Once a Cisco IP Phone has received its IP address, VLAN information and TFTP IP address information (see IP Phone Boot Process article) its next mission is to contact the TFTP server to attain its configuration files. There is a specific order in which the IP phone will request these files from the TFTP server.
The following is the sequential order in which the phone will look for these configuration files depending on whether it is registering as a Skinny or SIP device:
1. The phone will request the CTL<MAC Address>.tlv file (this is the Certificate Trust List file if security authentication is configured within the CUCM cluster)
2. The phone will then request the SEP<MAC Address>.cnf.xml file (the phone is hoping there is a specific configuration file for it on the TFTP server)
- If the phone is registering as a SIP device it will request a SIP<MAC Address>.cnf file
3. If a specific configuration file is not available it will request the DefaultXML.cnf.xml file during auto-registration
- If the phone is registering as a SIP device it will request a SIPDefault.cnf file
Note: There are a couple of ways to have a device register as a SIP endpoint.
- Manually configuring a SIP phone with the physical device’s MAC address and choosing SIP as the device’s default protocol
- Modifying the default Enterprise Parameter for auto-registering phones. The default auto-registration protocol is SCCP however this can be changed to SIP under Enterprise Parameters.