Core Issue
Cisco IP phones run their own operating system, which is stored locally in flash memory. This copy of the operating system loaded into the phone's flash memory is known as a phone load. Cisco IP phone loads are typically geared to work with a particular version of Cisco CallManager. Cisco CallManager has a built-in method to automatically upgrade the version of the phone load on phones whenever the phone registers to the CallManager server. There is no automatic downgrade function.
Here are two ways the phone can get into the above state:
- The Cisco CallManager server has been downgraded, and the phones registering to that server still have the load from the later version of Cisco CallManager.
- A Cisco 79xx phone running 3.0(x) firmware is connected to a network running both 3.0(x) and 3.1(x). Cisco CallManager servers with the DHCP boot server point the phones to the 3.1 TFTP server, and auto registration is enabled.
The phone starts up and broadcasts for a DHCP server. The DHCP server responds and gives the IP phone the TFTP address of the 3.1 server. The phone is automatically upgraded with the latest 3.1 load for its model, as would be expected in an upgrade situation. Configurations on the phone, however, direct it to try and register itself to the 3.0 Cisco CallManager. This is where the problem occurs.
Resolution
These are among the workarounds for this problem:
- If possible, downgrade to 3.0-based phone loads before downgrading the Cisco CallManager server to 3.0(x).
Note: Make sure that the 3.0 load exists in the 3.1 TFTP path.
- If Cisco CallManager has already been downgraded, edit the SEPXXXXXXXXXXXX.cnf.xml file, replacing the Xs with the phone's MAC address (upper case), and place on the TFTP path. Repeat this for each phone.
- Refer to Resetting 7900 Series IP Phones to Factory Defaults to downgrade the load to the version you specified.
Note: If multiple Cisco CallManager servers are on the network and if DHCP for your segment points the phone to a 3.1(x) TFTP server, you need to manually configure the phone's TFTP address to point to your 3.0(x) TFTP server.
For more information, refer to Cisco 79xx Phone Stuck with 3.1(x) Load, will not Connect to CallManager.
