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From: urlichs@smurf.sub.org (Matthias Urlichs)
Newsgroups: comp.mail.uucp
Subject: Re: UUCP path cost reduction
Message-ID: <2r-/e2.s9@smurf.sub.org>
Date: 9 Aug 90 16:15:20 GMT
References: <1990Aug5.205619.9277@kth.se> <--058L5@ggpc2.ferranti.com> <42693@mcdchg.chg.mcd.mot.com>
Organization: University of Karlsruhe, FRG
Lines: 35

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". [...]
< Thinking about it some, the only objection I can think of is related
< to possible order dependancies in where smail 3.1 looks to try to
< resolve an address.  I can't point to a problem, though.  Is there
< one?
< 
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.

It seems that to be safe, you can only drop paths from your table which point
to UUCP names, but not to subdomains or subdomainized hosts, viz.
anyone	smart!bang!there	(dropped)
some.domain smart!bang!here!%s	(not dropped)
.domain	smart!bing!bang!%s	(also not dropped)


-- 
Matthias Urlichs -- urlichs@smurf.sub.org -- urlichs@smurf.ira.uka.de
Humboldtstrasse 7 - 7500 Karlsruhe 1 - FRG -- +49+721+621127(Voice)/621227(PEP)