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[ Followups to comp.mail.uucp ]

[Bushnell]
# This allows us to handle two cases of passive routing: where we are given
# only an address and no path at all, and where the next hop of the path is
# unreacheable.  In the second case, we are justified in rerouting since the
# original path was invalid.

You are certainly justified in finding a route to the first host in the
path (or the only host in an address) is not a direct neighbor.  There is
great controversy over the practice of peeking ahead, beyond the first host
in the path, no matter what kicked your mailer into that mode.

Canonically, this is usually put: "given a!b!c!user, go ahead and get to 'a'
by any means available, but don't assume that your 'c' is the same as the 'c'
known to 'b'".  Details such as 'c' being a fully qualified domain are not
really that interesting, since your route to that fully qualified domain may
not be as good as the one that's being chosen, and you have no way of knowing
that unless you monitor all the links as they go through their daily dance of
the yo-yo.

Forgive me, everyone, if this seems like I'm picking nits.  The word 
"reroute" in the above-quoted text can be taken two ways.  I support one
way, and oppose the other.  The difference seems very important to me.
--
Paul Vixie
Work:    vixie@decwrl.dec.com    decwrl!vixie    +1 415 853 6600
Play:    paul@vixie.sf.ca.us     vixie!paul      +1 415 864 7013