Is an IPv6 link local next-hop currently supported for BGP?

[bgshacklett]

Hello,

I'm trying to get BGP up and running between two routers. I've got an adjacency up and running using link local addresses, and routes are being advertised, but they're not being installed in the routing table on either router. The problem appears to be related to link local addressing and lack of an interface identifier, but BGP is not my strong suit, especially with IPv6.

Examples from show bgp ipv6 detail and show bgp nexthop:

Router A:

BGP routing table entry for 2600:1700:36a0:2550::/64, version 1
Paths: (1 available, best #1, table default)
  Advertised to non peer-group peers:
  fe80::6662:66ff:fe22:b5a6
  Local
    :: from :: (192.168.4.1)
      Origin incomplete, metric 1, weight 32768, valid, sourced, best (First path received)
      Last update: Mon Jul 21 12:31:46 2025
      
# show bgp nexthop
Current BGP nexthop cache:
 fe80::6662:66ff:fe22:b5a6 valid [IGP metric 1], #paths 0, peer fe80::6662:66ff:fe22:b5a6
  Resolved prefix fe80::/64
  if lo0, ifindex 5
  Last update: Mon Jul 21 12:26:18 2025
 fe80::6662:66ff:fe22:b5a6 invalid, #paths 6
  Last update: Mon Jul 21 02:55:01 2025      

Router B:

BGP routing table entry for 2600:1700:36a0:255e::/64, version 0
Paths: (1 available, no best path)
  Not advertised to any peer
  Local
    fe80::6662:66ff:fe21:d0e6 (inaccessible) from fe80::6662:66ff:fe21:d0e6 (192.168.4.1)
    (fe80::6662:66ff:fe21:d0e6) (used)
      Origin incomplete, metric 1, localpref 100, invalid, internal
      Last update: Mon Jul 21 12:53:59 2025
      
# show bgp nexthop
Current BGP nexthop cache:
 fe80::6662:66ff:fe21:d0e6 valid [IGP metric 0], #paths 0, peer fe80::6662:66ff:fe21:d0e6
  if lo
  Last update: Sun Jul 20 19:02:02 2025
 fe80::6662:66ff:fe21:d0e6 invalid, #paths 6
  Last update: Sun Jul  6 15:37:41 2025

[donaldsharp]

https://docs.frrouting.org/en/latest/bgp.html#clicmd-neighbor-PEER-interface-IFNAME

So configure the LL address as the neighbor and then issue the above command. Additionally you can do it this way:

https://docs.frrouting.org/en/latest/bgp.html#clicmd-neighbor-PEER-interface-remote-as-internal-external-auto-ASN

[bgshacklett]

Seems like I was a little premature in marking this as the answer. It solves part of the puzzle, but it appears that there's at least some additional required functionality targeting v10.5:
db853cc