iBGP RR IPv6 link-local next-hop not kept

[Alexander Zubkov]

Hi,

As far as I remember, you can set in your income filter the interface, then
the gateway (in that order) to force the interface you want.

On Wed, Mar 1, 2023, 02:18 Mirai Azayaka <azayaka at apernet.io> wrote:

> 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."
>
>
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