Policers - Cisco WS-SUP32-GE-3B - Supervisor Engine 32 Software Configuration Manual

Chapter 38 Configuring PFC QoS
Traffic that is Layer 3 switched on the PFC3B does not go through the PISA and retains the CoS value
Note
assigned by the PFC3B.

Policers

These sections describe policers:
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•
•
Interfaces on which you configure PISA-accelerated features do not support policing in hardware on the
Note
PFC.
Overview of Policers
Policing allows you to rate limit incoming and outgoing traffic so that it adheres to the traffic forwarding
rules defined by the QoS configuration. Sometimes these configured rules for how traffic should be
forwarded through the system are referred to as a contract. If the traffic does not adhere to this contract,
it is marked down to a lower DSCP value or dropped.
Policing does not buffer out-of-profile packets. As a result, policing does not affect transmission delay.
In contrast, traffic shaping works by buffering out-of-profile traffic, which moderates the traffic bursts.
(PFC QoS does not support shaping.)
The PFC3B supports both ingress and egress PFC QoS, which includes ingress and egress policing.
Traffic shaping is supported on some WAN modules. For more information about traffic shaping on the
FlexWAN module, refer to the FlexWAN QoS documentation at this URL:
http://www.cisco.com/en/US/docs/routers/7600/install_config/flexwan_config/flexqos.html
Policers can act on ingress traffic per-port or per-VLAN. The policers can act on egress traffic per-VLAN
Note
only.
You can create policers to do the following:
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•
OL-11439-03
Overview of Policers, page 38-17
Aggregate Policers, page 38-18
Microflow Policers, page 38-18
Mark traffic
Limit bandwidth utilization and mark traffic
Catalyst Supervisor Engine 32 PISA Cisco IOS Software Configuration Guide, Release 12.2ZY
Understanding How PFC QoS Works
38-17