Linux Server Not Communicating With Most Clients

[SiliconJon]

Running Mandriva 2006.0
Services running include Samba, Squid

ARP table is not obtaining entries from clients that can ping the server
Three clients can ping and access server, but no others can. Those three clients cannot access the internet. Everything worked well through last Thursday. Coming in today the system was down.

We have reset the switches & modem, and even restarted the entire network (workstations, server and all, it's a small network).

The issue does not appear to be IP related, as using working IP addresses on other machines does not allow other machines to connect.

The issue does not appear to be a physical connectivity issue, as switching to known working ports/switches does not alleviate non-connecting clients

It seems as though the issue is with MAC addresses, perhaps the MAC addresses have wound up on a forbidden list? We're pretty lost for a solution...any help is greatly appreciated.

[jkrohn]

Are you running msec? This happened to me years ago, and I think msec was the cause. It did drop the MAC into a deny list.

Check your IPTables, they could be causing the problem.

[SiliconJon]

I'm second guessing myself now. Some of the ports for the network have so much interference running through them they cancel out the tone generator....but then some of the non-working ports don't have that issue.

[SiliconJon]

I didn't post my discovery the next day, how rude of me. It was one of the switches. While both switches had working ports, I discovered after removing all the connections and doing a port by port check on both switches that when disconnected from each other, one of the switches would not work at all. It was that switch that was polluting almost the entire network with massive noise interference. Exactly why it was behaving in the way it was is beyond the scope of my intended analysis, as a replacement switch resolved all the issues.