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Verifying the IS-IS Configuration on a Router in a Network

Purpose

For IS-IS to run on a router (intermediate system) in your network, you must enable IS-IS on the router, configure a network entity title (NET) on the loopback interface (lo0), and configure family iso on all interfaces on which you want to run IS-IS. When you enable IS-IS on a router, Level 1 and Level 2 are enabled by default.

Figure 1 illustrates an example of routers at different levels in an IS-IS topology.

Figure 1: Levels in an IS-IS Network TopologyLevels in an IS-IS Network Topology

The network in Figure 1 is organized hierarchically and consists of Level 2, Level 1/Level 2, and Level 1 routers in one autonomous system (AS) divided into four areas: 49.0001, 49.0002, 49.0003, and 49.0004. The Level 2 routers route toward other autonomous systems. The Level 1/Level 2 routers route between areas and to other autonomous systems. The Level 1 routers route within an area, and when the destination is outside the local area, they route toward a Level1/Level2 system.

In the following topics, the configuration of the various types of routers is examined.

Figure 2 provides more details about the IS-IS network topology in Figure 1 so that you can verify the configuration output of the various routers.

Figure 2: IS-IS Network Topology with DetailsIS-IS Network Topology with Details

To verify that IS-IS is configured correctly on routers at different levels, follow these steps:

Check the Configuration of a Level 1/Level 2 Router

Purpose

Check the configuration of a Level 1/Level 2 router.

Action

To verify the IS-IS configuration of a Level 1/Level 2 router in your network, enter the following Junos OS command-line interface (CLI) commands:

The following output is for an IS-IS configuration on R2, a Level 1/Level 2 router in the network shown.

Sample Output

command-name

Meaning

The sample output shows a basic configuration of IS-IS on R2, a Level 1/Level 2 router. The basic configuration is at the [edit protocols isis] and [edit interfaces] hierarchy levels.

At the [edit protocols isis] level, five interfaces are included: so-0/0/0, so-0/0/1, so-0/0/2, fxp0, and the loopback interface (lo0). Two interfaces, so-0/0/0.0 and so-0/0/2.0, have Level 1 disabled, making them Level 2 interfaces. One interface, so-0/0/1.0, has Level 2 disabled, making it a Level 1 interface. The management interface (fxp0) is disabled so that IS-IS packets are not sent over it, and the loopback interface (lo0) is included because it becomes a point of connection from the router to the IS-IS network.

At the [edit interfaces] hierarchy level, all of the interfaces included in the [edit protocols isis] hierarchy level are configured with family iso, and the loopback interface (lo0) is configured with the NET address 49.0002.1000.0000.0002.00. Every router in an IS-IS network must have at least one NET address that identifies a point of connection to the IS-IS network. The NET address is generally configured on the loopback interface (lo0). Routers that participate in multiple areas can have multiple NET addresses.

Check the Configuration of a Level 1 Router

Purpose

To check the configuration of a Level 1 router.

Action

To check the configuration of a Level 1 router, enter the following CLI commands:

The following sample output is for R4, a Level 1 router in the network shown in The following output is for an IS-IS configuration on R2, a Level 1/Level 2 router in the network shown.

Sample Output

command-name

Meaning

The sample output shows a basic configuration of IS-IS on R4, a Level 1 router. The basic configuration is at the [edit protocols isis] and [edit interfaces] hierarchy levels.

At the [edit protocols isis] hierarchy level, three interfaces are included: so-0/0/2.0, fxp0, and the loopback interface (lo0). Level 2 is disabled on the router, making it a Level 1 router that sends packets within its local area, 49.0001. When a packet destination is outside the local area, R4 establishes an adjacency with the nearest Level 1/Level 2 router (R5) that forwards the packets. For more information about adjacencies, see Displaying the Status of IS-IS Adjacencies.

One interface, so-0/0/2.0, is configured for IS-IS. The management interface (fxp0) is disabled so that IS-IS packets are not sent over it, and the loopback interface (lo0) is included because it becomes a point of connection from the router to the IS-IS network.

At the [edit interfaces] hierarchy level, the interface included in the [edit protocols isis] hierarchy level is also configured with family iso, and the loopback interface (lo0) is configured with the NET address of 49.0001.1000.0000.0004.00. Every router in an IS-IS network must have at least one NET address that identifies a point of connection to the IS-IS network. The NET address is generally configured on the loopback interface (lo0). Routers that participate in multiple areas can have multiple NET addresses.

Check the Configuration of a Level 2 Router

Purpose

Check the configuration of a Level 2 router.

Action

To check the configuration of a Level 2 router, enter the following CLI commands:

The following sample output is for R6, a Level 2 router in the network shown.

Sample Output

command-name

Meaning

The sample output shows a basic configuration of IS-IS on R6, a Level 2 router. The basic configuration is at the [edit protocols isis] and [edit interfaces] hierarchy levels.

At the [edit protocols isis] level, four interfaces are included: so-0/0/0.0, so-0/0/2.0, fxp0, and the loopback interface (lo0). Level 1 is disabled on the two SONET/SDH interfaces, making this a Level 2 router that routes between areas and toward other ASs. The management interface (fxp0) is disabled so that IS-IS packets are not sent over it, and the loopback interface (lo0) is included because it becomes a point of connection from the router to the IS-IS network.

At the [edit interfaces] hierarchy level, the interfaces included in the [edit protocols isis] hierarchy level are also configured with family iso, and the loopback interface (lo0) is configured with the NET address of 49.0003.1000.0000.0006.00. Every router in an IS-IS network must have at least one NET address that identifies a point of connection to the IS-IS network. The NET address is generally configured on the loopback interface (lo0). Routers that participate in multiple areas can have multiple NET addresses.