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

[Joakim Tjernlund]

On Fri, 2021-05-07 at 13:09 +0200, Ondrej Zajicek wrote:
> On Fri, May 07, 2021 at 04:53:44AM +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 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.
> 
> I do not think that should be true (at least on Linux). OSPF sockets are
> bound to specific interface using SO_BINDTODEVICE and use SO_DONTROUTE to
> avoid route lookups, so even unicast packets should be sent to specific
> interface. If that really happens, that is worth investigating. What is
> your OS and BIRD version? Did you verify that using tcpdump or similar
> tool?
> 

That may be so, but I still think that the issue reported in 1) is valid bug, don't you?

 Jocke