From: Darren Johnson (dazza_johnson@yahoo.co.uk)
Date: Thu Dec 13 2007 - 15:39:46 ART
Good evening all, and good questions Phuc!
See my responses below:
From: nhatphuc [mailto:nhatphuc@gmail.com]
Sent: 13 December 2007 18:24
To: Darren Johnson
Cc: Cisco certification
Subject: Re: Trust VoIP and remark Data
Hi Darren and all,
I used "override" because without it, switch only remarks untagged frame,
and leaves other frame intact. I use this together with "mls qos trust
device cisco-phone" because I think trust device have higher priority than
"mls qos cos 1 override". Am I correct?
Not sure if override has a lower priority than mls qos trust device
Cisco-phone but I cannot see what you are achieving here. I thought your
post wanted to trust COS from phone and from PC (untagged) set COS to 1
override is uneccsary in this instance.
About your configuration, can we "trust device" and "trust cos" together? I
haven't tried yet
Yes. You tell the switch to either trust COS or DSCP. The switch will then
trust these values no matter what. If you add mls qos trust device
Cisco-phone, the trust of the COS or DSCP command configured previously,
will only apply if a Cisco phone is detected. Therefore:
Option 1
Mls qos trust dscp --` Trusts dscp irrecspective of device attached
Option 2
Mls qost trust dscp
Mls qos trust device Cisco-phone --` trust DSCP only if Cisco phone is
connected
After reading all of your answers and thinking again. I have a third option.
I repost all 3:
option 1:
mls qos trust cos
switchport priority extend cos 1
option 2:
mls qos trust device cisco-phone
mls qos cos 1 override
option 3 :
mls qos trust device cisco-phone
switchport priority extend cos 1
In my opinion:
Option 1 would work
Option 2 would NOT work
Option 3 would work, not sure if you need to add mls qos trust cos
though
In fact, I took the first option from IEWB. I used to choose that, but now I
think why don't we choose the 3rd one? Isn't it better than the 1st?
Thank you
Phuc
On Dec 13, 2007 6:45 PM, Darren Johnson <dazza_johnson@yahoo.co.uk> wrote:
Hey there! I believe your second option is wrong, you don't need the
override and you need to trust cos. I would do it like this....
mls qos trust device cisco-phone
mls qos trust cos
mls qos cos 1
This says trust the COS value ONLY if a Cisco phone is detected via CDP, and
any packets/frames without a COS value (such as those received from a PC on
the native vlan) use a COS value of 1. The COS override would 'override' any
COS values to 1, including COS values received from the phone!! I don't
believe you want to do this!
Dazzler
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
nhatphuc
Sent: 12 December 2007 17:55
To: Cisco certification
Subject: Trust VoIP and remark Data
Hi Group,
With question: Ensure that VoIP traffic originating from the IP phones
maintains its CoS value, while traffic originating from the PCs is
remarked with a CoS of 1
I see 2 ways to answer. The first seems to be better, but I don't see
anything wrong with the second. Which one do you choose? Please explain.
mls qos trust cos
switchport priority extend cos 1
and
mls qos trust device cisco-phone
mls qos cos 1 override
Thank you
Phuc
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