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New Member

voice vlan in catalyst 3550


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The Catalyst 6000 and the Catalyst 4000 switches support a special multiservice port to connect to the Cisco IP phones. The Catalyst 3500 series XL switches provide the same level of functionality as the multiservice ports using the standard IEEE 802.1Q trunk ports.

I want to know when I configure voice vlan in catalyst 3550, the interface should be configure as catalyst 3500 xl(trunk port) or catalyst 4000( access port)? Can someone give me some doc about how to configure catalyst 3550's port to forward voice and data traffic on different virtual LANs ?

Cisco Employee

Re: voice vlan in catalyst 3550


If your connection is like this:

3550-----IP phone-----PC

whereas IP phone and PC will be on seperate VLANs, then the switchport should be configured as a layer 2 802.1q trunk port:

Int fa0/1

switchport mode trunk

switchport trunk encap dot1q

swithport trunk native vlan X (data vlan #)

switchport voice vlan Y (voice vlan #)

There's no difference between how the CAT4K/6K handles voice vlan and how the 35xx does it, the only difference is the CLI syntax where CAT4K/6K uses "auxilary vlan" and the 35xx uses "voice vlan". Both are standard 802.1Q trunks.

3550 also has layer 3 capabilities, please note that the configuration listed above only apply to layer 2 trunk ports on the 3550.



New Member

Re: voice vlan in catalyst 3550


Thank you for your replay.

I want to ask a question about voice vlan Y. The voice vlan Y is like the normal vlan X? And I should create voice vlan Y like this :

sw#vlan data

sw(vlan)# vlan Y


interface vlan Y

ip add

The voice vlan Y is like normal vlan X?


Cisco Employee

Re: voice vlan in catalyst 3550

Yes, that is correct. Voice vlan is a normal vlan.


New Member

Re: voice vlan in catalyst 3550

Hi zoushan,

I have a question about this topic:

the config you mentioned is the standard one for 3500xl. I've seen that in the last config QOS design guide for IPT that the config for 3550-2950 is quite different:

see this link for the voice vlan config and you see that the trunk is not configured for exmple:

Then, in design QOS guide, the natvi vlan for data is not configured and is configured the ACCESS VLAN!!!!! See the exmaple:


When the Catalyst 3550 is connected to an IP phone, you must do the following:

Step 1 Configure the switch to trust CoS from the IP phone.

3550G-Access(config)#interface g 0/11

3550G-Access(config-if)#mls qos trust cos

Step 2 Enable the voice and data VLANs.

3550G-Access(config-if)#switchport voice vlan 111

3550G-Access(config-if)#switchport access vlan 11

Step 3 Set the IP phone’s trust boundary.

3550G-Access(config-if)#switchport priority extend cos 0


This sound strange to me, because I thinked that this command has sense when the port is not a trunk!!! And then, the native vlan doesn't work?

I hope that you can clear me the situation,

thanks in advance,


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