Help us improve your experience.

Let us know what you think.

Do you have time for a two-minute survey?

Configure IS-IS as the IGP

 

Before you can run MPLS on your network, you should have an IGP running on all specified routers and interfaces. The IGP can be either IS-IS or OSPF. For the steps to configure OSPF, see Configure OSPF as the IGP.

Figure 1: IS-IS Network Topology
IS-IS Network Topology

The IS-IS IGP in the MPLS network in Figure 1 consists of the following:

  • All routers are configured for Level 2, therefore default CSPF LSPs can occur.

  • All routers are in IS-IS area 49.0004. However, the routers in this network could be in any area because Level 2 adjacencies occur between all directly connected Level 2 routers regardless of which area they are in.

  • Level 2 adjacencies between all directly connected Level 2 routers as follows:

    • R1 is adjacent to R2, R3, and R5

    • R2 is adjacent to R1, R3, R4, and R6

    • R3 is adjacent to R1, R2, R4, and R6

    • R4 is adjacent to R2, R3, R5, and R6

    • R5 is adjacent to R1, R4, and R6

    • R6 is adjacent to R2, R3, R4, and R5

When you configure IS-IS as the IGP, you must enable IS-IS on the router, configure International Organization for Standardization (ISO) addressing, and enable IS-IS on all router interfaces.

You can enable IS-IS throughout the rest of the network by repeating Step 1, Enable IS-IS on Routers in Your Network through Step 3, Enable IS-IS on Router Interfaces as appropriate on other routers until all routers and interfaces establish IS-IS adjacencies.

To configure IS-IS and establish IS-IS adjacencies, follow these steps:



Enable IS-IS on Routers in Your Network

Action

To enable IS-IS on routers in your network, follow these steps:

  1. In configuration mode, go to the following hierarchy level:

  2. Disable Level 1 if appropriate for your network:

  3. Configure the interface:

  4. Disable the management interface if you have included the interface all statement, as shown in Sample Output 2:

  5. Include the loopback interface (lo0) if you have listed all interfaces separately, as shown in Sample Output 1:

  6. Set the loopback interface (lo0) to passive:

  7. Verify and commit the configuration:

Sample Output 1

Sample Output 2

Meaning

Sample Output 1 shows that IS-IS Level 1 is disabled, making this a Level 2 router. When all routers in the network are running at one IS-IS level (Level 2), default CSPF LSPs can occur.

Because R1 in Sample Output 1 has all IS-IS enabled interfaces listed, including the loopback interface (lo0), you do not need to include the disable statement for the management interface (fxp0). All interfaces have unit number 0, the default if a unit number is not specified. When you configure an interface at the [edit protocols isis] hierarchy level, and you do not include the logical unit, the default 0 is appended to the interface name, for example, so-0/0/1.0.

Sample Output 2 does not list the interfaces configured with IS-IS; instead, all interfaces are configured, including the loopback interface (lo0) and the management interface (fxp0). Therefore, you do not need to include a separate statement for the loopback (lo0) interface. However, in this instance, it is best practice to disable the management interface (fxp0) so that IS-IS packets are not sent over it. If you do not disable the management interface (fxp0) when you include the interface-all statement, the IS-IS protocol can form adjacencies over the management backbone, but traffic does not flow because transit traffic does not go out of the management interface.

Sample Output 2 also shows that all interfaces on R6 are configured with a metric of 15. A metric is not required to configure IS-IS on your interfaces. The default metric value is 10 (with the exception of the loopback [lo0] interface, which has a default metric of 0). A metric is included to demonstrate that you can configure a metric for IS-IS if the default (10) is not appropriate for your network.

Both sample outputs show the passive statement included in the configuration of the loopback (lo0) interface. Including the passive statement is considered best practice and ensures the following:

  • Protocols are not run over the loopback (lo0) interface

  • When the router ID (RID) is configured manually, ensures that the loopback (lo0) interface is advertised to other networks.

    Note

    It is considered best practice to configure the RID manually to avoid duplicate RID problems.





Configure ISO Addressing

Purpose

For a router to support IS-IS, you must configure an ISO network entity title (NET) address on one of the router’s interfaces, preferably the loopback interface (lo0).

Action

To configure ISO addressing, follow these steps:

  1. In configuration mode, go to the following hierarchy level:

  2. Include a NET address for the loopback interface:

  3. Verify and commit the configuration:

Sample Output

Meaning

The sample output shows that the loopback (lo0) interface is configured with the NET address 49.0004.1000.0000.0001.00. The loopback interface (lo0) becomes a point of connection from the router to the IS-IS network. Every router in an IS-IS network must have at least one ISO NET address that identifies a point of connection to the IS-IS network. The NET address is generally configured on the loopback (lo0) interface. Routers that participate in multiple areas can have multiple NET addresses.

All the routers in the network share a Level 2 database containing identical information. A common Level 2 database occurs in this case because all adjacencies are Level 2, and all routers are within the same IS-IS area (49.0004). Level 2 LSP flooding reaches all routers in the network due to the presence of a single level. For more information on determining the NET address, see the Junos Routing Protocols Configuration Guide.

Enable IS-IS on Router Interfaces

Purpose

Enable reception and transmission of ISO protocol data units (PDUs) on each router interface in the network with the family statement, which identifies which protocol packets are accepted into the interfaces. For example, valid IS-IS packets are dropped if the interface is not configured with the family iso statement.

Action

To configure support for IS-IS on router interfaces in your network, follow these steps:

  1. In configuration mode, go to the following hierarchy level:

  2. Configure IS-IS:

  3. Verify and commit the configuration:

Sample Output

Meaning

The sample output shows that the interface so-0/0/2 is configured with IS-IS.

Verify That IS-IS Adjacencies Are Established

Purpose

After configuring IS-IS, you must verify that neighboring routers have formed adjacencies with each other.

Action

To verify IS-IS adjacencies, enter the following Junos OS command-line interface (CLI) operational mode command:

Sample Output

Sample Output

Meaning

The sample output from the ingress, transit, and egress routers shows that all routers in the network have formed IS-IS adjacencies.