Re: hidden interface (ARP) 2.4.20

From: Bill Davidsen (
Date: Wed Dec 11 2002 - 11:15:29 EST

On Tue, 10 Dec 2002, Roberto Nibali wrote:

> > I have in mid multiple ISPs for redundancy, perhaps a pair of OC12s or
> > similar. Sites would be reachable from either, but fewer hops to one or
> > the other. When the client connects, it avoids asymmetric routing to reply
> > on the same router.
> I understand everything but the last sentence. You have a couple of
> redundant ISP links which can all act as a router to the Internet, the
> only difference is that if you go over some of them you need less hops.
> Now in order to avoid asymmetric routing you need the hidden patch? I
> apologise for being so narrow minded but I still don't get it.

Don't. You are right about this one, a client originated connection will
have an ARP entry and route back by the original route. Connections
originated on the dual-homed system might put a packet out on either NIC,
from any IP, that's a different issue, and the whole hidden interface
patch really doesn't address it.

I was mixing things from two problems I've seen, sorry for any confusion.

bill davidsen <>
  CTO, TMR Associates, Inc
Doing interesting things with little computers since 1979.

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