Cisco WS-SUP32-GE-3B Software Configuration Guide - Page 649

Chapter 39 Configuring MPLS QoS Understanding MPLS QoS Classification for MPLS-to-IP The PFC3B assigns the internal DSCP (internal priority that the PFC3B assigns to each frame) based on the QoS result. The QoS result is affected by the following: • Default trust EXP value • Label type (per-prefix or aggregate) • Number of VPNs • Explicit NULL use • QoS policy There are three different classification modes: • Regular MPLS classification-For nonaggregate labels, in the absence of MPLS recirculation, the PFC3B classifies the packet based on MPLS EXP ingress or egress policy. The PFC3B queues the packet based on COS derived from EXP-to-DSCP-to-CoS mapping. The underlying IP DSCP is either preserved after egress decapsulation, or overwritten from the EXP (through the EXP-to-DSCP map). • IP classification for aggregate label hits in VPN CAM-The PFC3B does one of the following: - Preserves the underlying IP ToS - Rewrites the IP ToS by a value derived from the EXP-to-DSCP global map - Changes the IP ToS to any value derived from the egress IP policy In all cases, egress queueing is based on the final IP ToS from the DSCP-to-CoS map. • IP classification with aggregate labels not in VPN CAM-After recirculation, the PFC3B differentiates the MPLS-to-IP packets from the regular IP-to-IP packets based on the ingress reserved VLAN specified in the MPLS decapsulation adjacency. The reserved VLAN is allocated per VRF both for VPN and non-VPN cases. The ingress ToS after recirculation can be either the original IP ToS value, or derived from the original EXP value. The egress IP policy can overwrite this ingress ToS to an arbitrary value. Note For information about recirculation, see the "Recirculation" section on page 21-4. For incoming MPLS packets on the PE-to-CE ingress, the PFC3B supports MPLS classification only. Ingress IP policies are not supported. PE-to-CE traffic from the MPLS core is classified or policed on egress as IP. Classification for MPLS-to-IP MPLS QoS MPLS QoS at the ingress to PE2 supports matching on the EXP value and the police command. MPLS QoS at the egress of PE2 supports matching on IP precedence or DSCP values or filtering with an access group and the police command. Classification at MPLS-to-IP Ingress Port LAN port classification is based on the EXP value. OSM and FlexWAN interfaces classify traffic using the match mpls experimental command. The match mpls experimental command matches on the EXP value in the received topmost label. OL-11439-03 Catalyst Supervisor Engine 32 PISA Cisco IOS Software Configuration Guide, Release 12.2ZY 39-11