3548XL With VOIP Phone

[jbeebe]

I am getting ready to install a number of 7912 and 7040 VOIP phones on an existing network with a large number of 3548XL switches. The phones will be configured with a PC on the outgoing port. I am trying to find basic information regarding configuring the individual ports on the 3548s to pass the VOIP VLAN through. A typical port is currently configured like this:

interface FastEthernet0/5

switchport access vlan 100

spanning-tree portfast

I will need to add support for the secondary VLAN (VLAN 410) that will have the VOIP traffic. So, I have two questions:

1. What config command lets me put two VLANs on a port, or do I need to use 802.1q? Does the phone automatically switch traffic through to the PC on the second port?

2. Can I configure all ports with the VOIP VLAN by default so that I don't have to set it per port, or will this degrade my network performance.

Any advice would be appreciated.

[brent.williams]

I have a similar installation at one of my offices. The following config seems to work quite well:

interface FastEthernet0/1

switchport trunk encapsulation dot1q

switchport trunk native vlan 100

switchport trunk allowed vlan 100,410

switchport mode trunk

switchport voice vlan 410

switchport priority extend cos 0

This configuration will allow you to configure all ports to support a phone, but if a PC is connected, it will use VLAN 100 by default. The "priority" line also tells the phones to override any CoS setting set by a PC connected to the phone and set it to 0. If you want to maintain your PC's CoS settings, use "switchport priority extend trust" instead.

The phone gets its settings (including which VLAN to use for voice and which to use for the PC) through the CDP protocol, so make sure it is activated.

[jbeebe]

Excellent, that is exactly what I was looking for. One more silly question - do I need to disable Spantree Portfast?

[brent.williams · Accepted solution]

Recent versions of IOS disable portfast on ports configured for trunking. So, leaving it there will not cause a problem, but it might be better to remove that command while you are in there.