Loadbalance outgoing traffic over two cable modems in same network

Mel Flynn mel.flynn+fbsd.questions at mailing.thruhere.net
Tue Dec 22 00:46:12 UTC 2009

On Monday 21 December 2009 09:56:11 Nikos Vassiliadis wrote:
> On 12/21/2009 6:03 AM, Mel Flynn wrote:
> > Hi,
> >
> > I've looked over http://www.openbsd.org/faq/pf/pools.html but this
> > assumes two different gateways for the two interfaces.
> > I'm faced with two cable modems from the same ISP, with the same gateway.
> > I can't lagg(4) the interfaces, since specific IP's are bound to specific
> > modems.
> This can probably be fixed from the ISP side. It should probably be some
> antispoofing rule that drops the packets you are sending via the "wrong"
> interface. You could try communicating the problem to the ISP and hope for
> the best...

I'd rather not go that route. However, I might ask the ISP to move swap two 
IP's, so that I have two consecutive IPs on two modems and can use /31 
notation for the pool. Source hash should then work better.

> > So I'm wondering if using stick-address with a round-robin nat pool is
> > really sufficient to do load balancing of outgoing traffic and not get
> > into session problems with various protocols. Has anybody had similar
> > experiences?
> I have no experience on this, but theoretically a state can expire while
>  the upper layers are still active... so, I *think* you may have
>  problems... Of course, you could increase the lifetime of states

True, I'm mostly worried about DNS queries and other UDP protocols. TCP should 
theoretically be fine.
Thanks for your feedback.

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