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

[Ondrej Zajicek]

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?

-- 
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."