Unnumbered PtP links (Was: Re: OSPF: incorrect path computation for v2.0.5+?)

[Ondrej Zajicek]

On Fri, May 22, 2020 at 07:14:44PM +0000, Kenth Eriksson wrote:
> On Thu, 2020-05-21 at 12:43 +0200, Ondrej Zajicek wrote:
> > This patch should fix the issue, could you try it?
> 
> Looks promising, applied on top of 2.0.7, and a quick test on the 5
> node setup looks correct. Will do some more testing.
> 
> We definitely need this fix in the pending 2.0.8 :-)

This issue has a long history. In 2012, we changed data field for
unnumbered PtP links from iface id (specified by RFC) to IP address based
on reports of bugs in Quagga that required it, and we used out-of-band
information to distinquish unnumberred PtPs with the same local IP
address.

Then with OSPF graceful restart implementation, we found that we can no
longer use out-of-band information, and we need to use only LSAdb info
for routing table calculation, but i forgot to finish handling of this
case, so multiple unnumbered PtPs with the same local IP addresses were
broken.

This patch returned back iface id to data field for unnumbered PtP links
(i.e. reverted back the change from 2012), while doing computation just
from LSAdb info. It fixed your case (multiple unnumbered PtPs with the
same local IP address) and is correct per RFC, but it may trigger bugs
with other implementations (like the one that led to the 2012 change).

Hopefully Quagga/FRR already fixed that issue and perhaps we should add
an option to revert back to the old behavior in case someone noticed a
compatibility issue.

It would be useful if anybody could try OSPFv2 unnumbered PtP links
between BIRD with this patch and other implementations.

-- 
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."
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 195 bytes
Desc: not available
URL: <http://trubka.network.cz/pipermail/bird-users/attachments/20200522/2c64103a/attachment.sig>