Intermediate System-to-Intermediate System (IS-IS) is a dynamic routing protocol designed by the International Organization for Standardization (ISO) to operate on the connectionless network protocol (CLNP).

The IS-IS routing protocol has been modified and extended in RFC 1195 by the International Engineer Task Force (IETF) for application in both TCP/IP and OSI reference models, and the new one is called Integrated IS-IS or Dual IS-IS.

IS-IS is an interior gateway protocol (IGP) used within an Autonomous System. It adopts the Shortest Path First (SPF) algorithm for route calculation.

1.1.1 Basic Concepts

I. IS-IS terminology

l Intermediate system (IS). An IS, similar to a router in TCP/IP, is the basic unit in IS-IS protocol to generate and propagate routing information. In the following text, an IS is a router.

l End system (ES). An ES refers to a host system in TCP/IP. ISO defines the ES-IS protocol for communication between an ES and an IS, therefore an ES does not participate in the IS-IS process.

l Routing domain (RD). A group of ISs exchange routing information with the same routing protocol in a routing domain.

l Area. An area is a division unit in a routing domain. The IS-IS protocol allows a routing domain to be divided into multiple areas.

l Link State Database (LSDB). All link states in the network forms the LSDB. There is at least one LSDB in each IS. The IS uses SPF algorithm and LSDB to generate its own routes.

l Link State Protocol Data Unit (LSPDU) or link-state packet (LSP). Each IS can generate an LSP which contains all the link state information of the IS. Each IS collects all the LSPs in the local area to generate its own LSDB.

l Network Protocol Data Unit (NPDU). An NPDU is a network layer protocol packet in ISO, which is equivalent to an IP packet in TCP/IP.

l Designated IS. On a broadcast network, the designated intermediate system is also known as the designated IS or a pseudonode.

l Network service access point (NSAP). The NSAP is the ISO network layer address. It identifies an abstract network service access point and describes the network address in the ISO reference model.

II. IS-IS address structure

1) NSAP

As shown in Figure 1-1, the NSAP address consists of the Initial Domain Part (IDP) and the Domain Specific Part (DSP). The IDP is equal to the network ID of the IP address, and the DSP is equal to the subnet and host IDs.

The IDP, defined by ISO, includes the Authority and Format Identifier (AFI) and the Initial Domain Identifier (IDI).

The DSP includes the High Order DSP (HODSP), the System ID and SEL, where the HODSP identifies the area, the System ID identifies the host, and the SEL indicates the type of service.

The length of IDP and DSP is variable. The length of the NSAP address varies from 8 bytes to 20 bytes.

Figure 1-1 NSAP address structure

2) Area address

The area address of IS-IS is comprised of the IDP and the HODSP of the DSP, which identify the area and the routing domain. Different routing domains cannot have the same area address.

Generally, a router only needs one area address, and all nodes in the same routing domain must share the same area address. However, a router can have three area addresses at most to support smooth area merging, partitioning and switching.

3) System ID

The system ID identifies the host or router uniquely. It has a fixed length of 48 bits (6 bytes).

The system ID is used in cooperation with the Router ID in practical. For example, a router uses the IP address 168.10.1.1 of the Loopback 0 as the Router ID, the system ID in IS-IS can be obtained in the following way:

l Extend each decimal number of the IP address to 3 digits by adding 0s from the left, like 168.010.001.001;

l Divide the extended IP address into 3 sections with 4 digits in each section to get the System ID 1680.1000.1001.

There are other methods to define a system ID. Just make sure it can uniquely identify a host or router.

4) SEL

The NSAP Selector (SEL), sometimes present in N-SEL, is similar with the protocol identifier in IP. Different transport layer protocols use different SELs. All SELs in IP are 00.

5) Routing method

Since the area is explicitly defined in the address structure, the Level-1 router can easily recognize the packets sent out of the area. These packets are forwarded to the Level-2 router.

The Level-1 router makes routing decisions based on the system ID. If the destination is not in the area, the packet is forwarded to the nearest Level-1-2 router.

The Level-2 router routes packets across areas according to the area address.

III. NET

The Network Entity Title (NET) is an NSAP with SEL of 0. It indicates the network layer information of the IS itself, where SEL=0 means no transport layer information. Therefore, the length of NET is equal to NSAP, in the range 8 bytes to 20 bytes.

Generally, a router only needs one NET, but it can have three NETs at most for smooth area merging and partitioning. When you configure multiple NETs, make sure their system IDs are the same.

For example, a NET is ab.cdef.1234.5678.9abc.00, where,

Area = ab.cdef, System ID = 1234.5678.9abc, and SEL = 00.

1.1.2 IS-IS Area

I. Two-level hierarchy

IS-IS uses two-level hierarchy in the routing domain to support large scale routing networks. A large routing domain is divided into multiple Areas. The Level-1 router is in charge of forwarding routes within an area, and the Level-2 router is in charge of forwarding routes between areas.

II. Level-1 and Level-2

1) Level-1 router

The Level-1 router only establishes the neighbor relationship with Level-1 and Level-1-2 routers in the same area. The LSDB maintained by the Level-1 router contains the local area routing information. It directs the packets out of the area to the nearest Level-1-2 router.

2) Level-2 router

The Level-2 router establishes the neighbor relationships with the Level-2 and Level-1-2 routers in the same or in different areas. It maintains a Level-2 LSDB which contains inter area routing information. All the Level-2 and Level-1-2 routers form the backbone in a routing domain. The backbone must be contiguous. Only Level-2 routers can directly communicate with routers outside the routing domain.

3) Level-1-2 router

A router with both Level-1 and Level-2 router functions is called a Level-1-2 router. It can establish the Level-1 neighbor relationship with the Level-1 and Level-1-2 routers in the same area, or establish Level-2 neighbor relationship with the Level-2 and Level-1-2 routers in different areas. A Level-1 router must be connected to other areas via a Level-1-2 router. The Level-1-2 router maintains two LSDBs, where the Level-1 LSDB is for routing within the area, and the Level-2 LSDB is for routing between areas.

& Note:

l The Level-1 routers in different areas cannot establish the neighbor relationship.

l The neighbor relationship establishment of Level-2 routers has nothing to do with area.

Figure 1-2 shows a network topology running the IS-IS protocol. Area 1 is a set of Level-2 routers, called backbone network. The other four areas are non-backbone networks connected to the backbone through Level-1-2 routers.

Figure 1-2 IS-IS topology

Figure 1-3 shows another network topology running the IS-IS protocol. The Level-1-2 routers connect the Level-1 and Level-2 routers, and also form the IS-IS backbone together with the Level-2 routers. There is no area defined as the backbone in this topology. The backbone is composed of all contiguous Level-2 and Level-1-2 routers which can reside in different areas.

Figure 1-3 IS-IS topology

& Note:

The IS-IS backbone does not need to be a specific area.

Both the Level-1 and Level-2 routers use the SPF algorithm to generate the Shortest Path Tree (SPT).

III. Interface routing hierarchy type

You can configure the routing type for each interface. For a Level-1-2 router, one interface may establish Level-1 adjacency with a router, and another one may establish Level-2 adjacency with another router. You can limit the adjacency type by configuring the routing hierarchy on the interface. For example, the level-1 interface can only establish Level-1 adjacency, while the level-2 interface can only establish Level-2 adjacency.

By having this function, you can prevent the Level-1 hello packets from propagating to the Level-2 backbone through the Lever-1-2 router. This can result in bandwidth saving.

IV. Route leaking

An IS-IS routing domain is comprised of only one Level-2 area and multiple Level-1 areas. A Level-1 area is connected with the Level-2 area rather than other Level-1 areas.

The routing information of the Level-1 area is sent to the Level-2 area through the Level-1-2 router. Therefore, the Level-2 router knows the routing information of the entire IS-IS routing domain but does not share the information with the Level-1 area by default.

Since the Level-1 router simply sends the routing information for destinations outside the area to the nearest Level-1-2 router, this may cause a problem that the best path cannot be selected.

To solve this problem, route leaking was introduced. The Level-2 router can advertise the Level-2 routing information to a specified Level-1 area. By having the routing information of other areas, the Level-1 router can make a better routing choice for the packets destined outside the area.

1.1.3 IS-IS Network Type

I. Network type

IS-IS supports two network types:

l Broadcast network, such as Ethernet, Token-Ring.

l Point-to-point network, such as PPP, HDLC.

& Note:

For the Non-Broadcast Multi-Access (NBMA) network, such as ATM, you need to configure point-to-point or broadcast network on its configured subinterfaces. IS-IS does not run on Point to Multipoint (P2MP) links.

II. DIS and pseudonodes

On an IS-IS broadcast network, a router has to be selected as the Designated Intermediate System (DIS).

The Level-1 and Level-2 DISs are selected respectively. You can assign different priorities for different level DIS selections. The higher a router’s priority is, the more likelihood the router becomes the DIS. If there are multiple routers with the same highest DIS priority, the one with the highest SNPA (Subnetwork Point of Attachment) address (which is the MAC address on a broadcast network) will be selected. A router can be the DIS for different levels.

As shown in Figure 1-4, the same level routers on the same network segment can establish adjacencies.

Figure 1-4 DIS in the IS-IS broadcast network

The DIS creates and updates pseudonodes as well as their LSP to describe all routers on the network.

The pseudonode emulates a virtual node on the broadcast network. It is not a real router. In IS-IS, it is identified by the system ID and one byte Circuit ID (a non zero value) of the DIS.

Using pseudonodes can reduce LSPs, the resources used by SPF and simplify the network topology.

& Note:

On IS-IS broadcast networks, all routers are adjacent with each other. The DIS is responsible for the synchronization of their LSDBs.

1.1.4 IS-IS PDU Format

I. PDU header format

The IS-IS packets are encapsulated into link layer frames. The Protocol Data Unit (PDU) consists of two parts, the headers and the variable length field, where the headers can be further divided into the common header and the specific header. The common headers are the same for all PDUs, while the specific headers vary by PDU type. The following figure shows the PDU format.

Figure 1-5 PDU format

II. Common header format

Figure 1-6 shows the common header format.

Figure 1-6 PDU common header format

l Intradomain Routing Protocol Discriminator: Set to 0x83.

l Length Indicator: The length of the PDU header, including both common and specific headers, present in bytes.

l Version/Protocol ID Extension: Set to 1(0x01).

l ID Length: The length of the NSAP address and NET ID.

l R(Reserved): Set to 0.

l PDU Type: For detail information, refer to Table 1-1.

l Version: Set to 1(0x01).

l Maximum Area Address: Maximum number of area addresses supported.

Table 1-1 PDU type

Type	PDU Type	Acronym
15	Level-1 LAN IS-IS hello PDU	L1 LAN IIH
16	Level-2 LAN IS-IS hello PDU	L2 LAN IIH
17	Point-to-Point IS-IS hello PDU	P2P IIH
18	Level-1 Link State PDU	L1 LSP
20	Level-2 Link State PDU	L2 LSP
24	Level-1 Complete Sequence Numbers PDU	L1 CSNP
25	Level-2 Complete Sequence Numbers PDU	L2 CSNP
26	Level-1 Partial Sequence Numbers PDU	L1 PSNP
27	Level-2 Partial Sequence Numbers PDU	L2 PSNP

III. Hello

The hello packet is used by routers to establish and maintain the neighbor relationship. It is also called IS-to-IS hello PDU (IIH). For broadcast network, the Level-1 router uses the Level-1 LAN IIH; and the Level-2 device uses the Level-2 LAN IIH. The P2P IIH is used on the point-to-point network.

Figure 1-7 illustrates the hello packet format in broadcast networks, where the blue fields are the common header.

Figure 1-7 L1/L2 LAN IIH format

l Reserved/Circuit Type: The first 6 bits are reserved with value 0. The last 2 bits indicates router types: 00 means reserved, 01 indicates L1, 10 indicates L2, and 11 indicates L1/2.

l Source ID: The system ID of the router advertising the hello packet.

l Holding Time: If no hello packets are received from a neighbor within the holding time, the neighbor is considered dead.

l PDU Length: The total length of the PDU in bytes.

l Priority: DIS priority.

l LAN ID: Includes the system ID and one byte pseudonode ID.

Figure 1-8 shows the hello packet format on the point-to-point network.

Figure 1-8 P2P IIH format

Instead of the priority and LAN ID fields in the LAN IIH, the P2P IIH has a Local Circuit ID field.

IV. LSP packet format

The Link State PDUs (LSP) carries link state information. There are two types: Level-1 LSP and Level-2 LSP. The Level-2 LSP is sent by the Level-2 router, and the Level-1 LSP is sent by the Level-1 router. The level-1-2 router can sent both types of the LSPs.

Two types of LSPs have the same format, as shown in Figure 1-9.

Figure 1-9 L1/L2 LSP format

l PDU Length: Total length of the PDU in bytes.

l Remaining Lifetime: LSP remaining lifetime in seconds.

l LSP ID: Consists of the system ID, the pseudonode ID (one byte) and the LSP fragment number (one byte).

l Sequence Number: LSP sequence number.

l Checksum: LSP checksum.

l P (Partition Repair): Only related with L2 LSP, indicates whether the router supports partition repair.

l ATT (Attachment): Generated by the L1/L1 router, only related with L1 LSP, indicates that the router generating the LSP is connected with multiple areas.

l OL (LSDB Overload): Indicates that the LSDB is not complete because the router is running out of system resources. In this condition, other routers will not send packets to the overloaded router, except packets destined to the networks directly connected to the router. For example, in Figure 1-10, Router A uses Router B to forward its packets to Router C in normal condition. Once other routers know the OL field on Router B is set to 1, Router A will send packets to Router C via Router D and Router E, but still send to Router B packets destined to the network directly connected to Router B.

Figure 1-10 LSDB overload

l IS Type: Type of the router generating the LSP.

V. SNP format

The Sequence Number PDU (SNP) confirms the latest received LSPs. It is similar to the Acknowledge packet, but more efficient.

SNP contains Complete SNP (CSNP) and Partial SNP (PSNP), which are further divided into Level-1 CSNP, Level-2 CSNP, Level-1 PSNP and Level-2 PSNP.

CSNP covers the summary of all LSPs in the LSDB to synchronize the LSDB between neighboring routers. On broadcast networks, CSNP is sent by the DIS periodically (10s by default). On point-to-point networks, CSNP is only sent during the first adjacency establishment.

The CSNP packet format is shown in Figure 1-11.

Figure 1-11 L1/L2 CSNP format

PSNP only contains the sequence numbers of one or multiple latest received LSPs. It can acknowledge multiple LSPs at one time. When LSDBs are not synchronized, a PSNP is used to request new LSPs from neighbors.

Figure 1-12 shows the PSNP packet format.

Figure 1-12 L1/L2 PSNP format

VI. CLV

The variable fields of PDU are composed of multiple Code-Length-Value (CLV) triplets. Figure 1-13 shows the CLV format.

Figure 1-13 CLV format

Table 1-2 shows different PDUs contain different CLVs.

Table 1-2 CLV name and the corresponding PDU type

CLV Code	Name	PDU Type
1	Area Addresses	IIH, LSP
2	IS Neighbors (LSP)	LSP
4	Partition Designated Level-2 IS	L2 LSP
6	IS Neighbors (MAC Address)	LAN IIH
7	IS Neighbors (SNPA Address)	LAN IIH
8	Padding	IIH
9	LSP Entries	SNP
10	Authentication Information	IIH, LSP, SNP
128	IP Internal Reachability Information	LSP
129	Protocols Supported	IIH, LSP
130	IP External Reachability Information	L2 LSP
131	Inter-Domain Routing Protocol Information	L2 LSP
132	IP Interface Address	IIH, LSP

Code 1 to 10 of CLV are defined in ISO 10589 (code 3 and 5 are not shown in the table), and others are defined in RFC 1195.

1.1.5 IS-IS Features Supported

I. Multiple instances and processes

IS-IS supports multiple instances and processes. Multiple processes allow a designated IS-IS process to work in concert with a group of interfaces. This means that a router can run multiple IS-IS processes, and each process corresponds to a unique group of interfaces.

For routers supporting VPN, each IS-IS process is associated with a designated VPN instance. Thus, the VPN instance is also associated with interfaces corresponding to the process.

II. Hot standby

A distributed router supports IS-IS Hot Standby (HSB) function. The data are copied from the Active Main Board (AMB) to the Standby Main Board (SMB). Whenever the AMB is down, the SMB can switch to the active status to maintain IS-IS normal operation.

There are two kinds of IS-IS HSB. One is IS-IS data synchronization backup. After switching from AMB to SMB, IS-IS can work immediately.

The other HSB is to backup the configuration information of IS-IS during the switching from AMB to SMB. After the graceful restart (GR), the router will send a request to neighbors to synchronize the LSDB.

& Note:

l For detailed information about the GR configuration, refer to GR configuration in the System Volume.

l For detailed information about the IS-IS hot standby configuration, refer to HA configuration in the System Volume.

III. IS-IS TE

IS-IS Traffic Engineering (TE) creates and maintains the Label Switched Path (LSP).

When creating the Constraint-based Routed LSP (CR LSP), MPLS needs to get the traffic attribute information of all links in the local area. The Traffic Engineering information of links is obtained from IS-IS.

& Note:

For detailed configuration of the IS-IS TE, refer to MPLS TE Configuration.

IV. Management tag

Management tag carries the management information of the IP address prefixes and BGP community attribute. It controls the redistribution from other routing protocols.

V. LSP fragment extension

IS-IS advertises link-state information by flooding LSPs. One LSP carries a limited amount of link-state information; therefore, IS-IS fragments LSPs. Each LSP fragment is uniquely identified by a combination of the System ID, Pseudonode ID (0 for a common LSP or a non-zero value for a Pseudonode LSP), and LSP Number (LSP fragment number) of the node or pseudo node that generated the LSP. The one-byte LSP number field, allowing a maximum of only 256 fragments to be generated by an IS-IS router, limits the amount of link-state information that the IS-IS router can advertise.

The LSP fragment extension feature allows an IS-IS router to generate more LSP fragments. Up to 50 additional virtual systems can be configured on the router, and each virtual system is capable of generating 256 LSP fragments to enable the IS-IS router to generate up to 13056 LSP fragments.

Fragment zero generated by a virtual system needs to carry some key information, including area address, protocol type, link to the originating system, and authentication information, and therefore, the corresponding LSP is long. To enable such LSPs to carry complete information and to be correctly flooded through all the IS-IS interfaces, the MTUs of all the IS-IS interfaces must not be less than 512; otherwise, LSP fragment extension will not take effect.

1) Terms

l Originating System

It is the router actually running IS-IS. After LSP fragment extension is enabled, additional virtual systems can be configured for the router. The originating system is the actual IS-IS process.

l System ID

System ID of the Originating System

l Additional System ID

Additional virtual system IDs are configured for the IS-IS router after LSP fragment extension is enabled. Each additional system ID can generate 256 LSP fragments. Both an additional system ID and a system ID must be unique in the entire routing domain.

l Virtual System

A virtual system is identified by an additional system ID and generates extended LSP fragments.

l Original LSP

It is the LSP generated by the originating system. The system ID in its LSP ID field is the system ID of the originating system.

l Extended LSP

Extended LSPs are generated by virtual systems. The system ID in the LSP ID field of an extended LSP is the virtual system ID.

After additional system IDs are configured, an IS-IS router can advertise more link-state information in extended LSP fragments. Each virtual system can be considered a virtual router. An extended LSP fragment is advertised by a virtual system identified by an additional system ID.

2) Operation modes

The LSP fragment extension feature operates in two modes:.

l Mode-1: Applicable to a network where some routers do not support LSP fragment extension. In this mode, adjacencies are formed between the originating system and virtual systems, with the link cost from the originating system to each virtual system as 0. Thus, each virtual system acts as a router connected to the originating system in the network, but the virtual systems are reachable through the originating system only. Therefore, the IS-IS routers not supporting LSP fragment extension can operate normally without modifying the extended LSP fragments received, but some limitation is imposed on the link state information in the extended LSP fragments advertised by the virtual systems.

l Mode-2: Applicable to a network where all the routers support LSP fragment extension. In this mode, all the IS-IS routers know which virtual system belongs to which originating system; therefore, no limitation is imposed on the link state information of the extended LSP fragments advertised by the virtual systems.

The operation mode of LSP fragment extension is configured based on area and routing level. Mode-1 is backward-compatible and allows the routers supporting and not supporting LSP fragment extension to interoperate with each other, but it restricts the link state information in the extended fragments. Mode-2 does not restrict the link state information in the extended fragments, and is recommended for an area where all the routers are at the same routing level and support LSP fragment extension.

VI. Dynamic host name mapping mechanism

The dynamic host name mapping mechanism provides the mapping between the host names and the system IDs for the IS-IS routers. The dynamic host name information is announced in the dynamic host name CLV of an LSP.

This mechanism also provides the mapping between a host name and the DIS of a broadcast network, which is announced in a dynamic host name TLV of a pseudonode LSP.

A host name is intuitionally easier to remember than a system ID. After enabling this feature on the router, you can see the host names instead of system IDs after using the display command.

1.1.6 Protocols and Standards

l ISO 10589 ISO IS-IS Routing Protocol

l ISO 9542 ES-IS Routing Protocol

l ISO 8348/Ad2 Network Services Access Points

l RFC 1195 - Use of OSI IS-IS for Routing in TCP/IP and Dual Environments

l RFC 2763 - Dynamic Hostname Exchange Mechanism for IS-IS

l RFC 2966 - Domain-wide Prefix Distribution with Two-Level IS-IS

l RFC 2973 - IS-IS Mesh Groups

l RFC 3277 - IS-IS Transient Blackhole Avoidance

l RFC 3358 - Optional Checksums in ISIS

l RFC 3373 - Three-Way Handshake for IS-IS Point-to-Point Adjacencies

l RFC 3567 - Intermediate System to Intermediate System (IS-IS) Cryptographic Authentication

l RFC 3719 - Recommendations for Interoperable Networks using IS-IS

l RFC 3786 - Extending the Number of IS-IS LSP Fragments Beyond the 256 Limit

l RFC 3787 - Recommendations for Interoperable IP Networks using IS-IS

l RFC 3784 - IS-IS extensions for Traffic Engineering

l RFC 3847 - Restart signaling for IS-IS

1.2 IS-IS Configuration Task List

Complete the following tasks to configure IS-IS:

Task		Remarks
Configuring IS-IS Basic Functions		Required
Configuring IS-IS Routing Information Control	Specifying a Priority for IS-IS	Optional
	Configuring IS-IS Link Cost	Required
	Configuring the Maximum Number of Equal Cost Routes	Optional
	Configuring IS-IS Route Summarization	Optional
	Advertising a Default Route	Optional
	Configuring Inbound Route Filtering	Optional
	Configuring Route Redistribution	Optional
	Configuring IS-IS Route Leaking	Optional
Tuning and Optimizing IS-IS Network	Configuring a DIS Priority for an Interface	Optional
	Configuring IS-IS Timers	Optional
	Disabling an Interface from Sending/Receiving IS-IS Hello Packets	Optional
	Configuring LSP Parameters	Optional
	Configuring SPF Parameters	Optional
	Configuring Dynamic Host Name Mapping	Optional
	Configuring IS-IS Authentication	Optional
	Configuring LSDB Overload Tag	Optional
	Logging the Adjacency Changes	Optional
	Enabling an Interface to Send Small Hello Packets	Optional
	Enabling IS-IS SNMP Trap	Optional

1.3 Configuring IS-IS Basic Functions

1.3.1 Configuration Prerequisites

Before the configuration, accomplish the following tasks first:

l Configure the link layer protocol.

l Configure an IP address for each interface, and make sure all nodes are reachable.

1.3.2 Configuration Procedure

Follow these steps to configure IS-IS basic functions:

To do…	Use the command…	Remarks
Enter system view	system-view	––
Enable an IS-IS process and enter its view	isis [ process-id ] [ vpn-instance vpn-instance-name ]	Required Not enabled by default
Assign a network entity title (NET)	network-entity net	Required Not assigned by default
Specify a router type	is-level { level-1 \| level-1-2 \| level-2 }	Optional The default type is level-1-2.
Return to system view	quit	––
Enter interface view	interface interface-type interface-number	––
Enable the IS-IS process on the interface	isis enable [ process-id ]	Required Disabled by default
Specify network type for the interface as P2P	isis circuit-type p2p	Optional By default, the network type of an interface depends on the physical media. The network type of a VLAN interface is broadcast.
Specify the adjacency type for the interface	isis circuit-level [ level-1 \| level-1-2 \| level-2 ]	Optional The default type is level-1-2.
Disable peer IP address check on the PPP interface	isis peer-ip-ignore	Optional The command only applies to the PPP interface. Enabled by default, meaning two peers must be in the same network.

& Note:

l You need to enable the IS-IS process, specify a NET, and enable IS-IS on the interface before configuring or validating other functions.

l If a router’s type is configured as Level-1 or Level-2, the type of interfaces must be the same, and cannot be changed with the isis circuit-level command. However, an interface’s type can be changed with this command when the router’s type is Level-1-2 for the establishment of a specific level adjacency.

1.4 Configuring IS-IS Routing Information Control

1.4.1 Configuration Prerequisites

Before the configuration, accomplish the following tasks first:

l Configure an IP address on each interface, and make sure all nodes are reachable.

l Configure basic IS-IS functions

1.4.2 Specifying a Priority for IS-IS

A router can run multiple routing protocols. When a route to the same destination is learned by multiple routing protocols, the one with the highest protocol priority wins. You can reference a routing policy to specify a priority for specific routes.

Follow these steps to configure the IS-IS protocol priority.

To do…	Use the command…	Remarks
Enter system view	system-view	––
Enter IS-IS view	isis [ process-id ] [ vpn-instance vpn-instance-name ]	––
Specify a priority for IS-IS	preference { route-policy route-policy-name \| preference } *	Optional 15 by default

1.4.3 Configuring IS-IS Link Cost

There are three ways to configure the interface link cost, from high to low priority:

l Interface cost: Assign a link cost for a single interface.

l Global cost: Assign a link cost for all interfaces.

l Automatically calculated cost: Calculate the link cost based on the bandwidth of an interface.

If none of the above costs is used, a default cost of 10 applies.

I. Configure an IS-IS cost for an interface

Follow these steps to configure an interface’s cost:

To do…	Use the command…	Remarks
Enter system view	system-view	––
Enter IS-IS view	isis [ process-id ] [ vpn-instance vpn-instance-name ]	––
Specify a cost style	cost-style { narrow \| wide \| wide-compatible \| { compatible \| narrow-compatible } [ relax-spf-limit ] }	Optional narrow by default
Return to system view	quit	––
Enter interface view	interface interface-type interface-number	Required
Specify a cost for the interface	isis cost value [ level-1 \| level-2 ]	Optional 10 by default

II. Configure a global IS-IS cost

Follow these steps to configure global IS-IS cost:

To do…	Use the command…	Remarks
Enter system view	system-view	—
Enter IS-IS view	isis [ process-id ] [ vpn-instance vpn-instance-name ]	—
Specify an IS-IS cost style	cost-style { narrow \| wide \| wide-compatible \| { compatible \| narrow-compatible } [ relax-spf-limit ] }	Optional Defaulted as narrow.
Specify a global IS-IS cost	circuit-cost value [ level-1 \| level-2 ]	Required Not specified by default.

III. Enable automatic IS-IS cost calculation

Follow these steps to enable automatic IS-IS cost calculation:

To do…	Use the command…	Remarks
Enter system view	system-view	—
Enter IS-IS view	isis [ process-id ] [ vpn-instance vpn-instance-name ]	—
Specify an IS-IS cost style	cost-style { narrow \| wide \| wide-compatible \| { compatible \| narrow-compatible } [ relax-spf-limit ] }	Optional narrow by default
Configure a bandwidth reference value for automatic IS-IS cost calculation	bandwidth-reference value	Optional 100 Mbps by default
Enable automatic IS-IS cost calculation	auto-cost enable	Required Disabled by default.

& Note:

l After the auto-cost enable command is executed for an IS-IS process with the cost style as wide or wide-compatible, IS-IS automatically calculates the cost for an interface using the formula: interface cost = (bandwidth reference value/interface bandwidth) × 10. If the calculated cost is greater than 16777214, the cost of 16777214 is used.

l The priority of an interface’s cost from high to low is: the cost configured with the isis cost command, the global cost configured with the circuit cost command, the cost automatically calculated after the auto-cost command is used, the default cost. The default cost of an interface is 10.

1.4.4 Configuring the Maximum Number of Equal Cost Routes

If there are more than one equal cost routes to the same destination, the traffic can be load balanced to enhance efficiency.

Follow these steps to configure the maximum number of load balanced routes:

To do…	Use the command…	Remarks
Enter system view	system-view	––
Enter IS-IS view	isis [ process-id ] [ vpn-instance vpn-instance-name ]	––
Specify the maximum number of equal cost routes for load balancing	maximum load-balancing number	Optional

1.4.5 Configuring IS-IS Route Summarization

This task is to configure a summary route, so routes falling into the network range of the summary route are summarized with one route for advertisement. Doing so can reduce the size of routing tables, as well as the LSP and LSDB generated by the router itself. Both IS-IS and redistributed routes can be summarized.

Follow these steps to configure route summarization:

To do…	Use the command...	Remarks
Enter system view	system-view	—
Enter IS-IS view	isis [ process-id ] [ vpn-instance vpn-instance-name ]	––
Configure IS-IS route summarization	summary ip-address { mask \| mask-length } [ avoid-feedback \| generate_null0_route \| tag tag \| [ level-1 \| level-1-2 \| level-2 ] ] *	Required Not configured by default

& Note:

The cost of the summary route is the lowest cost among those summarized routes.

1.4.6 Advertising a Default Route

Follow these steps to advertise a default route:

To do…	Use the command…	Remarks
Enter system view	system-view	––
Enter IS-IS view	isis [ process-id ] [ vpn-instance vpn-instance-name ]	—
Advertise a default route	default-route-advertise [ route-policy route-policy-name ] [ level-1 \| level-2 \| level-1-2 ]	Required Level-2 router generates a default route by default.

& Note:

The default route is only advertised to routers at the same level. You can use a routing policy to generate the default route only when a local routing entry is matched by the policy.

1.4.7 Configuring Inbound Route Filtering

Follow these steps to configure inbound route filtering:

To do…	Use the command…	Remarks
Enter system view	system-view	––
Enter IS-IS view	isis [ process-id ] [ vpn-instance vpn-instance-name ]	––
Configure inbound route filtering	filter-policy { acl-number \| ip-prefix ip-prefix-name \| route-policy route-policy-name } import	Required Not configured by default

1.4.8 Configuring Route Redistribution

Follow these steps to configure IS-IS route redistribution from other routing protocols:

To do…	Use the command…	Remarks
Enter system view	system-view	––
Enter IS-IS view	isis [ process-id ] [ vpn-instance vpn-instance-name ]	––
Redistribute routes from another routing protocol	import-route { isis [ process-id ] \| ospf [ process-id ] \| rip [ process-id ] \| bgp [ allow-ibgp ] \| direct \| static } [ cost cost \| cost-type { external \| internal } \| [ level-1 \| level-1-2 \| level-2 ] \| route-policy route-policy-name \| tag tag ] *	Required No route is redistributed by default. If no level is specified, routes are redistributed into the Level-2 routing table by default.
Configure a filtering policy to filter redistributed routes	filter-policy { acl-number \| ip-prefix ip-prefix-name \| route-policy route-policy-name } export [ isis process-id \| ospf process-id \| rip process-id \| bgp \| direct \| static]	Optional Not configured by default

1.4.9 Configuring IS-IS Route Leaking

With this feature enabled, the Level-1-2 router can advertise both Level-1 and Level-2 area routing information to the Level-1 router.

Follow these steps to configure IS-IS route leaking:

To do…	Use the command…	Remarks
Enter system view	system-view	––
Enter IS-IS view	isis [ process-id ] [ vpn-instance vpn-instance-name ]	––
Enable IS-IS route leaking	import-route isis level-2 into level-1 [ filter-policy { acl-number \| ip-prefix ip-prefix-name \| route-policy route-policy-name } \| tag tag ] *	Required Disabled by default

& Note:

l If a filter policy is configured, only routes passing it can be advertised into the Level-1 area.

l You can specify a routing policy in the import-route isis level-2 into level-1 command to filter routes from Level-2 to Level-1. Other routing policies specified for route reception and redistribution does not affect the route leaking.

1.5 Tuning and Optimizing IS-IS Network

1.5.1 Configuration Prerequisites

Before the configuration, accomplish the following tasks first:

l Configure an IP address on each interface, and make sure all nodes are reachable.

l Configure basic IS-IS functions

1.5.2 Configuring a DIS Priority for an Interface

On an IS-IS broadcast network, a router should be selected as the DIS at a specific level, Level-1 or Level-2. You can specify a DIS priority at a level for an interface. The bigger the interface’s priority value, the more likelihood it becomes the DIS.

Follow these steps to configure a DIS priority for an interface:

To do…	Use the command…	Remarks
Enter system view	system-view	––
Enter interface view	interface interface-type interface-number	––
Specify a DIS priority for the interface	isis dis-priority value [ level-1 \| level-2 ]	Optional 64 by default

& Note:

If multiple routers in the broadcast network have the same highest DIS priority, the router with the highest MAC address becomes the DIS. This rule applies even all routers’ DIS priority is 0.

1.5.3 Configuring IS-IS Timers

Follow these steps to configure the IS-IS timers:

To do…	Use the command…	Remarks
Enter system view	system-view	––
Enter interface view	interface interface-type interface-number	––
Specify the interval between hello packets	isis timer hello seconds [ level-1 \| level-2 ]	Optional 10 seconds by default
Specify the number of hello packets; within the time for receiving the specified hello packets, if no hello packets are received on the interface, the neighbor is considered dead.	isis timer holding-multiplier value [ level-1 \| level-2 ]	Optional 3 by default
Specify the interval for sending CSNP packets	isis timer csnp seconds [ level-1 \| level-2 ]	Optional 10 seconds by default
Specify the interval for sending LSP packets	isis timer lsp time [ count count ]	Optional By default, the sending interval is 33 milliseconds, and the maximum number of LSPs that can be sent at a time is 5.
Specify the LSP retransmission interval on the point-to-point link	isis timer retransmit seconds	Optional 5 seconds by default

& Note:

l On the broadcast link, you can specify different intervals for Level-1 and Level-2 hello packets; if no level is specified, the interval applies to both Level-1 and Level-2 hello packets, but only takes effect on the level of the current process; if a level is specified, it applies to hello packets at this level. The point-to-point link does not distinguish between Level-1 and Level-2 hello packets, so you need not specify a level.

l Hello packets are used to establish and maintain neighbor relationships. If no hello packets are received from a neighbor within the time for receiving the specified hello packets, the neighbor is considered dead.

l CSNPs are sent by the DIS on a broadcast network for LSDB synchronization. If no level is included, the specified CSNP interval applies to both Level-1 and Level-2 of the current IS-IS process. If a level is specified, it applies to the level.

l On a point-to-point link, if there is no response to an LSP sent by the local router within the specified retransmission interval, the LSP is considered lost, and the same LSP will be retransmitted. On broadcast links, responses to the sent LSPs are not required.

l The interval between hello packets sent by the DIS is 1/3 the hello interval.

1.5.4 Disabling an Interface from Sending/Receiving IS-IS Hello Packets

Follow these steps to disable an interface from sending hello packets:

To do…	Use the command…	Remarks
Enter system view	system-view	––
Enter interface view	interface interface-type interface-number	––
Disable the interface from sending and receiving hello packets	isis silent	Required Not disabled by default

1.5.5 Configuring LSP Parameters

An IS-IS router periodically advertises all the local LSPs to maintain the LSP synchronization in the entire area.

An LSP is given an aging time when generated by the router. When the LSP is received by another router, its aging time begins to decrease. If the receiving router does not get the update for the LSP within the aging time, the LSP will be deleted from the LSDB.

The router will discard an LSP with incorrect checksum. You can configure the router to ignore the incorrect checksum, which means an LSP will be processed even with an incorrect LSP checksum.

On the NBMA network, the router will flood a new LSP received from an interface to other interfaces. This can cause the LSP reflooding on the high connectivity networks. To avoid this problem, you can make a mesh group of interfaces. The interface in this group will only flood the new LSP to interfaces outside the mesh group.

Follow these steps to configure the LSP parameters:

To do…	Use the command…	Remarks
Enter system view	system-view	––
Enter IS-IS view	isis [ process-id ] [ vpn-instance vpn-instance-name ]	––
Specify an LSP refresh interval	timer lsp-refresh seconds	Optional 900 seconds by default
Specify the maximum LSP aging time	timer lsp-max-age seconds	Optional 1200 seconds by default
Specify LSP generation interval	timer lsp-generation maximum-interval [ initial-interval [ incremental-interval ] ] [ level-1 \| level-2 ]	Optional 2 seconds by default
Enable the LSP flash flooding function	flash-flood [ flood-count flooding-count \| max-timer-interval flooding-interval \| [ level-1 \| level-2 ] ] *	Optional Not enabled by default
Specify the maximum size of the originated Level-1 or Level-2 LSP	lsp-length originate size [ level-1 \| level-2 ]	Optional Both are 1497 bytes by default
Specify the maximum size of the received Level-1 or Level-2 LSP	lsp-length receive size	Optional Both are 1497 bytes by default
Enable LSP fragment extension	lsp-fragments-extend [ level-1 \| level-2 \| level-1-2 ] [ mode-1 \| mode-2 ]	Optional Disabled by default
Create a virtual system	virtual-system virtual-system-id	Optional Not created by default
Return to system view	quit	––
Enter interface view	interface interface-type interface-number	––
Add the interface to a mesh group	isis mesh-group [ mesh-group-number \| mesh-blocked ]	Optional Not added by default If the mesh-blocked keyword is included, the interface is blocked from flooding LSPs.

& Note:

Note the following when configuring LSP fragment extension:

l At least one virtual system needs to be created for the device to generate extended LSP fragments. An IS-IS process allows 50 virtual systems at most.

l Fragment zero generated by a virtual system needs to carry some key information, including area address, protocol type, link to the originating system, and authentication information and therefore the corresponding LSP is long. To enable such LSPs to carry complete information and to be correctly flooded on all the IS-IS interfaces, the MTUs of all the IS-IS interfaces must not be less than 512; otherwise, LSP fragment extension will not take effect.

1.5.6 Configuring SPF Parameters

When the LSDB changes in an IS-IS network, a routing calculation starts. If the changes happen frequently, it will take a lot of system resources. You can set the interval for SPF calculation for efficiency consideration.

The SPF calculation may occupy the CPU for a long time when the routing entries are too many (more than 150 thousand). You can split the SPF calculation time into multiple durations with a default interval of 10s in between.

Follow these steps to configure the SPF parameters:

To do…	Use the command...	Remarks
Enter system view	system-view	––
Enter IS-IS view	isis [ process-id ] [ vpn-instance vpn-instance-name ]	––
Configure the SPF calculation intervals	timer spf maximum-interval [ minimum-interval [ incremental-interval ] ]	Optional The default SPF calculation intervals are 10 seconds, 0 ms, 0 ms respectively.
Specify the SPF calculation duration	spf-slice-size duration-time	Optional Not specified by default By default, the SPF calculation time is not split.

1.5.7 Configuring Dynamic Host Name Mapping

Follow these steps to configure the dynamic host name mapping:

To do…	Use the command...	Remarks
Enter system view	system-view	––
Enter IS-IS view	isis [ process-id ] [ vpn-instance vpn-instance-name ]	––
Assign a local host name	is-name sys-name	Required No name is assigned by default. This command also enables the mapping between the local system ID and host name
Assign a remote host name and create a mapping between the host name and a system ID	is-name map sys-id map-sys-name	Optional One system ID only maps to one name. No name is assigned by default
Return to system view	quit	––
Enter interface view	interface interface-type interface-number	––
Assign a DIS name for the local network	isis dis-name symbolic-name	Optional Not assigned by default This command is only applicable on the router with dynamic host name mapping enabled. It is invalid on point-to-point links.

& Note:

The local host name on the local IS overwrites the remote host name on the remote IS.

1.5.8 Configuring IS-IS Authentication

For area authentication, the area authentication password is encapsulated into the Level-1 LSP, CSNP, and PSNP packets. On area authentication enabled routers in the same area, the authentication mode and password must be same.

For routing domain authentication, the domain authentication password is encapsulated into the Level-2 LSP, CSNP, and PSNP packets. The domain authentication enabled Level-2 routers in the backbone must adopt the same authentication mode and share the same password.

The authentication configured on an interface applies to the hello packet in order to authenticate neighbors. All interfaces within a network must share the same authentication password at the same level.

Follow these steps to configure the authentication function:

To do…	Use the command…	Remarks
Enter system view	system-view	––
Enter IS-IS view	isis [ process-id ] [ vpn-instance vpn-instance-name ]	––
Specify the area authentication mode	area-authentication-mode { simple \| md5 } password [ ip \| osi ]	Required No authentication is enabled for Level-1 routing information, and no password is specified by default.
Specify the routing domain authentication mode	domain-authentication-mode { simple \| md5 } password [ ip \| osi ]	Required No authentication is enabled for Level-2 routing information, and no password is specified by default.
Return to system view	quit	––
Enter interface view	interface interface-type interface-number	––
Specify the authentication mode and password	isis authentication-mode { simple \| md5 } password [ level-1 \| level-2 ] [ ip \| osi ]	Optional No authentication and password are available by default.

& Note:

The level-1 and level-2 keywords in the isis authentication-mode command are only supported on the Ethernet interface, and the interface must be configured with the isis enable command first.

1.5.9 Configuring LSDB Overload Tag

When the overload tag is set on a router, other routers will not send packets to the router except for the packets destined to the network directly connected to the router.

The overload tag can be used for troubleshooting as well. You can temporarily isolate a router from the IS-IS network by setting the overload tag.

Follow these steps to configure the LSDB overload tag:

To do…	Use the command…	Remarks
Enter system view	system-view	––
Enter IS-IS view	isis [ process-id ] [ vpn-instance vpn-instance-name ]	––
Set the overload tag	set-overload [ on-startup start-from-nbr system-id [ timeout [ nbr-timeout ] ] ] [ allow { interlevel \| external } * ]	Required Not set by default

1.5.10 Logging the Adjacency Changes

Follow these steps to configure this task:

To do…	Use the command…	Remarks
Enter system view	system-view	––
Enter IS-IS view	isis [ process-id ] [ vpn-instance vpn-instance-name ]	––
Enable to log the adjacency changes	log-peer-change	Required Enabled by default

& Note:

With this feature enabled, the state information of the adjacency is displayed on the configuration terminal.

1.5.11 Enabling an Interface to Send Small Hello Packets

Follow these steps to enable an interface to send small hello packets (without the padding field):

To do…	Use the command…	Remarks
Enter system view	system-view	––
Enter interface view	interface interface-type interface-number	––
Enable the interface to send small hello packets that have no padding field	isis small-hello	Required Standard hello packets are sent by default.

1.5.12 Enabling IS-IS SNMP Trap

Follow these steps to enable IS-IS SNMP trap:

To do…	Use the command…	Remarks
Enter system view	system-view	––
Enter IS-IS view	isis [ process-id ] [ vpn-instance vpn-instance-name ]	––
Enable IS-IS SNMP trap	is-snmp-traps enable	Required Enabled by default

1.6 Displaying and Maintaining IS-IS Configuration

To do…	Use the command…	Remarks
Display brief IS-IS information	display isis brief [ process-id \| vpn-instance vpn-instance-name ]	Available in any view
Display the status of the debug switch	display isis debug-switches { process-id \| vpn-instance vpn-instance-name }	Available in any view
Display information about IS-IS enabled interfaces	display isis interface [ [ traffic-eng \| verbose ] * \| tunnel ] [ process-id \| vpn-instance vpn-instance-name ]	Available in any view
Display IS-IS license information	display isis license	Available in any view
Display IS-IS LSDB information	display isis lsdb [ [ l1 \| l2 \| level-1 \| level-2 ] \| [ lsp-id LSPID \| lsp-name lspname ] \| local \| verbose ] * [ process-id \| vpn-instance vpn-instance-name ]	Available in any view
Display IS-IS mesh group information	display isis mesh-group [ process-id \| vpn-instance vpn-instance-name ]	Available in any view
Display the host-name-to-system-ID mapping table	display isis name-table [ process-id \| vpn-instance vpn-instance-name ]	Available in any view
Display IS-IS neighbor information	display isis peer [ verbose ] [ process-id \| vpn-instance vpn-instance-name ]	Available in any view
Display IS-IS routing information	display isis route [ ipv4 ] [ [ level-1 \| level-2 ] \| verbose ] * [ process-id \| vpn-instance vpn-instance-name ]	Available in any view
Display SPF calculation log information	display isis spf-log [ process-id \| vpn-instance vpn-instance-name ]	Available in any view
Display statistic about an IS-IS process	display isis statistics [ level-1 \| level-2 \| level-1-2 ] [ process-id \| vpn-instance vpn-instance-name ]	Available in any view
Clear the data structure information of an IS-IS process	reset isis all [ process-id \| vpn-instance vpn-instance-name ]	Available in user view
Clear the data structure information of an IS-IS neighbor	reset isis peer system-id [ process-id \| vpn vpn-instance-name ]	Available in user view

1.7 IS-IS Configuration Examples

1.7.1 IS-IS Basic Configuration

I. Network requirements

As shown in Figure 1-14, Switch A, Switch B, Switch C and Switch D reside in an IS-IS AS. Switch A and B are Level-1 switches, Switch D is a Level-2 switch and Switch C is a Level-1-2 switch. Switch A, B and C are in area 10, while Switch D is in area 20.

II. Network diagram

Figure 1-14 Network diagram for IS-IS basic configuration

III. Configuration procedure

1) Configure IP addresses for interfaces (omitted)

2) Configure IS-IS

# Configure Switch A.

<SwitchA> system-view

[SwitchA] isis 1

[SwitchA-isis-1] is-level level-1

[SwitchA-isis-1] network-entity 10.0000.0000.0001.00

[SwitchA-isis-1] quit

[SwitchA] interface vlan-interface 100

[SwitchA-Vlan-interface100] isis enable 1

[SwitchA-Vlan-interface100] quit

# Configure Switch B.

<SwitchB> system-view

[SwitchB] isis 1

[SwitchB-isis-1] is-level level-1

[SwitchB-isis-1] network-entity 10.0000.0000.0002.00

[SwitchB-isis-1] quit

[SwitchB] interface vlan-interface 200

[SwitchB-Vlan-interface200] isis enable 1

[SwitchB-Vlan-interface200] quit

# Configure Switch C.

<SwitchC> system-view

[SwitchC] isis 1

[SwitchC-isis-1] network-entity 10.0000.0000.0003.00

[SwitchC-isis-1] quit

[SwitchC] interface vlan-interface 100

[SwitchC-Vlan-interface100] isis enable 1

[SwitchC-Vlan-interface100] quit

[SwitchC] interface vlan-interface 200

[SwitchC-Vlan-interface200] isis enable 1

[SwitchC-Vlan-interface200] quit

[SwitchC] interface vlan-interface 300

[SwitchC-Vlan-interface300] isis enable 1

[SwitchC-Vlan-interface300] quit

# Configure Switch D.

<SwitchD> system-view

[SwitchD] isis 1

[SwitchD-isis-1] is-level level-2

[SwitchD-isis-1] network-entity 20.0000.0000.0004.00

[SwitchD-isis-1] quit

[SwitchD] interface vlan-interface 100

[SwitchD-Vlan-interface100] isis enable 1

[SwitchD-Vlan-interface100] quit

[SwitchD] interface vlan-interface 300

[SwitchD-Vlan-interface300] isis enable 1

[SwitchD-Vlan-interface300] quit

3) Verify the configuration

# Display the IS-IS LSDB of each switch to check the LSP integrity.

[SwitchA] display isis lsdb

Database information for ISIS(1)

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

Level-1 Link State Database

LSPID Seq Num Checksum Holdtime Length ATT/P/OL

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

0000.0000.0001.00-00* 0x00000004 0xdf5e 1096 68 0/0/0

0000.0000.0002.00-00 0x00000004 0xee4d 1102 68 0/0/0

0000.0000.0002.01-00 0x00000001 0xdaaf 1102 55 0/0/0

0000.0000.0003.00-00 0x00000009 0xcaa3 1161 111 1/0/0

0000.0000.0003.01-00 0x00000001 0xadda 1112 55 0/0/0

*-Self LSP, +-Self LSP(Extended), ATT-Attached, P-Partition, OL-Overload

[SwitchB] display isis lsdb

Database information for ISIS(1)

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

Level-1 Link State Database

LSPID Seq Num Checksum Holdtime Length ATT/P/OL

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

0000.0000.0001.00-00 0x00000006 0xdb60 988 68 0/0/0

0000.0000.0002.00-00* 0x00000008 0xe651 1189 68 0/0/0

0000.0000.0002.01-00* 0x00000005 0xd2b3 1188 55 0/0/0

0000.0000.0003.00-00 0x00000014 0x194a 1190 111 1/0/0

0000.0000.0003.01-00 0x00000002 0xabdb 995 55 0/0/0

*-Self LSP, +-Self LSP(Extended), ATT-Attached, P-Partition, OL-Overload

[SwitchC] display isis lsdb

Database information for ISIS(1)

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

Level-1 Link State Database

LSPID Seq Num Checksum Holdtime Length ATT/P/OL

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

0000.0000.0001.00-00 0x00000006 0xdb60 847 68 0/0/0

0000.0000.0002.00-00 0x00000008 0xe651 1053 68 0/0/0

0000.0000.0002.01-00 0x00000005 0xd2b3 1052 55 0/0/0

0000.0000.0003.00-00* 0x00000014 0x194a 1051 111 1/0/0

0000.0000.0003.01-00* 0x00000002 0xabdb 854 55 0/0/0

*-Self LSP, +-Self LSP(Extended), ATT-Attached, P-Partition, OL-Overload

Level-2 Link State Database

LSPID Seq Num Checksum Holdtime Length ATT/P/OL

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

0000.0000.0003.00-00* 0x00000012 0xc93c 842 100 0/0/0

0000.0000.0004.00-00 0x00000026 0x331 1173 84 0/0/0

0000.0000.0004.01-00 0x00000001 0xee95 668 55 0/0/0

*-Self LSP, +-Self LSP(Extended), ATT-Attached, P-Partition, OL-Overload

[SwitchD] display isis lsdb

Database information for ISIS(1)

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

Level-2 Link State Database

LSPID Seq Num Checksum Holdtime Length ATT/P/OL

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

0000.0000.0003.00-00 0x00000013 0xc73d 1003 100 0/0/0

0000.0000.0004.00-00* 0x0000003c 0xd647 1194 84 0/0/0

0000.0000.0004.01-00* 0x00000002 0xec96 1007 55 0/0/0

*-Self LSP, +-Self LSP(Extended), ATT-Attached, P-Partition, OL-Overload

# Display the IS-IS routing information of each switch. Level-1 switches should have a default route with the next hop being the Level-1-2 switch. The Level-2 switch should have both routing information of Level-1 and Level-2.

[SwitchA] display isis route

Route information for ISIS(1)

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

ISIS(1) IPv4 Level-1 Forwarding Table

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

IPV4 Destination IntCost ExtCost ExitInterface NextHop Flags

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

10.1.1.0/24 10 NULL Vlan100 Direct R/L/-

10.1.2.0/24 20 NULL Vlan100 10.1.1.1 R/-/-

192.168.0.0/24 20 NULL Vlan100 10.1.1.1 R/-/-

0.0.0.0/0 10 NULL Vlan100 10.1.1.1 R/-/-

Flags: R-Added to RM, L-Advertised in LSPs, U-Up/Down Bit Set

[SwitchC] display isis route

Route information for ISIS(1)

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

ISIS(1) IPv4 Level-1 Forwarding Table

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

IPV4 Destination IntCost ExtCost ExitInterface NextHop Flags

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

192.168.0.0/24 10 NULL Vlan300 Direct R/L/-

10.1.1.0/24 10 NULL Vlan100 Direct R/L/-

10.1.2.0/24 10 NULL Vlan200 Direct R/L/-

Flags: R-Added to RM, L-Advertised in LSPs, U-Up/Down Bit Set

ISIS(1) IPv4 Level-2 Forwarding Table

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

IPV4 Destination IntCost ExtCost ExitInterface NextHop Flags

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

192.168.0.0/24 10 NULL Vlan300 Direct R/L/-

10.1.1.0/24 10 NULL Vlan100 Direct R/L/-

10.1.2.0/24 10 NULL Vlan200 Direct R/L/-

172.16.0.0/16 20 NULL Vlan300 192.168.0.2 R/-/-

Flags: R-Added to RM, L-Advertised in LSPs, U-Up/Down Bit Set

[SwitchD] display isis route

Route information for ISIS(1)

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

ISIS(1) IPv4 Level-2 Forwarding Table

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

IPV4 Destination IntCost ExtCost ExitInterface NextHop Flags

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

192.168.0.0/24 10 NULL Vlan300 Direct R/L/-

10.1.1.0/24 20 NULL Vlan300 192.168.0.1 R/-/-

10.1.2.0/24 20 NULL Vlan300 192.168.0.1 R/-/-

172.16.0.0/16 10 NULL Vlan100 Direct R/L/-

Flags: R-Added to RM, L-Advertised in LSPs, U-Up/Down Bit Set

1.7.2 DIS Selection Configuration

I. Network requirements

As shown in the following figure, Switch A, Switch B, Switch C and Switch D reside in IS-IS area 10 on a broadcast network (Ethernet). Switch A and Switch B are Level-1-2 switches, Switch C is a Level-1 switch, and Switch D is a Level-2 switch.

Change the DIS priority of Switch A to make it elected as the Level-1 DIS router and the Level-2 DIS router.

II. Network diagram

Figure 1-15 Network diagram for DIS selection

III. Configuration procedure

1) Create VLANs and configure an IP address for each VLAN interface (omitted)

2) Enable IS-IS

# Configure Switch A.

<SwitchA> system-view

[SwitchA] isis 1

[SwitchA-isis-1] network-entity 10.0000.0000.0001.00

[SwitchA-isis-1] quit

[SwitchA] interface vlan-interface 100

[SwitchA-Vlan-interface100] isis enable 1

[SwitchA-Vlan-interface100] quit

# Configure Switch B.

<SwitchB> system-view

[SwitchB] isis 1

[SwitchB-isis-1] network-entity 10.0000.0000.0002.00

[SwitchB-isis-1] quit

[SwitchB] interface vlan-interface 100

[SwitchB-Vlan-interface100] isis enable 1

[SwitchB-Vlan-interface100] quit

# Configure Switch C.

<SwitchC> system-view

[SwitchC] isis 1

[SwitchC-isis-1] network-entity 10.0000.0000.0003.00

[SwitchC-isis-1] is-level level-1

[SwitchC-isis-1] quit

[SwitchC] interface vlan-interface 100

[SwitchC-Vlan-interface100] isis enable 1

[SwitchC-Vlan-interface100] quit

# Configure Switch D.

<SwitchD> system-view

[SwitchD] isis 1

[SwitchD-isis-1] network-entity 10.0000.0000.0004.00

[SwitchD-isis-1] is-level level-2

[SwitchD-isis-1] quit

[SwitchD] interface vlan-interface 100

[SwitchD-Vlan-interface100] isis enable 1

[SwitchD-Vlan-interface100] quit

# Display information about IS-IS neighbors of Switch A.

[SwitchA] display isis peer

Peer information for ISIS(1)

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

System Id: 0000.0000.0002

Interface: Vlan-interface100 Circuit Id: 0000.0000.0003.01

State: Up HoldTime: 21s Type: L1(L1L2) PRI: 64

System Id: 0000.0000.0003

Interface: Vlan-interface100 Circuit Id: 0000.0000.0003.01

State: Up HoldTime: 27s Type: L1 PRI: 64

System Id: 0000.0000.0002

Interface: Vlan-interface100 Circuit Id: 0000.0000.0004.01

State: Up HoldTime: 28s Type: L2(L1L2) PRI: 64

System Id: 0000.0000.0004

Interface: Vlan-interface100 Circuit Id: 0000.0000.0004.01

State: Up HoldTime: 30s Type: L2 PRI: 64

# Display information about IS-IS interfaces of Switch A.

[SwitchA] display isis interface

Interface information for ISIS(1)

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

Interface: Vlan-interface100

Id IPV4.State IPV6.State MTU Type DIS

001 Up Down 1497 L1/L2 No/No

# Display information about IS-IS interfaces of Switch C.

[SwitchC] display isis interface

Interface information for ISIS(1)

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

Interface: Vlan-interface100

Id IPV4.State IPV6.State MTU Type DIS

001 Up Down 1497 L1 Yes/No

# Display information about IS-IS interfaces of Switch D.

[SwitchD] display isis interface

Interface information for ISIS(1)

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

Interface: Vlan-interface100

Id IPV4.State IPV6.State MTU Type DIS

001 Up Down 1497 L2 No/Yes

& Note:

By using the default DIS priority, Switch C is the Level-1 DIS, and Switch D is the Level-2 DIS. The pseudonodes of Level-1 and Level-2 are 0000.0000.0003.01 and 0000.0000.0004.01 respectively.

3) Configure the DIS priority of Switch A.

[SwitchA] interface vlan-interface 100

[SwitchA-Vlan-interface100] isis dis-priority 100

[SwitchA-Vlan-interface100] quit

# Display IS-IS neighbors of Switch A.

[SwitchA] display isis peer

Peer information for ISIS(1)

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

System Id: 0000.0000.0002

Interface: Vlan-interface100 Circuit Id: 0000.0000.0001.01

State: Up HoldTime: 21s Type: L1(L1L2) PRI: 64

System Id: 0000.0000.0003

Interface: Vlan-interface100 Circuit Id: 0000.0000.0001.01

State: Up HoldTime: 27s Type: L1 PRI: 64

System Id: 0000.0000.0002

Interface: Vlan-interface100 Circuit Id: 0000.0000.0001.01

State: Up HoldTime: 28s Type: L2(L1L2) PRI: 64

System Id: 0000.0000.0004

Interface: Vlan-interface100 Circuit Id: 0000.0000.0001.01

State: Up HoldTime: 30s Type: L2 PRI: 64

# Display information about IS-IS interfaces of Switch A.

[SwitchA] display isis interface

Interface information for ISIS(1)

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

Interface: Vlan-interface100

Id IPV4.State IPV6.State MTU Type DIS

001 Up Down 1497 L1/L2 Yes/Yes

& Note:

After the DIS priority configuration, Switch A becomes the Level-1 DIS router and the Level-2 DIS router, and the pseudonode is 0000.0000.0001.01.

# Display information about IS-IS neighbors and interfaces of Switch C.

[SwitchC] display isis peer

Peer information for ISIS(1)

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

System Id: 0000.0000.0002

Interface: Vlan-interface100 Circuit Id: 0000.0000.0001.01

State: Up HoldTime: 25s Type: L1 PRI: 64

System Id: 0000.0000.0001

Interface: Vlan-interface100 Circuit Id: 0000.0000.0001.01

State: Up HoldTime: 7s Type: L1 PRI: 100

[SwitchC] display isis interface

Interface information for ISIS(1)

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

Interface: Vlan-interface100

Id IPV4.State IPV6.State MTU Type DIS

001 Up Down 1497 L1/L2 No/No

# Display information about IS-IS neighbors and interfaces of Switch D.

[SwitchD] display isis peer

Peer information for ISIS(1)

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

System Id: 0000.0000.0001

Interface: Vlan-interface100 Circuit Id: 0000.0000.0001.01

State: Up HoldTime: 9s Type: L2 PRI: 100

System Id: 0000.0000.0002

Interface: Vlan-interface100 Circuit Id: 0000.0000.0001.01

State: Up HoldTime: 28s Type: L2 PRI: 64

[SwitchD] display isis interface

Interface information for ISIS(1)

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

Interface: Vlan-interface100

Id IPV4.State IPV6.State MTU Type DIS

001 Up Down 1497 L1/L2 No/No

H3C S9500 Operation Manual-Release2132[V2.03]-03 IP Routing Volume

Chapter 1 IS-IS Configuration

1.1 IS-IS Overview

I. IS-IS terminology

II. IS-IS address structure

III. NET

1.1.2 IS-IS Area

I. Two-level hierarchy

II. Level-1 and Level-2

III. Interface routing hierarchy type

IV. Route leaking

I. Network type

II. DIS and pseudonodes

I. PDU header format

II. Common header format

III. Hello

IV. LSP packet format

V. SNP format

VI. CLV

1.1.5 IS-IS Features Supported

I. Multiple instances and processes

II. Hot standby

III. IS-IS TE

IV. Management tag

V. LSP fragment extension

VI. Dynamic host name mapping mechanism

1.1.6 Protocols and Standards

1.2 IS-IS Configuration Task List

1.3 Configuring IS-IS Basic Functions

1.4 Configuring IS-IS Routing Information Control

1.4.2 Specifying a Priority for IS-IS

1.4.3 Configuring IS-IS Link Cost

I. Configure an IS-IS cost for an interface

II. Configure a global IS-IS cost

III. Enable automatic IS-IS cost calculation

1.4.4 Configuring the Maximum Number of Equal Cost Routes

1.4.5 Configuring IS-IS Route Summarization

1.4.6 Advertising a Default Route

1.4.7 Configuring Inbound Route Filtering

1.4.8 Configuring Route Redistribution

1.4.9 Configuring IS-IS Route Leaking

1.5 Tuning and Optimizing IS-IS Network

1.5.2 Configuring a DIS Priority for an Interface

1.5.3 Configuring IS-IS Timers

1.5.4 Disabling an Interface from Sending/Receiving IS-IS Hello Packets

1.5.5 Configuring LSP Parameters

1.5.6 Configuring SPF Parameters

1.5.7 Configuring Dynamic Host Name Mapping

1.5.9 Configuring LSDB Overload Tag

1.5.10 Logging the Adjacency Changes

1.5.11 Enabling an Interface to Send Small Hello Packets

1.5.12 Enabling IS-IS SNMP Trap

1.6 Displaying and Maintaining IS-IS Configuration

1.7 IS-IS Configuration Examples

1.7.1 IS-IS Basic Configuration

I. Network requirements

II. Network diagram

III. Configuration procedure

I. Network requirements

II. Network diagram

III. Configuration procedure

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