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Software Configuration Guide—Release 12.2(25)SG
OL-7659-03
Chapter27 Configuring Quality of Service
Overview of QoS
When configuring policing and policers, keep these items in mind:
•For IP packets, only the length of the IP payload (the total le ngth field in the IP header) is used by
the policer for policing computation. The Layer 2 header and trailer length are not taken into
account. For example, for a 64-byte Ethernet II IP packet, only 46 bytes are taken into account for
policing (64 bytes - 14 byte Ethernet Header - 4 bytes Ethernet CRC).
For non-IP packets, the Layer 2 length as specified in the Layer 2 Header is used by the policer for
policing computation. To specify additional Layer 2 encapsulation length when policing IP packets,
use the qos account layer2 encapsulation command.
•By default, no policers are configured.
•Only the average rate and committed burst parameters are configurable.
•Policing for individual and aggregate policers can occur in ingress and egress interfaces.
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With the Supervisor Engine V-10GE (WS-X4516-10GE), 8192 policers are supported on
ingress and on egress.
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With all other supervisor engines, 1024 policers are supported on ingress and on egress.
Note Four policers in ingress and egress direction are reserved.
•Policers can be of individual or aggregate type. On the Supervisor Engine V-10GE, flow based
policers are supported.
•Policing for flow policers can occur on ingress Layer 3 interfaces only.
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512 unique flow policers can be configured on the Supervisor Engine V-10GE.
Note Because one flow policer is reserved by software, 511 unique flow policers can be de fined.
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Greater than 100,000 flows can be microflow policed.
Note Microflow currently supports two flow matching options (source IP address based an d
destination IP address based). When microflow policing is used together with Netflow Statistics
Collection, full flow statistics for the flows matching the source IP address or destination IP
address will not be available. For information on configuring Netflow Statistics, refer to
“Enabling NetFlow Statistics Collection” on page7.
•On an interface configured for QoS, all traffic received or sent through the interface is classified,
policed, and marked according to the policy map attached to the interface. However, if the interface
is configured to use VLAN-based QoS (using the qos vlan-based command), the traffic received or
sent through the interface is classified, policed, and marked according to the policy map attached to
the VLAN (configured on the VLAN interface) to which th e packet belongs. If there is no policy
map attached to the VLAN to which the packet belongs, the policy map attached to the interface is
used.
After you configure the policy map and policing actions, atta ch the policy to an ingress or egress
interface by using the service-policy interface configuration command. For configuration information,
see the “Configuring a QoS Policy” section on page27-29 and the “Creating Named Aggregate Policers”
section on page 27-27.