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VMPS and 802.1q Trunks?


A customer of mine has implemented VMPS across their campus, consisting for 3650 and 3500XL access switches.

We have been testing a non-Cisco IP telephone that requires the phone to switch connection to be a 802.1q trunk.

With a PC connected to the data port on the IP phone, the VMPS seems to work on the 3560 switch. This doesn't work on the 3500XL switch. I did some reading and found that VMPS is not supported on dot1q trunks. That makes sense to me, but what doesn't is why the 3560 still seemed to hand off the correct VLAN to the phone.

My suspicion is that the phone was using the untagged VLAN on the trunk and the "switchport access vlan dynamic" command was changing the native VLAN to the dynamic VLAN?

I really have no idea why this works. I was hoping someone with more experience with VMPS could explain why this might work on a 3560 and not a 3500XL?

Thanks in advance!

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