In scenarios where we have Cisco based Networking infrastructure and some other Vendor IP Voice setup like Avaya etc., inspite of configuring voice VLAN on Cisco Switches ,we notice that configured voice VLAN is not correctly provisioned to the IP phone. Still the IP phone is part of data VLAN and not Voice VLAN. A second look at Switchport configuration also does not show any configuration anomaly.
Below is the configuration on Cisco Switch –
SW1(config-vlan)#int range gi1/0/10
SW1(config-if-range)#switchport access vlan 10
SW1(config-if-range)#switchport voice vlan 20
On careful analysis we diagnose that since CDP (Cisco Discovery Protocol) is running on the switch, non-Cisco devices can’t be learnt by catalyst Switch since the protocol is Cisco proprietary.
Next we will configure LLDP (Link Layer Discovery Protocol) referred to in the IEEE 802.1AB specification and Open standard protocol unlike CDP.LLDP should be able to learn the Avaya phone (or any other non-Cisco IP Phone) and also will know knows how much power to supply to it. The phone will also discover what the voice VLAN ID is.
The configuration to enable LLDP is given below –
This enables LLDP using the default settings, which is sufficient for basic setup. The diagram below is shows the end state on how non-Cisco IP phone and Cisco Switch communicate and discover each other. Thereon power and Voice VLAN parameters are shared –