HELP!!! EMERGENCY!!! What is happening to my Network???

Sorry for the alarming heading, but something is going very wrong on my network. First symptoms were people not being able to print. This was weird becuase it was all the network prionters, yet there a several seperate print servers, and even the PCs that are directly connected over the network by an IP port stopped working. Sometimes I could ping these printers, sometimes intermittent ping returns, sometimes nothing. The HP printer in the offce was taking ages to start up, when I remove the network cable it gets to ready state prompto.

Then there is the network switches. They all seem to be flashing weird, like every port is flashing simultaniously and this is on ALL of the switches around school. Those that have configuration pages I am unable to get to them, and I get 'Destination Unreachable' when I try and ping.

The thing that throws me is that the switches must be working to some extent because I can log on, ping the network servers, get on the internet and send you this message, there have been no log on issues reported anywhere. So I am starting to think something sinister is happening, maybe something flooding the network on sertain ports? I am not a network engineer so I don;t know where to start investigating. Is there any software that can give me a picture of my network and where all the traffic is?

Any help at this stage would be helpfull

Thanks!

Sounds like you have a loop. can you try isolating different segments of the network to pin it down?

Try enabling STP too. :)

I agree with simongrahamuk have you pluged in any new network hardware or done any new recableing.

Agree, definately sounds like you have a loop somewhere.

Start by disconnecing one switch at a time from the network. When you have taken a switch down check the network traffic to see if things return to normal. Do this until you find the offending switch, then work through all ports patched into this switch.

Thanks Guys, will try isolating the problem.

Geoff, what do you mean be STP?

Its a feature of managed switches. The full name is spanning tree protocol. Basically it detects loops and deactivates the looping port(s).

If you search the forums you'll find a few threads on the subject, we've discussed it (and network loops) before.

Thanks Geoff, problem is at the moment I can't access the web configuration pages so can't switch it on :(

Most managed switches have serial and telnet based console access.

Then use the method as mentioned by Marco to track down and solve the problem, then switch on STP when it's all better :)

Probably a kid playing silly beggars plugging one cable into two ports! We've had it here, as probably most others have. Most of the points aren't patched into the switch now if they're not being used.

Andy

I am currently going round switching off the ones that I am able to at this time. I take it that when I turn off the offending switch, the others will immediately calm down and return to normal flashine of activity lights?

Yep! Thats correct. However if you are have some throughput on the network then it's possible you have Rapid Spanning Tree/Spanning Tree Protocol working upto a point. But we have had broadcast loops like that to as others have already mentioned. Best to unplug all ports that aren't used to cut down on this ever happening again.


Wes

Only when you turn off the one that has the loop.

Ok thanks guys, this would have to happen when one of my staff is off sick, and the other doesn't work wednesdays :( Will let you know how I get on