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Example: Configuring IS-IS Dual Stacking of IPv4 and IPv6 Unicast Addresses

This example shows how to configure IPv4 and IPv6 dual stacking in IS-IS.


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


You can use IPv4 and IPv6 dual stacking to begin your migration from IPv4 to IPv6 by implementing IPv6 alongside IPv4 in your existing networks. This allows you to implement IPv6 so that you can provide the same services over IPv6—for example, video, voice, high-quality data—that you currently provide in your IPv4 networks. You can then perform incremental upgrades to IPv6 and avoid service disruptions while migrating from IPv4 to IPv6.

Unlike RIP and OSPF, IS-IS does not require a distinct protocol or a new version to support IPv6. Because IS-IS uses ISO addresses, the configuration for IPv6 and IPv4 is identical in the Junos OS implementation of IS-IS. For IS-IS to carry IPv6 routes, you only need to add IPv6 addresses to IS-IS enabled interfaces or include other IPv6 routes in your IS-IS export policy.

The only explicit configuration needed in IS-IS with regard to IPv6 is if you want to disable it. Alternatively, you can disable IPv4 routing and use IS-IS with IPv6 only. An example of each is provided here:

Disable IPv6 routing in IS-IS:

Use IS-IS exclusively for IPv6 routing:

Figure 1 shows the topology used in this example.

Figure 1: IS-IS IPv4 and IPv6 Dual Stacking TopologyIS-IS IPv4 and IPv6 Dual Stacking Topology

CLI Quick Configuration shows the configuration for all of the devices in Figure 1. The section #configuration326__isis-dual-stack-step-by-step describes the steps on Device R1.



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

Device R3

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 Junos OS CLI User Guide.

To configure IS-IS dual stacking:

  1. Configure the interfaces, including both IPv4 and IPv6 addresses on each interface.

    Optionally, include the eui-64 statement to automatically generate the host number portion of interface addresses.

  2. Enable IS-IS on the interfaces.


From configuration mode, confirm your configuration by entering the show interfaces and show protocols commands. 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.

Checking the Neighbor Adjacencies


Determine what topologies are supported on neighboring IS-IS devices.


From operational mode, enter the show isis adjacency detail command.


As expected, the output shows that the two neighbors support both IPv4 and IPv6. The IPv4 address and the IPv6 link-local address are also shown.

Pinging the IPv6 Interfaces


Make sure that you can ping the remote IPv6 interfaces.


From operational mode, enter the ping command to ping from Device R2 to Device R3.

  1. Determine the IPv6 address assigned to Device R3.

    If you use EUI-64 addressing as shown in the example, the host portion of the IPv6 addresses is assigned automatically. To determine what addresses are assigned, use the show interfaces terse command on Device R3.

    The IPv6 addresses that should be pingable are 2001:db8:0:1:2a0:a514:0:124c and 2001:db8::3.

  2. From Device R2, ping the Device R3 fe-1/2/0.0 IPv6 interface address and the lo0.0 IPv6 interface address.


This test confirms that IS-IS has learned the IPv6 routes.

Checking the IPv6 Routing Table


Verify that the expected routes are in the IPv6 routing table.



The output shows the IPv6 interface routes (direct and local) and the IPv6 routes learned through IS-IS.