I was recently troubleshooting Avaya phones not going into their correct voice vlan.
interface GigabitEthernet1/0/1 switchport access vlan 100 switchport mode access switchport voice vlan 200
The phone kept on going into vlan 100. I checked CDP and also enabled LLDP which didn’t help. LLDP showed me the phone sitting nicely in the access vlan.
The solution was to place option 176 in the access vlan. The Avaya phone gets this options and then puts itself in the vlan with tagging held within that option.
DHCP Option 176 : L2Q=1, L2QVLAN=200
The above shows L2Q = 1 meaning tag the traffic, and L2QVLAN=200 being the vlan tag.
Straight after this was applied the phones moved themselves in to the correct vlan.