In the 7280R3/7500R3/7800R3 platform, EXP rewrite for IP-MPLS routed flows is derived from the DSCP of the packet. Using Qos Policy map , DSCP can be set as needed. But in this process, the egress IP TOS was also changed, which may cause issues later at customer edge. 

This feature allows the user to have a custom DSCP To TC map per subInterface. By default,