[SOLVED] Reverse DNS Problem

[Nicko72]

Hi Everyone,

I am new to the forum so be gentle.

We use ISPCP Omega on our corporate LAN and host a couple on intranet pages and our company email. That is beside the point as I don't think this is where the problem is.

We have an intermittent reverse DNS problem. Anything that does a reverse DNS lookup is very slow, however it only happens for a day or 2 every month or so. I am at a total loss, and so is the consultant that charged us $500 to say we had a reverse DNS problem, which I told him when he first arrived.

Symptoms: Sending email messages take 20 seconds from Windows clients, its usually instant. Our older network scanner times out and can't connect to the network to send scanned documents, I can't change its timeout time, when logging in to one of our servers via Putty there is a 20 or 30 second delay from entering username to the password dialog. Nslookup from windows results in both of our internal DNS servers timing out, dig from windows works instantly and returns expected results.

I have run nmap on the network just to make sure a staff member hasn't brought in a device that could be causing a conflict. I used a packet sniffer yesterday, and will compare its logs once the network is back to normal, which I expect it will be tomorrow.

Nothing at all on our network has changed, I just don't have any idea where to look now, can anyone make any suggestions? Would a failing NIC on a workstation cause something like this?

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I should add, symptoms remain when all workstations are shut down, and I turned off SAMBA.