One of the bigger systems that I find myself supporting in my infrastructure is our Unified Communications system from Cisco Systems.
With Cisco's IP phone system the end phone devices are dumb devices, they store no configuration at all and have to be fed up to date firmware revisions.
MGCP gateway has a CUCM group that includes only one CUCM and that the gateway is currently registered.
When changes are made to the configuration in the CUCM database, a message is sent by CUCM to the MGCP gateway instructing the gateway devices to download the updated XML configuration file.
Wireshark opens a pop up window that begins with the GET string from the phone to the CUCM, then we see the 200 OK from the CUCM to the phone and we can look at the config file.
The problem is the option for TFTP server, option 150, is not built a default option on any DHCP servers that I've ever worked with.
Contains a string of 0 or 1 for each line (in this example line button 1 and line button 2 log missed calls while line 3 does not log any calls).
Currently, my script runs with an account that already has administrator rights on the remote systems.
This option enables you to indicate a local server to be used for firmware upgrades, which can assist in reducing install times, particularly for upgrades over a WAN.
If you really needed to propagate out the change afterwards you could just do a select all of your phones and tell them to reset after hours.
That information is passed to the device as an option when it receives its IP address from the DHCP server, much in the same way it learns the default gateway and DNS servers.
As I'm sure your voice guys will tell you the IP phones will need to go on their own VLAN and defined through the network, an item for another post.
If not, check your DHCP bindings and confirm the phone is getting an address with the option 150 set.
Because TFTP operates on top of UDP, there is a high risk of corrupted load file delivery at the completion of the TFTP process due to undetected data loss in the network.
Once you have your laptop and the phone in the same vlan with the TFTP server running, you should start to see the magic happen.
Scroll down until your see option 150 and check the box, and finally enter in the IP address(es) of your TFTP server(s) and you should be good to go.
