From: Kenneth Wygand (KWygand@customonline.com)
Date: Wed May 05 2004 - 18:17:49 GMT-3
OK, I think I understand this correctly now. Maybe someone can confirm.
If I set the following configuration on a Cat3550:
<snip>
mls qos
Interface FastEthernet0/1
switchport access vlan 10
mls qos trust cos
switchport voice vlan 20
</snip>
Then my voice packets will be on VLAN 20 and will be tagged with a COS
value of 5 in the Dot1q frame header (technically considered the Dot1p
priority bits).
Now if I set the following configuration instead:
<snip>
mls qos
Interface FastEthernet0/1
switchport access vlan 10
mls qos trust cos
switchport voice vlan dot1p
</snip>
Then my voice packets will be on the native VLAN, which is not defined
in my configuration so should default to VLAN 1. The voice frames will
once again be tagged with a COS value of 5 in the Dot1q frame header
(technically considered the Dot1p priority bits).
Now I don't see anywhere in the cisco documentation that I have to
define a particular encapsulation type on the interface, let alone set
the native VLAN. Is it possible to use ISL encapsulation on voice
vlans?
Kenneth E. Wygand
Systems Engineer, Project Services
CISSP #37102, CCNP, CCDP, ACSP, Cisco IPT Design Specialist, MCP, CNA,
Network+, A+
Custom Computer Specialists, Inc.
"The only unattainable goal is the one not attempted."
-Anonymous
-----Original Message-----
From: Richard Davidson [mailto:rich@myhomemail.net]
Sent: Wednesday, May 05, 2004 4:07 PM
To: Kenneth Wygand; ccielab@groupstudy.com
Subject: Re: 802.1q/p
Yes, Dot1Q is a trunking protocol. When the link is
trunked the trunk header is placed on the frame. When
you want to mark some traffic with a higher layer 2
priority you adjust the 3 bit dot1p field that is in
the Dot1Q header.
http://www.cisco.com/univercd/cc/td/doc/product/lan/c3550/12119ea1/3550s
cg/swqos.htm#1032169
Rich
--- Kenneth Wygand <KWygand@customonline.com> wrote:
> Is 802.1p just the ISO standard nomenclature for the
> IP COS bits in an
> 802.1q frame? In other words, if a question says
> "make sure to use
> 802.1p for QoS" or "make sure to set high priority
> with 802.1p", does
> this just mean make sure to set the COS bits within
> an 802.1q frame?
>
>
>
> Sorry if this seems like a basic question, but I
> can't find any
> documentation that specifically solidifies this
> concept. I just want to
> make sure that I completely understand what is
> implied when a
> requirement is presented to employ 802.1p.
>
>
> Thanks!
>
>
>
> Kenneth E. Wygand
> Systems Engineer, Project Services
>
> CISSP #37102, CCNP, CCDP, ACSP, Cisco IPT Design
> Specialist, MCP, CNA,
> Network+, A+
> Custom Computer Specialists, Inc.
>
> "I am not really smart. I just stick with problems
> longer."
> -Albert Einstein
>
>
>
> Custom Computer Specialists, Inc.
>
> "Celebrating 25 Years of Excellence"
>
> [GroupStudy removed an attachment of type image/gif
> which had a name of image001.gif]
>
>
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