IT Employment

Some of the virii out lately cause piles of ICMP. These tie up router cpu cycles.

You need to clean your PCs. You might be able to isolate your problem PC by doing an extended ping and disconnecting PCs one by one until the time drops.

A packet analyzer is an essential tool for finding out what is happening on a segment.

You can get a free packet analyzer at http://www.ethereal.com/ - it lacks a few of the bells and whistles but does the job.

You can go to http://www.etherscan.com/ and get an evaluation copy of Etherscan.

I have in the past found Etherpeek to be an excellent tool, but it isn't free. http://www.wildpackets.com/products/etherpeek

A couple of other suggestions IF you can access the router.
Check the event log.
Check the route tables.
Check the route tables after disconnecting the suspect segment.

If that segment is not too large, connect the segment to the router but disconnect all other nodes. Add the nodes one at a time and recheck both ping response and events/route tables for changes. If it is a virus, do not assume the first node you find causing a problem to be the only node. Tag and disconnect the suspect node (caused changes in routes or performance when added) and continue the process until all nodes are either tagged as suspect or known to have no impact.