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

IPv4 BGP Global SRv6 services

Updated: September 8, 2026

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Explains how SRv6 provides IPv4 global BGP services and describes the endpoint behaviors used to decapsulate and forward IPv4 traffic.

IPv4 BGP global is a BGP service that operates within an IPv4 network, and is supported by SRv6-based services through the implementation of uDX4, uDT4, and uDT46 SRv6 functions at the PE node.

Key concepts

  • IPv4 global BGP: Refers to BGP routing specifically for IPv4 addresses within the global routing table, typically used for internet-wide connectivity rather than within a Virtual Routing and Forwarding (VRF) instance.

  • uDX4, uDT4, and uDT46 SRv6 Functions: These are specific SRv6 Segment Identifiers (SIDs) or behaviors that define how a packet is processed at an SRv6-enabled node.

    • uDX4 (Endpoint with decapsulation and IPv4 lookup): This behavior indicates that the PE node decapsulates the SRv6 header and then performs an IPv4 lookup in its routing table to forward the packet.

    • uDT4 (Endpoint with decapsulation and IPv4 table lookup): This behavior is similar to uDX4, specifically indicating a lookup in an IPv4 routing table.

    • uDT46 (Endpoint with decapsulation and IPv4/IPv6 table lookup): This behavior supports decapsulation and a lookup in either an IPv4 or IPv6 routing table, enabling dual-stack forwarding.

Restrictions of IPv4 BGP Global SRv6 Services

  • SRv6 locator can be assigned globally, to all VRFs, to an individual VRF, or per-prefix. Per prefix locator assignment is supported starting with Release 7.5.1.

  • Equal-Cost Multi-path (ECMP) and Unequal Cost Multipath (UCMP) are supported.

  • BGP (iBGP, eBGP), OSPF, static are supported as PE-CE protocols.

    Support for iBGP as a PE-CE protocol (RFC 6368, configured with internal-vpn-client under the VRF neighbor) is available starting with Release 7.5.1.

  • BGP route leaking between BGP global table and L3VPN is supported starting with Release 7.5.1. This feature allows importing routes from the default VRF into a non-default VRF, and from a non-default VRF into the default VRF.

  • Starting from Release 7.8.1, Dual-Stack L3 Services (IPv4 BGP global, IPv6 BGP global) are supported.

Configure BGP global IPv4 Over SRv6 with Per-CE SID allocation mode

Procedure

Configure BGP global IPv4 over SRv6 with per-CE SID allocation.

Example:

router bgp 1
 bgp router-id 10.1.0.1
 address-family ipv4 unicast
  segment-routing srv6
   alloc mode per-ce  
  !
 !
 neighbor 60::2
  remote-as 1
  update-source Loopback1
  address-family ipv4 unicast
   route-policy passall in
   encapsulation-type srv6
   route-policy passall out
  !
 !
 neighbor 52.52.52.1
  remote-as 3
  address-family ipv4 unicast
   route-policy passall in
   route-policy passall out
  !
 !
!