BGP Next-Hop for SRv6 Service Routes

As specified in draft-ietf-bess-srv6-services, the egress PE may set the next hop to any of its IPv6 addresses. When the IPv6 address value is not covered by the SRv6 Locator from which the SRv6 Service SID is allocated, the ingress PE performs reachability checks for the SRv6 Service SID in addition to the BGP next-hop reachability procedures.

Next hop and locator resolution considerations:

On reception of a BGP SRv6 service route, both, locator and next hop are resolved independently in the route table.
For base instance routes (not Service routes), no ignore-received-srv6-tlvs triggers the independent resolution of the next-hop and the locator reachability (and collates their states that will drive route programming). The locator state is considered only if the no ignore-received-srv6-tlvs command is configured.
Whether the router does next-hop-self or next-hop-unchanged does not affect the rib-in processing and reachability (since the next-hop behavior is a rib-out parameter).
In case a received route has a resolved next-hop but unresolved locator, the show router bgp routes commands will show ‘valid/best’ but not ‘used’ in the route flags. The command show router bgp next-hop displays the locator and the resolution of the locator:

*A:PE-4# show router bgp next-hop 192.0.2.3 detail vpn-ipv4               
===============================================================================
 BGP Router ID:192.0.2.4        AS:64500       Local AS:64500      
===============================================================================

===============================================================================
BGP VPN Next Hop
===============================================================================
-------------------------------------------------------------------------------
VPN Next Hop          : 192.0.2.3
Autobind              : gre 
Labels                : --
Admin-tag-policy      : --
Strict-tunnel-tagging : N
Color                 : --
Locator               : cafe:1:0:3::/64
-------------------------------------------------------------------------------
Resolving Prefix : 192.0.2.3/32
Preference       : 18                   Metric           : 10
Reference Count  : 6                    Owner            : GRE
Fib Programmed   : Y                    
Resolved Next Hop: 192.168.34.1
Egress Label     : n/a                  TunnelId         : 4294967293
Locator State    : Resolved             
-------------------------------------------------------------------------------
Next Hops : 1
===============================================================================