234 Cisco LAN Switching Configuration Handbook
5. (Optional; Layer 3 only) Create a policer to control inbound packet flow.
a. (Optional) Use an aggregate policer:
(global) mls qos aggregate-policer aggregate-name rate burst [max-burst]
[pir peak-rate] [conform-action action] [exceed-action action]
[violate-action action]
On an IOS switch, set the CIR rate (32,000 to 4,000,000,000 in bps) and the
burst size (1000 to 512,000,000 bytes). With a PFC2 module, you can also speci-
fy a PIR with the pir keyword and a peak-rate (32,000 to 4,000,000,000 in bps)
and a maximum burst size max-burst (1000 to 512,000,000 bytes).
The policer can take the following actions, based on how it measures the traffic
rate:
â– Conforming (in-profile, less than the CIR): Forwarded by default. An IOS
switch allows a conform-action to be taken instead: drop (the frame is
dropped and not forwarded), policed-dscp-transmit (the internal DSCP
value is marked down by a mapping), or transmit (the frame is forwarded
as is).
â– Exceeding (out-of-profile, exceeds the CIR): Dropped by default. A switch
allows an exceed-action to be taken: drop (the frame is dropped and not
forwarded), policed-dscp-transmit (the internal DSCP value is marked down
by a mapping), or transmit (the frame is forwarded as is).
â– Violating (out-of-profile, exceeds the PIR): By default, the action is the
same as the Exceeding action. A switch allows a violate-action to be taken:
drop (the frame is dropped and not forwarded), policed-dscp-transmit (the
internal DSCP value is marked down by a mapping), or transmit (the frame
is forwarded as is).
b. (Optional) Use a microflow policer.
On a switch, microflow policers are configured as a part of a policy map. See the
second bullet point in Step 8d for more information.
The policer can take the following actions, based on how it measures the traffic
rate:
â– Conforming (in-profile, less than the CIR): Forwarded by default.
â– Exceeding (out-of-profile, exceeds the CIR): Dropped by default. A COS
switch allows drop (frame is not forwarded) or police-dscp (the internal
DSCP value is marked down by a mapping).
Tip The rate value you specify for a CIR might be different from the value that is actual-
ly used. The QoS hardware uses values that are the specified rate rounded to the nearest
multiple of the rate granularity as shown in Table 13-3.
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