[SOLVED] Reverse DNS Problem

[Nicko72]

We are only a small company, our switch is a single HP Procurve 2650 and our ADSL router is a Cisco 857.

I just don't understand how it can work perfectly for a couple of months and then go down for 2 or 3 days and then correct itself. Bind wouldn't contact the root servers for an internal Lan reverse lookup would it? Just wondering if maybe when we see these symptoms if our ISP, thus our domain/IP address has ended up in a blacklist.