This chapter covered the important issues of policy routing, bandwidth management, and QoS architectures at Layer 2 (802.1P/Q, MPLS) and Layer 3(IP ToS, precedence, CoS, IntServ/RSVP, and DiffServ) of the Open System Interconnection (OSI) stack. The UNIX approaches were compared to Cisco QoS architecture, and the entanglement of QoS and packet filtering on the UNIX side was discussed.