ]

By default, OSPF is disabled on an interface.

Configuring OSPF areas

About OSPF area configuration

This task allows you to configure an OSPF area as a stub area or NSSA area. It also allows you to create a virtual link if no connectivity can be achieved between a non-backbone area and backbone area, or in the backbone area.

Configuring a stub area

About this task

You can configure a non-backbone area at an AS edge as a stub area. To do so, execute the stub command on all routers attached to the area. The routing table size is reduced because Type-5 LSAs will not be flooded within the stub area. The ABR generates a default route into the stub area so all packets destined outside of the AS are sent through the default route.

To further reduce the routing table size and routing information exchanged in the stub area, configure a totally stub area by using the stub no-summary command on the ABR. AS external routes and inter-area routes will not be distributed into the area. All the packets destined for outside of the AS or area will be sent to the ABR for forwarding.

A stub or totally stub area cannot have an ASBR because external routes cannot be distributed into the area.

Restrictions and guidelines

Do not configure the backbone area as a stub area or totally stub area.

To configure an area as a stub area, execute the stub command on all routers attached to the area.

To configure an area as a totally stub area, execute the stub command on all routers attached to the area, and execute the stub no-summary command on the ABR.

Procedure (OSPF area view)

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Enter area view.

area area-id

4. Configure the area as a stub area.

stub [ default-route-advertise-always | no-summary ] *

By default, no stub area is configured.

5. (Optional.) Set a cost for the default route advertised to the stub area.

default-cost cost-value

By default, the cost is 1 for the default route advertised to the stub area.

This command takes effect only on the ABR of a stub area or totally stub area.

Configuring an NSSA area

About this task

A stub area cannot import external routes, but an NSSA area can import external routes into the OSPF routing domain while retaining other stub area characteristics.

To configure an area as a totally NSSA area, use the nssa no-summary command. The ABR of the area does not advertise inter-area routes into the area.

Restrictions and guidelines

Do not configure the backbone area as an NSSA area or totally NSSA area.

To configure an NSSA area, configure the nssa command on all the routers attached to the area.

To configure a totally NSSA area, configure the nssa command on all the routers attached to the area and configure the nssa no-summary command on the ABR.

Procedure (OSPF area view)

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Enter area view.

area area-id

4. Configure the area as an NSSA area.

By default, no area is configured as an NSSA area.

5. (Optional.) Set a cost for the default route advertised to the NSSA area.

default-cost cost-value

By default, the cost is 1 for the default route advertised to the NSSA area.

This command takes effect only on the ABR/ASBR on an NSSA area or totally NSSA area.

Configuring a virtual link

About this task

You can configure a virtual link to maintain connectivity between a non-backbone area and the backbone, or in the backbone itself.

Restrictions and guidelines

A virtual link cannot traverse a stub area, totally stub area, NSSA area, or totally NSSA area.

Procedure

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Enter OSPF area view.

area area-id

4. Configure a virtual link.

vlink-peer router-id [ dead seconds | hello seconds | { { hmac-md5 | hmac-sha-256 | md5 } key-id { cipher | plain } string | keychain keychain-name | simple { cipher | plain } string } | retransmit seconds | trans-delay seconds ] *

Configure this command on both ends of a virtual link. The hello and dead intervals must be identical on both ends of the virtual link.

This command is available only in OSPF area view.

Configuring OSPF network types

Based on the link layer protocol, OSPF classifies networks into different types, including broadcast, NBMA, P2MP, and P2P.

Restrictions and guidelines for configuring OSPF network types

When an NBMA network becomes fully meshed, change the network type to broadcast to avoid manual configuration of neighbors.

If any routers in a broadcast network do not support multicasting, change the network type to NBMA.

An NBMA network must be fully meshed. OSPF requires that an NBMA network be fully meshed. If a network is partially meshed, change the network type to P2MP.

If a router on an NBMA network has only one neighbor, you can change the network type to P2P to save costs.

Two broadcast-, NBMA-, and P2MP-interfaces can establish a neighbor relationship only when they are on the same network segment.

Configuring the broadcast network type for an interface

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Configure the OSPF network type for the interface as broadcast.

ospf network-type broadcast

By default, the network type of an interface depends on the link layer protocol.

When the link layer protocol is Ethernet or FDDI, OSPF classifies the network type as broadcast by default.

4. (Optional.) Set a router priority for the interface.

ospf dr-priority priority

The default router priority is 1.

Configuring the NBMA network type for an interface

Restrictions and guidelines

After you configure the network type as NBMA, you must specify neighbors and their router priorities because NBMA interfaces cannot find neighbors by broadcasting hello packets.

Procedure

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Configure the OSPF network type for the interface as NBMA.

ospf network-type nbma

By default, the network type of an interface depends on the link layer protocol.

4. (Optional.) Set a router priority for the interface.

ospf dr-priority priority

The default router priority for an interface is 1.

The router priority configured with this command is for DR election.

5. Return to system view.

quit

6. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

7. Specify an NBMA neighbor.

peer ip-address [ dr-priority priority ]

By default, no neighbor is specified.

The priority configured with this command indicates whether a neighbor has the election right or not. If you configure the router priority for a neighbor as 0, the local router determines the neighbor has no election right. It does not send hello packets to this neighbor. However, if the local router is the DR or BDR, it still sends hello packets to the neighbor for neighbor relationship establishment.

Configuring the P2MP network type for an interface

Restrictions and guidelines

After you configure the OSPF network type for an interface as P2MP unicast, all packets are unicast over the interface. The interface cannot broadcast hello packets to discover neighbors, so you must manually specify the neighbors.

Procedure

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Configure the OSPF network type for the interface as P2MP.

ospf network-type p2mp [ unicast ]

By default, the network type of an interface depends on the link layer protocol.

4. Return to system view.

quit

5. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

6. Specify a P2MP neighbor.

peer ip-address [ cost cost-value ]

By default, no neighbor is specified.

This step is required if the interface network type is P2MP unicast.

Configuring the P2P network type for an interface

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Configure the OSPF network type for the interface as P2P.

ospf network-type p2p [ multicast | peer-address-check ] *

By default, the network type of an interface depends on the link layer protocol.

When the link layer protocol is PPP, LAPB, or HDLC, OSPF classifies the network type as P2P by default.

Configuring OSPF route control

This section describes how to control the advertisement and reception of OSPF routing information, as well as route redistribution from other protocols.

Configuring OSPF inter-area route summarization

About this task

OSPF inter-area route summarization reduces the routing information exchanged between areas and the size of routing tables, and improves routing performance.

OSPF inter-area route summarization enables an ABR to summarize contiguous networks into a single network and advertise the network to other areas. For example, three internal networks 19.1.1.0/24, 19.1.2.0/24, and 19.1.3.0/24 are available within an area. You can configure the ABR to summarize the three networks into network 19.1.0.0/16, and advertise the summary network to other areas in a Type-3 LSA. This configuration reduces the scale of LSDBs on routers in other areas and the influence of topology changes.

Procedure

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Enter OSPF area view.

area area-id

4. Configure ABR route summarization.

abr-summary ip-address { mask-length | mask } [ advertise | not-advertise ] [ cost cost-value ]

By default, route summarization is not configured on an ABR.

Configuring redistributed route summarization

About this task

Perform this task to enable an ASBR to summarize external routes within the specified address range into a single route. The ASBR advertises only Type-5 LSAs to reduce the number of LSAs in the LSDB.

An ASBR can summarize routes in the following LSAs:

· Type-5 LSAs.

· Type-7 LSAs in an NSSA area.

Restrictions and guidelines

If an ASBR (also an ABR) is a translator in an NSSA area, it summarizes routes in Type-5 LSAs translated from Type-7 LSAs. If it is not a translator, it does not summarize routes in in Type-5 LSAs translated from Type-7 LSAs.

Procedure

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Configure ASBR route summarization.

asbr-summary ip-address { mask-length | mask } [ cost cost-value | not-advertise | nssa-only | tag tag ] *

By default, route summarization is not configured on an ASBR.

Configuring received OSPF route filtering

About this task

Perform this task to filter routes calculated using received LSAs.

The following filtering methods are available:

· Use an ACL or IP prefix list to filter routing information by destination address.

· Use the gateway prefix-list-name option to filter routing information by next hop.

· Use an ACL or IP prefix list to filter routing information by destination address. At the same time use the gateway prefix-list-name option to filter routing information by next hop.

· Use the route-policy route-policy-name option to filter routing information.

Procedure

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Configure OSPF to filter routes calculated using received LSAs.

filter-policy { ipv4-acl-number [ gateway prefix-list-name ] | gateway prefix-list-name | prefix-list prefix-list-name [ gateway prefix-list-name ] | route-policy route-policy-name } import

By default, OSPF accepts all routes calculated by using received LSAs.

Configuring Type-3 LSA filtering

About this task

Perform this task to filter Type-3 LSAs advertised into the local area or other areas on an ABR.

Procedure

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Enter OSPF area view.

area area-id

4. Configure Type-3 LSA filtering.

filter { ipv4-acl-number | prefix-list prefix-list-name | route-policy route-policy-name } { export | import }

By default, the ABR does not filter Type-3 LSAs.

Setting an OSPF cost for an interface

About this task

Set an OSPF cost for an interface by using either of the following methods:

· Set the cost value in interface view.

· Set a bandwidth reference value for the interface. OSPF computes the cost with this formula: Interface OSPF cost = Bandwidth reference value (100 Mbps) / Expected interface bandwidth (Mbps). The expected bandwidth of an interface is configured with the bandwidth command (see Interface Command Reference).

¡ If the calculated cost is greater than 65535, the value of 65535 is used. If the calculated cost is less than 1, the value of 1 is used.

¡ If no cost or bandwidth reference value is configured for an interface, OSPF computes the interface cost based on the interface bandwidth and default bandwidth reference value.

Setting an OSPF cost for an interface

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Set an OSPF cost for the interface.

ospf cost cost-value

By default, the OSPF cost is calculated according to the interface bandwidth. For a loopback interface, the OSPF cost is 0 by default.

Setting a bandwidth reference value

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance instance-name ] *

3. Set a bandwidth reference value.

bandwidth-reference value

The default setting is 100 Mbps.

Changing the link cost of a Layer 3 aggregate interface when its bandwidth falls below the threshold

About this task

When a member port of a Layer 3 aggregate interface goes down, the bandwidth of the aggregate interface decreases and services might be interrupted. To resolve this issue, perform this task to change the link cost of a Layer 3 aggregate interface as follows:

· When the bandwidth of the Layer 3 aggregate interface falls below the specified threshold, the aggregate interface uses the specified link cost. Make sure the link cost you specified is larger than the original link cost, so that OSPF can select an optimal path for traffic forwarding.

· When the bandwidth of the Layer 3 aggregate interface is equal to or larger than the bandwidth threshold, the aggregate interface uses the original link cost.

For more information about OSPF link cost, see "Setting an OSPF cost for an interface."

Restrictions and guidelines

This feature applies to only Layer 3 aggregate interfaces and Layer 3 aggregate subinterfaces.

Procedure

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Change the link cost of the interface to the specified value when the bandwidth of the interface falls below the specified threshold.

ospf cost-fallback cost-value threshold bandwidth-value [ instance instance-id ]

By default, an aggregate interface uses the original link cost.

Enabling OSPF to advertise the maximum link cost to neighbors

About this task

On an OSPF network, when a link recovers from failures or the state of an interface changes, OSPF will re-establish neighbor relationships and perform route convergence. During the route convergence process, routing loops and traffic loss might occur because the convergence speeds of the nodes are different. To address this issue, enable OSPF to advertise the maximum link cost to neighbors within the specified period of time, so the traffic forwarding path remains unchanged. After the specified period of time, OSPF advertises the original link cost to neighbors and performs optimal route selection again.

Procedure

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Enable OSPF to advertise the maximum link cost to neighbors within the specified period of time.

ospf peer hold-max-cost duration time

By default, OSPF advertises the original link cost to neighbors during a route convergence.

Setting the maximum number of ECMP routes

About this task

OSPF might find multiple optimal equal-cost routes to the same destination, which can be used to share the traffic load. This task allows you to set the maximum number of ECMP routes for OSPF.

As shown in Figure 9, Device A and Device B run OSPF. There are three equal-cost routes between Device A and Device B. You can use these routes to implement load sharing.

Figure 9 Equal-cost routes

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Procedure

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Set the maximum number of ECMP routes.

maximum load-balancing number

By default, the maximum number of OSPF ECMP routes is 64.

Setting OSPF preference

About this task

A router can run multiple routing protocols, and each protocol is assigned a preference. If multiple routes are available to the same destination, the one with the highest protocol preference is selected as the best route.

Procedure

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Set a preference for OSPF.

preference [ ase ] { preference | route-policy route-policy-name } *

By default, the preference of OSPF internal routes is 10 and the preference of OSPF external routes is 150.

Configuring discard routes for summary networks

About this task

Perform this task on an ABR or ASBR to specify whether to generate discard routes for summary networks. You can also specify a preference for the discard routes.

Procedure

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Configure discard routes for summary networks.

discard-route { external { preference | suppression } | internal { preference | suppression } } *

By default, the ABR or ASBR generates discard routes for summary networks and the default preference of discard routes is 255.

Redistributing routes from another routing protocol

About this task

When an OSPF device does not have routes from a non-OSPF routing protocol, it cannot access any devices that run the non-OSPF routing protocol. To resolve this issue, you can configure OSPF to redistribute routes from other protocols, such as IS-IS and BGP. OSPF can then advertise the routes in Type-5 LSAs or Type-7 LSAs.

In addition, you can configure OSPF to filter redistributed routes so that OSPF advertises only permitted routes.

Restrictions and guidelines

Although OSPF is a dynamic routing protocol that provides loop-free intra-area/inter-area routes, this protocol is not good at guarding against the routing loops caused by redistributed external routes. When you configure route redistribution for OSPF, make sure you have understood the potential impact.

OSPF redistributes only active routes. To view route status information, use the display ip routing-table protocol command.

Procedure

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Configure route redistribution.

import-route { direct | static | unr } [ [ cost cost-value | inherit-cost ] | nssa-only | route-policy route-policy-name | tag tag | type type ] *

import-route { isis | ospf | rip } [ process-id | all-processes ] [ allow-direct | [ cost cost-value | inherit-cost ] | nssa-only | route-policy route-policy-name | tag tag | type type ] *

By default, OSPF does not redistribute routes.

The import-route bgp command redistributes only EBGP routes. The import-route bgp allow-ibgp command redistributes both EBGP and IBGP routes, which might cause routing loops. Therefore, use it with caution.

4. (Optional.) Configure OSPF to filter redistributed routes.

filter-policy { ipv4-acl-number | prefix-list prefix-list-name } export [ bgp | direct | eigrp [ eigrp-as ] | { isis | ospf | rip } [ process-id ] | static | unr ]

By default, OSPF accepts all redistributed routes.

5. Configure the default parameters for redistributed routes (cost, tag, and type).

default { cost cost-value | tag tag | type type } *

By default, the cost is 1, the tag is 1, and the route type is 2.

Redistributing a default route

About this task

On a OSPF network, multiple ABRs and ASBRs work together to implement multi-egress load balancing. To save routing table capacity, you can configure default routes.

OSPF default routes are mostly used in the following scenarios:

· After receiving a Type 3 LSA that describes a default route from the ABR, the intra-area router can use the route for packet forwarding to another area in the same AS.

· After receiving a Type 5 or 7 LSA that describes a default route from the ASBR, the intra-area router can use the route for packet forwarding to another AS.

When a router cannot find a exactly matching route, it can use the default route for packet forwarding. The default route originated from a Type 3 LSA takes precedence over that originated from a Type 5 LSA.

As shown in Table 3, the advertisement method for a redistributed default route varies by its area type.

Table 3 Advertisement of redistributed default routes

Area type	Route redistribution condition	Advertiser	LSA type	LSA flooding scope
Common area	Use the default-route-advertise command.	ASBR	Type 5 LSA	Common area
Stub area	Automatic route redistribution.	ABR	Type 3 LSA	Stub area
NSSA area	Use the nssa [ default-route-advertise ] command.	ASBR	Type 7 LSA	NSSA area
Totally NSSA area	Automatic route redistribution.	ABR	Type 3 LSA	NSSA area

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The import-route command cannot redistribute a default route from an external routing protocol. To resolve this issue, perform this task on the ASBR to redistribute a default route.

Restrictions and guidelines

After receiving a default route from the ASBR, the device can add the default route to its routing table in one of the following scenarios:

· The device does not have a static route.

· The device has a static route, but the priority value for the default route is higher than that for the static route.

Procedure

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Redistribute a default route.

default-route-advertise [ [ always | permit-calculate-other ] | cost cost-value | route-policy route-policy-name | type type ] *

default-route-advertise [ summary cost cost-value ]

By default, no default route is redistributed.

This command is applicable only to VPNs. The PE router advertises a default route in a Type-3 LSA to a CE router.

4. Configure the default parameters for redistributed routes (cost, tag, and type).

default { cost cost-value | tag tag | type type } *

By default, the cost is 1, the tag is 1, and the route type is 2.

Advertising a host route

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Enter area view.

area area-id

4. Advertise a host route.

host-advertise ip-address cost-value

By default, OSPF does not advertise host routes that are not in the area.

Advertising OSPF link state information to BGP

About this task

After the device advertises OSPF link state information to BGP, BGP can advertise the information for intended applications. For more information about BGP LS, see "Configuring BGP."

Procedure

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Advertise OSPF link state information to BGP.

distribute bgp-ls [ instance-id id ] [ strict-link-checking ]

By default, the device does not advertise OSPF link state information to BGP.

Configuring OSPF to advertise network performance parameters

About OSPF network performance parameters

A controller in a network performance-sensitive scenario uses parameters that can reflect the network performance as route calculation metrics.

Perform this task to enable OSPF to advertise network performance parameters and report the information to the controller through BGP-LS. Then, the controller performs optimal route calculation based on the network performance parameters.

Network performance parameters include the following:

· Delay—Unidirectional link delay performance metrics, including:

¡ Average link delay—Average unidirectional link delay.

¡ Min/Max link delay—Minimum/maximum unidirectional link delay.

¡ Average link delay variation—Average unidirectional link delay variation.

· Bandwidth—Unidirectional link bandwidth performance metrics, including:

¡ Remaining bandwidth—Remaining unidirectional link bandwidth.

¡ Available bandwidth—Available unidirectional link bandwidth.

¡ Utilized bandwidth—Unidirectional link bandwidth usage.

Advertising link delay information

About this task

Perform this task to enable OSPF to advertise link delay information and report the information to the controller through BGP-LS. Then, the controller performs optimal route calculation based on the link delay information.

Perform either of the following tasks to obtain link delay information of an interface:

· Static configuration—Execute the ospf link-delay command to manually configure link delay parameters on the interface.

· Dynamic acquisition—Execute the test-session bind interface command to bind the interface as the out interface of a TWAMP Light test session. Then, TWAMP Light will send the detected link delay information to the interface, and the interface will report the link delay information to OSPF at periodic intervals. For more information about TWAMP Light, see NQA configuration in Network Management and Monitoring Configuration Guide.

In dynamic acquisition mode, an interface reports link delay information to OSPF at rather short intervals, for example, 100 milliseconds. As a result, OSPF needs to frequently process the link delay information and reports the information to the controller through BGP-LS, which consumes a lot of device and network resources. To resolve this issue, you can configure OSPF to suppress advertisement of link delay information.

Link delay advertisement suppression works as follows:

· An interface reports link delay information to OSPF at the specified interval.

· OSPF advertises link delay information through BGP-LS at the specified interval. OSPF does not advertise link delay information within the specified interval except for the following conditions:

¡ The variation ratio between two consecutive minimum delays is larger than or equivalent to the suppression threshold for the delay variation ratio.

¡ The absolute value of the difference between two consecutive minimum delays is larger than or equivalent to the suppression threshold for the absolute value of the delay variation.

Restrictions and guidelines

For an interface, static link delay parameters take precedence over the parameters obtained through dynamic acquisition.

As a best practice, set the link delay advertisement suppression interval to be larger than or equivalent to the NQA delay measurement interval.

Configuring link delay parameters

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Configure link delay parameters.

ospf link-delay { average average-delay-value | min min-delay-value max max-delay-value | variation variation-value} *

By default, link delay parameters are not configured.

Enabling OSPF to advertise link delay information

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Enable OSPF to advertise link delay information.

metric-delay advertisement enable

By default, OSPF does not advertise link delay information.

Configuring OSPF to suppress advertisement of link delay information

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Configure OSPF to suppress advertisement of link delay information.

metric-delay suppression timer time-value percent-threshold percent-value absolute-threshold absolute-value

By default, OSPF suppresses advertisement of link delay information. The suppression interval is 120 seconds, the suppression threshold for the delay variation ratio is 10%, and the suppression threshold for the absolute value of the delay variation is 1000 microseconds.

If you set an argument to 0, the corresponding suppression mechanism does not take effect. If you set all arguments to 0, OSPF does not suppress advertisement of link delay information.

Advertising link bandwidth information

About this task

Perform this task to enable OSPF to advertise link bandwidth information and report the information to the controller through BGP-LS. Then, the controller performs optimal route calculation based on the link bandwidth information.

By default, an interface reports link bandwidth information to OSPF at short intervals, for example, 100 milliseconds. As a result, OSPF needs to frequently process the link bandwidth information and reports the information to the controller through BGP-LS, which consumes a lot of device and network resources. To resolve this issue, you can configure OSPF to suppress advertisement of link bandwidth information.

Link bandwidth advertisement suppression works as follows:

· An interface reports link bandwidth information to OSPF at the specified interval.

· OSPF advertises link bandwidth information through BGP-LS at the specified interval.

Restrictions and guidelines

As a best practice, set the link bandwidth advertisement suppression interval to be larger than or equivalent to the Ethernet interface bandwidth measurement interval.

Enabling OSPF to advertise link bandwidth information

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Enable OSPF to advertise link bandwidth information.

metric-bandwidth advertisement enable

By default, OSPF does not advertise link bandwidth information.

Configuring OSPF to suppress advertisement of link bandwidth information

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Configure OSPF to suppress advertisement of link bandwidth information.

metric-bandwidth suppression timer time-value

By default, OSPF suppresses advertisement of link bandwidth information. The suppression interval is 120 seconds.

If you set the time-value argument to 0, OSPF does not suppress advertisement of link bandwidth information.

Setting OSPF timers

About setting OSPF timers

This task allows you to change OSPF packet timers to adjust the convergence speed and network load and tune the delay time for sending LSAs on low-speed links.

Configuring OSPF packet timers

About this task

An OSPF interface includes the following timers:

· Hello timer—Interval for sending hello packets. It must be identical on OSPF neighbors.

· Poll timer—Interval for sending hello packets to a neighbor that is down on the NBMA network.

· Dead timer—Interval within which if the interface does not receive any hello packet from the neighbor, it declares the neighbor is down.

· LSA retransmission timer—Interval within which if the interface does not receive any acknowledgment packets after sending an LSA to the neighbor, it retransmits the LSA.

Restrictions and guidelines

The default value for the hello interval and neighbor dead interval depends on the network type. When the network type for an interface is changed, the default hello interval and neighbor dead interval are restored. Make sure two neighboring interfaces are configured with the same hello interval and neighbor dead interval. Inconsistent settings will affect the OSPF neighbor relationship establishment.

Procedure

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Set the hello interval.

ospf timer hello seconds

By default, the hello interval is 10 seconds on P2P and broadcast interfaces and 30 seconds on P2MP and NBMA interfaces.

4. Set the poll interval.

ospf timer poll seconds

The default setting is 120 seconds.

The poll interval is a minimum of four times the hello interval.

5. Set the dead interval.

ospf timer dead seconds

By default, the dead interval is 40 seconds on P2P and broadcast interfaces and 120 seconds on P2MP and NBMA interfaces.

The dead interval must be a minimum of four times the hello interval on an interface.

6. Set the retransmission interval.

ospf timer retransmit interval

The default retransmission interval is 5 seconds.

A retransmission interval setting that is too small can cause unnecessary LSA retransmissions. Typically set a bigger interval than the round-trip time of a packet between two neighbors.

Setting LSA transmission delay

About this task

To avoid LSAs from aging out during transmission, set an LSA retransmission delay especially for low speed links.

Procedure

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Set the LSA transmission delay.

ospf trans-delay seconds

The default LSA transmission delay is 1 second.

Setting SPF calculation interval

About this task

LSDB changes result in SPF calculations. When the topology changes frequently, a large amount of network and router resources are occupied by SPF calculation. You can adjust the SPF calculation interval to reduce the impact.

For a stable network, the minimum interval is used. If network changes become frequent, the SPF calculation interval increases by the incremental interval × 2n-2 for each calculation until the maximum interval is reached. The value n is the number of calculation times.

Procedure

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Set the SPF calculation interval.

spf-schedule-interval { maximum-interval [ minimum-interval [ incremental-interval [ conservative ] ] ] | millisecond interval }

By default, the maximum interval is 5 seconds, the minimum interval is 50 milliseconds, and the incremental interval is 200 milliseconds.

Setting the LSA arrival interval

About this task

When the topology changes frequently, a large amount of bandwidth and router resources are occupied by LAS processing. You can adjust the LSA arrival interval to reduce the impact.

By default, OSPF adjusts the LSA arrival interval automatically. For a stable network, LSAs arrive at the minimum interval. If network changes become frequent, the LSA arrival interval increases by the incremental interval × 2n-2 for each arrival until the maximum interval is reached. The value n is the number of arrival times.

OSPF drops any duplicate LSAs within the LSA arrival interval. An LSA is a duplicate of a previous LSA if they have the same LSA type, LS ID, and router ID.

Restrictions and guidelines

On a stable network, you can set the LSA arrival interval to 0 to fasten route convergence.

Procedure

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Set the LSA arrival interval.

lsa-arrival-interval maximum-interval [ minimum-interval [ incremental-interval ] ]

By default, the maximum interval is 1000 milliseconds, the minimum interval is 500 milliseconds, and the incremental interval is 500 milliseconds.

Setting the LSA update interval

About this task

Adjust the LSA update interval to protect network resources and routers from being overwhelmed by LSAs at the time of frequent network changes.

By default, OSPF adjusts the LSA update interval automatically. For a stable network, the minimum interval is used. If network changes become frequent, the LSA update interval increases by the incremental interval × 2n-2 for each update until the maximum interval is reached. The value n is the number of update times.

Procedure

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Set the LSA update interval.

lsa-generation-interval maximum-interval [ minimum-interval [ incremental-interval ] ]

By default, the maximum interval is 5 seconds, the minimum interval is 50 milliseconds, and the incremental interval is 200 milliseconds.

Setting OSPF exit overflow interval

About this task

When the number of LSAs in the LSDB exceeds the upper limit, the LSDB is in an overflow state. In this state, OSPF does not receive any external LSAs and deletes the external LSAs generated by itself to save system resources.

This task allows you to configure the interval that OSPF exits overflow state.

Procedure

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Set the interval that OSPF exits overflow state.

lsdb-overflow-interval interval

By default, the OSPF exit overflow interval is 300 seconds. An interval of 0 means that OSPF does not exit overflow state.

Setting the LSU transmit rate

About this task

Sending large numbers of LSU packets affects router performance and consumes a large amount of network bandwidth. You can configure the router to send LSU packets at an interval and to limit the maximum number of LSU packets sent out of an OSPF interface at each interval.

Procedure

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Set the LSU transmit rate.

transmit-pacing interval interval count count

By default, an OSPF interface sends a maximum of three LSU packets every 20 milliseconds.

Configuring OSPF packet parameters

Disabling interfaces from receiving and sending OSPF packets

About this task

To enhance OSPF adaptability and reduce resource consumption, you can set an OSPF interface to "silent." A silent OSPF interface blocks OSPF packets and cannot establish any OSPF neighbor relationship. However, other interfaces on the router can still advertise direct routes of the interface in Router LSAs.

Restrictions and guidelines

You can execute either the silent-interface or ospf silent command or both commands for an interface to achieve the same effect. Choose an appropriate configuration method as needed.

Disabling interfaces from receiving and sending OSPF packets in OSPF view

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Disable interfaces from receiving and sending OSPF packets.

silent-interface { interface-type interface-number | all }

By default, an OSPF interface can receive and send OSPF packets.

This command disables only the interfaces associated with the current process rather than other processes. Multiple OSPF processes can disable the same interface from receiving and sending OSPF packets.

Disabling an interface from receiving and sending OSPF packets in interface view

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Disable an interface from receiving and sending OSPF packets.

ospf silent

By default, an OSPF interface can receive and send OSPF packets.

Adding the interface MTU into DD packets

About this task

By default, an OSPF interface adds a value of 0 into the interface MTU field of a DD packet rather than the actual interface MTU. On receipt of a DD packet, the interface does not check the interface MTU field of that packet. Such a mechanism ensures that two interfaces in different devices can establish a neighbor relationship regardless of the interface MTU. However, the device cannot establish neighbor relationships with the devices from another manufacturer that discard the DD packets whose interface MTU value is 0.

To resolve this issue, perform this task to enable an OSPF interface to add its interface MTU into DD packets and check the interface MTU in received DD packets. If the interface MTU in a received DD packet is higher than the MTU of the local interface, the interface will discard the DD packet. To ensure that two interfaces in different devices can establish a neighbor relationship, set the same MTU for these interfaces.

Procedure

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Enable the interface to add its MTU into DD packets.

ospf mtu-enable

By default, the interface adds an MTU value of 0 into DD packets.

Setting the DSCP value for outgoing OSPF packets

About this task

The DSCP value specifies the precedence of outgoing packets.

Procedure

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Set the DSCP value for outgoing OSPF packets.

dscp dscp-value

By default, the DSCP value for outgoing OSPF packets is 48.

Setting the maximum length of OSPF packets that can be sent by an interface

About this task

In some scenarios, for example, when you establish OSPF neighbors over a tunnel, you can perform this task to prevent OSPF packet fragmentation on the outgoing tunnel interface. Make sure the maximum length of the OSPF packets plus the encapsulated header length is no greater than the outgoing tunnel interface's MTU. For more information about tunnels, see Layer 3—IP Services Configuration Guide.

Procedure

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Set the maximum length of OSPF packets that can be sent by an interface.

ospf packet-size value

By default, the maximum length of OSPF packets that an interface can send equals the interface's MTU.

Controlling LSA generation, advertisement, and reception

Setting the maximum number of external LSAs in LSDB

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Set the maximum number of external LSAs in the LSDB.

lsdb-overflow-limit number

By default, the maximum number of external LSAs in the LSDB is not limited.

Filtering outbound LSAs on an interface

About this task

To reduce the LSDB size for the neighbor and save bandwidth, you can perform this task on an interface to filter LSAs to be sent to the neighbor.

Procedure

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Filter outbound LSAs on the interface.

ospf database-filter { all | { ase [ acl ipv4-acl-number ] | nssa [ acl ipv4-acl-number ] | summary [ acl ipv4-acl-number ] } * }

By default, the outbound LSAs are not filtered on the interface.

Filtering LSAs for the specified neighbor

About this task

On a P2MP network, a router might have multiple P2MP type OSPF neighbors. Perform this task to prevent the router from sending LSAs to the specified P2MP neighbor.

Procedure

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Filter LSAs for the specified P2MP neighbor.

database-filter peer ip-address { all | { ase [ acl ipv4-acl-number ] | nssa [ acl ipv4-acl-number ] | summary [ acl ipv4-acl-number ] } * }

By default, the LSAs for the specified P2MP neighbor are not filtered.

Configuring update suppression

About this task

When route flaps occur on an OSPF network, the devices consecutively flood LSAs into the network. This might cause more route flaps. Moreover, excessive LSAs can cause frequent route calculation, which costs too much CPU resources and degrades the performance of the devices. To prevent this problem, you can perform this task to suppress routing update during route flapping.

Procedure

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Suppress the update of LSAs during route flapping.

lsa-generation-interval suppress-flapping delay-interval [ threshold threshold-value ]

By default, LSA update is not suppressed during route flapping.

4. Suppress incoming LSAs during route flapping.

lsa-arrival-interval suppress-flapping delay-interval [ threshold threshold-value ]

By default, incoming LSAs are not suppressed during route flapping.

5. Set the delay for route calculation triggered by router LSAs with max age.

maxage-lsa route-calculate-delay delay-interval

By default, the delay is 10 seconds for route calculation triggered by router LSAs with max age.

Accelerating OSPF convergence speed

Enabling OSPF ISPF

About this task

When the topology changes, Incremental Shortest Path First (ISPF) computes only the affected part of the SPT, instead of the entire SPT.

Procedure

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Enable OSPF ISPF.

ispf enable

By default, OSPF ISPF is enabled.

Configuring prefix suppression

About this task

By default, an OSPF interface advertises all of its prefixes in LSAs. To speed up OSPF convergence, you can suppress interfaces from advertising all of their prefixes. This feature helps improve network security by preventing IP routing to the suppressed networks.

When prefix suppression is enabled:

· On P2P and P2MP networks, OSPF does not advertise Type-3 links in Type-1 LSAs. Other routing information can still be advertised to ensure traffic forwarding.

· On broadcast and NBMA networks, the DR generates Type-2 LSAs with a mask length of 32 to suppress network routes. Other routing information can still be advertised to ensure traffic forwarding. If no neighbors exist, the DR does not advertise Type-3 links in Type-1 LSAs.

Restrictions and guidelines for prefix suppression

As a best practice, configure prefix suppression on all OSPF routers if you want to use prefix suppression.

Configuring prefix suppression for an OSPF process

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Enable prefix suppression for the OSPF process.

prefix-suppression

By default, prefix suppression is disabled for an OSPF process.

This feature does not suppress the prefixes of secondary IP addresses, loopback interfaces, and passive interfaces.

Configuring prefix suppression for an interface

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Enable prefix suppression for the interface.

ospf prefix-suppression [ disable ]

By default, prefix suppression is disabled on an interface.

This feature does not suppress prefixes of secondary IP addresses.

Configuring prefix prioritization

About this task

OSPF calculates intra-area routes, inter-area routes, and AS external routes in descending convergence priority order: critical, high, medium, and low. When a route has multiple prefix priorities, it uses the highest priority.

To prioritize the convergence of specific routes, perform this task to set a higher convergence priority value for those routes.

Procedure

1. Enter system view.

system-view

2. Configure an IPv4 prefix list.

ip prefix-list prefix-list-name [ index index-number ] { deny | permit } ip-address mask-length [ greater-equal min-mask-length ] [ less-equal max-mask-length ]

3. Configure a routing policy.

route-policy route-policy-name { deny | permit } node node-number

4. Use the IPv4 prefix list as an IPv4 route filter.

if-match ip { address | next-hop | route-source } prefix-list prefix-list-name

By default, no IPv4 route filters are configured.

5. Set a prefix priority for matching routes.

apply prefix-priority { critical | high | medium }

By default, no prefix priority is set.

6. Return to system view.

quit

7. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

8. Enable prefix prioritization.

prefix-priority route-policy route-policy-name

By default, prefix prioritization is disabled.

Configuring OSPF PIC

About this task

Prefix Independent Convergence (PIC) enables the device to speed up network convergence by ignoring the number of prefixes.

Restrictions and guidelines for OSPF PIC

When both OSPF PIC and OSPF FRR are configured, OSPF FRR takes effect.

OSPF PIC applies only to inter-area routes and external routes.

Enabling OSPF PIC

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Enable PIC for OSPF.

pic [ additional-path-always ]

By default, OSPF PIC is disabled.

Configuring BFD control packet mode for OSPF PIC

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Enable BFD control packet mode for OSPF PIC.

ospf primary-path-detect bfd ctrl

By default, BFD control packet mode is disabled for OSPF PIC.

This mode requires BFD configuration on both OSPF routers on the link.

Configuring BFD echo packet mode for OSPF PIC

1. Enter system view.

system-view

2. (Optional.) Configure the source IP address of BFD echo packets.

bfd echo-source-ip ip-address

By default, the source IP address of BFD echo packets is not configured.

As a best practice to avoid network congestion caused by massive ICMP redirect packets from the remote end, execute this command and specify a source IP address that is not on the same network segment as any local interface's IP address.

For more information about this command, see BFD commands in High Availability Command Reference.

3. Enter interface view.

interface interface-type interface-number

4. Enable BFD echo packet mode for OSPF PIC.

ospf primary-path-detect bfd echo

By default, BFD echo packet mode is disabled for OSPF PIC.

This mode requires BFD configuration on one OSPF router on the link.

Configuring advanced OSPF features

Configuring stub routers

About this task

A stub router is used for traffic control. It reports its status as a stub router to neighboring OSPF routers. The neighboring routers can have a route to the stub router, but they do not use the stub router to forward data.

Router LSAs from the stub router might contain different link type values. A value of 3 means a link to a stub network, and the cost of the link will not be changed by default. To set the cost of the link to 65535, specify the include-stub keyword in the stub-router command. A value of 1, 2 or 4 means a point-to-point link, a link to a transit network, or a virtual link. On such links, a maximum cost value of 65535 is used. Neighbors do not send packets to the stub router as long as they have a route with a smaller cost.

As shown in Figure 10, Device A, Device B, Device C, and Device D run OSPF. Device C is the backup device for Device B. Device A and Device B, Device A and Device C, Device B and Device D, and Device C and Device D are IBGP peers.

When the network is stable, BGP and OSPF can finish route convergence completely. Device A forwards traffic destined for 10.3.1.0/30 to Device B. If Device B fails, Device C will take over to forward the traffic from Device A.

After Device B recovers, Device A immediately forwards the traffic Device B. However, BGP might have not finished route convergence when OSPF has finished route convergence, because OSPF has a higher route convergence speed than BGP. In this situation, Device B does not have a route to 10.3.1.0/30 and will discard the traffic destined for 10.3.1.0/30. To resolve this issue, configure Device B to act as a stub router during BGP route convergence. Device A will forward traffic to Device C instead of Device B until Device B finishes BGP route convergence.

Figure 10 Network diagram

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Procedure

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Configure the router as a stub router.

stub-router [ external-lsa [ max-metric-value ] | include-stub | on-startup { seconds | wait-for-bgp [ seconds ] } | summary-lsa [ max-metric-value ] ] *

By default, the router is not configured as a stub router.

A stub router is not related to a stub area.

Configuring OSPF isolation

About this task

Isolation is a method used for network device maintenance. It gracefully removes a device from the packet forwarding path for maintenance and gracefully adds the device to the network after maintenance.

To reduce impact on traffic forwarding, you can isolate a device before upgrading it. OSPF isolation works as follows:

1. After OSPF isolation is enabled for a device, OSPF increases the link cost in LSAs advertised by the device based on the following rules:

¡ The link cost in Type-1 LSAs (Router LSAs) is increased to 65535.

¡ The link cost in the following LSAs is increased to 16711680:

- Type-3 LSAs (Network summary LSAs).

- Type-5 LSAs (AS external LSAs).

- Type-7 LSAs (NSSA external LSAs).

2. Each neighbor of the device reselects an optimal route based on the LSAs and stops forwarding traffic to the device. The device is fully isolated from the network and you can upgrade the device.

3. After the maintenance, disable OSPF isolation on the device to restore its link cost and gracefully add it back to the network.

Procedure

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id router-id | vpn-instance vpn-instance-name ] *

3. Configure OSPF isolation.

¡ Enable OSPF isolation to gracefully isolate the device from the network.

isolate enable

¡ Disable OSPF isolation to gracefully add the device back to the network.

undo isolate enable

By default, OSPF isolation is disabled.

Configuring OSPF shutdown

About this task

For maintenance purposes, you can use this feature to shut down OSPF processes on the device with small impact on the network. If you shut down a process, it will perform the following operations:

· Send 1-way hello packets to its neighbors.

On receipt of the packets, the neighbors disconnect from the OSPF process and use the backup path to forward traffic.

· Stop receiving and sending OSPF packets.

· Clear its neighbor, LSDB, and OSPF route information.

After maintenance, you can use the undo shutdown process command to restart the process for neighbor relationship re-establishment.

This feature shuts down an OSPF process while retaining the process-associated settings to facilitate your maintenance.

Procedure

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id router-id | vpn-instance vpn-instance-name ] *

3. Configure OSPF shutdown.

¡ Shut down an OSPF process to isolate it from the network.

shutdown process

¡ Restart the OSPF process to add it back to the network.

undo shutdown process

By default, the OSPF process is not shut down.

Enabling compatibility with RFC 1583

About this task

RFC 1583 specifies a different method than RFC 2328 for selecting the optimal route to a destination in another AS. When multiple routes are available to the ASBR, OSPF selects the optimal route by using the following procedure:

1. Selects the route with the highest preference.

¡ If RFC 2328 is compatible with RFC 1583, all these routes have equal preference.

¡ If RFC 2328 is not compatible with RFC 1583, the intra-area route in a non-backbone area is preferred to reduce the burden of the backbone area. The inter-area route and intra-area route in the backbone area have equal preference.

2. Selects the route with the lower cost if two routes have equal preference.

3. Selects the route with the larger originating area ID if two routes have equal cost.

Restrictions and guidelines

To avoid routing loops, set identical RFC 1583-compatibility on all routers in a routing domain.

Procedure

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Enable compatibility with RFC 1583.

rfc1583 compatible

By default, compatibility with RFC 1583 is enabled.

Configuring OSPF dynamic host name mappings

About this task

OSPF uses a router ID to uniquely identify a router in an AS. The length of router IDs is fixed at 4 bytes. It is inconvenient for the network administrator to memorize the router IDs in dotted decimal notation when verifying the OSPF neighbor relationships, routing tables, and LSDBs.

This task allows you to map a router ID to a host name. The mapping table is maintained by OSPF routers. Host names are more straightforward than router IDs in network maintenance, management, and failure diagnosis.

Restrictions and guidelines

OSPF uses Type-10 LSAs and Type-11 LSAs to carry information about the dynamic host name attribute. Therefore, make sure the opaque LSA reception and advertisement capability is enabled.

Procedure

1. Enter system view.

system-view

2. Enable OSPF, and enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Enable the opaque LSA reception and advertisement capability.

opaque-capability enable

By default, the opaque LSA reception and advertisement capability is enabled.

4. Enable the OSPF dynamic host name mapping feature.

hostname [ host-name ]

By default, the OSPF dynamic host name mapping feature is disabled.

Configuring OSPF neighbor flapping suppression

About this task

Neighbor state changes will cause neighbor relationship reestablishment, LSDB synchronization, and route calculation. A large number of packets will be exchanged, which affects stability of existing neighbors and operation of OSPF and relevant services. To resolve this issue, enable OSPF neighbor flapping suppression to delay neighbor relationship establishment or traffic forwarding through neighbor links.

Use this command to avoid frequent flooding and topology changes during neighbor relationship establishment. Before the specified neighbor flapping suppression timer expires, OSPF does not establish neighbor relationships.

The OSPF neighbor flapping suppression mechanism is as follows:

· The interface starts a flapping counter to count neighbor flapping events. When the device detects a neighbor flapping event, it increases the flapping counter by 1.

A neighbor flapping event occurs when the time interval between two consecutive neighbor state changes (from Full to another state) is less than the specified detect interval.

· If the time interval between two consecutive neighbor state changes (from Full to another state) is greater than the specified resume interval, the flapping counter is reset.

· If the flapping counter reaches or exceeds the specified threshold, OSPF starts flapping suppression for all neighbors on the interface.

· During the flapping suppression period, if the device detects another neighbor flapping event, it resets the resume interval.

You can enable OSPF neighbor flapping suppression by executing the suppress-flapping hold-down or ospf peer suppress-flapping hold-max-cost command.

· Use the suppress-flapping hold-down command to avoid frequent flooding and topology changes during neighbor relationship establishment. Before the specified neighbor flapping suppression timer expires, OSPF does not establish neighbor relationships.

· Use the ospf peer suppress-flapping hold-max-cost command to set the cost of all neighbor links to the maximum value 65535 within the neighbor flapping suppression period (resume interval).

Restrictions and guidelines

If you execute both the suppress-flapping hold-down and ospf peer suppress-flapping hold-max-cost commands for an interface, the suppress-flapping hold-down command applies first. When neighbor suppression starts, OSPF performs the following operations in sequence:

1. Disables neighbor relationship establishment until the specified suppression timer expires.

2. Allows neighbor relationship establishment and sets the maximum cost for neighbor links until the specified resume interval expires.

3. Resumes the original link cost when the specified resume interval expires.

Procedure

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Enable OSPF neighbor flapping suppression. Choose one option as needed:

¡ Enable OSPF neighbor flapping suppression and set the suppression timer.

ospf peer suppress-flapping hold-down interval

¡ Enable OSPF neighbor flapping suppression and set the maximum cost for neighbor links.

ospf peer suppress-flapping hold-max-cost

By default, OSPF neighbor flapping suppression is disabled.

4. Configure detection parameters for OSPF neighbor flapping suppression.

ospf peer suppress-flapping { detect-interval detect-interval | threshold threshold | resume-interval resume-interval } *

By default, the detect interval is 60 seconds, the threshold value is 10, and the resume interval is 120 seconds.

For the ospf peer suppress-flapping hold-max-cost command, the resume interval specifies the suppression period. Before neighbor flapping suppression ends, the suppression period is updated with the resume interval.

Configuring the virtual system feature

About this task

In an AS, each OSPF node has a unique router ID and can manage multiple OSPF interfaces. The IP addresses of the interfaces managed by the same OSPF node cannot reside on the same network segment.

Procedure

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Enable the virtual system feature for the OSPF process.

virtual-system enable

By default, the virtual system feature is disabled.

4. Return to system view.

quit

5. Enter interface view.

interface interface-type interface-number

6. Enable the virtual system feature on the OSPF interface.

ospf virtual-system router-id router-id

By default, the virtual system feature is disabled.

Configuring OSPF GR

About OSPF GR

GR ensures forwarding continuity when a routing protocol restarts or an active/standby switchover occurs.

Two routers are required to complete a GR process. The following are router roles in a GR process:

· GR restarter—Graceful restarting router. It must have GR capability.

· GR helper—A neighbor of the GR restarter. It helps the GR restarter to complete the GR process.

OSPF GR has the following types:

· IETF GR—Uses Opaque LSAs to implement GR.

· Non-IETF GR—Uses link local signaling (LLS) to advertise GR capability and uses out of band synchronization to synchronize the LSDB.

A device can act as a GR restarter and GR helper at the same time.

Configuring OSPF GR restarter

Configuring the IETF OSPF GR restarter

1. Enter system view.

system-view

2. Enable OSPF and enter its view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Enable opaque LSA reception and advertisement capability.

opaque-capability enable

By default, opaque LSA reception and advertisement capability is enabled.

4. Enable the IETF GR.

graceful-restart ietf [ global | planned-only ] *

By default, the IETF GR capability is disabled.

5. (Optional.) Set the GR interval.

graceful-restart interval interval

By default, the GR interval is 120 seconds.

Configuring the non-IETF OSPF GR restarter

1. Enter system view.

system-view

2. Enable OSPF and enter its view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Enable the link-local signaling capability.

enable link-local-signaling

By default, the link-local signaling capability is disabled.

4. Enable the out-of-band re-synchronization capability.

enable out-of-band-resynchronization

By default, the out-of-band re-synchronization capability is disabled.

5. Enable non-IETF GR.

graceful-restart [ nonstandard ] [ global | planned-only ] *

By default, non-IETF GR capability is disabled.

6. (Optional.) Set the GR interval.

graceful-restart interval interval

By default, the GR interval is 120 seconds.

Configuring OSPF GR helper

Configuring the IETF OSPF GR helper

1. Enter system view.

system-view

2. Enable OSPF and enter its view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Enable opaque LSA reception and advertisement capability.

opaque-capability enable

By default, opaque LSA reception and advertisement capability is enabled.

4. Enable GR helper capability.

graceful-restart helper enable [ planned-only ]

By default, GR helper capability is enabled.

5. (Optional.) Enable strict LSA checking for the GR helper.

graceful-restart helper strict-lsa-checking

By default, strict LSA checking for the GR helper is disabled.

When an LSA change on the GR helper is detected, the GR helper device exits the GR helper mode.

Configuring the non-IETF OSPF GR helper

1. Enter system view.

system-view

2. Enable OSPF and enter its view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Enable the link-local signaling capability.

enable link-local-signaling

By default, the link-local signaling capability is disabled.

4. Enable the out-of-band re-synchronization capability.

enable out-of-band-resynchronization

By default, the out-of-band re-synchronization capability is disabled.

5. Enable GR helper.

graceful-restart helper enable

By default, GR helper is enabled.

6. (Optional.) Enable strict LSA checking for the GR helper.

graceful-restart helper strict-lsa-checking

By default, strict LSA checking for the GR helper is disabled.

When an LSA change on the GR helper is detected, the GR helper device exits the GR helper mode.

Triggering OSPF GR

About this task

You can trigger OSPF GR by performing an active/standby switchover or using the reset ospf process command.

Procedure

To trigger OSPF GR, execute the reset ospf [ process-id ] process graceful-restart command in user view.

Configuring BFD for OSPF

About BFD for OSPF

OSPF sends hello packets to neighbors at specific intervals to detect their state. If OSPF does not receive a hello packet from a neighbor within a specific period, OSPF considers the neighbor stale. Such a failure detection method cannot achieve high data reliability, because it takes a long time and causes data loss.

To resolve this issue, configure Bidirectional Forwarding Detection (BFD) for OSPF. This feature improves the route convergence speed against link state changes through fast link state detection. For more information about BFD, see High Availability Configuration Guide.

OSPF supports the following BFD detection modes:

· Bidirectional control detection—Requires BFD configuration to be made on both OSPF routers on the link.

· Single-hop echo detection—Requires BFD configuration to be made on one OSPF router on the link.

Configuring bidirectional control detection

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Enable BFD bidirectional control detection.

ospf bfd enable

By default, BFD bidirectional control detection is disabled.

Both ends of a BFD session must be on the same network segment and in the same area.

Configuring single-hop echo detection

1. Enter system view.

system-view

2. (Optional.) Configure the source address of echo packets.

bfd echo-source-ip ip-address

By default, the source address of echo packets is not configured.

For more information about this command, see BFD commands in High Availability Command Reference.

3. Enter interface view.

interface interface-type interface-number

4. Enable BFD single-hop echo detection.

ospf bfd enable echo

By default, BFD single-hop echo detection is disabled.

Enabling OSPF to adjust the interface cost according to the BFD session state

About this task

After you enable BFD for OSPF, the OSPF neighbor relationship goes down when the BFD session is down and comes up when the BFD session is up. When the BFD session state changes frequently, OSPF neighbor relationship flapping will occur and traffic forwarding might be affected.

To resolve this issue, enable OSPF to adjust the interface cost according to the BFD session state.

After you configure this feature on an interface, OSPF adjusts the interface cost as follows:

· When the BFD session on the interface goes down, OSPF increases the cost value for the interface.

· When the BFD session on the interface comes up, OSPF restores the cost value for the interface.

Procedure

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Enable OSPF to adjust the interface cost according to the BFD session state.

ospf bfd adjust-cost { cost-offset | max }

By default, OSPF does not adjust the link cost according to the BFD session state.

Suppressing interface cost adjustment according to the BFD session state upon BFD session flapping

About this task

After you enable OSPF to adjust the interface cost according to the BFD session state, if BFD session flaps frequently, the following conditions might occur:

· The OSPF interface cost changes frequently, resulting in repeated route calculations that greatly consume device resources.

· When the BFD session state changes from down to up, OSPF immediately resumes the original interface cost. If the link becomes unavailable again in a short time, packet loss will occur on this link before route convergence.

You can configure this feature to address the previous issues. When the BFD session state changes, OSPF performs the following operations instead of immediately adjusting the interface cost:

· When the BFD session state changes from up to down, OSPF starts a BFD session state detection timer, and records one BFD session down event. If the number of BFD session down events crosses the threshold within the detection interval, OSPF adjusts the interface cost based on configuration of the ospf bfd adjust-cost command. (The threshold is specified with the threshold keyword. The detection interval is specified with the detect-interval argument.) If this condition is not met, OSPF does not adjust the interface cost.

· After OSPF adjusts the interface cost (based on the configuration of the ospf bfd adjust-cost command), it starts a delay timer when the BFD session state changes from down to up. Before expiration of the delay timer (specified with the resume-interval argument), the following conditions will occur:

¡ If the BFD session remains up, OSPF resumes the original interface cost when the delay timer expires.

¡ If the BFD session state changes from up to down, OSPF deletes the delay timer and does not resume the original interface cost.

Restrictions and guidelines

This command takes effect only after you configure the ospf bfd adjust-cost command.

Procedure

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Suppress adjustment of the interface cost according to the BFD session state upon BFD session flapping.

ospf bfd adjust-cost suppress-flapping { detect-interval detect-interval | resume-interval resume-interval | threshold threshold } *

By default, OSPF does not suppress adjustment of the interface cost according to the BFD session state upon BFD session flapping.

Configuring OSPF FRR

About OSPF FRR

OSPF Fast Reroute (FRR) calculates a backup path based on the LSDB or specifies a backup path by using a routing policy. Then, it saves the backup path information to the FIB. When the primary path fails, the system immediately switches traffic to the backup path to prevent traffic loss and reduce the route convergence time.

OSPF supports Loop Free Alternate (LFA) FRR and remote LFA FRR.

The following OSPF FRR traffic protection types are available:

· Link protection—Protects traffic that traverses a specific link.

· Node protection—Protects traffic that traverses a specific node.

Node protection takes precedence over link protection.

Restrictions and guidelines for OSPF FRR

If both OSPF FRR and PIC are configured, OSPF FRR takes effect.

OSPF FRR tasks at a glance

To configure OSPF FRR, perform the following tasks:

1. Configuring an OSPF backup path

Perform a minimum of one task.

¡ Configuring OSPF LFA FRR

¡ Configuring OSPF remote LFA FRR

¡ Configuring OSPF FRR to use a backup next hop specified in a routing policy

2. (Optional.) Setting the priority for FRR backup path selection policies

3. (Optional.) Configuring BFD for OSPF FRR

¡ Configuring BFD control packet mode for OSPF FRR

¡ Configuring BFD echo packet mode for OSPF FRR

Configuring OSPF LFA FRR

About this task

A link or router failure on a path can cause packet loss until OSPF completes routing convergence based on the new network topology. FRR enables fast rerouting to minimize the impact of link or node failures.

Figure 11 Network diagram for OSPF FRR

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As shown in Figure 11, configure OSPF FRR on Router B to calculate a backup next hop by using the LFA algorithm. When the primary link fails, OSPF directs packets to the backup next hop. At the same time, OSPF calculates the shortest path based on the new network topology. It forwards packets over the path after network convergence.

Restrictions and guidelines for OSPF FRR

Do not use the fast-reroute lfa command together with the vlink-peer command.

Procedure

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. (Optional.) Enable LFA on an interface.

ospf fast-reroute lfa-backup

By default, the interface is enabled with LFA and it can be selected as a backup interface.

4. Return to system view.

quit

5. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

6. Enable OSPF FRR to use the LFA algorithm to calculate a backup next hop.

fast-reroute lfa [ abr-only | ecmp-shared ]

By default, OSPF FRR is disabled.

If abr-only is specified, the route to the ABR is selected as the backup path.

Configuring OSPF remote LFA FRR

About this task

In a network topology where OSPF LFA FRR cannot calculate the backup path, configure remote LFA FRR to ensure network reliability.

Remote LFA uses the following concepts:

· P space—Use the source node of the protected link as the root to establish a shortest path tree. All nodes that are reachable from the source node without passing the protected link form the P space. Nodes in the P space are called P nodes.

· Extended P space—Use the source node of the protected link and its neighbors as the roots to establish shortest path trees. All nodes that are reachable from the source node or one of its neighbors without passing the protected link form the extended P space. The P space is a subset of the extended P space.

· Q space—Use the destination node of the protected link as the root to establish a reverse shortest path tree. All nodes that are reachable from the root node without passing the protected link form the Q space. Nodes in the Q space are called Q nodes.

· PQ node—A PQ node refers to a node that resides in both the extended P space and the Q space. Remote LFA uses a PQ node as the destination node of a protected link.

As shown in Figure 12, the traffic forwarding path is PE 1—P 1—P 2—PE 2. To avoid traffic loss caused by link failures between P 1 and P 2, the system establishes an LDP tunnel between P 1 and P 4, which is the PQ node. When the link between P 1 and P 2 fails, P 1 encapsulates IP packets in MPLS packets and sends the MPLS packets to P 4 through the LDP tunnel. After receiving the MPLS packets, P 4 removes the MPLS labels of the packets and then forwards the packets to the next hop based on the IP routing table.

The system determines P 4 as the PQ node as follows:

1. Uses P 1 (source node of the protected link) and its neighbors except P 2 (which passes the protected link) as the roots to establish shortest path trees.

2. Finds out all nodes that are reachable from P 1 or one of its neighbors without passing the protected link, which are PE 1, P 1, P 3, and P 4.

These nodes form the extended P space.

3. Uses P 2 (destination node of the protected link) as the root to establish a reverse shortest path tree.

4. Finds out all nodes that are reachable from P 2 without passing the protected link, which are PE 2 and P 4.

These nodes form the Q space.

5. Finds out all nodes that reside in both the extended P space and the Q space.

Only P 4 resides in both the extended P space and the Q space, so P 4 is the PQ node of the protected link.

Figure 12 Network diagram for OSPF remote LFA FRR

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Prerequisites

Enable MPLS and MPLS LDP on all nodes and interfaces participating in MPLS forwarding. For more information, see basic MPLS configuration and LDP configuration in MPLS Configuration Guide.

Procedure

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Enable OSPF remote LFA FRR.

fast-reroute remote-lfa tunnel ldp

By default, OSPF remote LFA FRR is disabled.

4. (Optional.) Set the maximum cost from the source node of a protected link to a PQ node.

fast-reroute remote-lfa maximum-cost cost

By default, the maximum cost from the source node of a protected link to a PQ node is 16777215.

5. (Optional.) Specify a prefix list to filter PQ nodes.

fast-reroute remote-lfa prefix-list prefix-list-name

By default, no prefix list is specified to filter PQ nodes. Any PQ node can be selected as the backup next hop.

Multiple PQ nodes might reach the source node of a specific protected link. You can use this command to specify a prefix list to filter PQ nodes.

6. (Optional.) Disable remote LFA calculation on an interface.

a. Return to system view.

quit

b. Enter interface view.

interface interface-type interface-number

c. Disable remote LFA calculation on the interface.

ospf fast-reroute remote-lfa disable

By default, remote LFA calculation is enabled on the interface.

Configuring OSPF FRR to use a backup next hop specified in a routing policy

About this task

Before you perform this task, use the apply fast-reroute backup-interface command to specify a backup next hop in a routing policy for OSPF FRR. For more information about the apply fast-reroute backup-interface command and routing policy configuration, see "Configuring routing policies."

Procedure

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Enable OSPF FRR to use a backup next hop specified in a routing policy.

fast-reroute route-policy route-policy-name

By default, OSPF FRR is disabled.

Setting the priority for FRR backup path selection policies

About this task

OSPF FRR uses specific policies for backup path calculation. This command defines the priority for the backup path selection policy. The higher the value, the higher the priority of the associated backup path selection policy. Changing the backup path selection policy priority can affect the backup path calculation result for OSPF FRR. The backup paths can provide node protection or link protection for traffic, or provide both node protection and link protection.

OSPF FRR supports the following backup path selection policies that are used to generate different topologies for backup path calculation:

· Node protection—OSPF FRR performs backup path calculation after excluding the primary next hop node.

· Lowest cost—OSPF FRR performs backup path calculation after excluding the direct primary link.

· SRLG disjoint—When one link in the SRLG fails, the other links in the SRLG might also fail. If you use a link in this SRLG as the backup link for the failed link, protection does not take effect. To avoid this issue, OSPF FRR excludes the local links in the same SRLG as the direct primary link and then performs backup path calculation.

For OSPF FRR, the SRLG disjoint policy depends on the node protection and lowest cost policies.

If multiple backup path selection policies exist in an OSPF process, the policy with the highest priority is used to calculate the backup path. If the policy fails to calculate the backup path, another policy with higher priority is used. OSPF performs backup path calculation by using the node protection and lowest cost policies as follows:

· If the node protection policy has higher priority and fails to calculate the backup path, OSPF uses the lowest cost policy to calculate the backup path. If the lowest cost policy still fails to calculate the backup path, reliability cannot be ensured upon primary link failure.

· If the lowest cost policy has higher priority and fails to calculate the backup path, OSPF does not perform further backup path calculation with the node protection policy. Reliability cannot be ensured upon primary link failure.

Table 4 shows the backup path selection mechanism for OSPF FRR based on priorities of backup path selection policies.

Table 4 Backup path selection mechanism for OSPF FRR based on priorities of link selection policies

Priorities of link selection policies	Backup path selection mechanism for OSPF FRR
Node protection > lowest cost > SRLG-disjoint	OSPF FRR performs calculations based on the node protection and lowest cost policies in descending of priority. OSPF FRR performs a maximum of two calculations. If OSPF FRR calculates a backup path with a link selection policy, it does not perform further calculations.
Node protection > SRLG-disjoint > lowest cost	OSPF FRR performs calculations based on the node protection, node protection + SRLG-disjoint, lowest cost + SRLG-disjoint, and lowest cost policies in descending of priority. OSPF FRR performs a maximum of four calculations. If OSPF FRR calculates a backup path with a link selection policy, it does not perform further calculations.
SRLG-disjoint > node protection > lowest cost	OSPF FRR performs calculations based on the node protection + SRLG-disjoint, lowest cost + SRLG-disjoint, node protection, and lowest cost policies in descending of priority. OSPF FRR performs a maximum of four calculations. If OSPF FRR calculates a backup path with a link selection policy, it does not perform further calculations.
Lowest cost > node protection > SRLG-disjoint	OSPF FRR performs calculations based on the lowest cost policy. OSPF FRR performs only one calculation.
Lowest cost > SRLG-disjoint > node protection	OSPF FRR performs calculations based on the lowest cost policy. OSPF FRR performs only one calculation.
SRLG-disjoint > lowest cost > node protection	OSPF FRR performs calculations based on the node protection + SRLG-disjoint, lowest cost + SRLG-disjoint, and lowest cost policies in descending of priority. OSPF FRR performs a maximum of three calculations. If OSPF FRR calculates a backup path with a link selection policy, it does not perform further calculations.

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Procedure

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Set the priority for the node-protection, lowest-cost, or SRLG-disjoint backup path selection policy.

fast-reroute tiebreaker { lowest-cost | node-protecting | srlg-disjoint } preference preference

By default, the priority values of the node-protection, lowest-cost, and SRLG-disjoint backup path selection policies are 40, 20, and 10, respectively.

Configuring BFD control packet mode for OSPF FRR

About this task

By default, OSPF FRR does not use BFD to detect primary link failures. To speed up OSPF convergence, enable BFD control packet mode for OSPF FRR to detect primary link failures. This mode requires BFD configuration on both OSPF routers on the link.

Procedure

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Enable BFD control packet mode for OSPF FRR.

ospf primary-path-detect bfd ctrl

By default, BFD control packet mode is disabled for OSPF FRR.

Configuring BFD echo packet mode for OSPF FRR

About this task

By default, OSPF FRR does not use BFD to detect primary link failures. To speed up OSPF convergence, enable BFD echo packet mode for OSPF FRR to detect primary link failures. This mode requires BFD configuration on one OSPF router on the link.

Procedure

1. Enter system view.

system-view

2. Configure the source IP address of BFD echo packets.

bfd echo-source-ip ip-address

By default, the source IP address of BFD echo packets is not configured.

For more information about this command, see High Availability Command Reference.

3. Enter interface view.

interface interface-type interface-number

4. Enable BFD echo packet mode for OSPF FRR.

ospf primary-path-detect bfd echo

By default, BFD echo packet mode is disabled for OSPF FRR.

Enabling OSPF to adjust the interface cost according to the link quality

About this task

Error codes, which refer to bit differences between the received and source signals, cannot be avoided because of inevitable link aging and optical path jitter problems. A high error code ratio might cause service degradation or interruption.

To reduce the impact of error codes on an OSPF network, you can enable OSPF to adjust the interface cost according to the link quality.

After you configure this feature on an interface, OSPF adjusts the interface cost as follows:

· When the link quality of the interface becomes LOW, OSPF increases the cost value for the interface.

· When the link quality of the interface restores to GOOD, OSPF restores the cost value for the interface.

For more information about error code detection, see error code detection configuration in High Availability Configuration Guide.

Procedure

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Enable OSPF to adjust the link cost according to the link quality.

ospf link-quality adjust-cost { cost-offset | max }

By default, OSPF does not adjust the link cost according to the link quality.

Configuring OSPF authentication

About OSPF area and interface authentication

Perform this task to configure OSPF area and interface authentication.

OSPF adds the configured key into sent packets, and uses the key to authenticate received packets. Only packets that pass the authentication can be received. If a packet fails the authentication, the OSPF neighbor relationship cannot be established.

If you configure OSPF authentication for both an area and an interface in that area, the interface uses the OSPF authentication configured on it.

Configuring OSPF area authentication

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Enter area view.

area area-id

4. Configure area authentication mode.

¡ Configure MD5/HMAC-MD5/HMAC-SHA-256 authentication.

authentication-mode { hmac-md5 | hmac-sha-256 | md5 } key-id { cipher | plain } string

¡ Configure simple authentication.

authentication-mode simple { cipher | plain } string

¡ Configure keychain authentication.

authentication-mode keychain keychain-name

For information about keychains, see Security Configuration Guide.

By default, no authentication is configured.

You must configure the same authentication mode and key on all the routers in an area.

Configuring OSPF interface authentication

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Configure interface authentication mode.

¡ Configure simple authentication.

ospf authentication-mode simple { cipher | plain } string

¡ Configure MD5/HMAC-MD5/HMAC-SHA-256 authentication.

ospf authentication-mode { hmac-md5 | hmac-sha-256 | md5 } key-id { cipher | plain } string

¡ Configure keychain authentication.

ospf authentication-mode keychain keychain-name

For information about keychains, see Security Configuration Guide.

By default, no authentication is configured.

You must configure the same authentication mode and key on both the local interface and its peer interface.

Configuring GTSM for OSPF

About GTSM

The Generalized TTL Security Mechanism (GTSM) protects the device by comparing the TTL value in the IP header of incoming OSPF packets against a valid TTL range. If the TTL value is within the valid TTL range, the packet is accepted. If not, the packet is discarded.

The valid TTL range is from 255 – the configured hop count + 1 to 255.

When GTSM is configured, the OSPF packets sent by the device have a TTL of 255.

Restrictions and guidelines for GTSM

To use GTSM, you must configure GTSM on both the local and peer devices. You can specify different hop-count values for them.

The configuration in OSPF area view applies to all OSPF interfaces in the area. The configuration in interface view takes precedence over the configuration in OSPF area view.

GTSM checks OSPF packets from common neighbors and virtual link neighbors. It does not check OSPF packets from sham link neighbors. For information about GTSM for OSPF sham links, see MPLS L3VPN configuration in MPLS Configuration Guide.

Configuring GTSM in OSPF area view

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Enter OSPF area view.

area area-id

4. Enable GTSM for the OSPF area.

ttl-security [ hops hop-count ]

By default, GTSM is disabled for the OSPF area.

Editing the hop limit will clear GTSM dropped packet statistics from the interface.

Configuring GTSM in interface view

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Configure GTSM for the interface.

¡ Enable GTSM for the interface.

ospf ttl-security [ hops hop-count ]

¡ Disable GTSM for the interface.

ospf ttl-security disable

Disable GTSM for an interface when the following conditions exist:

- The area to which the interface belongs is enabled with GTSM.

- The neighbor of the interface does not support GTSM.

By default, an interface uses the GTSM configuration of the area to which the interface belongs.

Editing the hop limit will clear GTSM dropped packet statistics from the interface.

Configuring OSPF logging and SNMP notifications

Logging neighbor state changes

About this task

Perform this task to enable output of neighbor state change logs to the information center. The information center processes the logs according to user-defined output rules (whether and where to output logs). For more information about the information center, see Network Management and Monitoring Configuration Guide.

Procedure

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Enable the logging of neighbor state changes.

log-peer-change

By default, this feature of logging neighbor state changes is enabled.

Configuring the OSPF logging feature

About this task

OSPF logs include received and sent hello packet logs, LSA aging logs, route calculation logs, neighbor logs, OSPF route logs, and self-originated and received LSA logs.

Procedure

1. Enter system view.

system-view

2. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

3. Configure the OSPF logging feature.

event-log { hello { received [ abnormal | dropped ] | sent [ abnormal | failed ] } | lsa-flush | peer | route | spf } size count

event-log lsa-history { asbr | ase | include-duplicate | link-state-id | network | nssa | opaque-area | opaque-as | opaque-link | originate-router advertising-router-id | router | size count | summary | verbose } *

By default, the device can generate a maximum of 100 OSPF logs for each type.

Configuring OSPF network management

About this task

This task involves the following configurations:

· Bind an OSPF process to MIB so that you can use network management software to manage the specified OSPF process.

· Enable SNMP notifications for OSPF to report important events.

· Configure the SNMP notification output interval and the maximum number of SNMP notifications that can be output at each interval.

To report critical OSPF events to an NMS, enable SNMP notifications for OSPF. For SNMP notifications to be sent correctly, you must also configure SNMP on the device. For more information about SNMP configuration, see the network management and monitoring configuration guide for the device.

Procedure

1. Enter system view.

system-view

2. Bind MIB to an OSPF process.

ospf mib-binding process-id

By default, MIB is bound to the process with the smallest process ID.

3. Enable SNMP notifications for OSPF.

By default, SNMP notifications for OSPF are enabled.

4. (Optional.) Extend the format of SNMP notifications for neighbor state changes.

snmp-agent trap ospf neighbor-state-change extended

By default, OSPF does not extend the format of SNMP notifications for neighbor state changes.

5. Enter OSPF view.

ospf [ process-id | router-id { auto-select | router-id } | vpn-instance vpn-instance-name ] *

6. Configure the SNMP notification output interval and the maximum number of SNMP notifications that can be output at each interval.

snmp trap rate-limit interval trap-interval count trap-number

By default, OSPF outputs a maximum of seven SNMP notifications within 10 seconds.

Setting the maximum number of OSPF neighbor relationship troubleshooting entries

1. Enter system view.

system-view

2. Set the maximum number of OSPF neighbor relationship troubleshooting entries.

ospf troubleshooting max-number number

By default, OSPF can record a maximum of 100 neighbor relationship troubleshooting entries.

Display and maintenance commands for OSPF

Execute display commands in any view and reset commands in user view.

Task	Command
Display OSPF process information.	display ospf [ process-id ] [ verbose ]
Display OSPF GR information.	display ospf [ process-id ] graceful-restart [ verbose ]
Display OSPF FRR backup next hop information.	display ospf [ process-id ] [ area area-id ] fast-reroute lfa-candidate
Display OSPF LSDB information.	display ospf [ process-id ] lsdb [ brief \| originate-router advertising-router-id \| self-originate ] [ age { max-value max-age-value \| min-value min-age-value } * ] [ resolve-hostname ] display ospf [ process-id ] lsdb hostname host-name [ age { max-value max-age-value \| min-value min-age-value } * ] display ospf [ process-id ] lsdb opaque-as [ link-state-id ] [ originate-router advertising-router-id \| self-originate ] [ age { max-value max-age-value \| min-value min-age-value } * ] [ resolve-hostname ] display ospf [ process-id ] lsdb opaque-as [ link-state-id ] hostname host-name [ age { max-value max-age-value \| min-value min-age-value } * ] display ospf [ process-id ] lsdb ase [ link-state-id ] [ originate-router advertising-router-id \| self-originate ] [ age { max-value max-age-value \| min-value min-age-value } * ] [ resolve-hostname ] display ospf [ process-id ] lsdb ase [ link-state-id ] hostname host-name [ age { max-value max-age-value \| min-value min-age-value } * ] display ospf [ process-id ] [ area area-id ] lsdb { network \| opaque-area \| opaque-link } [ link-state-id ] [ originate-router advertising-router-id \| self-originate ] [ age { max-value max-age-value \| min-value min-age-value } * ] [ resolve-hostname ] display ospf [ process-id ] [ area area-id ] lsdb { network \| opaque-area \| opaque-link } [ link-state-id ] hostname host-name [ age { max-value max-age-value \| min-value min-age-value } * ] display ospf [ process-id ] [ area area-id ] lsdb { asbr \| nssa \| router \| summary } [ link-state-id ] [ originate-router advertising-router-id \| self-originate ] [ age { max-value max-age-value \| min-value min-age-value } * ] [ resolve-hostname ] display ospf [ process-id ] [ area area-id ] lsdb { asbr \| nssa \| router \| summary } [ link-state-id ] hostname host-name [ age { max-value max-age-value \| min-value min-age-value } * ]
Display OSPF next hop information.	display ospf [ process-id ] nexthop
Display OSPF NSR information.	display ospf [ process-id ] non-stop-routing status
Display OSPF neighbor information.	display ospf [ process-id ] peer [ hello \| verbose ] [ interface-type interface-number ] [ [ neighbor-id ] [ resolve-hostname ] \| hostname host-name ]
Display neighbor statistics for OSPF areas.	display ospf [ process-id ] peer statistics
Display OSPF routing table information.	display ospf [ process-id ] routing [ ip-address { mask-length \| mask } \| priority { critical \| high \| low \| medium } ] [ interface interface-type interface-number ] [ nexthop nexthop-address ] [ verbose ]
Display OSPF shortest path tree information.	display ospf [ process-id ] [ area area-id ] spf-tree [ verbose ]
Display OSPF statistics.	display ospf [ process-id ] statistics [ error \| packet [ hello \| interface-type interface-number ] ]
Display OSPF virtual link information.	display ospf [ process-id ] vlink
Display OSPF request queue information.	display ospf [ process-id ] request-queue [ interface-type interface-number ] [ neighbor-id ]
Display OSPF retransmission queue information.	display ospf [ process-id ] retrans-queue [ interface-type interface-number ] [ neighbor-id ]
Display OSPF ABR and ASBR information.	display ospf [ process-id ] abr-asbr [ verbose ]
Display summary route information on the OSPF ABR.	display ospf [ process-id ] [ area area-id ] abr-summary [ ip-address { mask-length \| mask } ] [ verbose ]
Display OSPF interface information.	display ospf [ process-id ] interface [ interface-type interface-number \| verbose ]
Display information about hello packets sent by OSPF interfaces.	display ospf [ process-id ] interface [ interface-type interface-number ] hello
Display OSPF route calculation log information.	In standalone mode: display ospf [ process-id ] event-log { lsa-flush \| lsa-history [ verbose ] \| peer [ slot slot-number [ cpu cpu-number ] \| route \| spf } In IRF mode: display ospf [ process-id ] event-log { lsa-flush \| lsa-history [ verbose ] \| peer [ chassis chassis-number slot slot-number [ cpu cpu-number ] ] \| route \| spf }
Display OSPF log information about received or sent hello packets.	In standalone mode: display ospf [ process-id ] event-log hello { received [ abnormal \| dropped ] \| sent } [ neighbor-id ] [ slot slot-number [ cpu cpu-number ] ] display ospf [ process-id ] event-log hello sent { abnormal \| failed } [ neighbor-address ] [ slot slot-number [ cpu cpu-number ] ] In IRF mode: display ospf [ process-id ] event-log hello { received [ abnormal \| dropped ] \| sent } [ neighbor-id ] [ chassis chassis-number slot slot-number [ cpu cpu-number ] ] display ospf [ process-id ] event-log hello sent { abnormal \| failed } [ neighbor-address ] [ chassis chassis-number slot slot-number [ cpu cpu-number ] ]
Display OSPF ASBR route summarization information.	display ospf [ process-id ] asbr-summary [ ip-address { mask-length \| mask } ]
Display the global route ID.	display router id
Display OSPF neighbor relationship troubleshooting information.	display ospf troubleshooting
Display the router ID-to-host name mapping table.	display ospf [ process-id ] hostname-table
Display global OSPF statistics.	display ospf global-statistics [ public \| vpn-instance vpn-instance-name ]
Clear OSPF statistics.	reset ospf [ process-id ] statistics
Clear OSPF log information.	In standalone mode: reset ospf [ process-id ] event-log [ lsa-flush \| lsa-history \| peer [ slot slot-number [ cpu cpu-number ] \| route \| spf ] In IRF mode: reset ospf [ process-id ] event-log [ lsa-flush \| lsa-history \| peer [ chassis chassis-number slot slot-number [ cpu cpu-number ] ] \| route \| spf ]
Clear OSPF log information about received or sent hello packets.	In standalone mode: reset ospf [ process-id ] event-log hello { received [ abnormal \| dropped ] \| sent [ abnormal \| failed ] } [ slot slot-number [ cpu cpu-number ] ] In IRF mode: reset ospf [ process-id ] event-log hello { received [ abnormal \| dropped ] \| sent [ abnormal \| failed ] } [ chassis chassis-number slot slot-number [ cpu cpu-number ] ]
Restart an OSPF process.	reset ospf [ process-id ] process [ graceful-restart ]
Re-enable OSPF route redistribution.	reset ospf [ process-id ] redistribution
Clear OSPF neighbor relationship troubleshooting information.	reset ospf troubleshooting

‌

OSPF configuration examples

Example: Configuring basic OSPF

Network configuration

As shown in Figure 13:

· Enable OSPF on all routers, and split the AS into three areas.

· Configure Router A and Router B as ABRs.

Figure 13 Network diagram

‌

Procedure

1. Configure IP addresses for interfaces. (Details not shown.)

2. Enable OSPF:

# Configure Router A.

<RouterA> system-view

[RouterA] router id 10.2.1.1

[RouterA] ospf

[RouterA-ospf-1] area 0

[RouterA-ospf-1-area-0.0.0.0] network 10.1.1.0 0.0.0.255

[RouterA-ospf-1-area-0.0.0.0] quit

[RouterA-ospf-1] area 1

[RouterA-ospf-1-area-0.0.0.1] network 10.2.1.0 0.0.0.255

[RouterA-ospf-1-area-0.0.0.1] quit

[RouterA-ospf-1] quit

# Configure Router B.

<RouterB> system-view

[RouterB] router id 10.3.1.1

[RouterB] ospf

[RouterB-ospf-1] area 0

[RouterB-ospf-1-area-0.0.0.0] network 10.1.1.0 0.0.0.255

[RouterB-ospf-1-area-0.0.0.0] quit

[RouterB-ospf-1] area 2

[RouterB-ospf-1-area-0.0.0.2] network 10.3.1.0 0.0.0.255

[RouterB-ospf-1-area-0.0.0.2] quit

[RouterB-ospf-1] quit

# Configure Router C.

<RouterC> system-view

[RouterC] router id 10.4.1.1

[RouterC] ospf

[RouterC-ospf-1] area 1

[RouterC-ospf-1-area-0.0.0.1] network 10.2.1.0 0.0.0.255

[RouterC-ospf-1-area-0.0.0.1] network 10.4.1.0 0.0.0.255

[RouterC-ospf-1-area-0.0.0.1] quit

[RouterC-ospf-1] quit

# Configure Router D.

<RouterD> system-view

[RouterD] router id 10.5.1.1

[RouterD] ospf

[RouterD-ospf-1] area 2

[RouterD-ospf-1-area-0.0.0.2] network 10.3.1.0 0.0.0.255

[RouterD-ospf-1-area-0.0.0.2] network 10.5.1.0 0.0.0.255

[RouterD-ospf-1-area-0.0.0.2] quit

[RouterD-ospf-1] quit

Verifying the configuration

# Display the OSPF neighbors of Router A.

[RouterA] display ospf peer verbose

OSPF Process 1 with Router ID 10.2.1.1

Neighbors

Area 0.0.0.0 interface 10.1.1.1(Ten-GigabitEthernet3/1/1)'s neighbors

Router ID: 10.3.1.1 Address: 10.1.1.2 GR State: Normal

State: Full Mode: Nbr is master Priority: 1

DR: 10.1.1.1 BDR: 10.1.1.2 MTU: 0

Options is 0x02 (-|-|-|-|-|-|E|-)

Dead timer due in 37 sec

Neighbor is up for 06:03:59

Authentication Sequence: [ 0 ]

Neighbor state change count: 5

BFD status: Disabled

Area 0.0.0.1 interface 10.2.1.1(Ten-GigabitEthernet3/1/2)'s neighbors

Router ID: 10.4.1.1 Address: 10.2.1.2 GR State: Normal

State: Full Mode: Nbr is master Priority: 1

DR: 10.2.1.1 BDR: 10.2.1.2 MTU: 0

Options is 0x02 (-|-|-|-|-|-|E|-)

Dead timer due in 32 sec

Neighbor is up for 06:03:12

Authentication Sequence: [ 0 ]

Neighbor state change count: 5

BFD status: Disabled

# Display OSPF routing information on Router A.

[RouterA] display ospf routing

OSPF Process 1 with Router ID 10.2.1.1

Routing Table

Topology base (MTID 0)

Routing for network

Destination Cost Type NextHop AdvRouter Area

10.2.1.0/24 1 Transit 10.2.1.1 10.2.1.1 0.0.0.1

10.3.1.0/24 2 Inter 10.1.1.2 10.3.1.1 0.0.0.0

10.4.1.0/24 2 Stub 10.2.1.2 10.4.1.1 0.0.0.1

10.5.1.0/24 3 Inter 10.1.1.2 10.3.1.1 0.0.0.0

10.1.1.0/24 1 Transit 10.1.1.1 10.2.1.1 0.0.0.0

Total nets: 5

Intra area: 3 Inter area: 2 ASE: 0 NSSA: 0

# Display OSPF routing information on Router D.

[RouterD] display ospf routing

OSPF Process 1 with Router ID 10.5.1.1

Routing Table

Topology base (MTID 0)

Routing for network

Destination Cost Type NextHop AdvRouter Area

10.2.1.0/24 3 Inter 10.3.1.1 10.3.1.1 0.0.0.2

10.3.1.0/24 1 Transit 10.3.1.2 10.3.1.1 0.0.0.2

10.4.1.0/24 4 Inter 10.3.1.1 10.3.1.1 0.0.0.2

10.5.1.0/24 1 Stub 10.5.1.1 10.5.1.1 0.0.0.2

10.1.1.0/24 2 Inter 10.3.1.1 10.3.1.1 0.0.0.2

Total nets: 5

Intra area: 2 Inter area: 3 ASE: 0 NSSA: 0

# Ping 10.4.1.1 to test reachability.

[RouterD] ping 10.4.1.1

Ping 10.4.1.1 (10.4.1.1): 56 data bytes, press CTRL+C to break

56 bytes from 10.4.1.1: icmp_seq=0 ttl=253 time=1.549 ms

56 bytes from 10.4.1.1: icmp_seq=1 ttl=253 time=1.539 ms

56 bytes from 10.4.1.1: icmp_seq=2 ttl=253 time=0.779 ms

56 bytes from 10.4.1.1: icmp_seq=3 ttl=253 time=1.702 ms

56 bytes from 10.4.1.1: icmp_seq=4 ttl=253 time=1.471 ms

--- Ping statistics for 10.4.1.1 ---

5 packet(s) transmitted, 5 packet(s) received, 0.0% packet loss

round-trip min/avg/max/std-dev = 0.779/1.408/1.702/0.323 ms

Example: Configuring OSPF route redistribution

Network configuration

As shown in Figure 14:

· Enable OSPF on all the routers.

· Split the AS into three areas.

· Configure Router A and Router B as ABRs.

· Configure Router C as an ASBR to redistribute external routes (static routes).

Figure 14 Network diagram

‌

Procedure

1. Configure IP addresses for interfaces. (Details not shown.)

2. Enable OSPF (see "Example: Configuring basic OSPF").

3. Configure OSPF to redistribute routes:

# On Router C, configure a static route destined for network 3.1.2.0/24.

<RouterC> system-view

[RouterC] ip route-static 3.1.2.1 24 10.4.1.2

# On Router C, configure OSPF to redistribute the static route.

[RouterC] ospf 1

[RouterC-ospf-1] import-route static

Verifying the configuration

# Display the ABR/ASBR information on Router D.

<RouterD> display ospf abr-asbr

OSPF Process 1 with Router ID 10.5.1.1

Routing Table to ABR and ASBR

Topology base (MTID 0)

Type Destination Area Cost Nexthop RtType

Intra 10.3.1.1 0.0.0.2 10 10.3.1.1 ABR

Inter 10.4.1.1 0.0.0.2 22 10.3.1.1 ASBR

# Display the OSPF routing information on Router D.

<RouterD> display ospf routing

OSPF Process 1 with Router ID 10.5.1.1

Routing Table

Topology base (MTID 0)

Routing for network

Destination Cost Type NextHop AdvRouter Area

10.2.1.0/24 22 Inter 10.3.1.1 10.3.1.1 0.0.0.2

10.3.1.0/24 10 Transit 10.3.1.2 10.3.1.1 0.0.0.2

10.4.1.0/24 25 Inter 10.3.1.1 10.3.1.1 0.0.0.2

10.5.1.0/24 10 Stub 10.5.1.1 10.5.1.1 0.0.0.2

10.1.1.0/24 12 Inter 10.3.1.1 10.3.1.1 0.0.0.2

Routing for ASEs

Destination Cost Type Tag NextHop AdvRouter

3.1.2.0/24 1 Type2 1 10.3.1.1 10.4.1.1

Total nets: 6

Intra area: 2 Inter area: 3 ASE: 1 NSSA: 0

Example: Configuring OSPF route summarization

Network configuration

As shown in Figure 15:

· Configure OSPF on Router A and Router B in AS 200.

· Configure OSPF on Router C, Router D, and Router E in AS 100.

· Configure an EBGP connection between Router B and Router C. Configure Router B and Router C to redistribute OSPF routes and direct routes into BGP and BGP routes into OSPF.

· Configure Router B to advertise only summary route 10.0.0.0/8 to Router A.

Figure 15 Network diagram

‌

Procedure

1. Configure IP addresses for interfaces. (Details not shown.)

2. Enable OSPF:

# Configure Router A.

<RouterA> system-view

[RouterA] router id 11.2.1.2

[RouterA] ospf

[RouterA-ospf-1] area 0

[RouterA-ospf-1-area-0.0.0.0] network 11.2.1.0 0.0.0.255

[RouterA-ospf-1-area-0.0.0.0] quit

[RouterA-ospf-1] quit

# Configure Router B.

<RouterB> system-view

[RouterB] router id 11.2.1.1

[RouterB] ospf

[RouterB-ospf-1] area 0

[RouterB-ospf-1-area-0.0.0.0] network 11.2.1.0 0.0.0.255

[RouterB-ospf-1-area-0.0.0.0] quit

[RouterB-ospf-1] quit

# Configure Router C.

<RouterC> system-view

[RouterC] router id 11.1.1.2

[RouterC] ospf

[RouterC-ospf-1] area 0

[RouterC-ospf-1-area-0.0.0.0] network 10.1.1.0 0.0.0.255

[RouterC-ospf-1-area-0.0.0.0] network 10.2.1.0 0.0.0.255

[RouterC-ospf-1-area-0.0.0.0] quit

[RouterC-ospf-1] quit

# Configure Router D.

<RouterD> system-view

[RouterD] router id 10.3.1.1

[RouterD] ospf

[RouterD-ospf-1] area 0

[RouterD-ospf-1-area-0.0.0.0] network 10.1.1.0 0.0.0.255

[RouterD-ospf-1-area-0.0.0.0] network 10.3.1.0 0.0.0.255

[RouterD-ospf-1-area-0.0.0.0] quit

[RouterD-ospf-1] quit

# Configure Router E.

<RouterE> system-view

[RouterE] router id 10.4.1.1

[RouterE] ospf

[RouterE-ospf-1] area 0

[RouterE-ospf-1-area-0.0.0.0] network 10.2.1.0 0.0.0.255

[RouterE-ospf-1-area-0.0.0.0] network 10.4.1.0 0.0.0.255

[RouterE-ospf-1-area-0.0.0.0] quit

[RouterE-ospf-1] quit

3. Configure BGP to redistribute OSPF routes and direct routes:

# Configure Router B.

[RouterB] bgp 200

[RouterB-bgp-default] peer 11.1.1.2 as-number 100

[RouterB-bgp-default] address-family ipv4 unicast

[RouterB-bgp-default-ipv4] peer 11.1.1.2 enable

[RouterB-bgp-default-ipv4] import-route ospf

[RouterB-bgp-default-ipv4] import-route direct

[RouterB-bgp-default-ipv4] quit

[RouterB-bgp-default] quit

# Configure Router C.

[RouterC] bgp 100

[RouterC-bgp-default] peer 11.1.1.1 as-number 200

[RouterC-bgp-default] address-family ipv4 unicast

[RouterC-bgp-default-ipv4] peer 11.1.1.1 enable

[RouterC-bgp-default-ipv4] import-route ospf

[RouterC-bgp-default-ipv4] import-route direct

[RouterB-bgp-default-ipv4] quit

[RouterC-bgp-default] quit

4. Configure Router B and Router C to redistribute BGP routes into OSPF:

# Configure OSPF to redistribute routes from BGP on Router B.

[RouterB] ospf

[RouterB-ospf-1] import-route bgp

# Configure OSPF to redistribute routes from BGP on Router C.

[RouterC] ospf

[RouterC-ospf-1] import-route bgp

# Display the IP routing table on Router A.

[RouterA] display ip routing-table

Destinations : 14 Routes : 14

Destination/Mask Proto Pre Cost NextHop Interface

0.0.0.0/32 Direct 0 0 127.0.0.1 InLoop0

10.1.1.0/24 O_ASE2 150 1 11.2.1.1 XGE3/1/1

10.2.1.0/24 O_ASE2 150 1 11.2.1.1 XGE3/1/1

10.3.1.0/24 O_ASE2 150 1 11.2.1.1 XGE3/1/1

10.4.1.0/24 O_ASE2 150 1 11.2.1.1 XGE3/1/1

11.2.1.0/24 Direct 0 0 11.2.1.2 XGE3/1/1

11.2.1.0/32 Direct 0 0 11.2.1.2 XGE3/1/1

11.2.1.2/32 Direct 0 0 127.0.0.1 InLoop0

11.2.1.255/32 Direct 0 0 11.2.1.2 XGE3/1/1

127.0.0.0/8 Direct 0 0 127.0.0.1 InLoop0

127.0.0.0/32 Direct 0 0 127.0.0.1 InLoop0

127.0.0.1/32 Direct 0 0 127.0.0.1 InLoop0

127.255.255.255/32 Direct 0 0 127.0.0.1 InLoop0

255.255.255.255/32 Direct 0 0 127.0.0.1 InLoop0

5. Configure route summarization:

# Configure route summarization on Router B to advertise a single route 10.0.0.0/8.

[RouterB-ospf-1] asbr-summary 10.0.0.0 8

# Display the IP routing table on Router A.

[RouterA] display ip routing-table

Destinations : 11 Routes : 11

Destination/Mask Proto Pre Cost NextHop Interface

0.0.0.0/32 Direct 0 0 127.0.0.1 InLoop0

10.0.0.0/8 O_ASE2 150 1 11.2.1.1 XGE3/1/1

11.2.1.0/24 Direct 0 0 11.2.1.2 XGE3/1/1

11.2.1.0/32 Direct 0 0 11.2.1.2 XGE3/1/1

11.2.1.2/32 Direct 0 0 127.0.0.1 InLoop0

11.2.1.255/32 Direct 0 0 11.2.1.2 XGE3/1/1

127.0.0.0/8 Direct 0 0 127.0.0.1 InLoop0

127.0.0.0/32 Direct 0 0 127.0.0.1 InLoop0

127.0.0.1/32 Direct 0 0 127.0.0.1 InLoop0

127.255.255.255/32 Direct 0 0 127.0.0.1 InLoop0

255.255.255.255/32 Direct 0 0 127.0.0.1 InLoop0

The output shows that routes 10.1.1.0/24, 10.2.1.0/24, 10.3.1.0/24 and 10.4.1.0/24 are summarized into a single route 10.0.0.0/8.

Example: Configuring OSPF stub area

Network configuration

As shown in Figure 16:

· Enable OSPF on all routers, and split the AS into three areas.

· Configure Router A and Router B as ABRs to forward routing information between areas.

· Configure Router D as the ASBR to redistribute static routes.

· Configure Area 1 as a stub area to reduce advertised LSAs without influencing reachability.

Figure 16 Network diagram

‌

Procedure

1. Configure IP addresses for interfaces. (Details not shown.)

2. Enable OSPF (see "Example: Configuring basic OSPF").

3. Configure route redistribution:

# Configure Router D to redistribute static routes.

<RouterD> system-view

[RouterD] ip route-static 3.1.2.1 24 10.5.1.2

[RouterD] ospf

[RouterD-ospf-1] import-route static

[RouterD-ospf-1] quit

# Display ABR/ASBR information on Router C.

<RouterC> display ospf abr-asbr

OSPF Process 1 with Router ID 10.4.1.1

Routing Table to ABR and ASBR

Topology base (MTID 0)

Type Destination Area Cost Nexthop RtType

Intra 10.2.1.1 0.0.0.1 3 10.2.1.1 ABR

Inter 10.5.1.1 0.0.0.1 7 10.2.1.1 ASBR

# Display OSPF routing information on Router C.

<RouterC> display ospf routing

OSPF Process 1 with Router ID 10.4.1.1

Routing Table

Topology base (MTID 0)

Routing for network

Destination Cost Type NextHop AdvRouter Area

10.2.1.0/24 3 Transit 0.0.0.0 10.2.1.1 0.0.0.1

10.3.1.0/24 7 Inter 10.2.1.1 10.2.1.1 0.0.0.1

10.4.1.0/24 3 Stub 10.4.1.1 10.4.1.1 0.0.0.1

10.5.1.0/24 17 Inter 10.2.1.1 10.2.1.1 0.0.0.1

10.1.1.0/24 5 Inter 10.2.1.1 10.2.1.1 0.0.0.1

Routing for ASEs

Destination Cost Type Tag NextHop AdvRouter

3.1.2.0/24 1 Type2 1 10.2.1.1 10.5.1.1

Total nets: 6

Intra area: 2 Inter area: 3 ASE: 1 NSSA: 0

The output shows that Router C's routing table contains an AS external route.

4. Configure Area 1 as a stub area:

# Configure Router A.

<RouterA> system-view

[RouterA] ospf

[RouterA-ospf-1] area 1

[RouterA-ospf-1-area-0.0.0.1] stub

[RouterA-ospf-1-area-0.0.0.1] quit

[RouterA-ospf-1] quit

# Configure Router C.

<RouterC> system-view

[RouterC] ospf

[RouterC-ospf-1] area 1

[RouterC-ospf-1-area-0.0.0.1] stub

[RouterC-ospf-1-area-0.0.0.1] quit

[RouterC-ospf-1] quit

# Display OSPF routing information on Router C.

[RouterC] display ospf routing

OSPF Process 1 with Router ID 10.4.1.1

Routing Table

Topology base (MTID 0)

Routing for network

Destination Cost Type NextHop AdvRouter Area

0.0.0.0/0 4 Inter 10.2.1.1 10.2.1.1 0.0.0.1

10.2.1.0/24 3 Transit 0.0.0.0 10.2.1.1 0.0.0.1

10.3.1.0/24 7 Inter 10.2.1.1 10.2.1.1 0.0.0.1

10.4.1.0/24 3 Stub 10.4.1.1 10.4.1.1 0.0.0.1

10.5.1.0/24 17 Inter 10.2.1.1 10.2.1.1 0.0.0.1

10.1.1.0/24 5 Inter 10.2.1.1 10.2.1.1 0.0.0.1

Total nets: 6

Intra area: 2 Inter area: 4 ASE: 0 NSSA: 0

The output shows that a default route replaces the AS external route.

# Configure Area 1 as a totally stub area.

[RouterA] ospf

[RouterA-ospf-1] area 1

[RouterA-ospf-1-area-0.0.0.1] stub no-summary

[RouterA-ospf-1-area-0.0.0.1] quit

# Display OSPF routing information on Router C.

[RouterC] display ospf routing

OSPF Process 1 with Router ID 10.4.1.1

Routing Table

Topology base (MTID 0)

Routing for network

Destination Cost Type NextHop AdvRouter Area

0.0.0.0/0 4 Inter 10.2.1.1 10.2.1.1 0.0.0.1

10.2.1.0/24 3 Transit 0.0.0.0 10.4.1.1 0.0.0.1

10.4.1.0/24 3 Stub 10.4.1.1 10.4.1.1 0.0.0.1

Total nets: 3

Intra area: 2 Inter area: 1 ASE: 0 NSSA: 0

The output shows that inter-area routes are removed, and only one external route (a default route) exists on Router C.

Example: Configuring OSPF NSSA area

Network configuration

As shown in Figure 17:

· Configure OSPF on all routers and split AS into three areas.

· Configure Router A and Router B as ABRs to forward routing information between areas.

· Configure Area 1 as an NSSA area and configure Router C as an ASBR to redistribute static routes into the AS.

Figure 17 Network diagram

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Procedure

1. Configure IP addresses for interfaces. (Details not shown.)

2. Enable OSPF (see "Example: Configuring basic OSPF").

3. Configure Area 1 as an NSSA area:

# Configure Router A.

<RouterA> system-view

[RouterA] ospf

[RouterA-ospf-1] area 1

[RouterA-ospf-1-area-0.0.0.1] nssa

[RouterA-ospf-1-area-0.0.0.1] quit

[RouterA-ospf-1] quit

# Configure Router C.

<RouterC> system-view

[RouterC] ospf

[RouterC-ospf-1] area 1

[RouterC-ospf-1-area-0.0.0.1] nssa

[RouterC-ospf-1-area-0.0.0.1] quit

[RouterC-ospf-1] quit

# Display routing information on Router C.

[RouterC] display ospf routing

OSPF Process 1 with Router ID 10.4.1.1

Routing Table

Topology base (MTID 0)

Routing for network

Destination Cost Type NextHop AdvRouter Area

10.2.1.0/24 3 Transit 10.2.1.2 10.4.1.1 0.0.0.1

10.3.1.0/24 7 Inter 10.2.1.1 10.2.1.1 0.0.0.1

10.4.1.0/24 3 Stub 10.4.1.1 10.4.1.1 0.0.0.1

10.5.1.0/24 17 Inter 10.2.1.1 10.2.1.1 0.0.0.1

10.1.1.0/24 5 Inter 10.2.1.1 10.2.1.1 0.0.0.1

Total nets: 5

Intra area: 2 Inter area: 3 ASE: 0 NSSA: 0

4. Configure route redistribution:

# Configure OSPF to redistribute the static route on Router C.

[RouterC] ip route-static 3.1.2.1 24 10.4.1.2

[RouterC] ospf

[RouterC-ospf-1] import-route static

[RouterC-ospf-1] quit

# Display routing information on Router D.

<RouterD> display ospf routing

OSPF Process 1 with Router ID 10.5.1.1

Routing Table

Topology base (MTID 0)

Routing for network

Destination Cost Type NextHop AdvRouter Area

10.2.1.0/24 22 Inter 10.3.1.1 10.3.1.1 0.0.0.2

10.3.1.0/24 10 Transit 10.3.1.2 10.3.1.1 0.0.0.2

10.4.1.0/24 25 Inter 10.3.1.1 10.3.1.1 0.0.0.2

10.5.1.0/24 10 Stub 10.5.1.1 10.5.1.1 0.0.0.2

10.1.1.0/24 12 Inter 10.3.1.1 10.3.1.1 0.0.0.2

Routing for ASEs

Destination Cost Type Tag NextHop AdvRouter

3.1.2.0/24 1 Type2 1 10.3.1.1 10.2.1.1

Total nets: 6

Intra area: 2 Inter area: 3 ASE: 1 NSSA: 0

The output shows that an AS external route imported from the NSSA area exists on Router D.

Example: Configuring OSPF DR election

Network configuration

As shown in Figure 18:

· Enable OSPF on Routers A, B, C, and D on the same network.

· Configure Router D as the DR, and configure Router C as the BDR.

· Change the router priorities on the interfaces to configure Router A as the DR and Router C as the BDR.

Figure 18 Network diagram

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Procedure

1. Configure IP addresses for interfaces. (Details not shown.)

2. Configure basic OSPF settings on all routers. (Details not shown.)

For more information, see "Example: Configuring basic OSPF."

3. Display neighbor information on Router A.

[RouterA] display ospf peer verbose

OSPF Process 1 with Router ID 1.1.1.1

Neighbors

Area 0.0.0.0 interface 192.168.1.1(Ten-GigabitEthernet3/1/1)'s neighbors

Router ID: 2.2.2.2 Address: 192.168.1.2 GR State: Normal

State: 2-Way Mode: None Priority: 1

DR: 192.168.1.4 BDR: 192.168.1.3 MTU: 0

Options is 0x02 (-|-|-|-|-|-|E|-)

Dead timer due in 38 sec

Neighbor is up for 00:01:31

Authentication Sequence: [ 0 ]

Neighbor state change count: 6

BFD status: Disabled

Router ID: 3.3.3.3 Address: 192.168.1.3 GR State: Normal

State: Full Mode: Nbr is master Priority: 1

DR: 192.168.1.4 BDR: 192.168.1.3 MTU: 0

Options is 0x02 (-|-|-|-|-|-|E|-)

Dead timer due in 31 sec

Neighbor is up for 00:01:28

Authentication Sequence: [ 0 ]

Neighbor state change count: 6

BFD status: Disabled

Router ID: 4.4.4.4 Address: 192.168.1.4 GR State: Normal

State: Full Mode: Nbr is master Priority: 1

DR: 192.168.1.4 BDR: 192.168.1.3 MTU: 0

Options is 0x02 (-|-|-|-|-|-|E|-)

Dead timer due in 31 sec

Neighbor is up for 00:01:28

Authentication Sequence: [ 0 ]

Neighbor state change count: 6

BFD status: Disabled

The output shows that Router D is the DR and Router C is the BDR.

4. Configure router priorities on interfaces:

# Configure Router A.

[RouterA] interface ten-gigabitethernet 3/1/1

[RouterA-Ten-GigabitEthernet3/1/1] ospf dr-priority 100

[RouterA-Ten-GigabitEthernet3/1/1] quit

[RouterA] quit

# Configure Router B.

[RouterB] interface ten-gigabitethernet 3/1/1

[RouterB-Ten-GigabitEthernet3/1/1] ospf dr-priority 0

[RouterB-Ten-GigabitEthernet3/1/1] quit

[RouterB] quit

# Configure Router C.

[RouterC] interface ten-gigabitethernet 3/1/1

[RouterC-Ten-GigabitEthernet3/1/1] ospf dr-priority 2

[RouterC-Ten-GigabitEthernet3/1/1] quit

[RouterC] quit

# Display information about neighbors of Router D.

<RouterD> display ospf peer verbose

OSPF Process 1 with Router ID 4.4.4.4

Neighbors

Area 0.0.0.0 interface 192.168.1.4(Ten-GigabitEthernet3/1/1)'s neighbors

Router ID: 1.1.1.1 Address: 192.168.1.1 GR State: Normal

State: Full Mode:Nbr is slave Priority: 100

DR: 192.168.1.4 BDR: 192.168.1.3 MTU: 0

Options is 0x02 (-|-|-|-|-|-|E|-)

Dead timer due in 31 sec

Neighbor is up for 00:11:17

Authentication Sequence: [ 0 ]

Neighbor state change count: 6

BFD status: Disabled

Router ID: 2.2.2.2 Address: 192.168.1.2 GR State: Normal

State: Full Mode:Nbr is slave Priority: 0

DR: 192.168.1.4 BDR: 192.168.1.3 MTU: 0

Options is 0x02 (-|-|-|-|-|-|E|-)

Dead timer due in 35 sec

Neighbor is up for 00:11:19

Authentication Sequence: [ 0 ]

Neighbor state change count: 6

BFD status: Disabled

Router ID: 3.3.3.3 Address: 192.168.1.3 GR State: Normal

State: Full Mode:Nbr is slave Priority: 2

DR: 192.168.1.4 BDR: 192.168.1.3 MTU: 0

Options is 0x02 (-|-|-|-|-|-|E|-)

Dead timer due in 33 sec

Neighbor is up for 00:11:15

Authentication Sequence: [ 0 ]

Neighbor state change count: 6

BFD status: Disabled

The output shows that the DR and BDR are not changed, because the new router priority settings do not take effect immediately.

5. Restart OSPF processes:

# Restart the OSPF process on Router A.

<RouterA> reset ospf 1 process

Warning : Reset OSPF process? [Y/N]:y

# Restart the OSPF process on Router B.

<RouterB> reset ospf 1 process

Warning : Reset OSPF process? [Y/N]:y

# Restart the OSPF process on Router C.

<RouterC> reset ospf 1 process

Warning : Reset OSPF process? [Y/N]:y

# Restart the OSPF process on Router D.

<RouterD> reset ospf 1 process

Warning : Reset OSPF process? [Y/N]:y

# Display neighbor information on Router D.

<RouterD> display ospf peer verbose

OSPF Process 1 with Router ID 4.4.4.4

Neighbors

Area 0.0.0.0 interface 192.168.1.4(Ten-GigabitEthernet3/1/1)'s neighbors

Router ID: 1.1.1.1 Address: 192.168.1.1 GR State: Normal

State: Full Mode: Nbr is slave Priority: 100

DR: 192.168.1.1 BDR: 192.168.1.3 MTU: 0

Options is 0x02 (-|-|-|-|-|-|E|-)

Dead timer due in 39 sec

Neighbor is up for 00:01:40

Authentication Sequence: [ 0 ]

Neighbor state change count: 6

BFD status: Disabled

Router ID: 2.2.2.2 Address: 192.168.1.2 GR State: Normal

State: 2-Way Mode: None Priority: 0

DR: 192.168.1.1 BDR: 192.168.1.3 MTU: 0

Options is 0x02 (-|-|-|-|-|-|E|-)

Dead timer due in 35 sec

Neighbor is up for 00:01:44

Authentication Sequence: [ 0 ]

Neighbor state change count: 6

BFD status: Disabled

Router ID: 3.3.3.3 Address: 192.168.1.3 GR State: Normal

State: Full Mode: Nbr is slave Priority: 2

DR: 192.168.1.1 BDR: 192.168.1.3 MTU: 0

Options is 0x02 (-|-|-|-|-|-|E|-)

Dead timer due in 39 sec

Neighbor is up for 00:01:41

Authentication Sequence: [ 0 ]

Neighbor state change count: 6

BFD status: Disabled

The output shows that Router A becomes the DR and Router C becomes the BDR.

The full neighbor state means an adjacency has been established. The 2-way neighbor state means the two routers are not the DR or BDR, and they do not exchange LSAs.

# Display OSPF interface information.

<RouterA> display ospf interface

OSPF Process 1 with Router ID 1.1.1.1

Interfaces

Area: 0.0.0.0

IP Address Type State Cost Pri DR BDR

192.168.1.1 Broadcast DR 1 100 192.168.1.1 192.168.1.3

<RouterB> display ospf interface

OSPF Process 1 with Router ID 2.2.2.2

Interfaces

Area: 0.0.0.0

IP Address Type State Cost Pri DR BDR

192.168.1.2 Broadcast DROther 1 0 192.168.1.1 192.168.1.3

The interface state DROther means the interface is not the DR or BDR.

Example: Configuring OSPF virtual link

Network configuration

As shown in Figure 19, configure a virtual link between Router B and Router C to connect Area 2 to the backbone area. After configuration, Router B can learn routes to Area 2.

Figure 19 Network diagram

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Procedure

1. Configure IP addresses for interfaces. (Details not shown.)

2. Enable OSPF:

# Configure Router A.

<RouterA> system-view

[RouterA] ospf 1 router-id 1.1.1.1

[RouterA-ospf-1] area 0

[RouterA-ospf-1-area-0.0.0.0] network 10.1.1.0 0.0.0.255

[RouterA-ospf-1-area-0.0.0.0] quit

[RouterA-ospf-1] quit

# Configure Router B.

<RouterB> system-view

[RouterB] ospf 1 router-id 2.2.2.2

[RouterB-ospf-1] area 0

[RouterB-ospf-1-area-0.0.0.0] network 10.1.1.0 0.0.0.255

[RouterB-ospf-1-area-0.0.0.0] quit

[RouterB-ospf-1] area 1

[RouterB–ospf-1-area-0.0.0.1] network 10.2.1.0 0.0.0.255

[RouterB–ospf-1-area-0.0.0.1] quit

[RouterB-ospf-1] quit

# Configure Router C.

<RouterC> system-view

[RouterC] ospf 1 router-id 3.3.3.3

[RouterC-ospf-1] area 1

[RouterC-ospf-1-area-0.0.0.1] network 10.2.1.0 0.0.0.255

[RouterC-ospf-1-area-0.0.0.1] quit

[RouterC-ospf-1] area 2

[RouterC–ospf-1-area-0.0.0.2] network 10.3.1.0 0.0.0.255

[RouterC–ospf-1-area-0.0.0.2] quit

[RouterC-ospf-1] quit

# Configure Router D.

<RouterD> system-view

[RouterD] ospf 1 router-id 4.4.4.4

[RouterD-ospf-1] area 2

[RouterD-ospf-1-area-0.0.0.2] network 10.3.1.0 0.0.0.255

[RouterD-ospf-1-area-0.0.0.2] quit

[RouterD-ospf-1] quit

# Display OSPF routing information on Router B.

[RouterB] display ospf routing

OSPF Process 1 with Router ID 2.2.2.2

Routing Table

Topology base (MTID 0)

Routing for network

Destination Cost Type NextHop AdvRouter Area

10.2.1.0/24 2 Transit 10.2.1.1 3.3.3.3 0.0.0.1

10.1.1.0/24 2 Transit 10.1.1.2 2.2.2.2 0.0.0.0

Total nets: 2

Intra area: 2 Inter area: 0 ASE: 0 NSSA: 0

The output shows that Router B does not have routes to Area 2 because Area 0 is not directly connected to Area 2.

3. Configure a virtual link:

# Configure Router B.

[RouterB] ospf

[RouterB-ospf-1] area 1

[RouterB-ospf-1-area-0.0.0.1] vlink-peer 3.3.3.3

[RouterB-ospf-1-area-0.0.0.1] quit

[RouterB-ospf-1] quit

# Configure Router C.

[RouterC] ospf

[RouterC-ospf-1] area 1

[RouterC-ospf-1-area-0.0.0.1] vlink-peer 2.2.2.2

[RouterC-ospf-1-area-0.0.0.1] quit

[RouterC-ospf-1] quit

# Display OSPF routing information on Router B.

[RouterB] display ospf routing

OSPF Process 1 with Router ID 2.2.2.2

Routing Table

Topology base (MTID 0)

Routing for network

Destination Cost Type NextHop AdvRouter Area

10.2.1.0/24 2 Transit 10.2.1.1 3.3.3.3 0.0.0.1

10.3.1.0/24 5 Inter 10.2.1.2 3.3.3.3 0.0.0.0

10.1.1.0/24 2 Transit 10.1.1.2 2.2.2.2 0.0.0.0

Total nets: 3

Intra area: 2 Inter area: 1 ASE: 0 NSSA: 0

The output shows that Router B has learned the route 10.3.1.0/24 to Area 2.

Example: Configuring OSPF GR

Network configuration

As shown in Figure 20:

· Router A, Router B, and Router C that belong to the same autonomous system and the same OSPF routing domain are GR capable.

· Router A acts as the non-IETF GR restarter. Router B and Router C are the GR helpers, and synchronize their LSDBs with Router A through OOB communication of GR.

Figure 20 Network diagram

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Procedure

1. Configure IP addresses for interfaces. (Details not shown.)

2. Enable OSPF:

# Configure Router A.

<RouterA> system-view

[RouterA] router id 1.1.1.1

[RouterA] ospf 100

[RouterA-ospf-100] area 0

[RouterA-ospf-100-area-0.0.0.0] network 192.1.1.0 0.0.0.255

[RouterA-ospf-100-area-0.0.0.0] quit

[RouterA-ospf-100] quit

# Configure Router B.

<RouterB> system-view

[RouterB] router id 2.2.2.2

[RouterB] ospf 100

[RouterB-ospf-100] area 0

[RouterB-ospf-100-area-0.0.0.0] network 192.1.1.0 0.0.0.255

[RouterB-ospf-100-area-0.0.0.0] quit

[RouterB-ospf-100] quit

# Configure Router C.

<RouterC> system-view

[RouterC] router id 3.3.3.3

[RouterC] ospf 100

[RouterC-ospf-100] area 0

[RouterC-ospf-100-area-0.0.0.0] network 192.1.1.0 0.0.0.255

[RouterC-ospf-100-area-0.0.0.0] quit

[RouterC-ospf-100] quit

3. Configure OSPF GR:

# Configure Router A as the non-IETF OSPF GR restarter: enable the link-local signaling capability, the out-of-band re-synchronization capability, and non-IETF GR for OSPF process 100.

[RouterA-ospf-100] enable link-local-signaling

[RouterA-ospf-100] enable out-of-band-resynchronization

[RouterA-ospf-100] graceful-restart

[RouterA-ospf-100] quit

# Configure Router B as the GR helper: enable the link-local signaling capability and the out-of-band re-synchronization capability for OSPF process 100.

[RouterB-ospf-100] enable link-local-signaling

[RouterB-ospf-100] enable out-of-band-resynchronization

# Configure Router C as the GR helper: enable the link-local signaling capability and the out-of-band re-synchronization capability for OSPF process 100.

[RouterC-ospf-100] enable link-local-signaling

[RouterC-ospf-100] enable out-of-band-resynchronization

Verifying the configuration

# Enable OSPF GR event debugging and restart the OSPF process by using GR on Router A.

<RouterA> debugging ospf event graceful-restart

<RouterA> terminal monitor

<RouterA> terminal logging level 7

<RouterA> reset ospf 100 process graceful-restart

Reset OSPF process? [Y/N]:y

%Oct 21 15:29:28:727 2011 RouterA OSPF/5/OSPF_NBR_CHG: OSPF 100 Neighbor 192.1.1.2(Ten-GigabitEthernet3/1/1) from Full to Down.

%Oct 21 15:29:28:729 2011 RouterA OSPF/5/OSPF_NBR_CHG: OSPF 100 Neighbor 192.1.1.3(Ten-GigabitEthernet3/1/1) from Full to Down.

*Oct 21 15:29:28:735 2011 RouterA OSPF/7/DEBUG:

OSPF 100 nonstandard GR Started for OSPF Router

*Oct 21 15:29:28:735 2011 RouterA OSPF/7/DEBUG:

OSPF 100 created GR wait timer,timeout interval is 40(s).

*Oct 21 15:29:28:735 2011 RouterA OSPF/7/DEBUG:

OSPF 100 created GR Interval timer,timeout interval is 120(s).

*Oct 21 15:29:28:758 2011 RouterA OSPF/7/DEBUG:

OSPF 100 created OOB Progress timer for neighbor 192.1.1.3.

*Oct 21 15:29:28:766 2011 RouterA OSPF/7/DEBUG:

OSPF 100 created OOB Progress timer for neighbor 192.1.1.2.

%Oct 21 15:29:29:902 2011 RouterA OSPF/5/OSPF_NBR_CHG: OSPF 100 Neighbor 192.1.1.2(Ten-GigabitEthernet3/1/1) from Loading to Full.

*Oct 21 15:29:29:902 2011 RouterA OSPF/7/DEBUG:

OSPF 100 deleted OOB Progress timer for neighbor 192.1.1.2.

%Oct 21 15:29:30:897 2011 RouterA OSPF/5/OSPF_NBR_CHG: OSPF 100 Neighbor 192.1.1.3(Ten-GigabitEthernet3/1/1) from Loading to Full.

*Oct 21 15:29:30:897 2011 RouterA OSPF/7/DEBUG:

OSPF 100 deleted OOB Progress timer for neighbor 192.1.1.3.

*Oct 21 15:29:30:911 2011 RouterA OSPF/7/DEBUG:

OSPF GR: Process 100 Exit Restart,Reason : DR or BDR change,for neighbor : 192.1.1.3.

*Oct 21 15:29:30:911 2011 RouterA OSPF/7/DEBUG:

OSPF 100 deleted GR Interval timer.

*Oct 21 15:29:30:912 2011 RouterA OSPF/7/DEBUG:

OSPF 100 deleted GR wait timer.

%Oct 21 15:29:30:920 2011 RouterA OSPF/5/OSPF_NBR_CHG: OSPF 100 Neighbor 192.1.1.2(Ten-GigabitEthernet3/1/1) from Full to Down.

%Oct 21 15:29:30:921 2011 RouterA OSPF/5/OSPF_NBR_CHG: OSPF 100 Neighbor 192.1.1.3(Ten-GigabitEthernet3/1/1) from Full to Down.

%Oct 21 15:29:33:815 2011 RouterA OSPF/5/OSPF_NBR_CHG: OSPF 100 Neighbor 192.1.1.3(Ten-GigabitEthernet3/1/1) from Loading to Full.

%Oct 21 15:29:35:578 2011 RouterA OSPF/5/OSPF_NBR_CHG: OSPF 100 Neighbor 192.1.1.2(Ten-GigabitEthernet3/1/1) from Loading to Full.

The output shows that Router A completes GR.

Example: Configuring BFD for OSPF

Network configuration

As shown in Figure 21, run OSPF on Router A, Router B, and Router C so that they can reach each other at the network layer.

· When the link over which Router A and Router B communicate through a Layer 2 switch fails, BFD can quickly detect the failure and notify OSPF of the failure.

· Router A and Router B then communicate through Router C.

Figure 21 Network diagram

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Table 5 Interface and IP address assignment

Device	Interface	IP address
Router A	XGE3/1/1	192.168.0.102/24
Router A	XGE3/1/2	10.1.1.102/24
Router A	Loop0	121.1.1.1/32
Router B	XGE3/1/1	192.168.0.100/24
Router B	XGE3/1/2	13.1.1.1/24
Router B	Loop0	120.1.1.1/32
Router C	XGE3/1/1	10.1.1.100/24
Router C	XGE3/1/2	13.1.1.2/24

‌

Procedure

1. Configure IP addresses for interfaces. (Details not shown.)

2. Enable OSPF:

# Configure Router A.

<RouterA> system-view

[RouterA] ospf

[RouterA-ospf-1] area 0

[RouterA-ospf-1-area-0.0.0.0] network 192.168.0.0 0.0.0.255

[RouterA-ospf-1-area-0.0.0.0] network 10.1.1.0 0.0.0.255

[RouterA-ospf-1-area-0.0.0.0] network 121.1.1.1 0.0.0.0

[RouterA-ospf-1-area-0.0.0.0] quit

[RouterA-ospf-1] quit

# Configure Router B.

<RouterB> system-view

[RouterB] ospf

[RouterB-ospf-1] area 0

[RouterB-ospf-1-area-0.0.0.0] network 192.168.0.0 0.0.0.255

[RouterB-ospf-1-area-0.0.0.0] network 13.1.1.0 0.0.0.255

[RouterB-ospf-1-area-0.0.0.0] network 120.1.1.1 0.0.0.0

[RouterB-ospf-1-area-0.0.0.0] quit

[RouterB-ospf-1] quit

# Configure Router C.

<RouterC> system-view

[RouterC] ospf

[RouterC-ospf-1] area 0

[RouterC-ospf-1-area-0.0.0.0] network 10.1.1.0 0.0.0.255

[RouterC-ospf-1-area-0.0.0.0] network 13.1.1.0 0.0.0.255

[RouterC-ospf-1-area-0.0.0.0] quit

[RouterC-ospf-1] quit

3. Configure BFD:

# Enable BFD on Router A and configure BFD parameters.

[RouterA] bfd session init-mode active

[RouterA] interface ten-gigabitethernet 3/1/1

[RouterA-Ten-GigabitEthernet3/1/1] ospf bfd enable

[RouterA-Ten-GigabitEthernet3/1/1] bfd min-transmit-interval 500

[RouterA-Ten-GigabitEthernet3/1/1] bfd min-receive-interval 500

[RouterA-Ten-GigabitEthernet3/1/1] bfd detect-multiplier 7

[RouterA-Ten-GigabitEthernet3/1/1] quit

# Enable BFD on Router B and configure BFD parameters.

[RouterB] bfd session init-mode active

[RouterB] interface ten-gigabitethernet 3/1/1

[RouterB-Ten-GigabitEthernet3/1/1] ospf bfd enable

[RouterB-Ten-GigabitEthernet3/1/1] bfd min-transmit-interval 500

[RouterB-Ten-GigabitEthernet3/1/1] bfd min-receive-interval 500

[RouterB-Ten-GigabitEthernet3/1/1] bfd detect-multiplier 6

[RouterB-Ten-GigabitEthernet3/1/1] quit

Verifying the configuration

# Display the BFD information on Router A.

<RouterA> display bfd session

Total sessions: 1 Up sessions: 1 Init mode: Active

IPv4 session working in control packet mode:

LD/RD SourceAddr DestAddr State Holdtime Interface

3/1 192.168.0.102 192.168.0.100 Up 1700ms XGE3/1/1

# Display routes destined for 120.1.1.1/32 on Router A.

<RouterA> display ip routing-table 120.1.1.1 verbose

Summary Count : 1

Destination: 120.1.1.1/32

Protocol: O_INTRA

Process ID: 1

SubProtID: 0x1 Age: 04h20m37s

FlushedAge: 15h28m49s

Cost: 1 Preference: 10

IpPre: N/A QosLocalID: N/A

Tag: 0 State: Active Adv

OrigTblID: 0x0 OrigVrf: default-vrf

TableID: 0x2 OrigAs: 0

NibID: 0x26000002 LastAs: 0

AttrID: 0xffffffff

BkAttrID: 0xffffffff Neighbor: 0.0.0.0

Flags: 0x1008c OrigNextHop: 192.168.0.100

Label: NULL RealNextHop: 192.168.0.100

BkLabel: NULL BkNextHop: N/A

SRLabel: NULL Interface: Ten-GigabitEthernet3/1/1

BkSRLabel: NULL BkInterface: N/A

Tunnel ID: Invalid IPInterface: Ten-GigabitEthernet3/1/1

BkTunnel ID: Invalid BkIPInterface: N/A

InLabel: NULL ColorInterface: N/A

SIDIndex: NULL BkColorInterface: N/A

FtnIndex: 0x0 TunnelInterface: N/A

TrafficIndex: N/A BkTunnelInterface: N/A

Connector: N/A PathID: 0x0

UserID: 0x0 SRTunnelID: Invalid

SID Type: N/A NID: Invalid

FlushNID: Invalid BkNID: Invalid

BkFlushNID: Invalid StatFlags: 0x0

SID: N/A

BkSID: N/A

CommBlockLen: 0 Priority: Critical

MemberPort: N/A

The output shows that Router A communicates with Router B through Ten-GigabitEthernet 3/1/1. Then the link over Ten-GigabitEthernet 3/1/1 fails.

# Display routes destined for 120.1.1.1/32 on Router A.

<RouterA> display ip routing-table 120.1.1.1 verbose

Summary Count : 1

Destination: 120.1.1.1/32

Protocol: O_INTRA

Process ID: 1

SubProtID: 0x1 Age: 04h20m37s

FlushedAge: 15h28m49s

Cost: 2 Preference: 10

IpPre: N/A QosLocalID: N/A

Tag: 0 State: Active Adv

OrigTblID: 0x0 OrigVrf: default-vrf

TableID: 0x2 OrigAs: 0

NibID: 0x26000002 LastAs: 0

AttrID: 0xffffffff

BkAttrID: 0xffffffff Neighbor: 0.0.0.0

Flags: 0x1008c OrigNextHop: 10.1.1.100

Label: NULL RealNextHop: 10.1.1.100

BkLabel: NULL BkNextHop: N/A

SRLabel: NULL Interface: Ten-GigabitEthernet3/1/2

BkSRLabel: NULL BkInterface: N/A

Tunnel ID: Invalid IPInterface: Ten-GigabitEthernet3/1/2

BkTunnel ID: Invalid BkIPInterface: N/A

InLabel: NULL ColorInterface: N/A

SIDIndex: NULL BkColorInterface: N/A

FtnIndex: 0x0 TunnelInterface: N/A

TrafficIndex: N/A BkTunnelInterface: N/A

Connector: N/A PathID: 0x0

UserID: 0x0 SRTunnelID: Invalid

SID Type: N/A NID: Invalid

FlushNID: Invalid BkNID: Invalid

BkFlushNID: Invalid StatFlags: 0x0

SID: N/A

BkSID: N/A

CommBlockLen: 0 Priority: Critical

MemberPort: N/A

The output shows that Router A communicates with Router B through Ten-GigabitEthernet 3/1/2.

Example: Configuring OSPF FRR

Network configuration

As shown in Figure 22, Router A, Router B, and Router C reside in the same OSPF domain. Configure OSPF FRR so that when Link A fails, traffic is immediately switched to Link B.

Figure 22 Network diagram

‌

Table 6 Interface and IP address assignment

Device	Interface	IP address
Router A	XGE3/1/1	12.12.12.1/24
Router A	XGE3/1/2	13.13.13.1/24
Router A	Loop0	1.1.1.1/32
Router B	XGE3/1/1	24.24.24.4/24
Router B	XGE3/1/2	13.13.13.2/24
Router B	Loop0	4.4.4.4/32
Router C	XGE3/1/1	12.12.12.2/24
Router C	XGE3/1/2	24.24.24.2/24

‌

Procedure

1. Configure IP addresses and subnet masks for interfaces on the routers. (Details not shown.)

2. Configure OSPF on the routers to ensure that Router A, Router B, and Router C can communicate with each other at the network layer. (Details not shown.)

3. Configure OSPF FRR:

You can enable OSPF FRR to either calculate a backup next hop by using the LFA algorithm, or specify a backup next hop by using a routing policy.

¡ (Method 1.) Enable OSPF FRR to calculate a backup next hop by using the LFA algorithm:

# Configure Router A.

<RouterA> system-view

[RouterA] ospf 1

[RouterA-ospf-1] fast-reroute lfa

[RouterA-ospf-1] quit

# Configure Router B.

<RouterB> system-view

[RouterB] ospf 1

[RouterB-ospf-1] fast-reroute lfa

[RouterB-ospf-1] quit

¡ (Method 2.) Enable OSPF FRR to specify a backup next hop by using a routing policy:

# Configure Router A.

<RouterA> system-view

[RouterA] ip prefix-list abc index 10 permit 4.4.4.4 32

[RouterA] route-policy frr permit node 10

[RouterA-route-policy-frr-10] if-match ip address prefix-list abc

[RouterA-route-policy-frr-10] apply fast-reroute backup-interface ten-gigabitethernet 3/1/1 backup-nexthop 12.12.12.2

[RouterA-route-policy-frr-10] quit

[RouterA] ospf 1

[RouterA-ospf-1] fast-reroute route-policy frr

[RouterA-ospf-1] quit

# Configure Router B.

<RouterB> system-view

[RouterB] ip prefix-list abc index 10 permit 1.1.1.1 32

[RouterB] route-policy frr permit node 10

[RouterB-route-policy-frr-10] if-match ip address prefix-list abc

[RouterB-route-policy-frr-10] apply fast-reroute backup-interface ten-gigabitethernet 3/1/1 backup-nexthop 24.24.24.2

[RouterB-route-policy-frr-10] quit

[RouterB] ospf 1

[RouterB-ospf-1] fast-reroute route-policy frr

[RouterB-ospf-1] quit

Verifying the configuration

# Display route 4.4.4.4/32 on Router A to view the backup next hop information.

[RouterA] display ip routing-table 4.4.4.4 verbose

Summary Count : 1

Destination: 4.4.4.4/32

Protocol: O_INTRA

Process ID: 1

SubProtID: 0x1 Age: 04h20m37s

FlushedAge: 15h28m49s

Cost: 1 Preference: 10

IpPre: N/A QosLocalID: N/A

Tag: 0 State: Active Adv

OrigTblID: 0x0 OrigVrf: default-vrf

TableID: 0x2 OrigAs: 0

NibID: 0x26000002 LastAs: 0

AttrID: 0xffffffff

BkAttrID: 0xffffffff Neighbor: 0.0.0.0

Flags: 0x1008c OrigNextHop: 13.13.13.2

Label: NULL RealNextHop: 13.13.13.2

BkLabel: NULL BkNextHop: 12.12.12.2

SRLabel: NULL Interface: Ten-GigabitEthernet3/1/2

BkSRLabel: NULL BkInterface: N/A

Tunnel ID: Invalid IPInterface: Ten-GigabitEthernet3/1/2

BkTunnel ID: Invalid BkIPInterface: Ten-GigabitEthernet3/1/1

InLabel: NULL ColorInterface: N/A

SIDIndex: NULL BkColorInterface: N/A

FtnIndex: 0x0 TunnelInterface: N/A

TrafficIndex: N/A BkTunnelInterface: N/A

Connector: N/A PathID: 0x0

UserID: 0x0 SRTunnelID: Invalid

SID Type: N/A NID: Invalid

FlushNID: Invalid BkNID: Invalid

BkFlushNID: Invalid StatFlags: 0x0

SID: N/A

BkSID: N/A

CommBlockLen: 0 Priority: Critical

MemberPort: N/A

# Display route 1.1.1.1/32 on Router B to view the backup next hop information.

[RouterB] display ip routing-table 1.1.1.1 verbose

Summary Count : 1

Destination: 1.1.1.1/32

Protocol: O_INTRA

Process ID: 1

SubProtID: 0x1 Age: 04h20m37s

FlushedAge: 15h28m49s

Cost: 1 Preference: 10

IpPre: N/A QosLocalID: N/A

Tag: 0 State: Active Adv

OrigTblID: 0x0 OrigVrf: default-vrf

TableID: 0x2 OrigAs: 0

NibID: 0x26000002 LastAs: 0

AttrID: 0xffffffff

BkAttrID: 0xffffffff Neighbor: 0.0.0.0

Flags: 0x1008c OrigNextHop: 13.13.13.1

Label: NULL RealNextHop: 13.13.13.1

BkLabel: NULL BkNextHop: 24.24.24.2

SRLabel: NULL Interface: Ten-GigabitEthernet3/1/2

BkSRLabel: NULL BkInterface: N/A

Tunnel ID: Invalid IPInterface: Ten-GigabitEthernet3/1/2

BkTunnel ID: Invalid BkIPInterface: Ten-GigabitEthernet3/1/1

InLabel: NULL ColorInterface: N/A

SIDIndex: NULL BkColorInterface: N/A

FtnIndex: 0x0 TunnelInterface: N/A

TrafficIndex: N/A BkTunnelInterface: N/A

Connector: N/A PathID: 0x0

UserID: 0x0 SRTunnelID: Invalid

SID Type: N/A NID: Invalid

FlushNID: Invalid BkNID: Invalid

BkFlushNID: Invalid StatFlags: 0x0

SID: N/A

BkSID: N/A

CommBlockLen: 0 Priority: Critical

MemberPort: N/A

Troubleshooting OSPF configuration

No OSPF neighbor relationship established

Symptom

No OSPF neighbor relationship can be established.

Analysis

If the physical link and lower layer protocols work correctly, verify OSPF parameters configured on interfaces. Two neighbors must have the same parameters, such as the area ID, network segment, and mask. (A P2P or virtual link can have different network segments and masks.)

Solution

To resolve the problem:

1. Use the display ospf peer command to verify OSPF neighbor information.

2. Use the display ospf interface command to verify OSPF interface information.

3. Ping the neighbor router's IP address to verify that the connectivity is normal.

4. Verify OSPF timers. The dead interval on an interface must be a minimum of four times the hello interval.

5. On an NBMA network, use the peer ip-address command to manually specify the neighbor.

6. A minimum of one interface must have a router priority higher than 0 on an NBMA or a broadcast network.

7. If the problem persists, contact H3C Support.

Incorrect routing information

Symptom

OSPF cannot find routes to other areas.

Analysis

The backbone area must maintain connectivity to all other areas. If a router connects to more than one area, a minimum of one area must be connected to the backbone. The backbone cannot be configured as a stub area.

In a stub area, all routers cannot receive external routes, and all interfaces connected to the stub area must belong to the stub area.

Solution

To resolve the problem:

1. Use the display ospf peer command to verify neighbor information.

2. Use the display ospf interface command to verify OSPF interface information.

3. Use the display ospf lsdb command to verify the LSDB.

4. Use the display current-configuration configuration ospf command to verify area configuration. If more than two areas are configured, a minimum of one area is connected to the backbone.

5. In a stub area, all routers attached are configured with the stub command. In an NSSA area, all routers attached are configured with the nssa command.

6. If a virtual link is configured, use the display ospf vlink command to verify the state of the virtual link.

7. If the problem persists, contact H3C Support.

07-Layer 3—IP Routing Configuration Guide

Configuring OSPF

Area-based OSPF network partition

Backbone area

Virtual links

Stub area and totally stub area

NSSA area and totally NSSA area

Router types

Internal router

ABR

Backbone router

ASBR

Manual configuration

Automatic configuration

Using the global router ID

DR and BDR

DR and BDR mechanism

DR and BDR election

OSPF state machines

Interface state machine

Neighbor state machine

OSPF tasks at a glance

About this task

Restrictions and guidelines for enabling OSPF

Enabling OSPF on a network

Enabling OSPF on an interface

Configuring OSPF areas

About this task

Restrictions and guidelines

Procedure (OSPF area view)

About this task

Restrictions and guidelines

Procedure (OSPF area view)

About this task

Restrictions and guidelines

Procedure

Configuring OSPF network types

Configuring the broadcast network type for an interface

Configuring the NBMA network type for an interface

Restrictions and guidelines

Procedure

Restrictions and guidelines

Procedure

Configuring OSPF route control

Configuring OSPF inter-area route summarization

About this task

Procedure

About this task

Restrictions and guidelines

Procedure

Configuring received OSPF route filtering

About this task

Procedure

About this task

Procedure

Setting an OSPF cost for an interface

About this task

Setting an OSPF cost for an interface

About this task

Restrictions and guidelines

Procedure

Enabling OSPF to advertise the maximum link cost to neighbors

About this task

Procedure

Setting the maximum number of ECMP routes

About this task

Procedure

Setting OSPF preference

About this task

Procedure

About this task

Procedure

Redistributing routes from another routing protocol

About this task

Restrictions and guidelines

Procedure

About this task

Restrictions and guidelines

Procedure

About this task

I nterface state machine

N eighbor state machine