Is mls qos trust necessary in the following scenario?

[suelange]

We are deploying riverbed steelhead devices between our core switch and routers in each of our offices.  These all connect to each other over an MPLS network.

Before the Steelheads, we had a simple policy on each router that identified several types of traffic we most cared about and set the DSCP marking right at the router,just before the traffic was handed off to mpls.

The steelhead will now be marking the traffic for us. This is because in the mode we've deployed, it changes the IP address and port numbers so that our router, with only a few exceptions (voice, video) can not recognize the traffic.  So the Steelhead will mark it for us.

The question I have is, do I need ot issue any commands such as the MLS Qos Trust command on the router interface coming in from the Steelehead in order to retain those markings, or will the router just pass my steelhead markings through?

Haven't done much QoS, and the course has been soooooooo long ago...

[Joseph W. Doherty · Accepted solution]

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Routers normally leave untouched ingress ToS, unless you configure a policy to something else.

Catalyst switches, if QoS disabled, also normally leave ToS alone.  With QoS enabled, by default, they often will reset ToS unless you config them to do otherwise (e.g. a trust statement).  (NB: Some of the newer Catalysts might follow "router" rules, e.g. 4500 sup7.)