From: Scott Morris (smorris@internetworkexpert.com)
Date: Thu Sep 04 2008 - 09:46:07 ART
In short, no.
CoS fields are on tagged/trunked frames. Namely that coming from the phone
itself. Anything from the PC behind the phone will come in untagged and
therefore not have a CoS/802.1p field. The switch then applies the default
CoS to the traffic.
Now, the "device cisco-phone" portion will ALSO trust Cos/DSCP, but puts an
extra little caveat on there of needing to check the CDP (which means you
need to have it running, of course) of the IP Phone. This prevents some
brain-child user from disconnecting their phone and plugging in a
computer/NIC that has trunking capabilities into the port.
So either solution is a plausible one for the trusting. But you'll still
want that default CoS to overwrite the rest of the information!
HTH,
Scott Morris, CCIE4 #4713, JNCIE-M #153, JNCIS-ER, CISSP, et al.
CCSI/JNCI-M/JNCI-ER
Senior CCIE Instructor
smorris@internetworkexpert.com
Internetwork Expert, Inc.
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-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
ricky ong
Sent: Thursday, September 04, 2008 2:41 AM
To: ccielab@groupstudy.com
Subject: IEWB2 LAB 11 Q 1.8
hi ALL,
I was working on IEWB2 LAB 11 Q 1.8 and was a bit puzzled about the
solution provided.. the question ask to "ensure all traffic originating
from the cisco IP phone maintain its cos, while setting cos to 0 for the
traffic coming from the pcs attached to the phone".. the solution actually
uses "mls qos trust cos". Shouldn't it be "mls qos trust cisco-phone"? If
i use "mls qos trust cos" on the port effectively i am trusting all
traffics' cos value right?
Best REgards,
Ricky
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