QOS trust settings

DevilWAH

Hi,

I am trying to get my head around QOS trusting.

On a switch I have devices connected that mark there traffic with DSCP and COS markings. Some can only do COS some one DSCP, so I have various streams some with default values, some with no dscp but COS 5, some with DSCP 46, and no COS.

(keeping it simpleish )

AS I under stand it if I have

#no mls qos trust configured, then all packets will get there markings striped, is that correct.

#mls qos trust COS, then all packets with COS 5 will keep the marking and DSCP will be set to 46 (assuming map defines that), but packets that only have a DSCP value of 46 will get set to 0 as the COS 0 will be the trusted value?

What I am trying to say is I want the switch to look at in coming packets, if they have the DSCP field non default then use this, if not use the COS value.

Also for some switch's it is not possible to trust DSCP, so how do I get the switch to honour this field and not over write it?