In Cisco Unified Communications Manager, often times werequire to upgrade or downgrade the firmware of a high number of IP Phones, onbusy systems where the TFTP server it is being used to provide firmware to theIP phones, sometimes will not be possible to just change the default firmwareload on your TFTP.
To solve this problem we can create an external TFTP serverwith the firmware we need and point the IP phones to use that server.
Here are the steps to configure the external TFTP using anopen source TFTP.
1.Installthe TFTP server.
2.Download the firmware files.
3.Configurethe TFTP server.
4.Configure the DHCP server.
5.Configure the XMLDefault.cnf.xml
6.Perform afactory reset or point the IP phones to the correct TFTP.