re: Port Collisions


Benson I. Margulies (Margulies@SCRC-YUKON.ARPA)
Wed, 14 May 86 14:45 EDT


    Date: Tue, 13 May 86 21:22:49 -0400
    From: Craig Partridge <craig@loki.bbn.COM>

> We here at Symbolics are concerned with the process of assigning TCP/UDP
> port numbers. It is not always appropriate for us (and other vendors)
> to apply for ports in the Czar-controlled first 256 ports. Either
> because of time constraints or issues of proprietary information, we
> cannot always write and distribute an RFC for each of our protocols.

    Why not make the port numbers used user/site configurable? Berkeley
    actually did this quite nicely with a services list, which mapped
    a service name/protocol pair with a port number. Since programs
    use this database (or are supposed to) to find out what port they
    are supposed to us, one could run SMTP on TCP port 25 on the Internet
    but port 243 on some private network if one so chose.

We believe in 'plug-in-and-play' software. Expecting not-very-savy
users to figure out the port usage of all the various programs they are
using is a big expectation.

What if two sites disagree on the port for a protocol? They will never
be able to inter-operate!

We have logical services and protocols that are mapped to ports. The
only way to make that do what you want is to use a different protocol
name for each port assignment in use anyplace, so that the database of
hosts can indicate which hosts are going to talk over which ports. This
is an unreasonable burden.

    The advantage is the vendor need not necessarily worry about what
    port you pick for your special application -- it can always be
    changed among cooperating machines.

Its the vendor's job to worry so the user dosen't have to.

    Craig Partridge
    CSNET Technical Staff



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