Configuring Modular QoS Congestion Management on Cisco ASR 9000 Series Routers
Information About Configuring QoS Congestion Management on Cisco ASR 9000 Series Routers
QC-49
Cisco ASR 9000 Series Aggregation Services Router Modular Quality of Service Configuration Guide
OL-23108-02
Packet Marking Through the IP Precedence Value, IP DSCP Value, and the MPLS Experimental
Value Setting
In addition to rate-limiting, traffic policing allows you to independently mark (or classify) the packet
according to whether the packet conforms or violates a specified rate. Packet marking also allows you
to partition your network into multiple priority levels or CoS. Packet marking as a policer action is
conditional marking.
Use the traffic policer to set the IP precedence value, IP DSCP value, or Multiprotocol Label Switching
(MPLS) experimental value for packets that enter the network. Then networking devices within your
network can use this setting to determine how the traffic should be treated. For example, the Weighted
Random Early Detection (WRED) feature uses the IP precedence value to determine the probability that
a packet is dropped.
If you want to mark traffic but do not want to use traffic policing, see the “Class-based, Unconditional
Packet Marking Examples” section in this guide to learn how to perform packet classification.
Note Marking IP fields on an MPLS-enabled interface results in non-operation on that particular interface.
Regulation of Traffic with the Policing Mechanism
Figure 2 illustrates how a single-rate token bucket policer marks packets as either conforming or
exceeding a CIR.
Figure 2 How a Traffic Policing Mechanism Regulates Traffic
No
Packet of size B
No
Ye s
Action
B>Tc
Exceed
Action
Conform
CIR
Bc
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