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Example: Configuring IS-IS

This example shows how to configure IS-IS in a simple two-device network topology.


Our content testing team has validated and updated this example.


No special configuration beyond device initialization is required before configuring this example.


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In this example, you configure two devices, Device R1 and Device R2, within a single IS-IS area.

To enable IS-IS routing, you must:

  • Configure a NET address (also known as the system ID or the NSAP address) on one of the device interfaces (preferably, the lo0 interface) by including the family iso address net-address statement on the interface.

  • Configure the ISO family on all interfaces that are supporting the IS-IS protocol by including the family iso statement on the interface.

  • Advertise the device interfaces into IS-IS by inlcuding the interface interface-name statement in the protocol configuration.

  • (On security devices only) Enable the forwarding of IS-IS traffic by including the family mode packet-based statement in the security forwarding options configuration.


    Junos releases prior to and including 19.2R1-S2 supported ISIS PDU exchange without explicitly setting packet mode for ISIS under [edit security forwarding-options family iso]. In newer releases this setting is required in order for ISIS to operate properly. When upgrading an SRX device to a Junos version newer than 19.2R1-S2 you must configure packet mode for ISIS or adjacencies will not form.

Figure 1 shows the topology used in this example.

Figure 1: Simple IS-IS Topology Simple IS-IS Topology

CLI Quick Configuration shows the configuration for both of the devices in Figure 1.



CLI Quick Configuration

To quickly configure this example, copy the following commands, paste them into a text file, remove any line breaks, change any details necessary to match your network configuration, and then copy and paste the commands into the CLI at the [edit] hierarchy level.

Device R1

Device R2

Step-by-Step Procedure

The following example requires you to navigate various levels in the configuration hierarchy. For information about navigating the CLI, see Using the CLI Editor in Configuration Mode in the CLI User Guide.

To configure IS-IS:

  1. (On security devices only) Enable the forwarding of IS-IS traffic to overcome the default behavior of dropping IS-IS traffic.

  2. Configure the device interface, and enable the ISO family on the interface.

  3. Configure the loopback interface and set the NET address.

  4. Enable IS-IS for the device interfaces.


From configuration mode, confirm your configuration by entering the show command. If the output does not display the intended configuration, repeat the instructions in this example to correct the configuration.

If you are done configuring the device, enter commit from configuration mode.


Confirm that the configuration is working properly.

Verifying IS-IS Adjacencies and Interfaces


Verify that IS-IS adjacencies are up and that the IS-IS interfaces are included in the protocol configuration.


From operational mode, enter the show isis adjacency and show isis interface commands.


Device R1 has established adjacency with Device R2 as indicated by the State output field which is Up.

Device R1 interfaces are advertised into IS-IS with Device R2 as the designated router responsible for sending link-state advertisements. Both the devices are enabled with Level 1 and Level 2 IS-IS as indicated by the L 3 output field.

Verifying End-to-End Connectivity


Verify that the devices are reachable by pinging their loopback addresses.


From operational mode, enter the ping source count 100 rapid command.


The devices can succcessfully ping each other's loopback address.