Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!QueensU.CA!Andrew.S.Hooper
From: Andrew.S.Hooper@QueensU.CA
Newsgroups: comp.protocols.tcp-ip
Subject: FTP incompatibility
Message-ID: <10445*Andrew.S.Hooper@QueensU.CA>
Date: 26 Apr 89 15:38:00 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 23

Following is an FTP incompatibility we recently encountered. I'd
appreciate any comments on the correctness of the two implementations.

A user on host A makes an FTP control connection to host B at address
B1. B also has a second network connection with address B2. The user
requests a directory listing. The FTP server on host B then initiates
a data connection back to host A, but uses B2 as the source address.
Host A is prepared to accept a connection from B1, but refuses to
accept one from B2. Hence, no listings or transfers can be done. The
port number supplied by A is used correctly by B.

Host A runs IBM VM TCP/IP Release 1.2, host B runs Wollongong 3.2.

Nowhere in the FTP RFC (959) can I find a specifcation as to the source
address of the data connection, so I cannot point fingers. It does seem
appropriate to me to reject the mismatching address, as it could be
coming from who knows where, but there may be arguments for not doing so.
Two other TCP/IP packages do not check the source address.

Thanks in advance for any advice.

Andy Hooper         Queen's Univ. Computing Services       Bitnet: HOOPER@QUCDN
                    Kingston, Ontario, Canada        Telephone: +1 613 545 2019