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33-14
Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
OL-9639-06
Chapter 33 Configuring QoS
Understanding QoS
• CoS to precedence
• CoS to CoS
• Precedence to CoS
• Precedence to DSCP
• Precedence to precedence
Table maps modify only one parameter (CoS, IP precedence, or DSCP, whichever is configured) and are
only effective when configured with a set command in a policy map or with a conform-action or
exceed-action command in a police function.
Table maps are not supported in output policy maps. For more information, set the “Configuring Table
Maps” section on page 33-36.
Policing
After a packet is classified, you can use policing as shown in Figure 33-5 to regulate the class of traffic.
The policing function limits the amount of bandwidth available to a specific traffic flow or prevents a
traffic type from using excessive bandwidth and system resources. A policer identifies a packet as in or
out of profile by comparing the rate of the inbound traffic to the configuration profile of the policer and
traffic class. Packets that exceed the permitted average rate or burst rate are out of profile or
nonconforming. These packets are dropped or modified (marked for further processing), depending on
the policer configuration.
Policing is used primarily on receiving interfaces. You can attach a policy map with a policer only in an
input service policy. The only policing allowed in an output policy map is in priority classes. See the
“Unconditional Priority Policing” section on page 33-18.
Figure 33-5 Policing of Classified Packets
These sections describe the types of policing supported on the switch:
• Individual Policing, page 33-15
• Aggregate Policing, page 33-16
• Unconditional Priority Policing, page 33-18
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Receive
Classify
Drop
Queuing,
scheduling,
and shaping
An exceed-action at this
point results in dropped
or reclassified packets.
Packets that conform
to the committed
information rate (CIR)
Packets that exceed
the CIR