Voice Vlan question

[schadmin]

I was curious what the difference between the following 2 configs are? Both seem to work, but I wasn't sure what the fundamental difference of making the port a trunk or not would do?

config 1:

fa0/1

description CISCO PHONE

switchport access vlan 2

switchport trunk encapsulation dot1q

switchport trunk native vlan 2

switchport mode trunk

switchport voice vlan 3

no ip address

spanning-tree portfast

config 2:

int fa0/2

description CISCO PHONE

switchport access vlan 2

switchport voice vlan 3

no ip address

spanning-tree portfast

[Prashanth Krishnappa · Accepted solution]

config 1 is the old school way of connecting IP phones(Xls running 12.0 IOS). config 2 is the recommended way since it has less overhead and fewer STP instances.

[lgijssel]

In this case, I guess it doesn't make too much difference as long as you have configured a voice-vlan. The Cisco IP phone always checks (cisco-only) if a voice-vlan is active and will then start to communicate over this voice-vlan. When the voice-vlan is not the native vlan, this will require dot1p/q tagging which also comes in handy for QoS;-)

What I am missing in your config is something like:

int fa0/..

description CISCO PHONE

mls qos trust device cisco-phone

This line will instruct the switch to "trust" the QoS classifucation from the phone.

Regards,

Leo

[schadmin]

this is something I need if I use the second config? We are planning on putting it in, but not till we have all of our vlan structures built...

[Prashanth Krishnappa]

Most platforms support Auto-QoS and you can use it. You will need to enable QOS globally and enable "auto qos" under the interfaces.

Switch(config-if)#auto qos voip ?

cisco-phone Trust the QoS marking of Cisco IP Phone

cisco-softphone Trust the QoS marking of Cisco IP SoftPhone

trust Trust the DSCP/CoS marking