IPv6, route reflectors and link-local nexthops

[Ondrej Zajicek]

On Thu, Oct 10, 2019 at 04:57:28PM +0200, Jan-Philipp Litza wrote:
> Hi list,
> 
> maybe this question boils down to "How can I tell bird to always use
> global IPv6 addresses as nexthops". But let me give you a sketch of my
> problem:
> 
> RR ---- R1 ---- R2
> 
> Addresses:
> RR 2001:db8:1::100, fe80:1::100%I1
> R1 2001:db8:1::1,   fe80:1::1%I1
>    2001:db8:2::1,   fe80:2::1%I2
> R2 2001:db8:2::2,   fe80:2::2%I2
> 
> RR is an route reflector with
> * a direct iBGP session to R1 / 2001:db8:1::1, and
> * a multihop eBGP session to R2 / 2001:db8:2::2.
> As RR isn't supposed to forward any traffic, it has "missing lladdr
> ignore" set on the iBGP session.
> R1 and R2 don't talk to each other.
> 
> Now RR exports this route to R1, and this is where things go wrong:
> 
> > bird> show route all 2001:db8:3::/64> 2001:db8:3::/64 unicast [RR 2019-10-10 from 2001:db8:1::100] * (100/0)
> [AS4242424242?]
> > 	via fe80:1::100 on I2
> > 	Type: BGP univ
> > 	BGP.origin: Incomplete
> > 	BGP.as_path: 4242424242
> > 	BGP.next_hop: 2001:db8:2::2
> > 	BGP.local_pref: 100
> 
> R1 correctly identifies the BGP.next_hop as being on-link for I2, but
> uses the link-local address of RR on the interface to R2 as nexthop.
> 
> (Actually, it's even worse: R1 doesn't really use fe80:1::100 as
> nexthop, but the link-local address of the peer that was formerly in the
> place of RR. That address isn't even present anymore on any server
> anywhere!)

Hi

Not really sure how that might happen with direct session. What is your
BIRD version and configs? What routes do you have in routing table?

-- 
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."