I just confirmed that my server does have no firewall. The way I tested this is: ON THE SERVER tcpdump udp port 1812 ON THE CLIENT nc -u xx.xx.xx.xx 1812 <mash the keyboard repeatedly to send fake packets> When I do this I send some raw packets to my radius server on port 1812 for testing, and my tcpdump output shows each packet being received just fine. So I don't think this is a firewall issue. Run radtest on the server to verify that the server actually works - radtest bob badpassword localhost 1 <shared secret>. Then run radtest from another client that is on the same network that the AS5400 is on. My guess is that there is a firewall in front of your Linux server running FreeRADIUS. Rackspace typically puts a Cisco ASA firewall in front of a customer's Linux server. When you ran the nc test, was the system that you ran nc from on the same network with the Linux server running FreeRADIUS? They both might have been behind the same firewall. Check with Rackspace to see if there is a Cisco Firewall in front of your Linux server. Tim