Intermittent 3COM Switch Problems

I have a LAN that comprises of 30 x 3com 4226 switches with a top level 3com 3824 gigabit switch.  All WAN kit is based upon Cisco technologies i.e. 3600 routers, Cisco PIX's etc. to interconnect ten UK offices back to HQ.  I use What's Up Gold to monitor the entire network.  The problem encountered is only apparent at our HQ site.

Periodically I receive reports of loss of network connectivity and What's Up Gold reports the loss of a few switches.  There is never a pattern to which switches are lost, although it usually starts with one or two and increases to several for a 2 to 3 minute period before recovering.  

In desparation we've revamped our three comms rooms (for other reasons as well) to take out the possibility of loopbacks and found the problem to go away for a three month period.  Over the past couple of weeks it's occurred every couple of days, although only for a period of two to three minutes. On Friday 26th Nov we rolled out Symantec's Ghost Imaging Server and when imaging our first PC the network problem occurred.  Having spotted a pattern here we tested the Ghost imaging software after hours on Friday night and found that every time we ran it we lost connectivity with a number of switches.  To confirm whether this was purely a Symantec product problem with our network I used a packet generator to utilise the network by 50% and found I could bring the network down in the same way.  Increasing the generator to 60% I lost all my LAN switches and therefore concluded that the problems we had been experiencing were down the network utilisation.

Any suggestions as to how I resolve this problem or where to start looking ?
What additional information do I need to supply ?

I've exhausted the 3com site and Google groups and therefore have turning to Experts Exchange for much needed help.
wayneinukAsked:
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lrmooreCommented:
Sounds like an issue with duplex mismatches between the switches. I would start by looking at the switch interfaces for signs of high error counts and/or collisions, then making sure all the connecting ports are hard-set to 1000/full-duplex - make sure you do it on both ends of the wire, not just on one end with the other set to "auto".
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EladlaCommented:
If you havn`t done so yet, try installing the 3Com network monitor.
Sometimes it might give you info about the switches that other software doesn`t.
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wayneinukAuthor Commented:
Thanks (lrmoore), will ensure all switch to switch are 1000/full-duplex on Saturday PM (04/12/04) when I've arranged for downtime.  I've checked error counts and collisions and found some switches to have high values, will check again once I've carried out your suggestion.
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wayneinukAuthor Commented:
Thanks, (Eladla), I installed the 3Com Network Supervisor and Director and found that the software will not discover all my switches correctly and the network topology.  It did alert me to excessive collisions on those devices found.  It's almost as if the switches are not learning since a PC moved from one switch to another does not seem to always create a mac address record in the switches table.  I will attempt another discovery once I've configured the switches as suggested above.
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