Core Issue
Cisco 7912 IP phones with phone load 418A become stuck in an Address Resolution Protocol (ARP) storm and cannot complete the registration with Cisco CallManager.
Once stuck, the IP phone does not respond to any key presses and this is displayed:
Configuring CM list
These symptoms are specific to the Cisco 7912 IP phones with specific phone loads, such as 418A.
Resolution
Cisco 7912 IP Phones have a function to protect the phone from a flood attack. This function causes the phone to enter the protection mode and does not reset the Ethernet interface when the phone returns to normal. The Ethernet then enters into an unknown state and keeps sending ARP. This causes the IP phone to cycle through the registration and never register to the Cisco CallManager.
These symptoms are found to be due to Cisco bug ID CSCec65479 or Cisco bug ID CSCec69448. It has been fixed in Cisco IP Phone Firmware version 1.2, Maintenance Release 1. Therefore, upgrading the Cisco IP Phone Firmware to version 1.2(1) should fix the problem.
For additional information, refer to Cisco IP Phone7912G Release Notes for Firmware Release 3.3(6) for Cisco CallManager Version 3.3.3.
