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

[Joakim Tjernlund]

On Sat, 2020-05-23 at 01:54 +0200, Ondrej Zajicek wrote:
> 
> On Fri, May 22, 2020 at 10:59:52PM +0200, Ondrej Zajicek wrote:
> 
> > 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.

I fixed this particular problem in Quagga before suggesting the same change in Bird so
Quagga should be fine, as should FFR as it is derived from Quagga.
This is the commit:
    http://git.savannah.gnu.org/cgit/quagga.git/commit/?id=c81ee5c94f5b34375f3ef276fdb9bde9098e7ecb
> 
> 
> Unfortunately, it seems that at least recent Mikrotik is broken w.r.t.
> 
> unnumbered PtP links, so we cannot reasonably use this patch and we
> 
> would need to find another approach.

well, Microtik is broken to begin with and if you struggle with keeping a workaround in place I would
just drop Microtic compatibility.

 Jocke