Switch interface config for IP Phones

Question

I have seen both of the following methods of switch interface configuration for supporting IP Phones.

 switchport access vlan <data-vlan>
 switchport voice vlan <voice-vlan>
 switchport mode access

and

 switchport trunk native vlan <data-vlan>
 switchport trunk allowed vlan <data-vlan>,<voice-vlan>
 switchport mode trunk

Can anyone provide a good pro or con of standardizing on either method or does it just come down to a matter of personal preference which one you should choose to implement?

Answer 1

The first method also works for Avaya phones - only they must have the proper DHCP option strings on the data vlan to know which voice vlan it should try and tag its traffic to afterwards.

I usually add #sw host (which adds spanning-tree portfast and sw mode access automatically when configuring ports)

Portfast allows the port to go directly into forwarding state when the interface is up - otherwise you're going to be waiting 45 seconds per port!

Answer 2

I prefer the latter, as it allows easy addition of new VLAN and does not introduce new concepts.

However the former is needed, if you want to use CDP to communicate the voice VLAN to the phone. Otherwise normal behavior is that phone will first boot in data VLAN, then get instruction from DHCP to change VLAN, and then it'll boot again in voice VLAN.

Answer 3

The first is the Cisco Way™ -- only works with cisco switches and cisco phones, and requires CDP (as that's how the phone gets the voice-vlan information.) The second will work with any VoIP phone configured to process (and strip) the VLAN -- how it gets configured depends on the phone.

[They're functionally identical at the ethernet level.]

Answer 4

I prefer the first method when using Cisco phones on Cisco switches. This naturally allows the use of CDP for QoS (auto-qos).