One of the new features available in Cisco UCM 8.x is Extension Mobility Cross Cluster. With this feature, a user who has a device profile on one cluster can log into a phone controlled by a different cluster. Many customers were quite pleased when this feature became available. This feature definitely works when the person moves from site to site, but what about when the phone itself moves from site to site? Well, let’s walk through it.
The phone will power up at the new site, load it’s firmware, determine the voice VLAN ID using the Cisco Discovery Protocol (CDP), get an IP address via DHCP, and then contact the TFTP server. At this point, the phone should encounter a problem. Since this phone has not been configured in the Cisco UCM database, the will be no phone configuration file on the TFTP server. If auto-registration is enabled, that process would then kick in.
Cisco gave us at least one option. We can configure the TFTP server to perform a sequential search of the “Alternate Cisco File Servers” in hopes of finding the configuration file requested by the IP phone. These Alternate Cisco File Servers are configured under the TFTP Service Parameters in CUCM Administration. This is how you tell the TFTP server where to proxy a request if it cannot serve up the file locally.
In some environments it might be helpful to have an on-site TFTP server to reduce delay or lessen load on the central TFTP server. As you probably know, a Cisco router can be configured as a TFTP server. However you would need to manually copy the required files from the central TFTP server to the local router as this doesn’t happen automatically. You would also need to manually copy the files when a change to an IP phone’s configuration takes place. Lastly, don’t forget to make sure the firmware and locale files are also present on the router along with the “defaults” file.