[cisco-voip] Re: cisco-voip Digest, Vol 30, Issue 95

[Mike Armstrong]

One of the charming things about IOS on switches is seems to have been 
custom-crafted for each switch; even in "families" (e.g., 3500XL), it's 
different in individual models.   We use 3524s for most of our access 
switches, and a typical configuration for a phone/pc port looks like:

interface FastEthernet0/1
switchport trunk encapsulation dot1q
switchport trunk native vlan 101
switchport trunk allowed vlan 1,2,101,1002-1005
switchport mode trunk
switchport voice vlan 2
switchport priority extend cos 0
spanning-tree portfast

...which also works on our old 2924s, but apparently doesn't work on other 
3500 models.  This allows us to plug in either a phone or a PC, or a 
phone/PC and everything works as you want.

Mike Armstrong
UF/IFAS CREC
Lake Alfred, FL

> Date: Sat, 27 Aug 2005 01:34:14 -0400
> From: Brian Feeny <bfeeny at mac.com>
> Subject: [cisco-voip] "switchport" command behavior on 3500XL
> To: cisco-voip at puck.nether.net
> Message-ID: <621B2D39-5798-49B4-8A62-8A8D470C5DFE at mac.com>
> Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed
>
>
> I have a question regarding the behavior of some "switchport"
> commands on the 3500XL vs. other cisco switches.
>
> On a 4000 (IOS) you can do:
>
> switchport trunk encapsulation dot1q
> switchport access vlan 100
> switchport voice vlan 200
>
> And that will allow you to:
>
> connect a regular device, and it will use vlan 100
> connect a cisco phone and it will trunk, placing the phone into vlan
> 200, and device connected thru the phone into vlan 100
>
> But on a 3500XL, which supports those same commands, it apparently
> does not behave that way.  You have to do:
>
> switchport trunk encapsulation dot1q
> switchport mode trunk
> switchport access vlan 100
> switchport voice vlan 200
>
> which then allows the phone to work as you would expect, but a PC
> connected directly to the switch will not work so you have
> to add the native vlan:
>
> switchport trunk encapsulation dot1q
> switchport trunk native vlan 100
> switchport mode trunk
> switchport access vlan 100
> switchport voice vlan 200
>
> which once you have done that, doesn't even make sense to have
> "switchport access vlan 100", so end up with:
>
> switchport trunk encapsulation dot1q
> switchport trunk native vlan 100
> switchport mode trunk
> switchport voice vlan 200
>
> I am just trying to nail down what config I should use to allow the
> port to be used directly by a device such as a PC, and also allow it
> to trunk to a cisco phone that would carry voice/data vlans.  It
> seems these commands change alot as IOS gets updated.  What is the
> correct configuration to do what I am wanting on the 3500XL?
>
> Brian