Cisco 500 Series Administration Manual page 625

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This can be done by using the ACLs in the class map(s) to match the desired
traffic, and by using a policer to apply the QoS on the matching traffic.
A policer is configured with a QoS specification. There are two kinds of policers:
• Single (Regular) Policer—A single policer applies the QoS to a single class
map, and to a single flow based on the policer's QoS specification. When a
class map using single policer is bound to multiple ports, each port has its
own instance of single policer; each applying the QoS on the class map
(flow) at ports that are otherwise independent of each other. A single
policer is created in the Policy Table page.
• Aggregate Policer—An aggregate policer applies the QoS to one or more
class maps, and one or more flows. An aggregation policer can support
class maps from different policies. An aggregate policer applies QoS to all
its flow(s) in aggregation regardless of policies and ports. An aggregate
policer is created in the Aggregate Policer page.
An aggregate policer is defined if the policer is to be shared with more than
one class. Policers on a port cannot be shared with other policers in another
device.
Each policer is defined with its own QoS specification with a combination of the
following parameters:
• A maximum allowed rate, called a Committed Information Rate (CIR),
measured in Kbps.
• An amount of traffic, measured in bytes, called a Committed Burst Size
(CBS). This is traffic that is allowed to pass as a temporary burst even if it is
above the defined maximum rate.
• An action to be applied to frames that are over the limits (called out-of-
profile traffic), where such frames can be passed as is, dropped, or passed,
but remapped to a new DSCP value that marks them as lower-priority
frames for all subsequent handling within the device.
Assigning a policer to a class map is done when a class map is added to a policy.
If the policer is an aggregate policer, you must create it using the Aggregate
Policer page.
Cisco 500 Series Stackable Managed Switch Administration Guide
Quality of Service
QoS Advanced Mode