[sclug] the case of the exploding switch

ed ed at s5h.net
Wed Jul 2 18:52:19 UTC 2008

On Wed, 02 Jul 2008 16:11:18 +0100
Tom Carbert-Allen <tom at randominter.net> wrote:

> 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.

You could do it in binary fashion also, keep dividing the blown switch
device by two if you don't have an endless supply of 4-ports.

Also take a close look at the contacts in the switch and look for sings
of problems. Does the switch have that tell-tale smell of
electrical problems?

Just some thoughts...
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