The dscp mutation map is a per-port configuration that permits to modify the dscp field of a packet. The mutation map works for EGRESS traffic only We trust the documentation but it's event better to verify it. The topology si simple: PC1 11.0.0.1 --> G1/0/1 C3750-24 G1/0/24 --> G1/0/24 C3750-48 G1/0/1 --> PC2 11.0.0.2 …