[c-nsp] Voice VLAN Question - QOS

Paul Stewart paul at paulstewart.org
Fri Jan 26 11:53:23 EST 2007


Thanks... we've had to use the second method because of the mixed
environment here and also have learned that the Snom's don't do tagging as
we thought they did (another poster confirmed this offline)....
 
Take care,
 
Paul
 

  _____  

From: Tim Jackson [mailto:jackson.tim at gmail.com] 
Sent: Friday, January 26, 2007 10:45 AM
To: Paul Stewart
Cc: cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] Voice VLAN Question - QOS


That's partially correct.. Usually IP phones tag the voice traffic and pass
through any data from the switch in the phone as untagged... So you would
need to either configure as follows:

int fa0/8
 descr xxxx 
 switchport mode access
 switchport access vlan 101
 switchport voice vlan 102
!

That usually will work for any Polycom/Cisco phone w/ CDP enabled (using CDP
to discover the VLAN to tag voice on as well)... It should work for non-CDP
enabled phones (I've had mixed success with this on different platforms), so
you may have to configure it: 

int fa0/8
 descr xxxx
 switchport mode trunk
 switchport trunk allowed vlan 101,102
 switchport trunk native vlan 101
!

The other thing that we always did here, was to enable "mls trust cos" and
all of the IP phones set CoS5 on the tagged traffic (not positive about your
phones, polycom and cisco both do if configured).. 

--
Tim 


On 1/26/07, Paul Stewart <paul at paulstewart.org> wrote: 

Hi there...

We have a network of about 60-65 desktops and each one now has an IP phone
(mixture of phones - mainly Snom and Aastra) ... we I've been researching
the Voice VLAN option as a possible QOS enhancement... 

I've configured a test port like this:

interface FastEthernet0/8
description xxxxxxxxx
switchport trunk allowed vlan 101,102
switchport mode trunk
switchport voice vlan 102
switchport priority extend cos 5 
spanning-tree portfast


VLAN 101 is data and VLAN 102 is voice ...

Is this the correct way to do it?  Does my configuration above make cos 0
for data and cos 5 for voice automatically without honouring whatever the 
phone defaults to?

On the trunk ports between switches how do I make sure cos 5 gets passed
through?

Finally, when it reaches the switch facing our Cisco ASA it's broken into
ports (one for data and one for voice) - is there a way to flag cos=5 for 
everything off a port?  I've opened a ticket at Cisco to understand how the
ASA handles cos values... they have told me so far that it just passes
through without any configuration required but I'm thinking there must be 
more to it...;)

Sorry for all the questions... been reading a lot on this and want to make
sure my reading = good configuration..

Paul

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