Hi, A message between bug report and feature request, unless it's a silly oversight on my side.
On Linux it's possible to configure interfaces with /32 (or v6 /128) IPs. I detailed our use-case and examples on https://phabricator.wikimedia.org/phame/post/view/312/ganeti_on_modern_network_design/ if you're curious. So focusing on v4 only for now I have this configuration on a VM: testvm2006:~$ ip addr inet 10.192.24.4/32 brd 10.192.24.4 scope global ens13 testvm2006:~$ ip route default via 10.192.24.1 dev ens13 onlink And this on the hypervisor (but it could also be 2 physical servers, or a router and a server) : ganeti2033:~$ ip addr inet 10.192.24.1/32 scope link tap0 ganeti2033:~$ ip route 10.192.24.4 dev tap0 proto static scope link Note that 10.192.24.1 is close to 10.192.24.4, but they could be totally different IPs (see the v6 example bellow). Overall connectivity works well, TCP handshake as well: testvm2006:~$ nc -zv 10.192.24.1 179 Connection to 10.192.24.1 179 port [tcp/bgp] succeeded! The issue is that with a basic configuration like: protocol bgp { ipv4 { import none; export none; }; local 10.192.24.4 as 64613; neighbor 10.192.24.1 external; } Bird 2.0.12 doesn't try to established the session, and waits with: 2024-04-12T08:42:29.497756+00:00 testvm2006 bird: bgp1: Waiting for 10.192.24.1 to become my neighbor For IPv4 it's possible to workaround the issue by setting the session as "multihop;" on both side bgp1: Connecting to 10.192.24.1 from local address 10.192.24.4 bgp1: Connected bgp1: Sending OPEN(ver=4,as=64613,hold=240,id=0ac01804) bgp1: Got OPEN(as=64612,hold=240,id=10.192.21.6) bgp1: Sending KEEPALIVE bgp1: Got KEEPALIVE bgp1: BGP session established But for IPv6, it's cleaner to only require the router's link local address: testvm2006:~$ ip -6 addr inet6 2620:0:860:140:10:192:24:4/128 scope global testvm2006:~$ ip -6 route default via fe80::2022:22ff:fe22:2201 dev ens13 metric 1024 pref medium In Bird: neighbor fe80::2022:22ff:fe22:2201%ens13 external; But then the link local address doesn't work with multihop (for obvious reason). bird: /etc/bird/bird.conf:22:1 Multihop BGP cannot be used with link-local addresses The question is then, would it be possible to support that usecase, something along the lines of if the local IP is a /32 (or v6 /128), Treat the neighbor as directly connected, especially if it's a link local IP (unless nultihop is specified). I haven't looked at BFD yet, so not sure if anything would need to change there as well. Don't hesitate to ask if something needs any clarifications. Thank for that great tool, Bird is awesome, -- Arzhel
