I was having trouble getting UDT to learn MAC addresses for ports configured on a Cisco 3750 to use the voice vlan. I could see the computer attached to the VOIP phone but not the phone itself. After looking through some pcaps trying to figure out what was going on, my coworker came up with the idea to try setting one port as an access port in the voice vlan and voila, all of the phones showed up in UDT. The port that was configured as an access port didn't even have anything connected. It was one of the SFP ports that we'll probably never use in most cases.
While this is certainly a solution, I don't think it's the best solution. I can't seem to wrap my mind around why this is the case. Can anyone here explain this behavior? Is there a better workaround?
Thanks!