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Bronze

switchport voice vlan untagged

hi every body!

The context is a switch port is connected to ip phone.

please consider the following configuration

switch(config-if)switchport trunk native vlan 2

swith(config-if) switchport voice vlan untagged

switch(config-if) switchport access vlan 3

Now would the ip phone use native vlan 2 or access vlan 3 for voice and pc data?

thanks a lot!

1 ACCEPTED SOLUTION

Accepted Solutions

Re: switchport voice vlan untagged

9 REPLIES

Re: switchport voice vlan untagged

Hi Sarah,

That depends on whether the port is configured as an access port or trunk port. It's an access port (switchport mode access), all traffic will end up being in vlan 3. If it's a trunk, it will be in vlan 2.

HTH

Lejoe

Bronze

Re: switchport voice vlan untagged

Thanks for your reply!

My book says untagged option use 802.1q trunk

So if use the command with untagged option, the port is configured for tunk. Am i correct?

thanks a lot!

Re: switchport voice vlan untagged

Hi Sarah,

I guess they are presuming the port is already configured as a trunk. When the untagged option is used the phone no longer tags voice traffic. So it would fall into the native vlan configured with (switchport trunk native vlan x)

HTH

Lejoe

Bronze

Re: switchport voice vlan untagged

Thanks for your reply Lejoe!

The command switchport voice{ vlan id/ untagged etc}

itself enable trunking on the port so there is no need to explicitly configure the trunk by switch port trunk encapsulation dot1q.

Bronze

Re: switchport voice vlan untagged

I want to add something.

In order for trunk to work, both ends should be configured( manually or by DTP) for trunk operation. Trunk would not form if one end is in access mode and the other end is configured for trunk. The end result would be access mode on both ends.

For a switch port to receives frames from multiple vlans,, the port must be in trunk mode.

So it is impossible for a switch port to be in access mode say vlan 2 and receives the frame with vlan 3( for example) because it suggests the link is trunk link. Trunk link is only possible if both ends agrees to be trunk.

Having said that let revisit the scenario below.

sw1------------ip phone

switch port voice vlan 3

switchport mode access vlan 4

It is impossible for sw1 to receives vlan 3 frames and vlan 4 frames if the port is in access mode.That stipulates both ports on switch and ip phone must be in trunk mode.

Thanks a lot!

Re: switchport voice vlan untagged

Hi Sarah,

It is perfectly working configuration. The switchport need not be configured a trunk for an IP phone and PC connected to the ip phone to work.

sw1------------ip phone

switch port voice vlan 3

switchport access vlan 4

switchport mode access

http://www.cisco.com/en/US/products/hw/switches/ps4324/products_configuration_example09186a0080722cdb.shtml

The command switchport voice{ vlan id/ untagged etc}

itself enable trunking on the port so there is no need to explicitly configure the trunk by switch port trunk encapsulation dot1q.

No this command still does not define trunk mode on the switchport.

HTH

Lejoe

Silver

Re: switchport voice vlan untagged

No this command still does not define trunk mode on the switchport.

This command is not defining trunk but it is defining a Multivlan access port to carry voice and data.

Bronze

Re: switchport voice vlan untagged

thanks for your reply!

According to cisco press book, switchport voice vlan with option untagged,dot1p,vlan id all use dot1q trunk by default. If dtp is enabled, trunk will negotiate.

Re: switchport voice vlan untagged

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