Policing Guidelines - Cisco Catalyst 2960 Software Configuration Manual

Chapter 33 Configuring QoS
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Policing Guidelines

To use policing, the switch must be running the LAN Base image.
Note
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General QoS Guidelines
These are general QoS guidelines:
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OL-26520-01
Only one ACL per class map and only one match class-map configuration command per class map
are supported. The ACL can have multiple ACEs, which match fields against the contents of the
packet.
A trust statement in a policy map requires multiple TCAM entries per ACL line. If an input service
policy map contains a trust statement in an ACL, the access-list might be too large to fit into the
available QoS TCAM and an error can occur when you apply the policy map to a port. Whenever
possible, you should minimize the number of lines in a QoS ACL.
The port ASIC device, which controls more than one physical port, supports 256 policers
(255 user-configurable policers plus 1 policer reserved for system internal use). The maximum
number of user-configurable policers supported per port is 63. Policers are allocated on demand by
the software and are constrained by the hardware and ASIC boundaries. You cannot reserve policers
per port; there is no guarantee that a port will be assigned to any policer.
Only one policer is applied to a packet on an ingress port. Only the average rate and committed burst
parameters are configurable.
Catalyst 2960-S switches do not support ingress queueing.
Note
On a port configured for QoS, all traffic received through the port is classified, policed, and marked
according to the policy map attached to the port. On a trunk port configured for QoS, traffic in all
VLANs received through the port is classified, policed, and marked according to the policy map
attached to the port.
If you have EtherChannel ports configured on your switch, you must configure QoS classification,
policing, mapping, and queueing on the individual physical ports that comprise the EtherChannel.
You must decide whether the QoS configuration should match on all ports in the EtherChannel.
If you need to modify a policy map of an existing QoS policy, first remove the policy map from all
interfaces, and then modify or copy the policy map. After you finish the modification, apply the
modified policy map to the interfaces. If you do not first remove the policy map from all interfaces,
high CPU usage can occur, which, in turn, can cause the console to pause for a very long time.
You configure QoS only on physical ports; there is no support for it at the VLAN level.
Control traffic (such as spanning-tree bridge protocol data units [BPDUs] and routing update
packets) received by the switch are subject to all ingress QoS processing.
Catalyst 2960-S switches do not support ingress queueing.
Note
You are likely to lose data when you change queue settings; therefore, try to make changes when
traffic is at a minimum.
Catalyst 2960 and 2960-S Switches Software Configuration Guide, Release 15.0(1)SE
Configuring Standard QoS
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