[sclug] the case of the exploding switch

[Martin Summers]

The only other things I can think of that have not been mentioned yet are:-

1) Make sure the metal case of the switch is well earthed if possible. I've lost some switches in the past due to poor earthing when lightning strikes occurred in the area.

2) Mains power - Anything that can smooth the mains power feeding into the switch may help. A cheap low power UPS may help you a lot here.

3) I have not seen a large switch (i.e more than 8 ports) be written off completely yet by anything pushed down an RG45 cable - which includes mains power (....don't ask !). Smaller, non-intelligent models, I have seen glitch due to broken network cards, which can sometimes "jabber" continuously.  I have seen this on small 100 Mb/s switches as well as older 10 base 2 half-duplex old-style ethernet switches (which often have BNC connectors on them).

4) A long shot - Are there any strong magnetic fields close to where the switch is housed ? I have found that big water switches for central heating or thermostats can generate big enough fields within 12 inches or so that can really badly affect  computer gear.

....and I think the only other thing that no one has mentioned so far is "Aliens" ;-)

Regards,

Martin


-----Original Message-----
From: sclug-bounces at sclug.org.uk [mailto:sclug-bounces at sclug.org.uk] On Behalf Of Tom Carbert-Allen
Sent: 02 July 2008 16:11
To: sclug
Subject: [sclug] the case of the exploding switch

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.

TCA