[sclug] the case of the exploding switch

Tom Carbert-Allen tom at randominter.net
Wed Jul 2 15:11:18 UTC 2008

Ok so I volunteer to look after a local school network. They have been 
happy with there Linux box server and gateway for the last 5 years 
without issue (using a recycled p3 500) but are now having some very 
weird network problems.

First sign of problem was 4 months ago I arrive on site to find the 
central switch is 100% dead. I figure after 5 years in a hot cupboard it 
just gave up (was only cheapy ebuyer special). I replace it with a US 
robotics unit I was given and walk away expecting at least another 5 
years of trouble free packet forwarding. One month later I get a call 
again and find this switch is now 100% dead too. I then test every 
connection to the switch end 2 end with a cable tester and they all show 
ok. I connect switch number 3 and then test each socket with my laptop 
and they all give me 100mb full duplex and no packet loss. I run out of 
time so leave again very confused.

Today I get a call again and find the switch is not dead but all the 
lights are on (even for sockets with nothing plugged in) and no packets 
are forwarding. I come armed with a HP Procurve this time. I plug the 
procurve in and it lasts 3 minutes before shutting off, with nothing in 
the logs, it just freezes, I reboot it with nothing pluged in and it's 
failing to come up with error about transceiver VRM failed primary test, 
I call HP support for a RMA and they give me one but say I must have a 
shorted cable somewhere or a faulty ethernet device. I plug in another 
?20 ebuyer special cheap and cheerful switch and it works fine for 
today, but for how long.

Can anyone suggest to me how I might go about finding which cable/piece 
of equipment is faulty and causing the switch's to all die? I have a 
basic cable tester but that just test for continuity and pinout 
correctness. All the kit is connecting ok and not showing lost packets.

Thanks in advance for your help.

The only idea I have so far is to buy lots of smaller 4 port switch's 
and use them instead in a switchy mess of interconnects. That way I can 
atleast narrow it down to 3 cables/devices.


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