ECMP/multipath support

Joakim Tjernlund joakim.tjernlund at
Tue Dec 21 09:41:22 CET 2010

Ondrej Zajicek <santiago at> wrote on 2010/12/21 03:38:35:
> On Tue, Dec 21, 2010 at 01:20:41AM +0100, Joakim Tjernlund wrote:
> > > Or if you means case like: Router A having two interfaces (with IP1 and
> > > IP2)  connected to the same network N, router B also connected to
> > > network N may use multihop to IP1 and IP2 for routes that goes through
> > > router A. It is true that in that case BIRD does not use multihop (and
> > > there are some other corner cases, where multihop also is not used
> > > although it could be).
> >
> > yes, this one. Seems like multihop only works for ptp links then ?
> > perhaps not a big deal? I would think users of ECMP would like this case
> > to work too though.
> This scenario expects there is just one network between the routers and
> one router has two interfaces to that network, which is generally
> configuration not well supported by OSPFv2. So i don't think it is a big
> deal.

Not common but very cool if that worked too. You get higher bandwidth that way
and you are compliant with the OSPF spec too.

> But now i realized that a scenario with two parallel links where both
> are bcast (not ptp) would not work with ECMP, which is probably what
> you wanted to notify me of. This would be fixed.

Precisely :)

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