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QoS - Clarification

ragulan_dms
Level 1
Level 1

L2 switchport is trust the device. Then, will L2 switch use the dscp value to classify the traffic or the cos value ?

2 Replies 2

Aaron Harrison
VIP Alumni
VIP Alumni

Hi

You set the switchports (depending on hardware and software versions) like so:

mls qos trust dscp (to use DSCP to classify)

mls qos trust cos (to trust CoS)

If you have the port set up to conditionally trust the cisco-phone, then it uses CoS and can optionally instruct the phone to mark down PC-port traffic.

Regards

Aaron

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Aaron Please remember to rate helpful posts to identify useful responses, and mark 'Answered' if appropriate!

Steven Holl
Cisco Employee
Cisco Employee

L2 switchports won't look at DSCP values since DSCP is a L3 header. CoS tags are only carried through on trunk links. L3 switchports won't trust DSCP, and you need to trust it with the 'mls qos trust' commands recommended above.

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