Recently had a issue where Lync phones (Polycom CX600) using number and pin where unable to download the CA certificate chain. Tethered phones worked fine. Some network packet inspection revealed that the DHCP server did not provide any of the options 43 information. The client (phone) asked for the correct vendor class “MS-UC-Client”, but there was no response from DHCP server. To add these options to the DHCP server we used the same script as we always use, so it was sure there was nothing wrong with the server. Asked the crew running the network equipment to check but they did not notice anything being blocked. 

Went to the server and checked out server options :

This fooled me for a while. I did’nt notice this showd me the value of option 001 – “UCIdentifier”. Some more hair pulling. Finally looked at Vendor Classes for IP4.

Getting used to these hex values I did’nt notice anything wrong, but to be sure I went to another server (Windows 2008R2) to compare.

Dooh!.. So now I changed the value of my problem server. A reboot of the Lync phone – login success. I Wonder if this a bug in our script or in Windows 2012R2. But any issues on standalone Lync phone – check your DHCP .