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

[Senthil Kumar Nagappan]

 Hi Joakim,
Thanks for your response.
Will try to elaborate point2 with sample config.
1. Config at Router R1
lo interfaceinterface loopback lo has ip addr 100.100.100.125 
eth1for unnumbered borrowing the lo address for eth1 and 100.100.100.126 is the peer addressip addr add 100.100.100.125 peer 100.100.100.126 dev eth1
eth2for unnumbered borrowing the lo address for eth2 and 100.100.100.126 is the peer addressip addr add 100.100.100.125 peer 100.100.100.126 dev eth2
2. Config at Router R2Its identical to R1 config except for the loopback ip which is 100.100.100.126 and the correspondingpeer address config for eth1 and eth2

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 thedb 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 

  
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