Path: utzoo!mnetor!uunet!seismo!sundc!pitstop!sun!decwrl!decvax!ucbvax!TCGOULD.TN.CORNELL.EDU!swb
From: swb@TCGOULD.TN.CORNELL.EDU (Scott Brim)
Newsgroups: comp.sys.proteon
Subject: split horizon vs. static routes
Message-ID: <8802012206.AA21583@tcgould.TN.CORNELL.EDU>
Date: 1 Feb 88 22:06:01 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 26

I suspect this deserves to be called a bug......

We have a few static network routes installed in our campus gateways
(p4200s) in order to take care of some miscellaneous non-routing
gateways attached to some ethernets.  The way we do it is we put a
static route in the p4200 (or p4200s) which lie between the campus
backbones and the ethernet that particular box hangs off of.  The
problem is that with version 7.4 we also have "split horizon" route
announcements.  What we get, then, is 

	oddnet--oddgw--ethernet--p4200--backbone-->world

What we see is that the p4200 will announce (RIP) its static route out
with a reasonable metric to the backbone and the world, but in the
direction that the static route points (toward the ethernet) it always
sends out a metric of 16 (infinity).  That means that since 7.4
anything which is between the p4200 and the odd gateway (in this case
that means on the shared ethernet) has no route to the odd network,
despite the p4200's static route.

If there were some way to work around this with reasonable engineering
I wouldn't consider it a bug.  I just don't see a good solution though
(I don't like the idea of having to have a static route in everything
on that ethernet).  I believe that a static route entry should not be
affected by the split horizon rule.
						Scott