Inconsistent behaviour if voice VLAN == access VLAN
My customer has been using a working switchport config that included the same VLAN no. for voice & access. This is supported and documented, e.g. here: http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst2960x/software/15-0_2_EX/vlan/configuration_guide/b_vlan_152ex_2960-x_cg/b_vlan_152ex_2960-x_cg_chapter_0110.html#ID74
Now we are in the process of a platform exchange due to lifecycle reasons, with a similar config as much as possible. Surprisingly, the end devices (PC and phone, cascaded) connected to the new switch can't communicate anymore. The LED on the affected ports stay orange, the links are up/up and spanning tree wouldn't start changing state at all (the ports are missing in the 'sh spanning-tree vlan xxx' output). It's important to note that the new switch has the necessary VLANs configured.
As soon as I change the voice VLAN so that it differs from the access VLAN, or, as I remove the 'switchport voice vlan' command, the LEDs turn green and communication starts to flow. So it seems to me that there's some kind of bug or behaviour change on the new switch or its S/W.
Any idea what's happening here?
This is the configuration of the switches:
Old switch (WS-C3750-24PS-S, 12.2(44)SE2):
interface FastEthernet1/0/11 switchport access vlan 173 switchport mode access switchport voice vlan 173 srr-queue bandwidth share 10 10 60 20 priority-queue out mls qos trust device cisco-phone mls qos trust cos auto qos voip cisco-phone spanning-tree portfast service-policy input AutoQoS-Police-CiscoPhone
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