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From: les@chinet.chi.il.us (Leslie Mikesell)
Newsgroups: comp.mail.uucp
Subject: Re: UUCP path cost reduction
Message-ID: <1990Aug10.221547.13301@chinet.chi.il.us>
Date: 10 Aug 90 22:15:47 GMT
References: <--058L5@ggpc2.ferranti.com> <42693@mcdchg.chg.mcd.mot.com> <2r-/e2.s9@smurf.sub.org>
Organization: Chinet - Public Access UNIX
Lines: 42

In article <2r-/e2.s9@smurf.sub.org> urlichs@smurf.sub.org (Matthias Urlichs) writes:
>In comp.mail.uucp, article <42693@mcdchg.chg.mcd.mot.com>,
>  heiby@mcdchg.chg.mcd.mot.com (Ron Heiby) writes:
>< One of the questions in the original posting asked whether it was ok
>< to eliminate from the pathalias output all of the paths that began
>< with the system acting as the "smart host". [...]
 
>Yes.
>Consider the following connectivity:
>(<-> : directly connected, ---> : knows path to)
>you <-> smart
>smart ---> .some.domain
>you <-> somebody
>somebody ---> .domain

>Now suppose that mail from smarthost to .domain (if != .some.domain) goes
>through you.
>Now, if you delete all "smarthost" entries, and if "somebody" thinks that the
>best connection to "some.domain" goes through you and smarthost, then you
>obviously have a mail loop.

This shouldn't happen, because smail 3 doesn't re-route beyond the next
hop specified in the path.  If you get mail for you!smarthost!some.domain!user
you will hand it to smarthost without looking farther down the path, and
smarthost will deliver it without sending it back.  What's the problem?
Even if you hand off something to smarthost that is destined for .domain,
smarthost should expand the full path to you!somebody!whatever before
sending it back through you.  Loops only become a problem when the expansion
that others perform is not honored or 2 machines try to use each other
as smart-hosts.  The only difference that I can think of that might
happen because you delete paths starting with smarthost is that you
will run "uuname" for every host name that you don't find in the paths
file before using the smart-host route.  This is, of course, something
that can be changed in the configuration of smail.  If you know that
all direct neighbors are in the paths file, you could eliminate the
"uuname" router.  However, you normally should only have to route
locally generated mail unless someone else is using you as a smart-host.
Mail passing through should already have a next-hop of one of your
direct neighbors unless someone else made a mistake.

Les Mikesell
  les@chinet.chi.il.us