QoS Question

[cisconoobie]

Can someone please clear this QoS concern for me. I'm having ytrouble understanding it 100%

SWITCH_1 <--> 6500 <--> SWITCH_2

Packet is assigned a DSCP Value of 46 on SWITCH_1

The 6500 receives the packet on ingress from SWITCH_1.

The port state is set to trust CoS on the 6500 port connecting SWITCH_1

What happens to the packet when it exits the 6500? There is no CoS value on it from ingress, just DSCP. So does the 6500 overwrite it and make it lose it's DSCP value because the port is set to trust CoS and not DSCP?

Please clarify.

[Matthew Warrick]

CoS is a layer 2 marking.  DSCP is a layer 3 marking.  The switches aren't going to strip the marking unless they are configured to do so.  Also, the layer 3 marking is not going to be transferred to the layer 2 frame unless a device in the flow is configured to do so.  Since it's "EF", i.e DSCP 46, marked you should have a device remark the layer 2 frame as CoS 5 since I'm assuming this is voice bearer traffic.