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New Member

VLANs between switches - what am I missing??

I have 3 Cat 3548 switches in an IP telephony environment. I need to trunk VLANs between all of these switches to allow the phones to have access to the voice VLAN from any switch.

I have the following configured on the ports connecting the switches:

interface FastEthernet0/1

duplex full

speed 100

switchport trunk encapsulation dot1q

switchport trunk allowed vlan 1,102,1002-1005

switchport mode trunk

Is this a correct configuration? If not, please advise. Also the switchports the phones connect to need to be configured as trunk ports. This works on the switch that the Call Manager and phones are directly connected to, but no the other switches.

Thanks in advance.


Re: VLANs between switches - what am I missing??

This looks fine although you are only allowing vlan's 1 and 102 down your trunk port.

"show interface trunk" will show you trunk status and what vlans are allowed.

Also if these are static (never access) trunk ports you might think about nailing them up that way. "switchport mode trunk". If not they are dynamic and desirable and can become access ports in vlan 1 if your other end is not set up to be trunked.

Hope this helps,


New Member

Re: VLANs between switches - what am I missing??

Reading the reply you posted, I need to ask a question: What is the difference between the following?

switchport trunk encapsulation dot1q

switchport mode trunk

Cisco Employee

Re: VLANs between switches - what am I missing??

The first command specifies the encapsulation to be "dot1q". The second command sets the interface mode to trunk. You need both these commands unless the switch supports only one encapsulation type(example:2950's support only dot1q)

New Member

Re: VLANs between switches - what am I missing??

It looks correct. You are only trunking VLANs 1 and 102. Are your phones and

Call Manager on VLAN 102? The phones and call manager on all switches should

be plugged into interfaces with the configuration:

switchport access vlan 102

If you're using a different VLAN for voice, then you need to allow that VLAN on the

trunk by editing the "switchport trunk allowed vlan statement" on your trunking interfaces on all switches.