security audit

As of security audit, the MPLS EXP bits can be read (match command within a class map) and written (set command within a policy map) using MQC. When a packet enters the MPLS network at the provider edge (PE) router, the IP Precedence of the packet (by default) automatically is copied to the MPLS EXP field in the MPLS header. No explicit action is typically necessary to mark MPLS EXP values, unless the values require re-marking because of administrative policies

In theory, upon exiting the MPLS network, the original IP packet re-emerges unchanged with its IP header type of service (ToS) field intact. Again, no explicit action needs to be taken unless the value requires re-marking. While inside the MPLS network, the packet's ToS field (IP Precedence or DSCP) is irrelevant because the MPLS EXP bits are used to determine the QoS treatment of the packet within the security audit cloud