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ebarrouk

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sporadic network problems, network overload? 3com, dell switches

Network consists of about 30 stations (all XP pro current with updates), 1 large Dell 6600 file server (Win 2003), 1 email server (Exchange 2003), 1 SQL server, 3 large format plotters/printers.

1. All the building wiring is 1.5 year old CAT-6 professionally installed and fluke verified.  

2.  LAN switches consist of a 3com unmanaged gigabit switch (24 port), 1 3com 100/10 old switch (24 port), and a new linksys 10/100 24 port switch.  These switches are connected by crossover cables.  All the heavy users and server/plotters are connected to the 3com gigabit switch.

Problem:  About once a week, everyone on the Gigabit switch loses connectivity to the network.  Everyone loses connection to the servers, b/c they are plugged into the gigabit switch.  This only lasts about 10 minutes, then clears up and everything works great.

I have tried about 3 different Gigabit switches, both 3com and Dell, and it happens with all of them.  I cannot find a reason why, however, this was noticed by one of the users.

This only happens (supposedly) when some of the CAD users are trying to print about 80 large print files at once, to spool on the plotter.  Could this be overloading the network or causing collisions somehow?  

or does anyone else have a good explanation or have something similar happen to them?  I am kinda lost right now.  Thanks
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Computerguy107

Possible bad cable between the switches?
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Frabble
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I agree with Frabble.

I would tend to feel that the problem is with a bad NIC (even if it is in a non PC device) or a driver, as I have seen cause similar problems.

To track down the problem you could try running a network protocol analyzer, like Wireshark (the replacement to Ethereal). The only problem is that you might be capturing a lot of packets before you see the problem. It is possible to analize the trace file and determine exactly what is happening, who is causing it and when. The why is something that would hopefully follow.

Jon
A few questions
Is main file server also your print server ?
What is interface speed on your Printer/Plotters ?
Have you tried to run test to verify user suspicion re large volume printing causing the problem ?
One question...
You said this only happens when CAD printer is in heavy use (easy enough to check, I would think)... and you said that everyone on the Gig switch loses connection... and you said that the printer is on the Gig switch.  If it does ONLY happen when lots of files are spooled to the printer, does the printer also lose its connection?  I think a packet analyzer (mentioned above) is the best place to start, but if the problem is a bad NIC (on the printer?) then chattering and fragments might be flooding the network your packet analyzer won't see them because the drivers for NICs are designed to drop these bad packets.  You don't always see everything with Ethereal/WireShark.  That's why the expensive Sniffer laptops come with a special NIC and drivers that permit the capture of all packets even the useless broiken ones.

These are lightweight switches and I would recommend business grade managed switches, BUT I think the activity you describe should't buckle your network just because someone is sending some big print files.  Since both servers are unreachable, and if it does happen only during a print run then a bad NIC on the printer seems likely, or some freak packet storm which the analyzer WILL detect.

WGhen
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thanks guys, I'll try these suggestions, especially the packet analyzer and the managed switch (I have a new one I have not installed yet).  

I'll post an update once I figure out the problem.