[cisco-voip] "switchport" command behavior on 3500XL

[Erick Bergquist]

Here is the right way (from my understanding), with
Cisco IP phones. If you configure the port as a (full)
trunk then there may be extra traffic that gets sent
down port also which can cause problems on some phone
models if there is to much background/noisy traffic
going to phone. I have seen this in a number of places
(have seen it cause voice quality issues, etc) and
changing port config from trunk to access port clears
up the voice quality issues that were seen. Not all
the time but on chatty networks this way seems to
help.

switchport mode access
switchport access vlan 100
switchport voice vlan 200

This cisco doc saids "Voice VLAN is only supported on
access ports and not on trunk ports, even though the
configuration is allowed."

http://www.cisco.com/univercd/cc/td/doc/product/lan/cat3560/1225sea/3560
scg/swvoip.htm

The doc mentions 3560, but theres a 3550 doc with
similar note in it but can't find link to that now.

--- Brian Feeny <bfeeny at mac.com> wrote:

> 
> 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
> 
> _______________________________________________
> cisco-voip mailing list
> cisco-voip at puck.nether.net
> https://puck.nether.net/mailman/listinfo/cisco-voip
> 


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