Alrighty here's my situation. I need to setup a DNS server to host the DNS info for my company's domains. I have two physical servers, one will obviously be the dns server, and the second is going to be a mirror backup.

The company I work for has two internet connections, a T1 line and a cable modem. I need the DNS server to automatically detect when the T1 goes offline, and begin routing traffic to the cable modem's ip. Basically I'm setting up like an auto DNS failover.

So here are my questions.. Is there a software suite I could install to manage the dns settings and auto failover for me? I know how to configure BIND zone files and configure a DNS server manually, but how would I go about automatically switching the zone file to point to the cable modem's ip in the event of a T1 outage?

Any suggestions, tutorials, advice would be much appreciated.

Edit: I will be installing CentOS 4.3 on the servers.