Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!SUMEX-AIM.STANFORD.EDU!mrc
From: mrc@SUMEX-AIM.STANFORD.EDU (Mark Crispin)
Newsgroups: comp.protocols.tcp-ip
Subject: re: Odd FTP Problem
Message-ID: <MS-C.604267100.377401575.mrc@SUMEX-AIM.Stanford.EDU>
Date: 23 Feb 89 19:58:20 GMT
References: <8902221936.AA10826@ncs.dnd.ca>
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 22


     I've seen this problem in other forms.  Apparently there are a lot of
"ICMP Destination Network Unreachable" messages getting sent in instances
where network connectivity is broken for only a brief duration (perhaps due
merely to congestion at a gateway).

     Some versions of BSD Unix nuke the connection when this or "host
unreachable" occur; it is reputed that patching location _inetctlerrmap+8 in
the kernel from 0x3341 to 0x0 remedies this problem but I haven't been able to
verify it.

     Since the "425 Can't build data connection" message is coming from the
remote server, it suggests that the problem is occuring when the remote server
tries to open a connection to the FTP client on the 128.43 TOPS-20 host.
Because of this, I'm inclined to absolve the TOSP-20 host of guilt
(particularly in the "Network is unreachable" case), and more likely to blame
network routing.

     Question: could an ICMP Destination Network Unreachable happen when
something like an X.25 virtual circuit limitation is reached?

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