Typically, a router rewrites the DSCPs in outgoing packets once, when packets enter the DiffServ portion of the network, either because the packets do not arrive from the customer with the proper DSCP bit set or because the service provider wants to verify the that customer has set the DSCP properly. CoS implementations that accept the DSCP and classify and schedule traffic solely on DSCP value perform behavior aggregate (BA) DiffServ functions and do not usually rewrite the DSCP. DSCP rewrites typically occur in multifield (MF) DiffServ scenarios.
For instructions for configuring rewrite rules, see Configuring and Applying Rewrite Rules (Required).