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Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX
OL-4266-08
Chapter 42 Configuring PFC3BXL or PFC3B Mode MPLS QoS
PFC3BXL or PFC3B Mode MPLS QoS Features
• Packets carry traffic at Layer 3.
• Policing is limiting bandwidth used by a flow of traffic. Policing can mark or drop traffic.
PFC3BXL or PFC3B Mode MPLS QoS Features
QoS enables a network to provide improved service to selected network traffic. This section explains the
following PFC3BXL or PFC3B mode MPLS QoS features, which are supported in an MPLS network:
• MPLS Experimental Field, page 42-3
• Trust, page 42-3
• Classification, page 42-3
• Policing and Marking, page 42-4
• Preserving IP ToS, page 42-4
• EXP Mutation, page 42-4
• MPLS DiffServ Tunneling Modes, page 42-4
MPLS Experimental Field
Setting the MPLS experimental (EXP) field value satisfies the requirement of service providers who do
not want the value of the IP precedence field modified within IP packets transported through their
networks.
By choosing different values for the MPLS EXP field, you can mark packets so that packets have the
priority that they require during periods of congestion.
By default, the IP precedence value is copied into the MPLS EXP field during imposition.You can mark
the MPLS EXP bits with a PFC3BXL or PFC3B mode MPLS QoS policy.
Trust
For received Layer 3 MPLS packets, the PFC3BXL or PFC3B usually trusts the EXP value in the
received topmost label. None of the following have any effect on MPLS packets:
• Interface trust state
• Port CoS value
• Policy-map trust command
For received Layer 2 MPLS packets, the PFC3BXL or PFC3B can either trust the EXP value in the
received topmost label or apply port trust or policy trust to the MPLS packets for CoS and egress
queueing purposes.
Classification
Classification is the process that selects the traffic to be marked. Classification accomplishes this by
partitioning traffic into multiple priority levels, or classes of service. Traffic classification is the primary
component of class-based QoS provisioning. The PFC3BXL or PFC3B make classification decisions
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