Trying to trust cos value on a 2821 port

Answered Question
Jan 6th, 2009

I am trying to trust the cos value for trunk port fa 0/0/0 on a 2821 router. The trunk port is on a HWIC-4ESW 4 port switch module. I have configured the port to trust cos, but when I run the command "show mls qos interface" the port state shows "untrusted".

router#show mls qos interface


trust state: not trusted

trust mode: trust cos

COS override: dis

default COS: 0

pass-through: none

Here is the interface config:

interface FastEthernet0/0/0

switchport mode trunk

duplex full

speed 100

mls qos trust cos

arp timeout 270

hold-queue 300 in

hold-queue 300 out


Any ideas if the port is actually trusted and passing QOS markings?

Correct Answer by Yudong Wu about 8 years 1 month ago

"mls qos trust" command does not support. But the port should put the packet with COS 4-7 into high priority queue automatically.

Please refer to the following Q&A.

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Overall Rating: 5 (1 ratings)
Yudong Wu Tue, 01/06/2009 - 14:53

HWIC-4-ESW does not support mls qos trust options ( cos or dscp ). These CLIs are successfullt taken giving the impression that configurations are effective .. but they are not.

dziminski Tue, 01/06/2009 - 15:10

Ok, so I can only tag the traffic on the HWIC-4-ESW on a per-port basis? There is no way for the port to trust the COS markings that are already on the traffic passing through the port?

Here is what the product page says.

802.1P QoS (Traffic Prioritization) This feature provides support for QoS based on the IEEE class of service (CoS) and port-based prioritization, allowing the switch to change the CoS settings of tagged packets on a per-port basis.


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