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Network Stacked switches loose connectivity for about 1 minute


Wanted to find out if anyone has seen these issues, if yes please let me know how to fix this.

Detail about our environment:

we use 3Com Switches 3870 48 Port (Product number# 3CR17451-91).  3 of the switches are stacked together with specific 3com stack cable; other 2 switches are connected via fiber connection which runs to other office located down the hall from the server room.  we have multiple VLANs set up on these switches.  1 VLAN we use for server, 2 VLANfor all corporate client computers, 3 VLAN is used for printers, and 4th VLAN is used for internet traffic (VPN users, and all devices that provide any outside connections.  all VLAN can communicate with each other.

Here is a description of the problem that started to happen a while ago:

Over all we are very happy with the performance of these switches.  Lately i have noticed that all of a sudden my compute would indicate that it lost physical connection to the switch and then in approximately less then 60 seconds it would regain the connection.  at the same time all users  on the network that are connected to these switches have the same issues. They drop the connection as if someone would unplug their network cable and in 60 seconds everything becomes normal.  when i looked at the switches during this event, all indicating lights show that the switches are rebooting.  Only they are not actually rebooting since if you do an actually reboot it takes about 5 - 10 minutes for these switches to fully come up.  This happens only on the switches that are stacked together, the other 2 that are located in a the office down the hall  do not drop the connection, but of course since they are connected to the stacked switches via fiber all users loose the connection to the network until the switches come back up.  This is really a strange issue, i looked in to make sure that the switches are running on the latest firmware and software, i tried contacting 3Com support but unfortunately did not get any help.  I suspect that one of the stacked switches is having hardware problems. 3com tech. support had me run diagnostics on every single port of the switch and no errors have been found.

Please let me know if you have seen any similar issues, and if you did please let me know how to possibly resolve this.

Thanks in an advance for all your help.
1 Solution
Aaron StreetInfrastructure ManagerCommented:
dont use a calbe to stack them!!

i had lots of problems stacking 3com so dont any more

mirchevskyAuthor Commented:
so what do you use, just regular Ethernet cable to keep switches to talk to each other?
I have not used 3Com switchs, but I would assume that they have some type of logging function.  I would suggest that you enable as much logging as you can and see what the logs say.

Although we were not stacking them, we had a similar problem once with a Cisco switch.  We had weird loss of connectivity every now and then until one day every 8 minutes we lost access to all servers on that switch.  I was looking at the switch when all of a sudden all ports (execpt for the uplinks) went down at the same time and then started flashing amber and then went green.  The whole process took 30-60 seconds.  Examining the logs we found that one port went down 1st then all the other ports followed shortly there after.  The one port was connected to a Linux box that was miss-configured and was auto-rebooting every 8 minutes.  

Looking at the switch config I found that the person responsible for configuring the switch did not follow our standards.  Instead of putting each port in access mode only, execpt for the uplink ports, they configure each port to be negotiate mode for trunking.  I don't know if it was a IOS bug or not, but since all the ports where in negotiate mode, when any of the ports that were in negotiate mode went up and then down, all of the ports went through the negotiation process.  Once we changed the switch ports access mode only, all of our problems stopped.

Now, I am not sure of the terms that 3Com uses, but "access mode" in Cisco world is a port that uses non-tagged frames and a trunk mode port is a port that uses tagged frames.

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