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

Migrate an SRv6 network from format1 to uSID

Updated: September 8, 2026

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Guides the staged migration of IS-IS, BGP, and EVPN services to uSID F3216, including prerequisite upgrades, dual-mode operation, delayed deletion, and verification.

Migrate the network from SRv6 base format1 to uSID f3216. This migration enables faster convergence and seamless traffic transition.

Upgrade your routers to support SRv6 uSID f3216, which allows coexistence and phased migration from format1. This procedure guides network administrators through each transition stage: initial, in-migration, and end state.

Before you begin

  • Upgrade all network nodes (P and PE) to a software image that supports SRv6 uSID f3216 and allows the coexistence of format1 and f3216 locators.

  • Ensure IS-IS, BGP, and EVPN protocols are configured and operational with SRv6 format1 locators.

Procedure

  1. Configure SRv6 locators in the initial state using format1 only.

    This step sets up the base SRv6 configuration with format1 locators, if they are not already present.

    Example:

    
Router(config)# segment-routing srv6
Router(config-srv6)# locators
Router(config-srv6-locators)# locator myLoc0
Router(config-srv6-locators)# prefix f1bb:bbbb:bb00:0001::/64

  2. Configure IS-IS with the SRv6 format1 locator in the initial state.

    This step integrates IS-IS with the format1 SRv6 locator.

    Example:

    
Router(config)# router isis 100
Router(config-isis)# address-family ipv6 unicast
Router(config-isis-af)# segment-routing srv6
Router(config-isis-srv6)# locator myLoc0

  3. Configure BGP and EVPN with SRv6 locator in the initial state.

    This step integrates BGP and EVPN with the format1 SRv6 locator.

    Example:

    
Router(config)# router bgp 100
Router(config-bgp)# bgp router-id 10
Router(config-bgp)# segment-routing srv6
Router(config-bgp-srv6)# locator myLoc0

    
Router(config)# evpn
Router(config-evpn)# segment-routing srv6
Router(config-evpn-srv6)# locator myLoc0

  4. Initiate in-migration to dual mode by configuring the uSID locator.

    This step configures the uSID locator, enabling dual mode operation. The delayed-delete command ensures the format1 locator remains active during the transition.

    Example:

    
Router(config)# segment-routing srv6
Router(config-srv6)# locators
Router(config-srv6-locators)# locator myLoc0
Router(config-srv6-locators)# prefix f1bb:bbbb:bb00:0001::/64
Router(config-srv6-locators)# delayed-delete
Router(config-srv6-locators)# locator myuLoc0
Router(config-srv6-locators)# micro-segment behavior unode psp-usd
Router(config-srv6-locators)# prefix fcbb:bb00:0001::/48

  5. Update IS-IS and BGP/EVPN to use both locators during in-migration.

    This step modifies the IS-IS and BGP and EVPN configuration to recognize and use both locators.

    Example:

    
Router(config)# router isis 100
Router(config-isis)# address-family ipv6 unicast
Router(config-isis-af)# segment-routing srv6
Router(config-isis-srv6)# locator myLoc0
Router(config-isis-srv6)# locator myuLoc0
    
Router(config)# router bgp 100
Router(config-bgp)# bgp router-id 10
Router(config-bgp)# segment-routing srv6
Router(config-bgp-srv6)# locator myuLoc0
    
Router(config)# evpn
Router(config-evpn)# segment-routing srv6
Router(config-evpn-srv6)# locator myuLoc0

  6. Finalize end-state configuration by retaining only uSID locators.

    Example:

    
Router(config)# segment-routing srv6
Router(config-srv6)# locators
Router(config-srv6-locators)# locator myuLoc0
Router(config-srv6-locators)# micro-segment behavior unode psp-usd
Router(config-srv6-locators)# prefix fcbb:bb00:0001::/48
    
Router(config)# router isis 100
Router(config-isis)# address-family ipv6 unicast
Router(config-isis-af)# segment-routing srv6
Router(config-isis-srv6)# locator myuLoc0
    
Router(config)# router  bgp 100
Router(config-bgp)# bgp router-id 10
Router(config-bgp)# segment-routing srv6
Router(config-bgp-srv6)# locator myuLoc0

    
Router(config)# evpn
Router(config-evpn)# segment-routing srv6
Router(config-evpn-srv6)# locator myuLoc0
    show

    commands

  7. Verify SRv6 migration status to confirm that the SRv6 deployment is operating correctly with uSID locators.

    Example:

    
RP/0/RSP0/CPU0:Router# show route ipv6 fc00:cc30:600:e004:: detail

Routing entry for fc00:cc30:600::/48
    Known via "isis 2", distance 115, metric 141, SRv6-locator, type level-2
    Installed Nov 2 18:56:55.718 for 00:01:01
    Routing Descriptor Blocks
      fe80::232:17ff:fec3:58c0, from 7511::1, via TenGigE0/0/0/16.1, Protected
        Route metric is 141
        Label:	None
        Tunnel ID:	None
        Binding Label:	None
        Extended communities count: 0
        Path id:1		Path ref count:0
        NHID:0x20006(Ref:193)
        Backup path id:65
      fe80::226:80ff:fe36:7c01, from 7511::1, via TenGigE1/0/9/1.1, Backup (TI-LFA)
        Repair Node(s): 3888::1
        Route metric is 251
        Label:	None
        Tunnel ID:	None
        Binding Label:	None
        Extended communities count: 0
        Path id:65		Path ref count:1
        NHID:0x20007(Ref:163)
        SRv6 Headend:H.Insert.Red [f3216], SID-list {fc00:cc30:700::}
	Route version is 0x0 (8)
	No local label
	IP Precedence: Not Set
	QoS Group ID: Not Set
	Flow-tag: Not Set
	Fwd-Class: Not Set
	Route Priority:RIB_PRIORITY_NON_RECURSIVE_LOW (8) SVD Type RIB_SVD_TYPE_LOCAL
	Download Priority 2, Download Version 261731
	No advertising protos.