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Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
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Chapter 30 Configuring QoS
Understanding QoS
A policy map also has these characteristics:
• A policy map can contain multiple class statements.
• A separate policy-map class can exist for each type of traffic received through an interface.
• A policy-map configuration state supersedes any actions due to an interface trust state.
For configuration information, see the “Configuring a QoS Policy” section on page 30-26.
Policing and Marking
Note This feature is available only if your switch is running the EI.
Policing involves creating a policer that specifies the bandwidth limits for the traffic. Packets that exceed
the limits are out of profile or nonconforming. Each policer specifies the action to take for packets that
are in or out of profile. These actions, carried out by the marker, include dropping the packet or marking
down the packet with a new user-defined value.
You can create an individual policer. QoS applies the bandwidth limits specified in the policer separately
to each matched traffic class. You configure this type of policer within a policy map by using the
policy-map configuration command.
When configuring policing and policers, keep these items in mind:
• By default, no policers are configured.
• Policers can only be configured on a physical port. There is no support for policing at a VLAN level.
• Only one policer can be applied to a packet in the input direction.
• Only the average rate and committed burst parameters are configurable.
• Policing occurs on the ingress interfaces:
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60 policers are supported on ingress Gigabit-capable Ethernet ports.
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6 policers are supported on ingress 10/100 Ethernet ports.
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Granularity for the average burst rate is 1 Mbps for 10/100 ports and 8 Mbps for Gigabit
Ethernet ports.
• On an interface configured for QoS, all traffic received through the interface is classified, policed,
and marked according to the policy map attached to the interface. On a trunk interface configured
for QoS, traffic in all VLANs received through the interface is classified, policed, and marked
according to the policy map attached to the interface.
Note You cannot configure policers on the egress interfaces.