what could be causeing this?

[e_g_r]

Welcome to Network hell part3

After lunch today i lost all conectivity on our network.

Some but not all of our switch's were flashing like mad, usual symptom of a little darling connecting 2 wall outlets with a patch cable.

Searched high and low in all IT labs, offices, comms cabs etc but can't seem to find the loop.

Re started switchs, tried them one by one but still no connectivity.

Next guess spyware/virus.

Can you get internal DofS attacks?

Even re booted the servers.

Left still no connectivity

Any ideas (however mad) would be much appreciated.

[CyberNerd]

enable STP on the switches.
enable broadcast storm control on the switches
use ethereal to monitor broadcast traffic - look for anything suspicous like a single mac address broadcasting *lots* to the network.
yes you can DOS an internal network.

[e_g_r]

Cheapskate school has just dumb switch's

[CyberNerd]

probably like you suspected its a looped cable.
check if the switches have any sort of interface at all - some dumb switches have rs232 but no web interface - you may be able to hyperterminal/minicom into them ?

get ethereal http://www.ethereal.com/ and start looking at the traffic ( look for the broadcasts) if you know the macs of your switches you can narrow it down.
otherwise unplug switches until it stops.
The get some cash from the development fund....

[edie209]

I had alot of problems like this last year, over the summer holidays I had a company in to add more network points and they found many conections at the back of patch panels loose and some flapping around.

This term the network has been really stable (i did upgrade all my switches though) but if it carries on its got to worth looking at for the time it could save you.

good luck

[andy]

Why don't you...

Take 1 switch out of the network at a time until it settles. Put the offending switch back into the network and remove one connection at a time until it settles - and that should lead you to the offending outlet where you might find the "looped" patch cable that maybe you missed - or something amiss on the machine connected to it?

Maybe you've already done this.




Andy

[e_g_r]

The answer seems to be -

a dodgy netgear switch

2nd one this week it seems, lucky they are on 5 year warrenty.