ospf ptp link sending unicast packets instead of multicast; peer address config not required

[Joakim Tjernlund]

On Fri, 2021-05-07 at 04:53 +0000, Senthil Kumar Nagappan wrote:
> Hi Joakim,
> 
> Thanks for your response.
> 
> Will try to elaborate point2 with sample config.
> 
> 1. Config at Router R1
> 
> lo interface
> interface loopback lo has ip addr 100.100.100.125 
> 
> eth1
> for unnumbered borrowing the lo address for eth1 and 100.100.100.126 is the peer address
> ip addr add 100.100.100.125 peer 100.100.100.126 dev eth1
> 
> eth2
> for unnumbered borrowing the lo address for eth2 and 100.100.100.126 is the peer address
> ip addr add 100.100.100.125 peer 100.100.100.126 dev eth2
> 
> 2. Config at Router R2
> Its identical to R1 config except for the loopback ip which is 100.100.100.126 and the corresponding
> peer address config for eth1 and eth2

I see, this makes sense. I wonder if this problem would affect true PtoP links as well?

The only thing left then is when you have true PtoP links one does not need a remote address,
that is another issue though, maybe Ondrej can comment?

> 
> 
> 3. Enable ospf on eth1 and eth2 at R1 and R2
> 
> 4. Only one of the ospf adj will become FULL either over eth1 or eth2 and not both
> 
> 5. Since the peer address configurations adds a route to other end loopback address and since the
> db packets are sent as unicast, route lookup happens and db packets wont be sent out from one of the links.
> 
> 6. one ospf adj will be FULL and the other one will stay at EXSTART
> 
> 7. if we use different peer address for each interface then it will work.
> 
> Thanks and Regards,
> Senthil
> 
> 
> 
> 
>  On Friday, May 7, 2021, 12:33:11 AM GMT+5:30, Joakim Tjernlund <joakim.tjernlund at infinera.com> wrote: 
> 
> 
> On Thu, 2021-05-06 at 20:30 +0200, Joakim Tjernlund wrote:
> > On Thu, 2021-05-06 at 17:09 +0000, Senthil Kumar Nagappan wrote:
> > > Hi,
> > > 
> > > I did sent this message a week back but I could not see it in the mailing, moreover just now subscribed to this mailing list, so sending this again.
> > > 
> > > I’m seeing some issues with ospf adj over ptp numbered/unnumbered interface. 
> > > 
> > > 1. For p2p connections, ospf should be sending only multicast packets to allospfrouters, but I see its sending to unicast address.
> > > (From RFC “On physical point-to-point networks, the IP destination is always set to the address AllSPFRouters”)
> > 
> > Agreed, I recall fixing the same for Quagga long time ago.
> > 
> > > 2. For ptp over unnumbered interface, bird requires peer address configuration which is not required from the ospf perspective. Because bird is using peer address and
> > > sending
> > > unicast packets, bird cannot form multiple ospf adj over ptp unnumbered interface between 2 endpoints using same peer address.
> > > Made some quick changes and have attached the patch that addresses the issues. Relaxed the source ip address validation for ptp link in packet.c for now. More validation
> > > can be
> > > added to make it complete.
> > 
> > I don't quite understand what you are saying here, can you elaborate?
> > 
> 
> One thing I recall, BIRD OSPF seems to always require dest IP address for its routes. For a PtoP I/F
> this is optional/not needed so I guess this is a bug in BIRD. Possibly because of bug 1)
> 
> 
>  Jocke 
>