Multi-topology IPv6 for IS-IS

Updated: June 9, 2026

Want to summarize with AI?

Introduces multitopology IPv6 support in IS-IS, detailing key restrictions and providing step-by-step instructions for configuring multitopology routing to enable flexible IPv6 deployment in diverse network architectures.

Multi-topology IPv6 for IS-IS is a routing protocol feature that

enables simultaneous support for both IPv4 and IPv6 address families within IS-IS
uses multitopology as default behavior when interfaces are configured for both IPv6 and IPv4, and
requires explicit configuration to enable single-topology IPv6 using the single-topology command.

By default, multi-topology support is activated in software as soon as interfaces for both IPv4 and IPv6 are detected in the IS-IS configuration stanza.
To enable single-topology IPv6, configure the single-topology command in the IPv6 router address family configuration submode of the IS-IS router stanza.

Multitopology route restrictions

Only the default VRF is currently supported in multitopology solutions.
Currently, only protocol-independent multicast (PIM) and intermediate system–intermediate system (IS-IS) routing protocols are supported.
Topology selection is restricted to (S, G) route sources for both SM and SSM. Static and IS-IS are the only interior gateway protocols (IGPs) that support multitopology deployment.
For non-(S, G) route sources such as a rendezvous point or bootstrap router, or when no route policy is configured, the default policy is used; either a unicast-default or multicast-default table is selected based on OSPF, IS-IS, or MBGP configuration.
When configuring routing policy language (RPL), both multicast and unicast keywords are available with the address-family (ipv4 | ipv6 ) command, but only multicast SAFI topologies can be configured globally.

Configure multitopology IPv6 for IS-IS

Enable IS-IS to support IPv6 networks in their own independent topology, separate from IPv4, for greater routing flexibility.

Use this task when you require IPv6 routing to run in a dedicated topology within IS-IS, rather than sharing the IPv4 topology. This separation is essential for scenarios where the operational requirements for IPv4 and IPv6 differ.

Before you begin

Confirm IS-IS is enabled and supported on your device.
Ensure IPv6 address configuration is permitted on your interfaces.

Procedure

Configure the IS-IS instance and enable IPv6 on the interface.

Example:

Router(config)# router isis isp
Router(config-isis)# net 49.0000.0000.0001.00
Router(config-isis)# interface POS0/3/0/0
Router(config-isis-if)# address-family ipv6 unicast 
Router(config-isis-af)# metric-style wide level 1
Router(config-isis-af)# exit   
Router(config-isis)# interface POS0/3/0/0
Router(config-isis-if)# ipv6 address 2001::1/64
Router(config-isis)# exit

Need help?

Open a support case

(Requires a Cisco Service Contract)

The documentation set for this product strives to use bias-free language. For the purposes of this documentation set, bias-free is defined as language that does not imply discrimination based on age, disability, gender, racial identity, ethnic identity, sexual orientation, socioeconomic status, and intersectionality. Exceptions may be present in the documentation due to language that is hardcoded in the user interfaces of the product software, language used based on RFP documentation, or language that is used by a referenced third-party product. Learn more about how Cisco is using Inclusive Language.