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Old 24th May 2006   #1
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Network Switch problem


Hi

I have a 24 port switch connected to router (which is connected to the internet). Everything was working fine until yesterday, when I got the limited or no connectivity icon. If I connect the router or modem directly to my pc I can connect fine, if I plug it into the switch and connect the switch to my pc I get the error.

I have reset both the switch and router and all lights are on as they should be. The switch indicates activity from the router, however it does not seem to give the computer an ip address. I have checked all the settings DCHP etc. and cannot find what has suddenly caused the problem.

Network consists of:

Belkin 4 port router/firewall - with uplink port
Dynamode 24 port switch (2 Months old)
cat 5 patch panel and cable

Could it be a switch problem or router, is it possible the uplink function has stopped working.

Any help would be greatly appreciated

Many Thanks
Dave

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Old 24th May 2006   #2
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Well, it turns out it was on of the pc's on my network causing the problem. It looks like it crashed because when I turned the monitor on I got nothing, I reset it and once it loaded up I checked my other pc and everything seems to be working again.

I did notice on the switch that the port connected to the crashed pc was showing activity, not sure why if it crashed?

I think i'll now have to look into why it crashed, it has crashed a couple of times recently, (usually just used as a file server) but never affected the network before.

I'm using Zone Alarm and windows firewall on it, not sure if that is casuing problems.

Dave

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Old 24th May 2006   #3
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So if I read your postings correctly: you have a single PC that crashes and while it crashes it does something to the network that cause connection to the network (not just the internet) to fail on the other computers. While the connection fails, the main sympton on the other PCs is that a message pops at the bottom right of their screens (near the clock on the task bar) stating that there is limited or no connectivity.

It looks to me that the problem PC is taking out the switch.

If it was the router, you would get errors in Internet Explorer when you tried to connect to a website. My reading of you posting is that isn't where you are seeing the error messages.

So what could cause this? I think it will be one of two possible causes:
  1. The network card on the problem PC is faulty. This is causing it to send out corrupt network packets to the switch, which is crashing the switch. It is also causing problems for the Operating System on the PC, causing it to crash. As the network packet is sending out malformed network traffic, the switch and other devices on the network are asking to resend information all the time and that is why you are seeing so much traffic on that port now.
  2. You have got a trojan on the problem PC that is sending out Denial of Service packets. That is network packets that are specifically designed to crash network devices.

Of the two, I think the second is the most likely. I'd recommend a thorough scan with an anti-virus app. Personally, I'd create a BartPE boot CD on another PC, get hold of a virus scanner that will work at the command prompt and a set of the latest virus definitions and put them on a USB memory stick. Then boot the PC with the BartPE boot CD, and run the antivirus program on the memory stick.

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Old 24th May 2006   #4
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My System
yes, sounds like a trojan.
also, do not run two firewalls simultaneously. (ZA & Windows Firewall)

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Old 25th May 2006   #5
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Thanks for the replies

I have turned off one of the firewalls to start with, still had the same problem.
I was trying to copy some stuff accross the network and the pc crashed again, this time it didn't affect the switch though.

I have 2 network ports, 1 on a card and the other on the mobo, does the same with both, so will look into the virus suggestion. Norton AV hasn't picked anything up yet though.(it's on Auto protect).

Probably won't get a chance till the weekend, but will post and results/solutions.

Dave

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