During a recent engagement, I had ran into an issue updating the firmware version on Lync Phone Edition Devices.
I initially kicked off with checks around DNS, Certificates, Ports and everything checked out but phones would still not update.
Test Devices had been configured correctly (using serial number and one using MAC) – still no joy.
The IIS logs are extremely useful; Jeff Schertz has excellent blog posts on Configuring LPE for Lync and Updating LPE devices which go into reviewing the IIS logs. In summary, it enables you to confirm whether devices are communicating with the device update site running on within the front-end pool, or in our case – NOT.