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DHCP option 150
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. All of this is fed to the device via the transfer of a configuration file from the TFTP server integrated into Cisco Call Manager.
So how does the phone know where to find this TFTP server? 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. 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.
I’m going to proceed here as if you’re working with a bare server that is already a member of the domain. If you already have done some of these steps, please feel free to skip ahead to the parts you need.
- From Server Manager choose to add a role and choose DHCP Server.
- Once you have the DHCP Server installed and authorized, launch DHCP Manager.
- Next you’ll need to go ahead and create a scope for your Cisco IP telephony devices. 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. Setup the scope as you normally would with all the relevant information.
- Now you will need to right click on IPv4 and choose “Set Predefined Options…” Here you will find all of the options are predefined like Router and DNS Servers, but it also lets you create new ones.
- Now click the “Add…” button in the Predefined options window. I always enter in the information exactly as shown below, but honestly the Option number, type as IP address and array checked are the only things that matter, the rest you set as you like.
- Once done, OK through the Predefined Options windows until you are back at DHCP Manager. Now you will need to right click Scope Options under your scope and choose “Configure Scope Options…”
- 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.