You are enabling CoS throughout your enterprise network using the DSCP bits.

This scenario describes the standard transition of Class of Service (CoS) metadata from the network edge to the network core.

MF vs. BA Classification:Edge devices useMultifield (MF) classifiersbecause incoming traffic often lacks markings. MF classification assigns traffic to an internalforwarding classbased on multiple fields (IPs, ports, etc.). Core devices useBehavior Aggregate (BA) classifiersbecause they are faster; they only look at the CoS bits (like DSCP) in the header to determine the forwarding class.

The Problem:Internal forwarding class assignments made by an MF classifier on the edge device do not automatically travel with the packet. If the packet leaves the edge device with its original (potentially zeroed) DSCP bits, the core device's BA classifier will not be able to identify the priority.

The Solution (Option A):You must implementrewrite ruleson theegress interfacesof the edge devices. A rewrite rule takes the internal forwarding class and loss priority assigned by the MF classifier and "writes" the corresponding DSCP value into the packet header as it exits toward the core. This ensures that the core device sees the correct DSCP marking and can apply the appropriate BA classification.

Incorrect Options:Rewrite rules are strictly an egress function to modify the packet for thenexthop. Applying them on ingress (Option B) or core ingress (Option C) does not solve the problem of ensuring the packet header reflects the classification logic used during the internal switching process of the edge device.