Traffic Policing; Packet Marking Through The Ip Precedence Value, Ip Dscp Value, And The Mpls Experimental Value Setting - Cisco ASR 9000 Series Configuration Manual

Information About Configuring QoS Congestion Management on Cisco ASR 9000 Series Routers

Traffic Policing

In general, traffic policing allows you to control the maximum rate of traffic sent or received on an
interface, and to partition a network into multiple priority levels or class of service (CoS).
Traffic policing manages the maximum rate of traffic through a token bucket algorithm. The token bucket
algorithm can use the user-configured values to determine the maximum rate of traffic allowed on an
interface at a given moment in time. The token bucket algorithm is affected by all traffic entering or
leaving (depending on where the traffic policy with traffic policing is configured) and is useful in
managing network bandwidth in cases in which several large packets are sent in the same traffic stream.
Traffic entering the interface with traffic policing configured is placed into one of these categories.
Within these three categories, users can decide packet treatments. For instance, packets that conform can
be configured to be sent, packets that exceed can be configured to be sent with a decreased priority, and
packets that violate can be configured to be dropped.
Traffic policing is often configured on interfaces at the edge of a network to limit the rate of traffic
entering or leaving the network. In the most common traffic policing configurations, traffic that
conforms is sent and traffic that exceeds is sent with a decreased priority or is dropped. Users can change
these configuration options to suit their network needs. Traffic policing also provides a certain amount
of bandwidth management by allowing you to set the burst size (Bc) for the committed information rate
(CIR). When the peak information rate (PIR) is supported, a second token bucket is enforced and the
traffic policer is then called a two-rate policer.
Note The two-rate policer and two-token bucket algorithm is supported in Cisco IOS XR software.
For Cisco IOS XR software, a single-rate, two-color policer is supported that provides one token bucket
with two actions for each packet: a conform action and an exceed action. To support multiaction
set/policer, the following combinations are supported in the ingress direction for the conform and exceed
actions:
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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.
Cisco ASR 9000 Series Aggregation Services Router Modular Quality of Service Configuration Guide
QC-42
Configuring Modular Quality of Service Congestion Management on Cisco ASR 9000 Series Routers
D r a f t — C i s c o C o n f i d e n t i a l
mpls exp imp, qos-group and discard_class
mpls exp imp, qos-group
mpls exp imp, discard_class
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