OSPF interfaces issue

Jigar Mehta jgmehta at ncsu.edu
Sun Oct 11 15:20:38 CEST 2015

I tried some additional debugging with this setup :
(Note : All interfaces are tap interfaces)

eth-0 ( - ospf  and bgp configured
eth-1 ( - bgp
eth-2 (
eth-3 ( - bgp

Result : OSPF is up and running, BGP is in established state

Changed OSPF to be on eth-1. It stays in alone state. (Packet capture shows
hello packets being received from neighbor. Neighbor adds us(bird) and
changes to init state but bird seems to just not receive packets . Doing a
'netstat -an' , the receive and send queue are empty inspite of packets
being received on that interface.

Then when we change eth-0 to other subnet ( , OSPF on eth-1
immediately comes up , bgp on eth-1 is also in established state. But BGP
on eth-0 times out.
I think the kernel does not like the interfaces in same subnet ? (just a
guess here).
In my device protocol , i am just scanning interfaces every 10 seconds. I
have a custom forwarding plane and so, dont use kernel protocol( that does
not seem to be the issue here though).


On Sat, Oct 10, 2015 at 6:15 AM, Ondrej Zajicek <santiago at crfreenet.org>

> On Thu, Oct 08, 2015 at 06:48:19PM -0400, Jigar Mehta wrote:
> > Hi, I wanted some help regarding a problem I was seeing when i had
> multiple
> > interfaces with same ip address . I have multiple routing domains setup
> so
> > i have valid cases to have same ip address on different interfaces (so i
> > have seperate routing tables for each instance). When  I do a show ospf
> > interface for each ospf protocol instance, it seems to correctly dump the
> > interface . When I did a packet capture, it shows incoming/outgoing hello
> > packets, but when I enabled debug, i can see that it never prints a
> "hello
> > packet received" message(but prints "hello packet sent") although, i can
> > see the peer sending ospf hello packets.
> > This seems to be a problem with only one instance and not both.
> Hi
> I don't know. I just tested it, works for me. Does the other side see
> sent hello packets? (Should be in Init state.) If you disable the other
> interface with the same address, does the problematic iface start to work?
> --
> 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."

Jigar Mehta
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