3524 Phone Connectivity

I was configuring my router yesterday and discovered something a little quirky about these switches.

After I had configured my router, none of my phones were receiving IP information and could not connect to my CME router for an upgrade. I checked, double checked, and triple checked my configurations from the book. It all seemed valid. This was not my first tango with setting up IP phones, so I was confused as to what the issue was.

It turns out that 3524's and 2900's both need to have the interface configured one of two ways:

IF-

...the phone is going to be a standalone device (no computer attached).

Switch(config-if)#switchport mode access
Switch(config-if)#switchport access vlan 20 (or whatever voice vlan you want it to communicate to the CME router on)

...the phone is going to be a daisy chain device (computer attached).
Switch(config-if)#switch trunk encap dot1q
Switch(config-if)#switch trunk native vlan 10
Switch(config-if)#switch trunk allow vlan 10,20
Switch(config-if)#switch mode trunk
Switch(config-if)#switch voice vlan 20
Switch(config-if)#spanning-tree portfast trunk

Currently I have everything configured with the top one, but I'll be giving the bottom one a try in a later lab. It should be noted though, that the normal book way to do this is what cisco wants you to know.