Actually, you can specify the target port in the SRV resource record
(RFC 2052), which is currently Experimental and more or less ignored
by everyone. However, there is a move afoot to put it on standards
track (draft-ietf-dnsind-rfc2052bis-00.txt). If that happens and it
gets widely deployed, then in a few years it might solve your problem.
Donald
From: John C Klensin <klensin(_at_)mci(_dot_)net>
Date: Thu, 12 Nov 1998 23:32:00 -0500 (Eastern Standard Time)
In-reply-to: <364B6FED(_dot_)C1922BEC(_at_)taxxi(_dot_)com>
To: Alexey Melnikov <mel(_at_)taxxi(_dot_)com>
Cc: ietf-smtp(_at_)imc(_dot_)org
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On Fri, 13 Nov 1998 02:31:58 +0300 Alexey Melnikov
<mel(_at_)taxxi(_dot_)com> wrote:
There are also multiple reasons why this would be a bad idea.
They include reintroducing a reason for explicit source routes
Why?
So that one can specify different ports at different hops. If
there is enough requirement for this to introduce a protocol/
syntax change, then there ought to be enough that I might want
to use it down a successively-better-preference MX path. But
the DNS can't accomodate different port numbers, so one might
want
<@host1:port1, @host2:port2, @host3: user(_at_)host4:port4>
note this also points out a little problem with the syntax you
suggest.
I am not insisting on using <username>@<server>:<port> syntax.
I would like to know how this idea was implemented (if it was) : server is
specially configured to connect particular server on non standard port (i.e.
the use of configuration files), server uses DNS Well-known service record or
Service Location Protocol, other ways.
To the best of my knowledge, this has been done by private
client-side (more generally, sender-side) configuration and out
of band communication about the ports to use. There are no DNS
or SMTP facilities for specifying funny ports in an address.
john