On M-series routers, you can configure rewrite rules to change packet header information and attach it to an output interface. These rules can possibly overwrite the DSCP marking configured on the AS or MultiServices PIC. It is important to bear in mind that this adverse effect can take place and to create system-wide configurations carefully.
For example, knowing that the AS or MultiServices PIC can mark packets with any ToS or DSCP value and the output interface is restricted to only eight DSCP values, rewrite rules on the output interface condense the mapping from 64 to 8 values with overall loss of granularity. In this case, you have the following options: