iBGP RR IPv6 link-local next-hop not kept

[Mirai Azayaka]

Wow, thank you so much! Setting bgp_next_hop = gw; works for me! (yeah
I was worried that because link-local address is interface-dependent,
my router wouldn't be able to know the interface. It seems my router
(also running bird) chooses the same interface as the BGP session,
which is what I want.

On Tue, Feb 28, 2023 at 5:32 PM Ondrej Zajicek <santiago at crfreenet.org> wrote:
>
> On Tue, Feb 28, 2023 at 02:57:54PM -0500, Mirai Azayaka wrote:
> > Hello,
> >
> > I am trying to send routes from my DHCPv6 prefix delegation server to
> > my router using iBGP. Those delegated prefix routes on the DHCPv6
> > server are installed in its kernel table, such as 2001:db8:db8::/56
> > via <client's link-local addr>. I want to pass this information to my
> > router, but what the router receive is always 2001:db8:db8::/56 via
> > <global unicast addr of the DHCPv6 server>. Why would next-hop change
> > if it's iBGP?
>
> Hello
>
> Because link-local address is not resolvable through IGP routing table
> then it does not really make sense to keep it when propagating through
> IBGP.
>
> I.e., the regular next-hop is valid through the whole local AS, so we can
> pass it unmodified through IBGP, but link-local next-hop is valid only on
> a specific link.
>
> Note that BIRD almost always keep bgp_next_hop attribute when it is set
> manually in the export filter, so if you use something like:
>
>   bgp_next_hop = gw;
>
> in prefix_delegation export filter, it should keep the value, even if it
> is link-local.
>
> --
> Elen sila lumenn' omentielvo
>
> Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
> OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net)
> "To err is human -- to blame it on a computer is even more so."