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

SRv6 BGP-Based Services

Updated: September 8, 2026

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Explains how BGP advertises service SIDs for VPN and global routing services and describes the endpoint behaviors and allocation methods used to forward traffic.

The BGP in SRv6 Services is a routing protocol extension that

enables the signaling and distribution of SRv6 SIDs
supports advanced VPN and routing services over an SRv6 network, and
facilitates the encapsulation and interconnection of provider edge routers using SRv6 service SIDs.

Table 1. Feature History Table
Feature Name	Release	Description
Support for uDT46 SRv6 Endpoint Behavior	Release 25.4.1	Introduced in this release on: Fixed Systems (8700 [ASIC: K100], 8010 [ASIC: A100])(select variants only) This feature is supported on: 8711-48Z-M 8011-32Y8L2H2FH 8011-12G12X4Y-A/D
Support for uDT46 SRv6 Endpoint Behavior	Release 25.1.1	Introduced in this release on: Fixed Systems (8010 [ASIC: A100])(select variants only*) This feature is now supported on Cisco 8011-4G24Y4H-I routers.
VRF Allocation Mode for uDT46 Endpoint Behavior	Release 25.1.1	Introduced in this release on: Fixed Systems (8010 [ASIC: A100])(select variants only*) This feature is now supported on Cisco 8011-4G24Y4H-I routers.
VRF Allocation Mode for uDT46 Endpoint Behavior	Release 24.4.1	Introduced in this release on: Fixed Systems (8200 [ASIC: P100], 8700 [ASIC: P100, K100])(select variants only); Modular Systems (8800 [LC ASIC: P100])(select variants only) *This feature is supported on: 8212-48FH-M 8711-32FH-M 8712-MOD-M 88-LC1-36EH 88-LC1-12TH24FH-E 88-LC1-52Y8H-EM
Support for uDT46 SRv6 Endpoint Behavior	Release 24.4.1	Introduced in this release on: Fixed Systems (8200 [ASIC: P100], 8700 [ASIC: P100])(select variants only); Modular Systems (8800 [LC ASIC: P100])(select variants only) *This feature is supported on: 8212-48FH-M 8711-32FH-M 88-LC1-36EH 88-LC1-12TH24FH-E 88-LC1-52Y8H-EM
Support for uDT46 SRv6 Endpoint Behavior	Release 7.11.1 Release 7.5.3	This feature adds support for the “Endpoint with decapsulation and specific IP table lookup” SRv6 end-point behavior (uDT46). The End.DT46 behavior is used for dual-stack L3VPNs. This behavior is equivalent to the single per-VRF VPN label (for IPv4 and IPv6) in MPLS.
VRF Allocation Mode for uDT46 Endpoint Behavior	Release 7.11.1	This feature introduces a new VRF allocation mode for uDT46 SIDs for the following BGP-based services: IPv4 Layer-3 VPNs IPv6 Layer-3 VPNs IPv4 BGP global IPv6 BGP global L3 EVPN This allocation mode allows for both IPv4/IPv6 address families, and VPNv4/v6 address families, to use a single SID. When this allocation mode is configured under an address family, CE-learned routes, redistributed routes, aggregated routes, local routes, and imported routes will use uDT46 SID when advertised to remote peers. The feature introduces these changes: CLI: The per-vrf-46 allocation mode is introduced in the following commands: router bgp as-number address-family {ipv4 \| ipv6} unicast segment-routing srv6 alloc mode per-vrf-46 router bgp as-number address-family {vpnv4 \| vpnv6} unicast vrf all segment-routing srv6 alloc mode per-vrf-46 router bgp as-number vrf WORD address-family {ipv4 \| ipv6} unicast segment-routing srv6 alloc mode per-vrf-46

Extending BGP for SRv6-based overlay services

Building on the messages and procedures defined in IETF draft BGP/MPLS IP Virtual Private Networks (VPNs) BGP has been extended to provide services over an SRv6 network, such as:

IPv4 Layer-3 VPNs
IPv6 Layer-3 VPNs
IPv4 BGP global
IPv6 BGP global
Layer-2 VPNs - Ethernet VPNs (EVPN)

For more information about BGP, refer to the Implementing BGP chapter in the Routing Configuration Guide for Cisco 8000 Series Routers.

In SRv6-based services, the egress PE signals an SRv6 service SID with the BGP service route. The ingress PE encapsulates the payload in an outer IPv6 header where the destination address is the SRv6 Service SID advertised by the egress PE. BGP messages between PEs carry SRv6 service SIDs as a means to interconnect PEs and form VPNs. SRv6 service SID refers to a segment identifier associated with one of the SRv6 service-specific behaviors advertised by the egress PE router, such as:

uDT4 (Endpoint with decapsulation and IPv4 table lookup)
uDT6 (Endpoint with decapsulation and IPv6 table lookup)
uDT46 (Endpoint with decapsulation and specific IP table lookup)
uDX4 (Endpoint with decapsulation and IPv4 cross-connect)
uDX6 (Endpoint with decapsulation and IPv6 cross-connect)

Based on the messages and procedures defined in IETF draft SRv6 BGP based Overlay services, BGP encodes the SRv6 Service SID in the prefix-SID attribute of the corresponding BGP Network Layer Reachability Information (NLRI) and advertises it to its IPv6 BGP peers.

Usage guidelines for SRv6 BGP-based services

These SRv6 BGP-based services are supported:
- IPv4 Layer-3 VPNs
- IPv6 Layer-3 VPNs
- IPv4 BGP global
- IPv6 BGP global
uDT4 and uDT6 for L3VPN and BGP global are supported.
uDT4, uDT6, and uDT46 for L3VPN and BGP global are supported.
Dual-Stack L3 Services (IPv4 L3VPN, IPv6 L3VPN, IPv4 BGP global, IPv6 BGP global) are supported.

SRv6 Locator Inheritance Rules

SRv6 locators can be assigned at different levels inside the BGP routing process. BGP allocates SRv6 service SIDs from configured locator spaces according to these inheritance rules:

Use the locator as defined under the service.

If not defined under the specific service, then:
Use the locator as defined under the corresponding address-family.

If not defined under the corresponding address-family, then:
Use the locator as defined globally under BGP.

Configure SRv6 BGP-based services

Procedure

Use the router bgp as-number segment-routing srv6 command to enable SRv6 globally under the BGP routing process.

The as-number is from 1-65535.
Example:
```
Node1(config)# router bgp 100 segment-routing srv6
```
Use the router bgp as-number segment-routing srv6 locator WORD command to assign an SRv6 locator globally under the BGP routing process.

The as-number is from 1-65535.
Example:
```
Node1(config)# router bgp 100 segment-routing srv6 locator Node1-locator
```

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