Cisco WS-SUP32-GE-3B Software Configuration Guide - Page 644

Mode MPLS QoS Chapter 39 Configuring MPLS QoS These sections describe LER and LSR operation in an MPLS network. • LERs at the Input Edge of an MPLS Network, page 39-6 • LSRs in the Core of an MPLS Network, page 39-6 • LERs at the Output Edge of an MPLS Network, page 39-7 Note The QoS capabilities at the input interface differ depending on whether the input interface is a LAN port, a WAN port on an OSM, or a port adapter on a FlexWAN or Enhanced FlexWAN module. This section is for LAN ports. For information on OSMs, see the OSM Configuration Note, 12.2SX. For information on a FlexWAN or Enhanced FlexWAN module, see the FlexWAN and Enhanced FlexWAN Installation and Configuration Note. LERs at the Input Edge of an MPLS Network Note Incoming labels are aggregate or nonaggregate. The aggregate label indicates that the arriving MPLS or MPLS VPN packet must be switched through an IP lookup to find the next hop and the outgoing interface. The nonaggregate label indicates that the packet contains the IP next hop information. This section describes how edge LERs can operate at either the ingress or the egress side of an MPLS network. At the ingress side of an MPLS network, LERs process packets as follows: 1. Layer 2 or Layer 3 traffic enters the edge of the MPLS network at the edge LER (PE1). 2. The PFC3B receives the traffic from the input interface and uses the 802.1p bits or the IP ToS bits to determine the EXP bits and to perform any classification, marking, and policing. For classification of incoming IP packets, the input service policy can also use access control lists (ACLs). 3. For each incoming packet, the PFC3B performs a lookup on the IP address to determine the next-hop router. 4. The appropriate label is pushed (imposition) into the packet, and the EXP value resulting from the QoS decision is copied into the MPLS EXP field in the label header. 5. The PFC3B forwards the labeled packets to the appropriate output interface for processing. 6. The PFC3B also forwards the 802.1p bits or the IP ToS bits to the output interface. 7. At the output interface, the labeled packets are differentiated by class for marking or policing. For LAN interfaces, egress classification is still based on IP, not on MPLS. 8. The labeled packets (marked by EXP) are sent to the core MPLS network. LSRs in the Core of an MPLS Network This section describes how LSRs used at the core of an MPLS network process packets: 1. Incoming MPLS-labeled packets (and 802.1p bits or IP ToS bits) from an edge LER (or other core device) arrive at the core LSR. 2. The PFC3B receives the traffic from the input interface and uses the EXP bits to perform classification, marking, and policing. 39-6 Catalyst Supervisor Engine 32 PISA Cisco IOS Software Configuration Guide, Release 12.2ZY OL-11439-03