Voice VLAN Configuration Questions.

vazurahan

Does the commands switchport voice vlan vlan-id and switchport voice vlan dot1p override each other?

Here's the command descriptions

• vlan-id—Configure the phone to forward all voice traffic through the
specified VLAN. By default, the Cisco IP Phone forwards the voice
traffic with an IEEE 802.1Q priority of 5. Valid VLAN IDs are 1 to
4094.
• dot1p—Configure the phone to use IEEE 802.1p priority tagging for
voice traffic and to use the default native VLAN (VLAN 0) to carry all
traffic. By default, the Cisco IP Phone forwards the voice traffic with an
IEEE 802.1p priority of 5.
• none—Allow the phone to use its own configuration to send untagged
voice traffic.
• untagged—Configure the phone to send untagged voice traffic.

The switchport voice vlan vlan-id says it it will use the VLAN you specified. The switchport voice vlan dot1p says it's going to use VLAN 0.

Which VLAN is it really going to send the traffic if I entered both commands?

Also, vlan-id says it's going to use IEEE 802.1Q priority of 5. While, dot1q says it's going to use IEEE 802.1p priority of 5.

What's the difference between the 802.1Q priority and 802.1p priority?

Which priority is it going to use if I entered both commands?

pham0329

You can't enter both commands. The second command will override the first, so if you enter switchport voice vlan dot1p, it will replace whatever switchport voice vlan command was in there before.

vazurahan

Thanks.

I asked, because on example on the page 596 of CCNA Study Guide Lammle 7th Ed.

Switch(config-if)#switchport priority extend trust
Switch(config-if)#mls qos trust cos
Switch(config-if)#switchport voice vlan dot1p
Switch(config-if)#switchport mode access
Switch(config-if)#switchport access vlan 3
Switch(config-if)#switchport voice vlan 10

What about the difference between the 802.1Q priority and 802.1p priority?
It says that it will use 802.1Q if you specify a VLAN.

networker050184

As far as I know 802.1p is just the standard for marking priority in an 802.1q frame. So saying 802.1q priority 5 and 802.1p priority 5 are exactly the same thing. They are marking the same bits in the header. The 802.1p command uses VLAN 0, which is reserved and is only used so that priority can be sent.

vazurahan

Okay, so if I use only this command which send the traffic to VLAN 0.
Switch(config-if)#switchport voice vlan dot1p

To which VLAN is the traffic going to be sent? Is it going to be sent to the vlan assigned with:

Switch(config-if)#switchport access vlan 3