bird and OSPF on p2p

[Joakim Tjernlund]

Ondrej Zajicek <santiago at crfreenet.org> wrote on 2012/08/30 12:57:30:
>
> On Wed, Aug 22, 2012 at 04:32:26PM +0200, Joakim Tjernlund wrote:
> > owner-bird-users at atrey.karlin.mff.cuni.cz wrote on 2012/08/22 15:34:54:
> > >
> > > On Wed, Aug 22, 2012 at 04:32:24PM +0600, Eugene M. Zheganin wrote:
> > > > Hi.
> > > >
> > > > On 22.08.2012 14:39, Ondrej Zajicek wrote:
> > > >> As i understand it correctly, you have Quagga at one end and BIRD
> > > >> on the other? AFAIK there is some problem related to unnumbered
> > > >> ptp links in Quagga which causes incompatibility with BIRD,
> > > >> Joakim Tjernlund has some patches for that for Quagga.
> >
> > Yes, they went in a few weeks ago too :) ( there is one patch outstanding though)
> > current released quagga cannot handle ifindex in the LSA(like BIRD do for /32 masks).
> > This is an old defect in Q. so BIRD is not to blame.
>
> Although i agree that next hop computation in Quagga is mainly to blame,
> i reviewed the issue and it seems that there are some grey areas:
>
> 1) RFC 2328 does not really specify how next-hop should be computed on
> ptp ifaces (it is supposed that there is no need for next-hop). Although
> it is true that Quagga way is broken w.r.t. unnumbered links (and
> probably also parallel ptp links), it cannot be said that it is
> contrary to OSPF spec.
>
> 2) Surprisingly, even RFC 5309 (ptp links over LAN) does not specify how
> next-hop should be computed (although it notes its importance).
>
> 3) I thought that for some reasons the ifindex in 'data' value of link in
> router LSA is somehow important in link-back check or next-hop calculation
> when there are parallel links, but it seems to be completely useless
> - local router does not need it and neighboring routers can't map their
> links to links in local router LSA, because they don't know local
> ifindexes.

It is useless now but bird used ifindex earlier to find its interface
and I think many impl. still does.

>
> Therefore, i think about putting local IP address for ptp links with ptp
> addresses (i.e. merging the patch i sent before). Although it could be
> argued that it is contrary to RFC 2328 12.4.1 [*], the ifindex value
> is useless and using local IP addres would fix compatibility with Quagga
> and Mikrotik (which seems to have the same problem).
>
> Any comments?

That sounds like a good idea. In a way Quagga already does this as it doesn't
support unnumbered yet but allows /32 prefixes.

However, it could possibly break other routers unnumbered impl. I recall
from when I devised the clever way to find the interface that (at least
for Quagga), any other method would break when using unnumbered on just
one side of the ppp link. I cannot remember the details now. Think
about it and let me know if you come to the same conclusion.
To be on the safe side you could make it configurable.

 Jocke