You are configuring CoS throughout your enterprise network using DSCP.

In an end-to-end CoS (Class of Service) design, there is a clear distinction betweenclassificationat the ingress andrewrite rulesat the egress.

The Problem:Your edge devices are successfully classifying traffic (assigning packets to internal forwarding classes). However, the core devices—which useBA (Behavior Aggregate) classifiers—are not classifying correctly. BA classifiers look at the bits in the packet header (like DSCP or 802.1p) to determine priority.

The Missing Link (Option C):When a packet leaves the edge device, its internal forwarding class and loss priority must be "written" back into the packet header so that the next-hop (the core device) can see it. By default, Junos may not preserve or set these bits correctly on egress. You must applyrewrite ruleson the edge switches' egress interfaces facing the core. These rules ensure the DSCP values in the headers match the forwarding class determined by the edge's MF classifier, allowing the core's BA classifier to function properly.

Other Options:Option A(policer) handles rate limiting, not classification.Option Bis incorrect because core devices often have different hardware or scaling needs than edge switches, and standard BA configuration is preferred over templates in the core.Option Dis incorrect because MF classifiers are standard for edge devices where deep packet inspection is needed to identify traffic types.