Date: Wed, 12 Aug 1998 11:22:41 -0500 From: "sysadmin@mfn.org" <sysadmin@mfn.org> To: "'dg@root.com'" <dg@root.com>, "'dhw@whistle.com'" <dhw@whistle.com>, "'dwhite@resnet.uoregon.edu'" <dwhite@resnet.uoregon.edu> Cc: "'freebsd-questions@freebsd.org'" <freebsd-questions@FreeBSD.ORG> Subject: RE: FTP Symptom of Network Problem... Message-ID: <01BDC5E3.91EB31C0@noc.mfn.org>
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OK, thought the final resolution would be of interest to
everyone here, so...
(1) The terminator on the "monitor" side of the coax
was bad.
(2) One of the boxes on the hub *did* have tcp extensions
enabled, although this did not seem to affect anything.
(3) Having replaced the terminator, the problem did *not*
resolve, it merely got "better". I was finally able to
experience the phenomenon myself, and track it down
to the de0 driver ("server" is de0 based, all the rest are
NE2000's). When the de0 driver gets a lot of crc/framing
errors, it "gets lost", literally. In order to recover it, you
have to (a) wait for it, which could take from 2 seconds to
2 hours, or, (b) reset it by bringing it down/up with ifconfig.
I replaced the card with other known good cards, and the
problem did not change. The problem with de0 is specific
to this subnet however, so I did a little sniffing and research
overnight to verify the actual cause/effects here. This error
will only occur when the de0 is operating in an environment
with a lot of *slow* cards using even slower cpus. When the
"bad" de0 card is put in a fairly up-to-date environment
(being 486/100 and higher on the same subnet) it performs
fine (except for the normally complained about recieve
error messages you see on -questions so often). I believe
that the de0 driver needs serious looking at (and I am
*not* qualified to do it, or I would volunteer).
I have only managed to resolve this by scheduling a cron
to check connectivity every minute, and do ifconfig down/up
if it is found to be wanting: not a really good solution.
Please let me know if you need more info on this.
Yours,
J.A. Terranson
sysadmin@mfn.org
-----Original Message-----
From: David Greenman [SMTP:dg@root.com]
Sent: Thursday, August 06, 1998 5:34 PM
To: sysadmin@mfn.org
Cc: 'freebsd-questions@freebsd.org'
Subject: Re: FTP Symptom of Network Problem...
>I am completely out of ideas here. I am also completely
>out of patience :( I have a dozen angry users that I
>can't placate because I can't even verify their problem
>(other than on "monitor"), and I have what looks like a
>physically impossible interaction between "monitor" and
>"server"...
>
>Anyone have *any* (no matter _how_ off the wall) ideas?
A couple of things to try:
1) Make sure that server's ethernet is set to the proper duplex.
2) Check netstat -s on server and look at TCP checksum and other errors.
Do the same on a client machine. Also look at retransmits on both sides;
you should be able to tell in which direction the problem is occuring
by doing this.
3) I didn't see a mention of the type of NIC you were using; whatever that
is, you might try something entirely different in the server and a client
machine to see if that affects the problem.
4) Move server to a different hub port.
-DG
David Greenman
Co-founder/Principal Architect, The FreeBSD Project
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