Cisco WS-SUP32-GE-3B Software Configuration Guide - Page 643

Chapter 39 Configuring MPLS QoS Mode MPLS QoS Specifying the QoS in the IP Precedence Field When you send IP packets from one site to another, the IP precedence field (the first three bits of the DSCP field in the header of an IP packet) specifies the QoS. Based on the IP precedence marking, the packet is given the treatment configured for that quality of service. If the service provider network is an MPLS network, then the IP precedence bits are copied into the MPLS EXP field at the edge of the network. However, the service provider might want to set QoS for an MPLS packet to a different value determined by the service offering. In that case, the service provider can set the MPLS EXP field. The IP header remains available for the customer's use; the QoS of an IP packet is not changed as the packet travels through the MPLS network. For more information, see the "MPLS DiffServ Tunneling Modes" section on page 39-31. Mode MPLS QoS This section describes how MPLS QoS works. Figure 39-1 shows an MPLS network of a service provider that connects two sites of a customer network. Figure 39-1 MPLS Network Connecting Two Sites of a Customer's IP Network MPLS network IP network MPLS network IP network Host A CE1 PE1 P1 P2 PE2 Host B CE2 41867 Owned by service provider The network is bidirectional, but for the purpose of this document the packets move left to right. In Figure 39-1, the symbols have the following meanings: • CE1-Customer equipment 1 • PE1-Service provider ingress label edge router (LER) • P1-Label switch router (LSR) within the core of the network of the service provider • P2-LSR within the core of the network of the service provider • PE2-service provider egress LER • CE2-Customer equipment 2 Note PE1 and PE2 are at the boundaries between the MPLS network and the IP network. OL-11439-03 Catalyst Supervisor Engine 32 PISA Cisco IOS Software Configuration Guide, Release 12.2ZY 39-5