Question

A new Cisco IP Phone 8845 is being deployed on a CUCM 12.5 cluster configured for SIP. The phone completes DHCP and downloads its configuration file from TFTP successfully, but never registers. A packet capture on the phone's traffic shows the phone sending a SIP REGISTER to the CUCM subscriber, and CUCM responding with '403 Forbidden'. All other phones of the same model register normally. What is the MOST likely cause?

Accepted Answer

The phone's MAC address / device is not added to CUCM, or device security is misconfigured so the registration is rejected

Answer

The device is not associated with a device pool that has a valid CUCM Group, so the phone cannot reach a call processing node

Answer

The TFTP server is offline and the phone loaded a cached default configuration file

Answer

The phone firmware version is older than the load specified in the CUCM Device Defaults