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 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

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

Backbone area and virtual links

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.

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

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

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

Router types

OSPF routers are classified into the following types based on their positions in the AS:

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

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

Figure 5 OSPF router types

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.

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, 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

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.

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.

Protocols and standards

· RFC 1765, OSPF Database Overflow

· RFC 2328, OSPF Version 2

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

· RFC 3137, OSPF Stub Router Advertisement

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

· RFC 4812, OSPF Restart Signaling

· RFC 4813, OSPF Link-Local Signaling

OSPF configuration task list

To run OSPF, you must first enable OSPF on the router. Make a proper configuration plan to avoid incorrect settings that can result in route blocking and routing loops.

To configure OSPF, perform the following tasks:

Tasks at a glance
(Required.) Enabling OSPF
(Optional.) Configuring OSPF areas: · Configuring a stub area · Configuring an NSSA area · Configuring a virtual link
(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
(Optional.) Configuring OSPF route control: · Configuring OSPF route summarization ¡ Configuring route summarization on an ABR ¡ Configuring route summarization on an ASBR · Configuring received OSPF route filtering · Configuring Type-3 LSA filtering · Setting an OSPF cost for an interface · Setting the maximum number of ECMP routes · Setting OSPF preference · Configuring discard routes for summary networks · Configuring OSPF route redistribution ¡ Redistributing routes from another routing protocol ¡ Redistributing a default route ¡ Configuring default parameters for redistributed routes · Advertising a host route · Excluding interfaces in an OSPF area from the base topology
(Optional.) Tuning and optimizing OSPF networks: · Setting OSPF timers · Setting LSA transmission delay · Setting SPF calculation interval · Setting the LSA arrival interval · Setting the LSA generation interval · Disabling interfaces from receiving and sending OSPF packets · Configuring stub routers · Configuring OSPF authentication · Adding the interface MTU into DD packets · Setting the DSCP value for outgoing OSPF packets · Setting the maximum number of external LSAs in LSDB · Setting OSPF exit overflow interval · Enabling compatibility with RFC 1583 · Logging neighbor state changes · Configuring OSPF network management · Setting the LSU transmit rate · Setting the maximum length of OSPF packets that can be sent by an interface · Enabling OSPF ISPF · Configuring prefix suppression · Configuring prefix prioritization · Configuring OSPF PIC · Setting the number of OSPF logs · Filtering outbound LSAs on an interface · Filtering LSAs for the specified neighbor · Configuring GTSM for OSPF
(Optional.) Configuring OSPF GR · Configuring OSPF GR restarter · Configuring OSPF GR helper · Triggering OSPF GR
(Optional.) Configuring OSPF NSR
(Optional.) Configuring BFD for OSPF
(Optional.) Configuring OSPF FRR
(Optional.) Advertising OSPF link state information to BGP

Enabling OSPF

Enable OSPF before you perform other OSPF configuration tasks.

Configuration prerequisites

Configure the link layer protocol and IP addresses for interfaces to ensure IP connectivity between neighboring nodes.

Configuration guidelines

To enable OSPF on an interface, 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.

You can specify a global router ID, or specify a router ID when you create an OSPF process.

· If you specify a router ID when you create an OSPF process, any two routers in an AS must have different router IDs. A common practice is to specify the IP address of an interface as the router ID.

· If you specify no router ID when you create the OSPF process, the global router ID is used. As a best practice, specify a router ID when you create the OSPF process.

OSPF supports multiple processes and VPNs.

· 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 specified VPN instance. For more information about VPN, see MPLS L3VPN configuration in MPLS Configuration Guide.

Enabling OSPF on a network

Step	Command	Remarks
1. Enter system view.	system-view	N/A
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. Enable an OSPF process and enter OSPF view.	ospf [ process-id \| router-id 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	By default, no OSPF areas exist.
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.
7. 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.

Enabling OSPF on an interface

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter interface view.	interface interface-type interface-number	N/A
3. Enable an OSPF process on the interface.	ospf process-id area area-id [ exclude-subip ]	By default, OSPF is disabled on an interface. If the specified OSPF process and area do not exist, the command creates the OSPF process and area. Disabling an OSPF process on an interface does not delete the OSPF process or the area.

Configuring OSPF areas

Before you configure an OSPF area, perform the following tasks:

· Configure IP addresses for interfaces to ensure IP connectivity between neighboring nodes.

· Enable OSPF.

Configuring a stub area

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 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.

To configure an OSPF stub area:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
3. Enter area view.	area area-id	N/A
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	The default setting is 1. The default-cost cost command takes effect only on the ABR of a stub area or totally stub area.

Configuring an NSSA area

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.

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. The ABR of a totally NSSA area does not advertise inter-area routes into the area.

To configure an NSSA area:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
3. Enter area view.	area area-id	N/A
4. Configure the area as an NSSA area.	nssa [ default-route-advertise [ cost cost-value \| nssa-only \| route-policy route-policy-name \| type type ] * \| no-import-route \| no-summary \| suppress-fa \| [ [ [ translate-always ] [ translate-ignore-checking-backbone ] ] \| translate-never ] \| translator-stability-interval value ] *	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	The default setting is 1. This command takes effect only on the ABR/ASBR of an NSSA or totally NSSA area.

Configuring a virtual link

Virtual links are configured for connecting backbone area routers that have no direct physical links.

To configure a virtual link:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
3. Enter area view.	area area-id	N/A
4. Configure a virtual link.	vlink-peer router-id [ dead seconds \| hello seconds \| { { hmac-md5 \| md5 } key-id { cipher \| plain } string \| keychain keychain-name \| simple { cipher \| plain } string } \| retransmit seconds \| trans-delay seconds ] *	By default, no virtual links exist. 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.

Configuring OSPF network types

OSPF classifies networks into the following types based on the link layer protocol:

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

· NBMA—When the link layer protocol is Frame Relay, ATM, or X.25, OSPF classifies the network type as NBMA by default.

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

When you change the network type of an interface, follow these guidelines:

· 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.

Configuration prerequisites

Before you configure OSPF network types, perform the following tasks:

· Configure IP addresses for interfaces to ensure IP connectivity between neighboring nodes.

· Enable OSPF.

Configuring the broadcast network type for an interface

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter interface view.	interface interface-type interface-number	N/A
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.
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

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.

To configure the NBMA network type for an interface:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter interface view.	interface interface-type interface-number	N/A
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 setting is 1. The router priority configured with this command is for DR election.
5. Return to system view.	quit	N/A
6. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
7. Specify a neighbor and set its router priority.	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, and 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

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter interface view.	interface interface-type interface-number	N/A
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. 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.
4. Return to system view.	quit	N/A
5. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
6. (Optional.) Specify a neighbor and set its router priority.	peer ip-address [ cost cost-value ]	By default, no neighbor is specified. This step must be performed if the network type is P2MP unicast, and is optional if the network type is P2MP.

Configuring the P2P network type for an interface

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter interface view.	interface interface-type interface-number	N/A
3. Configure the OSPF network type for the interface as P2P.	ospf network-type p2p [ peer-address-check ]	By default, the network type of an interface depends on the link layer protocol.

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.

Configuration prerequisites

Before you configure OSPF route control, perform the following tasks:

· Configure IP addresses for interfaces to ensure IP connectivity between neighboring nodes.

· Enable OSPF.

· Configure filters if routing information filtering is needed.

Configuring OSPF route summarization

Route summarization enables an ABR or ASBR to summarize contiguous networks into a single network and advertise the network to other areas.

Route summarization reduces the routing information exchanged between areas and the size of routing tables, and improves routing performance. 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 summarize the three networks into network 19.1.0.0/16, and advertise the summary network to other areas.

Configuring route summarization on an ABR

After you configure a summary route on an ABR, the ABR generates a summary LSA instead of specific LSAs. The scale of LSDBs on routers in other areas and the influence of topology changes are reduced.

To configure route summarization on an ABR:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
3. Enter OSPF area view.	area area-id	N/A
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 route summarization on an ASBR

Perform this task to enable an ASBR to summarize external routes within the specified address range into a single route. The ASBR advertises only the summary route 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.

· Type-5 LSAs translated by the ASBR (also an ABR) from Type-7 LSAs in an NSSA area.

If the ASBR (ABR) is not a translator, it cannot summarize routes in Type-5 LSAs translated from Type-7 LSAs.

To configure route summarization on an ASBR:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
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

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 keyword 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 keyword to filter routing information by next hop.

· Use a routing policy to filter routing information.

To configure OSPF to filter routes calculated using received LSAs:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
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 using received LSAs.

Configuring Type-3 LSA filtering

Perform this task to filter Type-3 LSAs advertised to an area on an ABR.

To configure Type-3 LSA filtering:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
3. Enter area view.	area area-id	N/A
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

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.

To set an OSPF cost for an interface:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter interface view.	interface interface-type interface-number	N/A
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.

To set a bandwidth reference value:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
3. Set a bandwidth reference value.	bandwidth-reference value	The default setting is 100 Mbps.

Setting the maximum number of ECMP routes

Perform this task to implement load sharing over ECMP routes.

To set the maximum number of ECMP routes:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
3. Set the maximum number of ECMP routes.	maximum load-balancing number	By default, the maximum number of ECMP routes equals the maximum number of ECMP routes supported by the system.

Setting OSPF preference

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.

To set OSPF preference:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
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

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.

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
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. · The preference of discard routes is 255.

Configuring OSPF route redistribution

On a router running OSPF and other routing protocols, you can configure OSPF to redistribute static routes, direct routes, or routes from other protocols, such as RIP, IS-IS, and BGP. OSPF advertises 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.

IMPORTANT:

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

Redistributing routes from another routing protocol

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
3. Configure OSPF to redistribute routes from another routing protocol.	import-route protocol [ as-number ] [ process-id \| all-processes \| allow-ibgp ] [ allow-direct \| [ cost cost-value \| inherit-cost ] \| nssa-only \| route-policy route-policy-name \| tag tag \| type type ] *	By default, no route redistribution is configured. This command redistributes only active routes. To view information about active routes, use the display ip routing-table protocol command. The inherit-cost keyword is available in R2612 and later versions.
4. (Optional.) Configure OSPF to filter redistributed routes.	filter-policy { ipv4-acl-number \| prefix-list prefix-list-name } export [ protocol [ process-id ] ]	By default, OSPF accepts all redistributed routes.

Redistributing a default route

The import-route command cannot redistribute a default external route. Perform this task to redistribute a default route.

To redistribute a default route:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
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.

Configuring default parameters for redistributed routes

Perform this task to configure default parameters for redistributed routes, including cost, tag, and type. Tags identify information about protocols. For example, when redistributing BGP routes, OSPF uses tags to identify AS IDs.

To configure the default parameters for redistributed routes:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
3. Configure the default parameters for redistributed routes (cost, upper limit, tag, and type).	default { cost cost-value \| tag tag \| type type } *	By default, the cost is 1, the tag is 1, and the type is Type-2.

Advertising a host route

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
3. Enter area view.	area area-id	N/A
4. Advertise a host route.	host-advertise ip-address cost	By default, no host route is advertised.

Excluding interfaces in an OSPF area from the base topology

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
3. Enter area view.	area area-id	N/A
4. Exclude interfaces in the OSPF area from the base topology.	capability default-exclusion	By default, interfaces in an OSPF area belong to the base topology.

Tuning and optimizing OSPF networks

You can use one of the following methods to optimize an OSPF network:

· Change OSPF packet timers to adjust the convergence speed and network load. On low-speed links, consider the delay time for sending LSAs.

· Change the SPF calculation interval to reduce resource consumption caused by frequent network changes.

· Configure OSPF authentication to improve security.

Configuration prerequisites

Before you configure OSPF network optimization, perform the following tasks:

· Configure IP addresses for interfaces to ensure IP connectivity between neighboring nodes.

· Enable OSPF.

Setting OSPF timers

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.

To set OSPF timers:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter interface view.	interface interface-type interface-number	N/A
3. Set the hello interval.	ospf timer hello seconds	By default: · The hello interval on P2P and broadcast interfaces is 10 seconds. · The hello interval on P2MP and NBMA interfaces is 30 seconds. The default hello interval is restored when the network type for an interface is changed.
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 on P2P and broadcast interfaces is 40 seconds. · The dead interval on P2MP and NBMA interfaces is 120 seconds. The dead interval must be a minimum of four times the hello interval on an interface. The default dead interval is restored when the network type for an interface is changed.
6. Set the retransmission interval.	ospf timer retransmit interval	The default setting is 5 seconds. A retransmission interval setting that is too small can cause unnecessary LSA retransmissions. This interval is typically set bigger than the round-trip time of a packet between two neighbors.

Setting LSA transmission delay

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

To set the LSA transmission delay on an interface:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter interface view.	interface interface-type interface-number	N/A
3. Set the LSA transmission delay.	ospf trans-delay seconds	The default setting is 1 second.

Setting SPF calculation interval

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 is incremented by the incremental interval × 2n-2 for each calculation until the maximum interval is reached. The value n is the number of calculation times.

To set the SPF calculation interval:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
3. Set the SPF calculation interval.	spf-schedule-interval maximum-interval [ minimum-interval [ incremental-interval ] ]	By default: · The maximum interval is 5 seconds. · The minimum interval is 50 milliseconds. · The incremental interval is 200 milliseconds.

Setting the LSA arrival interval

If OSPF receives an LSA that has the same LSA type, LS ID, and router ID as the previously received LSA within the LSA arrival interval, OSPF discards the LSA to save bandwidth and route resources.

To set the LSA arrival interval:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
3. Set the LSA arrival interval.	lsa-arrival-interval interval	The default setting is 1000 milliseconds. Make sure this interval is smaller than or equal to the interval set with the lsa-generation-interval command.

Setting the LSA generation interval

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

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

To set the LSA generation interval:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
3. Set the LSA generation interval.	lsa-generation-interval maximum-interval [ minimum-interval [ incremental-interval ] ]	By default: · The maximum interval is 5 seconds. · The minimum interval is 50 milliseconds. · The incremental interval is 200 milliseconds.

Disabling interfaces from receiving and sending OSPF packets

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.

To disable interfaces from receiving and sending routing information:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
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. The silent-interface 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.

Configuring stub routers

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.

To configure a router as a stub router:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
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 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

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

To configure OSPF area authentication:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
3. Enter area view.	area area-id	N/A
4. Configure area authentication mode.	· Configure MD5 authentication: authentication-mode { hmac-md5 \| md5 } key-id { cipher \| plain } string · Configure simple authentication: authentication-mode simple { cipher \| plain } string · Configure keychain authentication: authentication-mode keychain keychain-name	By default, no authentication is configured. For information about keychains, see Security Configuration Guide.

Configuring OSPF interface authentication

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

To configure OSPF interface authentication:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter interface view.	interface interface-type interface-number	N/A
3. Configure interface authentication mode.	· Configure simple authentication: ospf authentication-mode simple { cipher \| plain } string · Configure MD5 authentication: ospf authentication-mode { hmac-md5 \| md5 } key-id { cipher \| plain } string · Configure keychain authentication: ospf authentication-mode keychain keychain-name	By default, no authentication is configured. For information about keychain, see Security Configuration Guide.

Adding the interface MTU into DD packets

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. You can enable an interface to add its MTU into DD packets.

To add the interface MTU into DD packets:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter interface view.	interface interface-type interface-number	N/A
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

The DSCP value specifies the precedence of outgoing packets.

To set the DSCP value for OSPF packets:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
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 number of external LSAs in LSDB

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
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.

Setting OSPF exit overflow interval

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

Perform this task to configure the interval that OSPF exits overflow state.

To set the OSPF exit overflow interval:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
3. Set the OSPF exit overflow interval.	lsdb-overflow-interval interval	The default setting is 300 seconds. The value of 0 indicates that OSPF does not exit overflow state.

Enabling compatibility with RFC 1583

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.

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

To enable compatibility with RFC 1583:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
3. Enable compatibility with RFC 1583.	rfc1583 compatible	By default, compatibility with RFC 1583 is enabled.

Logging neighbor state changes

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.

To enable the logging of neighbor state changes:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
3. Enable the logging of neighbor state changes.	log-peer-change	By default, this feature is enabled.

Configuring OSPF network management

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.

To configure OSPF network management:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Bind OSPF MIB to an OSPF process.	ospf mib-binding process-id	By default, OSPF MIB is bound to the process with the smallest process ID.
3. Enable SNMP notifications for OSPF.	snmp-agent trap enable ospf [ authentication-failure \| bad-packet \| config-error \| grhelper-status-change \| grrestarter-status-change \| if-state-change \| lsa-maxage \| lsa-originate \| lsdb-approaching-overflow \| lsdb-overflow \| neighbor-state-change \| nssatranslator-status-change \| retransmit \| virt-authentication-failure \| virt-bad-packet \| virt-config-error \| virt-retransmit \| virtgrhelper-status-change \| virtif-state-change \| virtneighbor-state-change ] *	By default, SNMP notifications for OSPF are enabled.
4. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
5. 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 LSU transmit rate

During LSDB synchronization, if the local router has multiple neighbors, it must send many LSUs to each neighbor. When a neighbor receives excessive LSUs within a short time period, the following events might occur:

· The neighbor experiences degraded performance because it uses too many system resources to process the received LSU packets.

· The neighbor drops hello packets used for maintaining the neighbor relationship because it is busy dealing with the LSUs. As a result, the neighbor relationship is torn down. To reestablish a relationship to the neighbor, the local router must send more LSUs to the neighbor. This exacerbates the performance degradation.

This task allows you to limit the LSU transmit rate by setting the LSU transmit interval and the maximum number of LSUs that can be sent at each interval.

To set the LSU transmit rate:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enable OSPF to limit the LSU transmit rate.	ospf lsu-flood- control [ interval count ]	By default, OSPF does not limit the LSU transmit rate. Inappropriate use of this command might cause abnormal routing. As a best practice, execute this command with the default values.
3. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
4. Set the LSU transmit interval and the maximum number of LSUs that can be sent at each interval.	transmit-pacing interval interval count count	By default, an OSPF interface sends a maximum of three LSU packets every 20 milliseconds.

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

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, see Layer 3—IP Services Configuration Guide.

To set the maximum length of OSPF packets that can be sent by an interface:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter interface view.	interface interface-type interface-number	N/A
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.

Enabling OSPF ISPF

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

To enable OSPF ISPF:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
3. Enable OSPF ISPF.	ispf enable	By default, OSPF ISPF is enabled.

Configuring prefix suppression

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 the primary IP addresses of interfaces in Type-1 LSAs.

IMPORTANT:

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

Enabling prefix suppression for an OSPF process does not suppress the prefixes of secondary IP addresses, loopback interfaces, and passive interfaces. To suppress the prefixes of loopback interfaces and passive interfaces, enable prefix suppression on the interfaces.

To configure prefix suppression for an OSPF process:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
3. Enable prefix suppression for the OSPF process.	prefix-suppression	By default, prefix suppression is disabled for an OSPF process.

Configuring prefix suppression for an interface

Interface prefix suppression does not suppress prefixes of secondary IP addresses.

To configure interface prefix suppression:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter interface view.	interface interface-type interface-number	N/A
3. Enable prefix suppression for the interface.	ospf prefix-suppression [ disable ]	By default, prefix suppression is disabled on an interface.

Configuring prefix prioritization

This feature enables the device to install prefixes in descending priority order: critical, high, medium, and low. The prefix priorities are assigned through routing policies. When a route is assigned multiple prefix priorities, the route uses the highest priority.

By default, the 32-bit OSPF host routes have a medium priority and other routes a low priority.

To configure prefix prioritization:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
3. Enable prefix prioritization.	prefix-priority route-policy route-policy-name	By default, prefix prioritization is disabled.

Configuring OSPF PIC

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

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

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
3. Enable PIC for OSPF.	pic [ additional-path-always ]	By default, OSPF PIC is enabled.

Configuring BFD for OSPF PIC

By default, OSPF PIC does not use BFD to detect primary link failures. To speed up OSPF convergence, enable BFD for OSPF PIC to detect the primary link failures.

To configure BFD control packet mode for OSPF PIC:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter interface view.	interface interface-type interface-number	N/A
3. Enable BFD control packet mode for OSPF PIC.	ospf primary-path-detect bfd ctrl	By default, BFD control packet mode for OSPF PIC is disabled.

To configure BFD echo packet mode for OSPF PIC:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
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. The source IP address cannot be on the same network segment as any local interface's IP address. For more information about this command, see High Availability Command Reference.
3. Enter interface view.	interface interface-type interface-number	N/A
4. Enable BFD echo packet mode for OSPF PIC.	ospf primary-path-detect bfd echo	By default, BFD echo packet mode for OSPF PIC is disabled.

Setting the number of OSPF logs

OSPF logs include LSA aging logs, route calculation logs, and neighbor logs.

To set the number of OSPF logs:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
3. Set the number of OSPF logs.	event-log { lsa-flush \| peer \| spf } size count	By default, the number of LSA aging logs, route calculation logs, or neighbor logs is 10.

Filtering outbound LSAs on an interface

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.

To filter outbound LSAs on an interface:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter interface view.	interface interface-type interface-number	N/A
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

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

To filter LSAs for the specified neighbor:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
3. Filter LSAs for the specified 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 neighbor are not filtered.

Configuring GTSM for OSPF

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.

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 Configuration Guide.

You can configure GTSM in OSPF area view or interface view.

· The configuration in OSPF area view applies to all OSPF interfaces in the area.

· The configuration in interface view takes precedence over OSPF area view.

IMPORTANT:

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

To configure GTSM in OSPF area view:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
3. Enter OSPF area view.	area area-id	N/A
4. Enable GTSM for the OSPF area.	ttl-security [ hops hop-count ]	By default, GTSM is disabled for the OSPF area.

To configure GTSM in interface view:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter interface view.	interface interface-type interface-number	N/A
3. Enable GTSM for the interface.	ospf ttl-security [ hops hop-count \| disable ]	By default, GTSM is disabled for the interface.

Configuring 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

You can configure the IETF or non-IETF OSPF GR restarter.

IMPORTANT:

You cannot enable OSPF NSR on a device that acts as GR restarter.

Configuring the IETF OSPF GR restarter

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enable OSPF and enter its view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
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

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enable OSPF and enter its view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
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

You can configure the IETF or non-IETF OSPF GR helper.

Configuring the IETF OSPF GR helper

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enable OSPF and enter its view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
3. Enable opaque LSA reception and advertisement capability.	opaque-capability enable	By default, opaque LSA reception and advertisement capability is enabled.
4. (Optional.) 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.

Configuring the non-IETF OSPF GR helper

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enable OSPF and enter its view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
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. (Optional.) 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.

Triggering OSPF GR

OSPF GR is triggered by an active/standby switchover or when the following command is executed.

To trigger OSPF GR, perform the following command in user view:

Task	Command
Trigger OSPF GR.	reset ospf [ process-id ] process graceful-restart

Configuring OSPF NSR

Nonstop routing (NSR) backs up OSPF link state information from the active process to the standby process. 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.

IMPORTANT:

A device that has OSPF NSR enabled cannot act as GR restarter.

To enable OSPF NSR:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
3. Enable OSPF NSR.	non-stop-routing	By default, OSPF NSR is disabled. This command takes effect only for the current process. As a best practice, enable OSPF NSR for each process if multiple OSPF processes exist.

Configuring BFD for OSPF

BFD provides a single mechanism to quickly detect and monitor the connectivity of links between OSPF neighbors, which improves the network convergence speed. 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

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter interface view.	interface interface-type interface-number	N/A
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

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Configure the source address of echo packets.	bfd echo-source-ip ip-address	By default, the source address of echo packets is not configured.
3. Enter interface view.	interface interface-type interface-number	N/A
4. Enable BFD single-hop echo detection.	ospf bfd enable echo	By default, BFD single-hop echo detection is disabled.

Configuring OSPF FRR

A link or router failure on a path can cause packet loss and even routing loop 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 7 Network diagram for OSPF FRR

As shown in Figure 7, configure FRR on Router B by using a routing policy to specify a backup next hop. 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.

You can configure OSPF FRR to calculate a backup next hop by using the loop free alternate (LFA) algorithm, or specify a backup next hop by using a routing policy.

Configuration prerequisites

Before you configure OSPF FRR, perform the following tasks:

· Configure IP addresses for interfaces to ensure IP connectivity between neighboring nodes.

· Enable OSPF.

Configuration guidelines

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

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

Configuration procedure

Configuring OSPF FRR to calculate a backup next hop using the LFA algorithm

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter interface view.	interface interface-type interface-number	N/A
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	N/A
5. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
6. Enable OSPF FRR to calculate a backup next hop by using the LFA algorithm.	fast-reroute lfa [ abr-only ]	By default, OSPF FRR is disabled. If abr-only is specified, the route to the ABR is selected as the backup path.

Configuring OSPF FRR to specify a backup next hop using a routing policy

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

To configure OSPF FRR to specify a backup next hop using a routing policy:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
3. Enable OSPF FRR to specify a backup next hop by using a routing policy.	fast-reroute route-policy route-policy-name	By default, OSPF FRR is disabled.

Configuring BFD for OSPF FRR

By default, OSPF FRR does not use BFD to detect primary link failures. To speed up OSPF convergence, enable BFD for OSPF FRR to detect primary link failures.

To configure BFD control packet mode for OSPF FRR:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter interface view.	interface interface-type interface-number	N/A
3. Enable BFD control packet mode for OSPF FRR.	ospf primary-path-detect bfd ctrl	By default, BFD control packet mode for OSPF FRR is disabled.

To configure BFD echo packet mode for OSPF FRR:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
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. The source IP address cannot be on the same network segment as any local interface's IP address. For more information about this command, see High Availability Command Reference.
3. Enter interface view.	interface interface-type interface-number	N/A
4. Enable BFD echo packet mode for OSPF FRR.	ospf primary-path-detect bfd echo	By default, BFD echo packet mode for OSPF FRR is disabled.

Advertising OSPF link state information to BGP

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."

To advertise OSPF link state information to BGP:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter OSPF view.	ospf [ process-id \| router-id router-id \| vpn-instance vpn-instance-name ] *	N/A
3. Advertise OSPF link state information to BGP.	distribute bgp-ls [ strict-link-checking ]	By default, the device does not advertise OSPF link state information to BGP.

Displaying and maintaining 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 ] display ospf [ process-id ] lsdb { opaque-as \| ase } [ link-state-id ] [ originate-router advertising-router-id \| self-originate ] display ospf [ process-id ] [ area area-id ] lsdb { asbr \| network \| nssa \| opaque-area \| opaque-link \| router \| summary } [ link-state-id ] [ originate-router advertising-router-id \| self-originate ]
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 [ verbose ] [ interface-type interface-number ] [ neighbor-id ]
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 } ] [ interface interface-type interface-number ] [ nexthop nexthop-address ] [ verbose ]
Display OSPF topology information.	display ospf [ process-id ] [ area area-id ] spf-tree [ verbose ]
Display OSPF statistics.	display ospf [ process-id ] statistics [ error \| packet [ 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 OSPF log information.	display ospf [ process-id ] event-log { lsa-flush \| peer \| spf }
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
Clear OSPF statistics.	reset ospf [ process-id ] statistics
Clear OSPF log information.	reset ospf [ process-id ] event-log [ lsa-flush \| peer \| spf ]
Restart an OSPF process.	reset ospf [ process-id ] process [ graceful-restart ]
Re-enable OSPF route redistribution.	reset ospf [ process-id ] redistribution

OSPF configuration examples

Basic OSPF configuration example

Network requirements

As shown in Figure 8:

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

· Configure Switch A and Switch B as ABRs.

Figure 8 Network diagram

Configuration procedure

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

2. Enable OSPF:

# Configure Switch A.

<SwitchA> system-view

[SwitchA] router id 10.2.1.1

[SwitchA] ospf

[SwitchA-ospf-1] area 0

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

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

[SwitchA-ospf-1] area 1

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

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

[SwitchA-ospf-1] quit

# Configure Switch B.

<SwitchB> system-view

[SwitchB] router id 10.3.1.1

[SwitchB] ospf

[SwitchB-ospf-1] area 0

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

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

[SwitchB-ospf-1] area 2

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

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

[SwitchB-ospf-1] quit

# Configure Switch C.

<SwitchC> system-view

[SwitchC] router id 10.4.1.1

[SwitchC] ospf

[SwitchC-ospf-1] area 1

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

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

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

[SwitchC-ospf-1] quit

# Configure Switch D.

<SwitchD> system-view

[SwitchD] router id 10.5.1.1

[SwitchD] ospf

[SwitchD-ospf-1] area 2

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

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

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

[SwitchD-ospf-1] quit

Verifying the configuration

# Display information about neighbors on Switch A.

[SwitchA] 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(Vlan-interface100)'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

Area 0.0.0.1 interface 10.2.1.1(Vlan-interface200)'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

# Display OSPF routing information on Switch A.

[SwitchA] display ospf routing

OSPF Process 1 with Router ID 10.2.1.1

Routing Table

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 Switch D.

[SwitchD] display ospf routing

OSPF Process 1 with Router ID 10.5.1.1

Routing Table

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

# On Switch D, ping the IP address 10.4.1.1 to test reachability.

[SwitchD] 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

OSPF route redistribution configuration example

Network requirements

As shown in Figure 9:

· Enable OSPF on all the switches.

· Split the AS into three areas.

· Configure Switch A and Switch B as ABRs.

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

Figure 9 Network diagram

Configuration procedure

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

2. Enable OSPF (see "

3. Basic OSPF configuration example").

4. Configure OSPF to redistribute routes:

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

<SwitchC> system-view

[SwitchC] ip route-static 3.1.2.1 24 10.4.1.2

# On Switch C, configure OSPF to redistribute static routes.

[SwitchC] ospf 1

[SwitchC-ospf-1] import-route static

Verifying the configuration

# Display the ABR/ASBR information on Switch D.

<SwitchD> display ospf abr-asbr

OSPF Process 1 with Router ID 10.5.1.1

Routing Table to ABR and ASBR

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 table on Switch D.

<SwitchD> display ospf routing

OSPF Process 1 with Router ID 10.5.1.1

Routing Table

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

OSPF route summarization configuration example

Network requirements

As shown in Figure 10:

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

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

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

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

Figure 10 Network diagram

Configuration procedure

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

2. Enable OSPF:

# Configure Switch A.

<SwitchA> system-view

[SwitchA] router id 11.2.1.2

[SwitchA] ospf

[SwitchA-ospf-1] area 0

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

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

[SwitchA-ospf-1] quit

# Configure Switch B.

<SwitchB> system-view

[SwitchB] router id 11.2.1.1

[SwitchB] ospf

[SwitchB-ospf-1] area 0

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

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

[SwitchB-ospf-1] quit

# Configure Switch C.

<SwitchC> system-view

[SwitchC] router id 11.1.1.2

[SwitchC] ospf

[SwitchC-ospf-1] area 0

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

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

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

[SwitchC-ospf-1] quit

# Configure Switch D.

<SwitchD> system-view

[SwitchD] router id 10.3.1.1

[SwitchD] ospf

[SwitchD-ospf-1] area 0

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

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

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

[SwitchD-ospf-1] quit

# Configure Switch E.

<SwitchE> system-view

[SwitchE] router id 10.4.1.1

[SwitchE] ospf

[SwitchE-ospf-1] area 0

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

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

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

[SwitchE-ospf-1] quit

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

# Configure Switch B.

[SwitchB] bgp 200

[SwitchB-bgp-default] peer 11.1.1.2 as 100

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

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

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

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

[SwitchB-bgp-default-ipv4] quit

[SwitchB-bgp-default] quit

# Configure Switch C.

[SwitchC] bgp 100

[SwitchC-bgp-default] peer 11.1.1.1 as 200

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

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

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

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

[SwitchC-bgp-default-ipv4] quit

[SwitchC-bgp-default] quit

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

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

[SwitchB] ospf

[SwitchB-ospf-1] import-route bgp

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

[SwitchC] ospf

[SwitchC-ospf-1] import-route bgp

# Display the OSPF routing table on Switch A.

[SwitchA] display ip routing-table

Destinations : 16 Routes : 16

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 Vlan100

10.2.1.0/24 O_ASE2 150 1 11.2.1.1 Vlan100

10.3.1.0/24 O_ASE2 150 1 11.2.1.1 Vlan100

10.4.1.0/24 O_ASE2 150 1 11.2.1.1 Vlan100

11.2.1.0/24 Direct 0 0 11.2.1.2 Vlan100

11.2.1.0/32 Direct 0 0 11.2.1.2 Vlan100

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 Vlan100

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

224.0.0.0/4 Direct 0 0 0.0.0.0 NULL0

224.0.0.0/24 Direct 0 0 0.0.0.0 NULL0

255.255.255.255/32 Direct 0 0 127.0.0.1 InLoop0

5. Configure route summarization:

# Configure route summarization on Switch B to advertise a summary route 10.0.0.0/8.

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

# Display the IP routing table on Switch A.

[SwitchA] display ip routing-table

Destinations : 13 Routes : 13

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 Vlan100

11.2.1.0/24 Direct 0 0 11.2.1.2 Vlan100

11.2.1.0/32 Direct 0 0 11.2.1.2 Vlan100

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 Vlan100

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

224.0.0.0/4 Direct 0 0 0.0.0.0 NULL0

224.0.0.0/24 Direct 0 0 0.0.0.0 NULL0

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.

OSPF stub area configuration example

Network requirements

As shown in Figure 11:

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

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

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

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

Figure 11 Network diagram

Configuration procedure

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

2. Enable OSPF (see "

3. Basic OSPF configuration example").

4. Configure route redistribution:

# Configure Switch D to redistribute static routes.

<SwitchD> system-view

[SwitchD] ip route-static 3.1.2.1 24 10.5.1.2

[SwitchD] ospf

[SwitchD-ospf-1] import-route static

[SwitchD-ospf-1] quit

# Display ABR/ASBR information on Switch C.

<SwitchC> display ospf abr-asbr

OSPF Process 1 with Router ID 10.4.1.1

Routing Table to ABR and ASBR

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 table on Switch C.

<SwitchC> display ospf routing

OSPF Process 1 with Router ID 10.4.1.1

Routing Table

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 Switch C's routing table contains an AS external route.

5. Configure Area 1 as a stub area:

# Configure Switch A.

<SwitchA> system-view

[SwitchA] ospf

[SwitchA-ospf-1] area 1

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

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

[SwitchA-ospf-1] quit

# Configure Switch C.

<SwitchC> system-view

[SwitchC] ospf

[SwitchC-ospf-1] area 1

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

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

[SwitchC-ospf-1] quit

# Display OSPF routing information on Switch C

[SwitchC] display ospf routing

OSPF Process 1 with Router ID 10.4.1.1

Routing Table

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.

[SwitchA] ospf

[SwitchA-ospf-1] area 1

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

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

[SwitchA-ospf-1] quit

# Display OSPF routing information on Switch C.

[SwitchC] display ospf routing

OSPF Process 1 with Router ID 10.4.1.1

Routing Table

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 Switch C.

OSPF NSSA area configuration example

Network requirements

As shown in Figure 12:

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

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

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

Figure 12 Network diagram

Configuration procedure

1. Configure IP addresses for interfaces.

2. Enable OSPF (see "

3. Basic OSPF configuration example").

4. Configure Area 1 as an NSSA area:

# Configure Switch A.

<SwitchA> system-view

[SwitchA] ospf

[SwitchA-ospf-1] area 1

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

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

[SwitchA-ospf-1] quit

# Configure Switch C.

<SwitchC> system-view

[SwitchC] ospf

[SwitchC-ospf-1] area 1

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

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

[SwitchC-ospf-1] quit

# Display OSPF routing information on Switch C.

[SwitchC] display ospf routing

OSPF Process 1 with Router ID 10.4.1.1

Routing Table

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

5. Configure route redistribution:

# Configure Switch C to redistribute static routes.

[SwitchC] ip route-static 3.1.3.1 24 10.4.1.2

[SwitchC] ospf

[SwitchC-ospf-1] import-route static

[SwitchC-ospf-1] quit

# Display OSPF routing information on Switch D.

<SwitchD> display ospf routing

OSPF Process 1 with Router ID 10.5.1.1

Routing Table

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

3.1.3.0/24 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 external route imported from the NSSA area exists on Switch D.

OSPF DR election configuration example

Network requirements

As shown in Figure 13:

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

· Configure Switch A as the DR, and configure Switch C as the BDR.

Figure 13 Network diagram

Configuration procedure

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

2. Enable OSPF:

# Configure Switch A.

<SwitchA> system-view

[SwitchA] router id 1.1.1.1

[SwitchA] ospf

[SwitchA-ospf-1] area 0

[SwitchA-ospf-1-area-0.0.0.0] network 192.168.1.0 0.0.0.255

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

[SwitchA-ospf-1] quit

# Configure Switch B.

<SwitchB> system-view

[SwitchB] router id 2.2.2.2

[SwitchB] ospf

[SwitchB-ospf-1] area 0

[SwitchB-ospf-1-area-0.0.0.0] network 192.168.1.0 0.0.0.255

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

[SwitchB-ospf-1] quit

# Configure Switch C.

<SwitchC> system-view

[SwitchC] router id 3.3.3.3

[SwitchC] ospf

[SwitchC-ospf-1] area 0

[SwitchC-ospf-1-area-0.0.0.0] network 192.168.1.0 0.0.0.255

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

[SwitchC-ospf-1] quit

# Configure Switch D.

<SwitchD> system-view

[SwitchD] router id 4.4.4.4

[SwitchD] ospf

[SwitchD-ospf-1] area 0

[SwitchD-ospf-1-area-0.0.0.0] network 192.168.1.0 0.0.0.255

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

[SwitchD-ospf-1] quit

# Display OSPF neighbor information on Switch A.

[SwitchA] 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(Vlan-interface1)'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 Switch D is the DR and Switch C is the BDR.

3. Configure router priorities on interfaces:

# Configure Switch A.

[SwitchA] interface vlan-interface 1

[SwitchA-Vlan-interface1] ospf dr-priority 100

[SwitchA-Vlan-interface1] quit

# Configure Switch B.

[SwitchB] interface vlan-interface 1

[SwitchB-Vlan-interface1] ospf dr-priority 0

[SwitchB-Vlan-interface1] quit

# Configure Switch C.

[SwitchC] interface vlan-interface 1

[SwitchC-Vlan-interface1] ospf dr-priority 2

[SwitchC-Vlan-interface1] quit

# Display neighbor information on Switch D.

<SwitchD> 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(Vlan-interface1)'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 priority settings do not take effect immediately.

4. Restart OSPF process:

# Restart the OSPF process of Switch D.

<SwitchD> reset ospf 1 process

Warning : Reset OSPF process? [Y/N]:y

# Display neighbor information on Switch D.

<SwitchD> 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(Vlan-interface1)'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 Switch A becomes the DR and Switch C becomes the BDR.

If the neighbor state is full, Switch D has established an adjacency with the neighbor. If the neighbor state is 2-way, the two switches are not the DR or the BDR, and they do not exchange LSAs.

# Display OSPF interface information.

[SwitchA] 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

[SwitchB] 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.

OSPF virtual link configuration example

Network requirements

As shown in Figure 14, configure a virtual link between Switch B and Switch C to connect Area 2 to the backbone area. After configuration, Switch B can learn routes to Area 2.

Figure 14 Network diagram

Configuration procedure

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

2. Enable OSPF:

# Configure Switch A.

<SwitchA> system-view

[SwitchA] ospf 1 router-id 1.1.1.1

[SwitchA-ospf-1] area 0

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

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

[SwitchA-ospf-1] quit

# Configure Switch B.

<SwitchB> system-view

[SwitchB] ospf 1 router-id 2.2.2.2

[SwitchB-ospf-1] area 0

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

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

[SwitchB-ospf-1] area 1

[SwitchB–ospf-1-area-0.0.0.1] network 10.2.1.0 0.0.0.255

[SwitchB–ospf-1-area-0.0.0.1] quit

[SwitchB-ospf-1] quit

# Configure Switch C.

<SwitchC> system-view

[SwitchC] ospf 1 router-id 3.3.3.3

[SwitchC-ospf-1] area 1

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

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

[SwitchC-ospf-1] area 2

[SwitchC–ospf-1-area-0.0.0.2] network 10.3.1.0 0.0.0.255

[SwitchC–ospf-1-area-0.0.0.2] quit

[SwitchC-ospf-1] quit

# Configure Switch D.

<SwitchD> system-view

[SwitchD] ospf 1 router-id 4.4.4.4

[SwitchD-ospf-1] area 2

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

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

[SwitchD-ospf-1] quit

# Display the OSPF routing table on Switch B.

[SwitchB] display ospf routing

OSPF Process 1 with Router ID 2.2.2.2

Routing Table

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 Switch B does not have routes to Area 2 because Area 0 is not directly connected to Area 2.

3. Configure a virtual link:

# Configure Switch B.

[SwitchB] ospf

[SwitchB-ospf-1] area 1

[SwitchB-ospf-1-area-0.0.0.1] vlink-peer 3.3.3.3

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

[SwitchB-ospf-1] quit

# Configure Switch C.

[SwitchC] ospf 1

[SwitchC-ospf-1] area 1

[SwitchC-ospf-1-area-0.0.0.1] vlink-peer 2.2.2.2

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

[SwitchC-ospf-1] quit

# Display the OSPF routing table on Switch B.

[SwitchB] display ospf routing

OSPF Process 1 with Router ID 2.2.2.2

Routing Table

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 Switch B has learned the route 10.3.1.0/24 to Area 2.

OSPF GR configuration example

Network requirements

As shown in Figure 15:

· Switch A, Switch B, and Switch C that belong to the same AS and the same OSPF routing domain are GR capable.

· Switch A acts as the non-IETF GR restarter. Switch B and Switch C are the GR helpers, and synchronize their LSDBs with Switch A through OOB communication of GR.

Figure 15 Network diagram

Configuration procedure

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

2. Enable OSPF:

# Configure Switch A.

SwitchA> system-view

[SwitchA] router id 1.1.1.1

[SwitchA] ospf 100

[SwitchA-ospf-100] area 0

[SwitchA-ospf-100-area-0.0.0.0] network 192.1.1.0 0.0.0.255

[SwitchA-ospf-100-area-0.0.0.0] quit

[SwitchA-ospf-1] quit

# Configure Switch B.

<SwitchB> system-view

[SwitchB] router id 2.2.2.2

[SwitchB] ospf 100

[SwitchB-ospf-100] area 0

[SwitchB-ospf-100-area-0.0.0.0] network 192.1.1.0 0.0.0.255

[SwitchB-ospf-100-area-0.0.0.0] quit

[SwitchB-ospf-1] quit

# Configure Switch C.

<SwitchC> system-view

[SwitchC] router id 3.3.3.3

[SwitchC] ospf 100

[SwitchC-ospf-100] area 0

[SwitchC-ospf-100-area-0.0.0.0] network 192.1.1.0 0.0.0.255

[SwitchC-ospf-100-area-0.0.0.0] quit

[SwitchC-ospf-1] quit

3. Configure OSPF GR:

# Configure Switch 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 capability for OSPF process 100.

[SwitchA-ospf-100] enable link-local-signaling

[SwitchA-ospf-100] enable out-of-band-resynchronization

[SwitchA-ospf-100] graceful-restart

[SwitchA-ospf-100] quit

# Configure Switch B as the GR helper: enable the link-local signaling capability and the out-of-band re-synchronization capability for OSPF process 100.

[SwitchB-ospf-100] enable link-local-signaling

[SwitchB-ospf-100] enable out-of-band-resynchronization

# Configure Switch C as the GR helper: enable the link-local signaling capability and the out-of-band re-synchronization capability for OSPF process 100.

[SwitchC-ospf-100] enable link-local-signaling

[SwitchC-ospf-100] enable out-of-band-resynchronization

Verifying the configuration

# Enable OSPF GR event debugging and restart the OSPF process by using GR on Switch A.

<SwitchA> debugging ospf event graceful-restart

<SwitchA> terminal monitor

<SwitchA> terminal logging level 7

<SwitchA> reset ospf 100 process graceful-restart

Reset OSPF process? [Y/N]:y

%Oct 21 15:29:28:727 2011 SwitchA OSPF/5/OSPF_NBR_CHG: OSPF 100 Neighbor 192.1.1.2(Vlan-interface100) from Full to Down.

%Oct 21 15:29:28:729 2011 SwitchA OSPF/5/OSPF_NBR_CHG: OSPF 100 Neighbor 192.1.1.3(Vlan-interface100) from Full to Down.

*Oct 21 15:29:28:735 2011 SwitchA OSPF/7/DEBUG:

OSPF 100 nonstandard GR Started for OSPF Router

*Oct 21 15:29:28:735 2011 SwitchA OSPF/7/DEBUG:

OSPF 100 created GR wait timer,timeout interval is 40(s).

*Oct 21 15:29:28:735 2011 SwitchA OSPF/7/DEBUG:

OSPF 100 created GR Interval timer,timeout interval is 120(s).

*Oct 21 15:29:28:758 2011 SwitchA OSPF/7/DEBUG:

OSPF 100 created OOB Progress timer for neighbor 192.1.1.3.

*Oct 21 15:29:28:766 2011 SwitchA OSPF/7/DEBUG:

OSPF 100 created OOB Progress timer for neighbor 192.1.1.2.

%Oct 21 15:29:29:902 2011 SwitchA OSPF/5/OSPF_NBR_CHG: OSPF 100 Neighbor 192.1.1.2(Vlan-interface100) from Loading to Full.

*Oct 21 15:29:29:902 2011 SwitchA OSPF/7/DEBUG:

OSPF 100 deleted OOB Progress timer for neighbor 192.1.1.2.

%Oct 21 15:29:30:897 2011 SwitchA OSPF/5/OSPF_NBR_CHG: OSPF 100 Neighbor 192.1.1.3(Vlan-interface100) from Loading to Full.

*Oct 21 15:29:30:897 2011 SwitchA OSPF/7/DEBUG:

OSPF 100 deleted OOB Progress timer for neighbor 192.1.1.3.

*Oct 21 15:29:30:911 2011 SwitchA 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 SwitchA OSPF/7/DEBUG:

OSPF 100 deleted GR Interval timer.

*Oct 21 15:29:30:912 2011 SwitchA OSPF/7/DEBUG:

OSPF 100 deleted GR wait timer.

%Oct 21 15:29:30:920 2011 SwitchA OSPF/5/OSPF_NBR_CHG: OSPF 100 Neighbor 192.1.1.2(Vlan-interface100) from Full to Down.

%Oct 21 15:29:30:921 2011 SwitchA OSPF/5/OSPF_NBR_CHG: OSPF 100 Neighbor 192.1.1.3(Vlan-interface100) from Full to Down.

%Oct 21 15:29:33:815 2011 SwitchA OSPF/5/OSPF_NBR_CHG: OSPF 100 Neighbor 192.1.1.3(Vlan-interface100) from Loading to Full.

%Oct 21 15:29:35:578 2011 SwitchA OSPF/5/OSPF_NBR_CHG: OSPF 100 Neighbor 192.1.1.2(Vlan-interface100) from Loading to Full.

The output shows that Switch A completes GR.

OSPF NSR configuration example

Network requirements

As shown in Figure 16, Switch S, Switch A, and Switch B belong to the same OSPF routing domain. Enable OSPF NSR on Switch S to ensure correct routing when an active/standby switchover occurs on Switch S.

Figure 16 Network diagram

Configuration procedure

1. Configure IP addresses and subnet masks for interfaces on the switches. (Details not shown.)

2. Configure OSPF on the switches to ensure the following: (Details not shown.)

¡ Switch S, Switch A, and Switch B can communicate with each other at Layer 3.

¡ Dynamic route update can be implemented among them with OSPF.

3. Enable OSPF NSR on Switch S.

<SwitchS> system-view

[SwitchS] ospf 100

[SwitchS-ospf-100] non-stop-routing

[SwitchS-ospf-100] quit

Verifying the configuration

# Perform an active/standby switchover on Switch S.

[SwitchS] placement reoptimize

Predicted changes to the placement

Program Current location New location

---------------------------------------------------------------------

lb 0/0 0/0

lsm 0/0 0/0

slsp 0/0 0/0

rib6 0/0 0/0

routepolicy 0/0 0/0

rib 0/0 0/0

staticroute6 0/0 0/0

staticroute 0/0 0/0

ospf 0/0 1/0

Continue? [y/n]:y

Re-optimization of the placement start. You will be notified on completion

Re-optimization of the placement complete. Use 'display placement' to view the new placement

# During the switchover period, display OSPF neighbors on Switch A to verify the neighbor relationship between Switch A and Switch S.

<SwitchA> display ospf peer

OSPF Process 1 with Router ID 2.2.2.1

Neighbor Brief Information

Area: 0.0.0.0

Router ID Address Pri Dead-Time State Interface

3.3.3.1 12.12.12.2 1 37 Full/BDR Vlan100

# Display OSPF routes on Switch A to verify if Switch A has a route to the loopback interface on Switch B.

<SwitchA> display ospf routing

OSPF Process 1 with Router ID 2.2.2.1

Routing Table

Routing for network

Destination Cost Type NextHop AdvRouter Area

44.44.44.44/32 2 Stub 12.12.12.2 4.4.4.1 0.0.0.0

14.14.14.0/24 2 Transit 12.12.12.2 4.4.4.1 0.0.0.0

22.22.22.22/32 0 Stub 22.22.22.22 2.2.2.1 0.0.0.0

12.12.12.0/24 1 Transit 12.12.12.1 2.2.2.1 0.0.0.0

Total nets: 4

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

# Display OSPF neighbors on Switch B to verify the neighbor relationship between Switch B and Switch S.

<SwitchB> display ospf peer

OSPF Process 1 with Router ID 4.4.4.1

Neighbor Brief Information

Area: 0.0.0.0

Router ID Address Pri Dead-Time State Interface

3.3.3.1 14.14.14.2 1 39 Full/BDR Vlan200

# Display OSPF routes on Switch B to verify if Switch B has a route to the loopback interface on Switch A.

<SwitchB> display ospf routing

OSPF Process 1 with Router ID 4.4.4.1

Routing Table

Routing for network

Destination Cost Type NextHop AdvRouter Area

44.44.44.44/32 0 Stub 44.44.44.44 4.4.4.1 0.0.0.0

14.14.14.0/24 1 Transit 14.14.14.1 4.4.4.1 0.0.0.0

22.22.22.22/32 2 Stub 14.14.14.2 2.2.2.1 0.0.0.0

12.12.12.0/24 2 Transit 14.14.14.2 2.2.2.1 0.0.0.0

Total nets: 4

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

The output shows the following when an active/standby switchover occurs on Switch S:

· The neighbor relationships and routing information on Switch A and Switch B have not changed.

· The traffic from Switch A to Switch B has not been impacted.

BFD for OSPF configuration example

Network requirements

As shown in Figure 17, run OSPF on Switch A, Switch B, and Switch C so that they are reachable to each other at the network layer.

· When the link over which Switch A and Switch B communicate through a Layer 2 switch fails, BFD can quickly detect the failure and notify OSPF of the failure.

· Switch A and Switch B then communicate through Switch C.

Figure 17 Network diagram

Table 1 Interface and IP address assignment

Device	Interface	IP address
Switch A	Vlan-int10	192.168.0.102/24
Switch A	Vlan-int11	10.1.1.102/24
Switch A	Loop0	121.1.1.1/32
Switch B	Vlan-int10	192.168.0.100/24
Switch B	Vlan-int13	13.1.1.1/24
Switch B	Loop0	120.1.1.1/32
Switch C	Vlan-int11	10.1.1.100/24
Switch C	Vlan-int13	13.1.1.2/24

Configuration procedure

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

2. Enable OSPF:

# Configure Switch A.

<SwitchA> system-view

[SwitchA] ospf

[SwitchA-ospf-1] area 0

[SwitchA-ospf-1-area-0.0.0.0] network 192.168.0.0 0.0.0.255

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

[SwitchA-ospf-1-area-0.0.0.0] network 121.1.1.1 0.0.0.0

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

[SwitchA-ospf-1] quit

# Configure Switch B.

<SwitchB> system-view

[SwitchB] ospf

[SwitchB-ospf-1] area 0

[SwitchB-ospf-1-area-0.0.0.0] network 192.168.0.0 0.0.0.255

[SwitchB-ospf-1-area-0.0.0.0] network 13.1.1.0 0.0.0.255

[SwitchB-ospf-1-area-0.0.0.0] network 120.1.1.1 0.0.0.0

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

[SwitchB-ospf-1] quit

# Configure Switch C.

<SwitchC> system-view

[SwitchC] ospf

[SwitchC-ospf-1] area 0

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

[SwitchC-ospf-1-area-0.0.0.0] network 13.1.1.0 0.0.0.255

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

[SwitchC-ospf-1] quit

3. Configure BFD:

# Enable BFD on Switch A and configure BFD parameters.

[SwitchA] bfd session init-mode active

[SwitchA] interface vlan-interface 10

[SwitchA-Vlan-interface10] ospf bfd enable

[SwitchA-Vlan-interface10] bfd min-transmit-interval 500

[SwitchA-Vlan-interface10] bfd min-receive-interval 500

[SwitchA-Vlan-interface10] bfd detect-multiplier 7

[SwitchA-Vlan-interface10] quit

# Enable BFD on Switch B and configure BFD parameters.

[SwitchB] bfd session init-mode active

[SwitchB] interface vlan-interface 10

[SwitchB-Vlan-interface10] ospf bfd enable

[SwitchB-Vlan-interface10] bfd min-transmit-interval 500

[SwitchB-Vlan-interface10] bfd min-receive-interval 500

[SwitchB-Vlan-interface10] bfd detect-multiplier 6

[SwitchB-Vlan-interface10] quit

Verifying the configuration

# Display the BFD information on Switch A.

<SwitchA> display bfd session

Total Session Num: 1 Up Session Num: 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 Vlan10

# Display routes destined for 120.1.1.1/32 on Switch A.

<SwitchA> 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

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 Neighbor: 0.0.0.0

Flags: 0x1008c OrigNextHop: 192.168.0.100

Label: NULL RealNextHop: 192.168.0.100

BkLabel: NULL BkNextHop: N/A

Tunnel ID: Invalid Interface: Vlan-interface10

BkTunnel ID: Invalid BkInterface: N/A

FtnIndex: 0x0 TrafficIndex: N/A

Connector: N/A PathID: 0x0

The output shows that Switch A communicates with Switch B through VLAN-interface 10. Then the link over VLAN-interface 10 fails.

# Display routes destined for 120.1.1.1/32 on Switch A.

<SwitchA> 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

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 Neighbor: 0.0.0.0

Flags: 0x1008c OrigNextHop: 10.1.1.100

Label: NULL RealNextHop: 10.1.1.100

BkLabel: NULL BkNextHop: N/A

Tunnel ID: Invalid Interface: Vlan-interface11

BkTunnel ID: Invalid BkInterface: N/A

FtnIndex: 0x0 TrafficIndex: N/A

Connector: N/A PathID: 0x0

The output shows that Switch A communicates with Switch B through VLAN-interface 11.

OSPF FRR configuration example

Network requirements

As shown in Figure 18, Switch A, Switch B, and Switch C reside in the same OSPF domain. Configure OSPF FRR so that when the link between Switch A and Switch B fails, traffic is immediately switched to Link B.

Figure 18 Network diagram

Table 2 Interface and IP address assignment

Device	Interface	IP address
Switch A	Vlan-int100	12.12.12.1/24
Switch A	Vlan-int200	13.13.13.1/24
Switch A	Loop0	1.1.1.1/32
Switch B	Vlan-int101	24.24.24.4/24
Switch B	Vlan-int200	13.13.13.2/24
Switch B	Loop0	4.4.4.4/32
Switch C	Vlan-int100	12.12.12.2/24
Switch C	Vlan-int101	24.24.24.2/24

Configuration procedure

1. Configure IP addresses and subnet masks for interfaces on the switches. (Details not shown.)

2. Configure OSPF on the switches to ensure that Switch A, Switch B, and Switch C can communicate with each other at the network layer. (Details not shown.)

3. Configure OSPF FRR to automatically calculate the backup next hop:

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 the backup next hop by using the LFA algorithm:

# Configure Switch A.

<SwitchA> system-view

[SwitchA] ospf 1

[SwitchA-ospf-1] fast-reroute lfa

[SwitchA-ospf-1] quit

# Configure Switch B.

<SwitchB> system-view

[SwitchB] ospf 1

[SwitchB-ospf-1] fast-reroute lfa

[SwitchB-ospf-1] quit

¡ (Method 2.) Enable OSPF FRR to designate a backup next hop by using a routing policy.

# Configure Switch A.

<SwitchA> system-view

[SwitchA] ip prefix-list abc index 10 permit 4.4.4.4 32

[SwitchA] route-policy frr permit node 10

[SwitchA-route-policy-frr-10] if-match ip address prefix-list abc

[SwitchA-route-policy-frr-10] apply fast-reroute backup-interface vlan-interface 100 backup-nexthop 12.12.12.2

[SwitchA-route-policy-frr-10] quit

[SwitchA] ospf 1

[SwitchA-ospf-1] fast-reroute route-policy frr

[SwitchA-ospf-1] quit

# Configure Switch B.

<SwitchB> system-view

[SwitchB] ip prefix-list abc index 10 permit 1.1.1.1 32

[SwitchB] route-policy frr permit node 10

[SwitchB-route-policy-frr-10] if-match ip address prefix-list abc

[SwitchB-route-policy-frr-10] apply fast-reroute backup-interface vlan-interface 101 backup-nexthop 24.24.24.2

[SwitchB-route-policy-frr-10] quit

[SwitchB] ospf 1

[SwitchB-ospf-1] fast-reroute route-policy frr

[SwitchB-ospf-1] quit

Verifying the configuration

# Display route 4.4.4.4/32 on Switch A to view the backup next hop information.

[SwitchA] 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

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 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

Tunnel ID: Invalid Interface: Vlan-interface200

BkTunnel ID: Invalid BkInterface: Vlan-interface100

FtnIndex: 0x0 TrafficIndex: N/A

Connector: N/A PathID: 0x0

# Display route 1.1.1.1/32 on Switch B to view the backup next hop information.

[SwitchB] 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

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 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

Tunnel ID: Invalid Interface: Vlan-interface200

BkTunnel ID: Invalid BkInterface: Vlan-interface101

FtnIndex: 0x0 TrafficIndex: N/A

Connector: N/A PathID: 0x0

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.

05-Layer 3—IP Routing Configuration Guide

Configuring OSPF

Backbone area and virtual links

Stub area and totally stub area

NSSA area and totally NSSA area

Router types

DR and BDR

DR and BDR mechanism

DR and BDR election

OSPF configuration task list

Enabling OSPF

Configuration guidelines

Configuring OSPF areas

Configuring OSPF network types

Configuration prerequisites

Configuring the broadcast network type for an interface

Configuring the NBMA network type for an interface

Configuring OSPF route control

Configuration prerequisites

Configuring OSPF route summarization

Configuring received OSPF route filtering

Setting an OSPF cost for an interface

Setting the maximum number of ECMP routes

Setting OSPF preference

Configuring OSPF route redistribution

Tuning and optimizing OSPF networks

Configuration prerequisites

Setting OSPF timers

Setting LSA transmission delay

Setting SPF calculation interval

Setting the LSA arrival interval

Setting the LSA generation interval

Configuring stub routers

Configuring OSPF authentication

Configuring OSPF area authentication

Configuring OSPF interface authentication

Adding the interface MTU into DD packets

Setting the DSCP value for outgoing OSPF packets

Setting OSPF exit overflow interval

Logging neighbor state changes

Configuring prefix suppression for an OSPF process

Configuring prefix suppression for an interface

Enabling OSPF PIC

Configuring BFD for OSPF PIC

Configuring OSPF GR restarter

Configuring the IETF OSPF GR restarter

Configuring the non-IETF OSPF GR restarter

Configuring OSPF GR helper

Configuring the IETF OSPF GR helper

Configuring the non-IETF OSPF GR helper

Triggering OSPF GR

Configuring OSPF FRR to calculate a backup next hop using the LFA algorithm

Configuring OSPF FRR to specify a backup next hop using a routing policy

Configuring BFD for OSPF FRR

Displaying and maintaining OSPF

OSPF configuration examples

Basic OSPF configuration example

Network requirements

Configuration procedure

Verifying the configuration

OSPF route redistribution configuration example

Network requirements

Configuration procedure

Verifying the configuration

OSPF route summarization configuration example

Network requirements

Configuration procedure

OSPF stub area configuration example

Network requirements

Configuration procedure

OSPF NSSA area configuration example

Network requirements

Configuration procedure

OSPF DR election configuration example

Network requirements

Configuration procedure

Network requirements

Configuration procedure

Network requirements

Configuration procedure