switch port in access mode, dscp-cos mapping

Unanswered Question
Jan 3rd, 2009
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Hi everybody!

I have a question.


sw1's f0/1 configured with following:

mls qos trust dscp

When f0/1 is in access mode:

When a switch receives the frame , Would switch drive the cos value from DScp-cos map even though the port is in access mode and place the frame in respective queue at ingress port?

thanks a lot!

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Jon Marshall Sat, 01/03/2009 - 12:20
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The Cos value is derived from the DSCP-Cos map for egress traffic not ingress traffic. This map is needed because the switch always uses an internal DSCP value for all packets.

Using a 3560 switch as an example, you decide which marking, DSCP or CoS, will be used to place the packets into the ingress queues.

So the switch derives the CoS value or the DSCP value from the incoming packet and then maps this to the relevant queue.



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