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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.
You are a life saver! I seriously thought I have bricked a brand new company phone. Thank you so much for a perfect write-up that has saved me big time!
Thanks a lot. After searching through lot of websites, finally I got a SIMPLE Walk-through in your article. You have saved my time. Thank you 🙂
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Is there a way to edit option 150 that was not created as an array to make it an array without deleting and recreating it?
Hi Carl, I just checked and it doesn’t look like you can. I think I ran into this as well. To be honest though it probably wouldn’t be that big of a deal to delete it and recreate. 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.
Thanks for the clarification….here’s a little more information. We are doing a phone migration. Existing phones are in scopes using option 150 with a single TFTP server (i.e. 1.1.1.1). The new phones will be in new scopes that need option 150 to be an array with multiple servers that are different from the current server (2.2.2.2 and 3.3.3.3). If I delete the pre-defined option 150 so that I can recreate it with the array option, what will be the impact to all the current scopes that are using option 150 with a single server?
Hi Carl,
you can test this with one scope by using Scope Options.
Just expand the scope, right-click Scope options and click Configure Options. Check option 150 and add the servers.
Regards,
Tim
The real question is what will happen to the existing scopes that have a single server in option 150 when I delete the pre-defined option and recreate it as an array? I have hundreds of scopes currently using option 150 to worry about.
Sir, can I set up option 150 on mikrotic router for Cisco ip phones.
I have a question… I have environment that has a Voice VLAN already DHCP scope is configured with option 66 pointing to TFTP server e.g: 10.28.2.20 and Avaya phone are running. We need to put cisco phone on the same vlan. So i configured DHCP scope with option 150 pointing to TFTP server e.g. 10.14.10.25 on the same voice vlan. Most of my cisco phones are working.. Couple of phone are picking OPTION 66 which leads to wrong TFTP leading to registration error.. My question is can i force cisco 7841, 7811 phone always use option 150. Please let me know
Hi Jim,
Nice information, I agree with Dave really Life saver.
Regards
Tippu
Hi god
please tell me where can I put the firmware file on the DHCP server?