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From: mogul@wrl.dec.com (Jeffrey Mogul)
Newsgroups: comp.unix.ultrix
Subject: Re: routing table wierdness
Message-ID: <1990Jul31.184659.6260@wrl.dec.com>
Date: 31 Jul 90 18:46:59 GMT
References: <1990Jul31.005036.17883@evax.arl.utexas.edu> <26B5005F.14260@orion.oac.uci.edu>
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In article <26B5005F.14260@orion.oac.uci.edu> iglesias@orion.oac.uci.edu (Mike Iglesias) writes:
>You might look around for a newly installed system, or a recently
>booted or (mis)reconfigured router that could be causing the
>ICMP redirects.

I didn't examine the routing tables in the original message that
carefully, so they could have reflected a problem of some sort ...
but please note that there is nothing intrinsically wrong with
having your host's routing tables built up out of redirects.

In fact, this is precisely the RIGHT way for things to work, under
current thinking.  Hosts should not know about routing protocols
or routes to non-local networks; rather, a host should know the
address of one or more "default routers", and for non-local destinations
should pick one of its default routers more or less at random (there
is a concept of "preference level" to confuse the issue here, but
one can ignore that in most cases).  The routers know the right routes,
and if a host makes the wrong choice, the router in question provides
an ICMP Redirect referring to the specific destination host.

I believe that recent versions of Ultrix properly handle incoming
Redirect messages.  The other piece of the puzzle is how an Ultrix
host finds the neighboring default routers; right now, you can either
run /etc/routed (which is "wrong" but works) or configure it by
hand (which is wrong but usually works).  The problem is that the
IETF working group on Router Discovery (of which I am a member) hasn't
quite finished specifying a standard for Router Discovery, so you
really cannot blame anyone for not having implemented it.

But within a year or two, Redirects in your routing tables will be
the moral equivalent of fiber in your breakfast: good for what ails
you and practically the only alternative.

-Jeff