Cisco IP Phones identify themselves using DHCP Option 60 - for example a 7940 sends 'Cisco Systems, Inc. IP Phone CP-7940G' in it's DHCP discover/requests. With other DHCP clients using vendor classes allows me to customise the DHCP offer/ACK for specific clients (using a Windows 2003 DHCP Server). I attempted to configure this up recently and it appeared to work - i.e. I was only replying with Option 150 to the Vendor Classes I had configured (7940, 7960 & 7970). However when I installed a new IP Phone it wouldn't register with CCM. I did a bit of playing around and found the TFTP server IP address wasn't in the phone, I could see the DHCP server replying correctly with the Option 150 embedded in Vendor Specific Info Option 43. I then modified DHCP to send Option 150 to all clients and the phone registered OK. I then changed DHCP back and the phone continued to work after several resets. I then did a factory reset on the phone and again it didn't work.
From this I can only conclude that Vendor Classes don't work with IP Phones, either that or I am configuring it wrong. The configuration of the DHCP Server is the same as I use for LWAPP AP's (obviously different vendor class & options). I am running the latest SCCP code on all the 7940/60 & 7970's.
Has anyone sucessfully used Vendor Classes with Cisco IP Phones?