As far as I know, the recent cilium releases are capable of running ipv6 only (although I didn't try it personally, yet). BGP-wise, the only change you should need to make is to specify the router id: https://docs.cilium.io/en/latest/network/bgp-control-plane/#specifying-router-id-ipv6-single-stack-only.

As for my case, I figured out the basic configuration that makes cilium push both ipv4 and ipv6 routes and it's actually working as intended. Here's a post with my notes https://farcaller.net/2024/making-cilium-bgp-work-with-ipv6/, but really, all the struggles I had were to do with my misunderstanding how exactly bird operates.

On Mon, May 6, 2024 at 8:43 AM Nico Schottelius <nico.schottelius@ungleich.ch> wrote:

Vladimir,

I love the direction you are going with cilium and bird. We actually had
cilium on our list for potential CNIs, but hold yourself: had to drop
it, because cilium does NOT work on IPv6 only hosts!

I.e. if the k8s workers are IPv6 only, cilium crashes [0].

In case you make any progress in that direction, I'd love to hear from
you.

BR from Switzerland,

Nico

[0] https://redmine.ungleich.ch/projects/open-infrastructure/wiki/The_ungleich_kubernetes_infrastructure#Cilium-CNI-experimental

Vladimir Pouzanov <farcaller@gmail.com> writes:

> On Sun, May 5, 2024 at 7:35 AM Maria Matejka <maria.matejka@nic.cz> wrote:
>
> The error message actually means "you requested direct connection but i can't see the right interface to use because there is no interface with this
> range assigned".
>
> Thanks, that was it!
>
> I must have missed the note in the docs on that, because with ipv4 I just had the same subnet, but with ipv6 I don't have a public address assigned on
> the bird side. `multihop 1` Fixed the negotiation issue. I got a few more, but those seem to be related to either gobgp sending malformed updates
> (Invalid NEXT_HOP attribute - mismatched address family (2a01:xx:yy:zz:4746:92e9:327c:d930 for ipv4)), or the bird configuration not being able to
> parse a `-` in the interface name. Both unrelated to this particular issue at hand.

--
Sustainable and modern Infrastructures by ungleich.ch