iBGP RR IPv6 link-local next-hop not kept

[Ondrej Zajicek]

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."