From: Bob Sinclair (bsin@cox.net)
Date: Wed Apr 28 2004 - 09:19:02 GMT-3
David,
The Cisco Catalyst QOS book by Flannagan suggests pretty strongly that the
default CoS is not applied unless you also trust COS on that port. I
confirmed this on my lab 3550 running 12.1(19)EA1.
It is necessary to trust CoS before the default will be applied. I tried
this on access port, but would expect the same result on a trunk or voice
vlan.
HTH,
Bob Sinclair
CCIE #10427, CISSP, MCSE
www.netmasterclass.net
----- Original Message -----
From: "Ng, Kim Seng David (David)" <ksng@avaya.com>
To: <ccielab@groupstudy.com>
Sent: Wednesday, April 28, 2004 5:31 AM
Subject: Cat3550 QOS confirmation
> Hello group,
>
> I would like to seek confirmation whether my understanding of the
following is correct. The following two configurations will produce the same
results i.e. the ingress data COS will be assigned "1" and ingress voice COS
(regardless of the original value of COS) will be overwritten to "1" also.
>
> Config 1:
> ======
> mls qos
> !
> interface FastEthernet0/1
> switchport access vlan 20
> switchport voice vlan 100
> mls qos cos 1
>
> Explaination: Since by default the cat3550 ports are not trusted, all
ingress COS values will be overwritten to the default COS which is
configured as "1" here. As for untagged ingress data, it will acquire
default COS of "1".
>
> Config 2:
> ======
> mls qos
> !
> interface FastEthernet0/1
> switchport access vlan 20
> switchport voice vlan 100
> mls qos cos 1
> mls qos trust cos
> mls qos cos override
>
> Explaination: Even though I configured COS trusting here, the "override"
command will still overwrite all ingress COS to "1". As for untagged ingress
data, it will acquire default COS of "1".
>
> What I am trying to get here is that I do not need to have the "override"
command to overwrite the COS value if the port is already in an "untrusted"
state. Is my understanding correct?
>
> Thanks in advance
> David
>
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