Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!amdahl!fai!edb
From: edb@fai.UUCP (Edward Bunch)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: Odd FTP Problem
Keywords: gateway
Message-ID: <1881@fai.UUCP>
Date: 25 Feb 89 00:05:45 GMT
References: <8902221936.AA10826@ncs.dnd.ca>
Reply-To: edb@fai.fai.com (Edward Bunch)
Organization: Fujitsu America, Inc.
Lines: 28

In article <8902221936.AA10826@ncs.dnd.ca> netcoor@NCS.DND.CA (DRENET) writes:
>We have users on network 128.43 who has reported trouble retrieving
>files from several hosts in the Internet.
>	< 425 Can't build data connection: Connection timed out
>Can anyone explain this? I would sure like to understand what is going on
>to create this situation, then I can try to do something about it.
>
>Bob Bradford				netcoor@ncs.dnd.ca


I saw this same problem here on our WAN. The problem was this. We were trying
to talk to a ethernet interface that was on the other end of the machine.

This is a little difficult to explain. Picture a machine with two interfaces
that we wish to contact to ftp something off. When we start the FTP we 
specify a host address of the interface on the far side. That is packets must
pass through the first interface and then through loop-back before arriving
at ftpd. When FTP trys to build the data connection the reverse way it fails.
ie. Loop-Back --> Other Interface -->  Me.
I suppose FTPD wasn't smart enough to avoid the loop-back network on the return
trip.
Solution: Use the interface address on the near side.

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Edward A. Bunch                       UUCP: {uunet,amdahl,sun}!fai!edb
Fujitsu America, Inc.                 DOMAIN: edb@fai.com
Computer Support and Administation.
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