We use a Cisco 2800 router with an NM-8AM-V2 (8port modem module) for users dialup applications.
A Vacman RADIUS server is used to authenticate the users.
This all works correctly, however when looking at the logs for the RADIUS server (and the RADIUS debugging on the Cisco 2800) it appears that the Cisco 2800 is requesting authentication from the RADIUS server for a user named "C" every 5 seconds.
Is this some sort of keep-alive that can be disabled on the Cisco 2800? It makes it difficult to locate useful information in the RADIUS logs when it is full of these messages.
I have attached a sample of the debug output from the Cisco 2800.