Hi, when qos is enabled on the switch (mls qos). It will rewrite anything that is not trusted of classified to 0. How would I change that to af11 0x28?
We may be talking cross purposes here.
My understanding is this. All Catalyst switches generate an internal DCSP value for the packet regardless of whether the packet is IP or non-IP. This internal value is used for QOS decisions but is not written into the packet itself.
How this internal DCSP value is generated depends on a number of things
1) If the port is set to Trust DSCP then the internal DCSP value is simply the same value as the value in the packet header.
2) If port is set to Trust IP Precedence then the internal DCSP value is obtained from the IPP to DCSP map.
3) If port is set to Trust CoS then the internal DSCP value is obtained from the CoS to DSCP map
4) If the port is set to Untrusted the received packet has a default CoS setting applied to it which is then mapped to an internal DSCP value using the CoS to DCSP map.
Now my understanding is that if you have "mls qos trust cos" on a port and the packet received has a DSCP value that is irrelevant. What will happen is that the packet either has
a) a CoS value, in which case that will be used and mapped to an internal DSCP value using the Cos to DSCP value.
b) No CoS value, in which case you assign the default CoS value of the port and then map that to an internal DSCP value using the Cos to DSCP map.
As far as i am aware the DSCP to CoS map is only used on the egress because the switch does not use an internal CoS value.
Perhaps i have misunderstood.