From: MMoniz (ccie2002@tampabay.rr.com)
Date: Wed May 05 2004 - 19:29:03 GMT-3
Remember though this is Cisco's implementation...Not necessarily other
vendors.
From a Lab standpoint I would say if the question states:config port x for
voice with all traffic in the
same VLAN but voice has a higher priority. Then I would use 802.1p
If it states voice and data should be seperate, then I would use 802.1q
just my opimion
mike
-----Original Message-----
From: Kenneth Wygand [mailto:KWygand@customonline.com]
Sent: Wednesday, May 05, 2004 5:51 PM
To: MMoniz; rich@myhomemail.net; ccielab@groupstudy.com
Subject: RE: 802.1q/p
So 802.1P is a field in an ISL frame and _not_ in an 802.1q frame? I
thought it was the other way around... ?????
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: MMoniz [mailto:ccie2002@tampabay.rr.com]
Sent: Wednesday, May 05, 2004 5:45 PM
To: Kenneth Wygand; rich@myhomemail.net; ccielab@groupstudy.com
Subject: RE: 802.1q/p
One thing to note is the order of bits for 802.1q and 802.1p for COS
Layer 2 Inter-Switch Link (ISL) frame headers have a 1-byte User field
that
carries an IEEE 802.1P class of service (CoS) value in the three
least-significant bits. On interfaces configured as Layer 2 ISL trunks,
all
traffic is in ISL frames.
Layer 2 802.1Q frame headers have a 2-byte Tag Control Information field
that carries the CoS value in the three most-significant bits, which are
called the User Priority bits. On interfaces configured as Layer 2
802.1Q
trunks, all traffic is in 802.1Q frames except for traffic in the native
VLAN.
In older switches, namely the 3524 you have to configure a port as a
trunk
port and specify encaps for voice. I have never done it with ISL, only
dot1.q.
One thing I am not certain of is if the Cat 3550 will consider the
access
VLAN ID as the default for 802.1p purposes.
But on this output it definitely shows that voice "IS NOT" on a seperate
VLAN merely 802.1p tagged
Name: Fa0/6
Switchport: Enabled
Administrative Mode: static access
Operational Mode: down
Administrative Trunking Encapsulation: negotiate
Negotiation of Trunking: Off
Access Mode VLAN: 6 (VLAN_6)
Trunking Native Mode VLAN: 1 (default)
Voice VLAN: dot1p
Maybe someone can clarify?
mike
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
Kenneth Wygand
Sent: Wednesday, May 05, 2004 5:18 PM
To: rich@myhomemail.net; ccielab@groupstudy.com
Subject: RE: 802.1q/p
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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