bird and OSPF on p2p

[Ondrej Zajicek]

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.

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?


[*] "For unnumbered point-to-point links, the Link Data field should be
set to the unnumbered interface's MIB-II [Ref8] ifIndex value."

-- 
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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