Segment Routing v6 Configuration Guide for Cisco 8000 Series Routers, Cisco IOS XR Releases

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Segment Routing v6 Configuration Guide for Cisco 8000 Series Routers, Cisco IOS XR Releases

Key concepts of SRv6 with IS-IS

Updated: September 8, 2026

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Describes the key concepts of SRv6 with IS-IS.

Intermediate System-to-Intermediate System (IS-IS) protocol already supports segment routing with MPLS dataplane (SR-MPLS). This feature enables extensions in IS-IS to support SRv6. The extensions include advertising the SRv6 capabilities of nodes and node and adjacency segments as SRv6 SIDs.

SRv6 IS-IS performs the following functionalities:

Interacts with SID Manager to learn local locator prefixes and announces the locator prefixes in the IGP domain.
Learns remote locator prefixes from other ISIS neighbor routers and installs the learned remote locator IPv6 prefix in RIB or FIB.
Allocate or learn prefix SID and adjacency SIDs, create local SID entries, and advertise them in the IGP domain.

SRv6 IS-IS guidelines and restrictions

Use this topic before configuring an SRv6 locator under IS-IS.

The following usage guidelines and restrictions apply for SRv6 IS-IS:

An IS-IS address family can support either SR-MPLS or SRv6, but not both at the same time.

Note

If no IS-IS level is specified, local locators are advertised into all configured IS-IS levels. Include locators in the redistribution or propagation policy to prevent potential loops when redistributing between multiple instances or propagating between Level 2 and Level 1.

Configure SRv6 with IS-IS

Set up SRv6 operation in an IS-IS environment by associating SRv6 locators with the IS-IS address-family.

Configuring SRv6 within IS-IS enables dynamic SRv6 locator advertisement for IPv6 segment routing. This supports advanced path engineering, scalability, and automated locator distribution via IS-IS.

Before you begin

Ensure that base SRv6 is configured.
Create an SRv6 locator before adding it under IS-IS.

Follow these steps to configure SRv6 with IS-IS:

Procedure

Configure SRv6 with IS-IS.
To configure SRv6 IS-IS, use the router isis command. Enable SRv6 under the IS-IS IPv6 address-family and assign SRv6 locator(s) to it. Use the level {1 | 2} keywords to advertise the locator only in the specified IS-IS level.
```
Router(config)# router isis core
Router(config-isis)# address-family ipv6 unicast
Router(config-isis-af)# segment-routing srv6
Router(config-isis-srv6)# locator myLoc1
Router(config-isis-srv6-loc)# exit
```
Verify the SRv6 locator advertisement using relevant show commands.

SRv6 locators are dynamically advertised within IS-IS, enabling SRv6 packet forwarding capabilities and automated locator distribution for IPv6 segment routing.

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