For redundancies sake, I have one radius server at the co-location facility and one at my home.  The one at my home is connected to the Internet via a T1.

The T1 circuit connecting the radius server at my home failed, and the radius server at the co-location facility was also unresponsive.  This caused about an hour long authentication failure for dial-up and DSL subscribers. Existing connections would not be affected.

I have restored the backup server to service.  The machine was up and running but for reasons unknown both radius and MySQL daemons had died.  Both restarted without incident and the backup server is now processing authentication requests.  A ticket has been generated with Isomedia to restore the T1 to service.