dscp Mutation question.

[sarahr202]

Hi everybody

I have a question.   Please consider the following config:

SW1(config) int f0/1

SW1(config-if) mls qos trust dscp

SW1(config-if) msl qos dscp-mutation DEMO

DEMO Mutation map;

dscp 24---> 26 

I.e incoming dscp value 24 will be mapped to 26

+++++++++++++++++++

Let say a packet with dscp value 24 arrives, " DEMO" mutation map is looked up and dscp value 26 overwrites 24.   This is ingress behavior.

How about egress behavior i.e a packet eggressing the port with dscp value 26 ?  Will switch perform the on  look up  " DEMO" mutation map" and find the corresponding dscp value for 26 which is in our case is 24 ?

Thanks

Have a great day.

[cadet alain · Accepted solution]

Hi,

taken from 3750 configuration guide:http://www.cisco.com/en/US/docs/switches/lan/catalyst3750/software/release/15.0_2_se/configuration/guide/swqos.html#wp1028614

"

If two QoS domains have different DSCP definitions, use the  DSCP-to-DSCP-mutation map to translate one set of DSCP values to match  the definition of another domain. You apply the DSCP-to-DSCP-mutation  map to the receiving port (ingress mutation) at the boundary of a QoS  administrative domain.

With ingress mutation, the new DSCP value overwrites the one in the  packet, and QoS treats the packet with this new value. The switch sends  the packet out the port with the new DSCP value.

You can configure multiple DSCP-to-DSCP-mutation maps on an ingress  port. The default DSCP-to-DSCP-mutation map is a null map, which maps an  incoming DSCP value to the same DSCP value. "

Regards

Alain

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