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'[EE]: Faulty 100 mBps Ethernet LAN - Help desparat'
2002\03\27@200724 by Russell McMahon

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A friend is having MAJOR network relaibility problems on a 100 Mbps ethernet
network using all 3-Com equipment. These problems have risen sudenly and
recently.

His concluding pargraph says

> Unfortunately, try as might I can find no sign of any diagnostic software
> for testing local Ethernet networks.  I can find any number of utilities
for
> testing remote networks (i.e. Internet) but nothing like what I think I
> need.  This I find strange.  I would have expected to be able to find
> utilities to test throughput and error rates etc.

Anyone know any useful software for this purpose (prefaerably (of course)
free but anything worth paying for also would be nice to know about ?

Rest of his comments attached for information.



       Russell McMahon

________________________________________________

> Russell,
>
> I am tearing my hair out here and rapidly becoming suicidal.
>
> Since returning from the US my PC at work has been increasingly unreliable
> and has now reached the point where I can't get more than a few minutes
work
> done before any one of many applications crashes.  Up until now the
crashes
> have been benign (in the sense that only my time is wasted in rebooting)
but
> as of this morning I had a crash which has corrupted a PADS schematic file
> and cost me a morning's work.
>
> My strong supsicion is that the crashes occur following an attempted
access
> over the 100-Mb Ethernet network to the our central server.  Other
machines
> on the network seem to be able to access the server without similar
> problems.  The machines all have 3COM 3C905B NIC's and the hub is a 3COM
> OfficeConnect TP800.  Both my machine and the server are running Win95.
The
> other machines run WIn98 and WinME.
>
> In some cases I get an error reported by the application about 30 seconds
> after the machine has "locked up"  - and I can then recover by allowing
> Windows to shut down the application.  This doesn't always work however
> since the application concerned will often then not restart at all or will
> crash immediately after starting.  In most cases I can recover from the
> crash by rebooting my PC, however in some instances it has also been
> necessary to reboot the server (most applications and most data reside on
> the server).  A possible explanation for the need to reboot the serever
may
> be that corrupt file data may be getting into the server cache.  As far as
I
> know there is no way to manually flush the server cache so its difficult
to
> prove the theory.
>
> The problem seems to have gotten worse as time goes by.  A supposedly
> comprehensive diagnostic ran on my machine all night without finding any
> problems, but it doesn't test the integrity of the Ethernet network.  The
> fact that my machine seems to run OK stand-alone, and that other machines
on
> the network don't seem to be afflicted, suggests to me that my 100-Mb
> network connection is the probable source of my problems.  Note that the
> network is 100-Mb and so is a star topology (with a central hub).
>
> Unfortunately, try as might I can find no sign of any diagnostic software
> for testing local Ethernet networks.  I can find any number of utilities
for
> testing remote networks (i.e. Internet) but nothing like what I think I
> need.  This I find strange.  I would have expected to be able to find
> utilities to test throughput and error rates etc.
>
> Any ideas ?
>
> Regards,
>
> Ken Mardle

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2002\03\27@212623 by Herbert Graf

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Umm, generally with NICs you treat them as disposible, if they cause a
problem you replace them.
For diagnostics get Linux, you can do pretty much whatever you want with
Linux, provided you have a NIC that supports what you want to do (ie. packet
sniffing). TTYL

> {Original Message removed}

2002\03\27@214327 by Patrick J

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> > Unfortunately, try as might I can find no sign of any diagnostic software
> > for testing local Ethernet networks.  I can find any number of utilities

There are such progs avail but they cost a bundle and I dubt you will have
any use for them. Better to start trouble shooting from scratch
If you want to make 100% sure your cabling is 100% ok, its best to get some
local company to test it with say a Fluke instrument and certifie it.

> > My strong supsicion is that the crashes occur following an attempted
> > access over the 100-Mb Ethernet network to the our central server.  Other
> > machines on the network seem to be able to access the server without similar
> > problems.  The machines all have 3COM 3C905B NIC's and the hub is a 3COM
> > OfficeConnect TP800.  Both my machine and the server are running Win95.

Ok, first of all, using W95 as a server is asking for trouble !
(I have first hand experience from a customer doing that *sigh*)
You can rule out your TP connection (cable) to the server by testing if another
PC gets the same problem if it is connected to the server from your TP-outlet.
If the cabling is done badly stuff like this could happen. Extremely rare if done
profesionally tho. From your description the setup doesnt sound that pro so... ;-)
Tried a new fresh CAT 5e patch cable yet ?

> > crash immediately after starting.  In most cases I can recover from the
> > crash by rebooting my PC, however in some instances it has also been
> > necessary to reboot the server (most applications and most data reside on
> > the server).  A possible explanation for the need to reboot the serever
> > may be that corrupt file data may be getting into the server cache.

Or more likely, that the 'server' aka win95 doesnt release the files since u crashed
out of it and didn't behave as a nice little computor should do (close files)

> > the fact that my machine seems to run OK stand-alone, and that other machines on
> > the network don't seem to be afflicted, suggests to me that my 100-Mb
> > network connection is the probable source of my problems.  Note that the
> > network is 100-Mb and so is a star topology (with a central hub).

Connect to the server from another working PC's outlet... works ok ?
Then it prolly is your cable/connection to the server that is causing all of this.
LAN problems can be due to a number of reasons:
- damaged network card (replace and test)
- damaged TP cable. The patchcable and/or the long one going to the HUB.
- interference from something near the TP-cable
- bad/corrupt NIC drivers
- u have the right cable for 100 MBPS, right ? (CAT5 or better yet: CAT5e/CAT6)
- More than 100 meters to the HUB ? (would violate ethernet specs)
- Broken port on the HUB ? (try another)


Best regards
Patrick J
Datech, Sweden

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2002\03\28@050802 by Alan B. Pearce

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He does have the software disc that comes with the network cards, right? My
memories of dealing with 3Com cards is that there is diagnostic software on
the disk or CD that will test the card in the machine. One of the tests is a
loopback test, which does an internal loopback connection within the card so
that it can test the transmit encoding/receive decoding without going out
onto the cable.

If that works alright, then change the port on the hub he is connected to.
If he now works OK then the port on the hub is stuffed, else his network
card is stuffed. Between those two items you know if it is the hub or
network card and it cannot be anything else as everyone else works
correctly.

The likelihood of a wiring problem is small unless someone tripped over a
cat 5 patch cable and wrecked it, or has been changing the office partitions
around and put a fastening through the cable.

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2002\03\28@061624 by michael brown

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> > My strong supsicion is that the crashes occur following an attempted
> access
> > over the 100-Mb Ethernet network to the our central server.  Other
> machines
> > on the network seem to be able to access the server without similar
> > problems.  The machines all have 3COM 3C905B NIC's and the hub is a 3COM
> > OfficeConnect TP800.  Both my machine and the server are running Win95.
> The
> > other machines run WIn98 and WinME.
> >
> > In some cases I get an error reported by the application about 30
seconds
> > after the machine has "locked up"  - and I can then recover by allowing
> > Windows to shut down the application.  This doesn't always work however
> > since the application concerned will often then not restart at all or
will
> > crash immediately after starting.  In most cases I can recover from the
> > crash by rebooting my PC, however in some instances it has also been
> > necessary to reboot the server (most applications and most data reside
on
> > the server).  A possible explanation for the need to reboot the serever
> may
> > be that corrupt file data may be getting into the server cache.  As far
as
> I
> > know there is no way to manually flush the server cache so its difficult
> to
> > prove the theory.

I did some work for a customer once that used to have an IPX network.  I
replaced the server with a Linux box and TCP/IP naturally.  They had been
using "silver satin" for patch cords (completely illegal in terms of
networks).  This caused all sorts of peculiar behavior including 'blue
screens of death'.

Some things to try:
1) change the patch cords
2) repunch the patch panel and wall plate connections
3) make sure wiring is not running over top of a flourescent light (a bad
ballast can make allot of junk on the line)
4) switch ports on the hub with another machine
5) replace the NIC
6) don't use Win95 for a "server"
7) don't use Win95 for anything  ;-)

Windows (95, 98 or Me) cannot handle an excessive error rate when using
TCP/IP.  It will cause lock-ups and blue screens and other assorted fun.

Find someone with a $2000.00 network analyzer and have them sweep the
connection.  This will tell you allot about the connection.  A cheaper test
is to string a new cable (on the floor of course) between the pc and the
hub.  If the problem goes away, then you've figured it out.

hope this helps

michael brown

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2002\03\28@070626 by Kathy Quinlan

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{Quote hidden}

If he has the disk / CD, it should also have an option in the test utility
to run a local and remote loop back, in remote loop back the same software
is run on two machines (ideally the server and his pc) and shows errors that
occur when the two communicate. I have never used 3 com cards, I use ACER
and aopen (although supplier has changed their brands) and sometimes SMC,
and all had the diagnostic utilities.

Regards,

Kat.


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2002\03\28@173647 by M. Adam Davis

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You might be surprised.

I had the most unlikely cable problem 've ever encountered last summer.
Someone's new computer wouldn't receive email.  They could browse,
access the company network fine, etc, but email always locked up the
computer.  It was the same when I tried telnetting to the pop3 server,
but I could telnet to web servers, etc just fine.

I replaced the driver, ran diagnostics on the card, swapped hub ports,
etc.  the problem (much to the amazement of my doubting colleague)
resolved itself when I replaced the cable.

I suspect that it was probably a marginal network interface in the new
computer (on board, davicom I think, but could've been SIS) coupled with
a marginal cable.  I'm still not sure why the email would have been a
problem except that it would create some of the smallest packets the
interface sees, so it could have been having a fit with dropped packets,
rerequesting them etc.

So far not a problem with the new cable, though.  It really defies
explanation...

If I were in his shoes I'd disconnect everything from the hub but one
computer and the server, then bring up each connection one by one with
some testing.  More likely then not it's a hardware issue.

-Adam

Alan B. Pearce wrote:

{Quote hidden}

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2002\03\28@200526 by michael brown

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> I replaced the driver, ran diagnostics on the card, swapped hub ports,
> etc.  the problem (much to the amazement of my doubting colleague)
> resolved itself when I replaced the cable.

I believe you.  See my post regarding this kind of stuff.

> So far not a problem with the new cable, though.  It really defies
> explanation...

That's the way networks are.  They will do the strangest things when
something is amiss with cabling.  Back in the old days, when we used coax
thin-net cabling (thank God it's gone), these strange problems came up where
I used to work.  Some computers could see some others, some computers were
completely useless, one could see everything and worked just fine.  Guess
which one had the problem.

This guy moved his office around and instead of extending the coax loop (as
he was specifically instructed), he just hooked an extension piece (about
10' - 15') to the Tee connector.  All I can figure is that it acted like a
"matching stub" and caused nulls (from reflections cancelling real data) in
certain spots on the lan.  That (and the silver satin story) are the
strangest things I've seen in dealing with networks.  But tomorrow is
another day.  ;-D

> If I were in his shoes I'd disconnect everything from the hub but one
> computer and the server, then bring up each connection one by one with
> some testing.  More likely then not it's a hardware issue.

This is probably a good idea.

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2002\03\28@202223 by Russell McMahon

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> something is amiss with cabling.  Back in the old days, when we used coax
> thin-net cabling (thank God it's gone), these strange problems came up
where
> I used to work.  Some computers could see some others, some computers were
> completely useless, one could see everything and worked just fine.  Guess
> which one had the problem.
>
> This guy moved his office around and instead of extending the coax loop
(as
> he was specifically instructed), he just hooked an extension piece (about
> 10' - 15') to the Tee connector.  All I can figure is that it acted like a
> "matching stub" and caused nulls (from reflections cancelling real data)
in
> certain spots on the lan.  That (and the silver satin story) are the
> strangest things I've seen in dealing with networks.  But tomorrow is
> another day.  ;-D


This is an ABSOLUTE no-no forbidden verboten must not do etc etc thing in
coax LANs.
Can and will destroy the whole network functionality. Such a "stub" is a
variable fraction of a wavelength long depending on its length, and places
an impedance bumb at that point which can be anything from a dead short to a
very high impedance point and will happily spread echoes across the whole
network. Good fun.

Another interesting tricj is to insert a length of different impedance coax
in the main backbone. Similar effect but not as severe usually as the bump
is better defind (usually 50/75/50 ohms) although the length will affect
what the echoes do. Rather hard to find without a TDR or similar tool.


       RM

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