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Software Configuration Guide—Release 15.0(2)SG
OL-23818-01
Chapter 37 Configuring Quality of Service About QoS
When configuring policing and policers, observe these guidelines:
On Supervisor Engine 6-E, Supervisor Engine 6L-E, Catalyst 4900M, and Catalyst 4948E, policers
account only for the Layer 2 header length when calculating policer rates. In contrast, shapers
account for header length as well as IPG in rate calculations. Starting with Cisco IOS Release
15.0(2)SG, Supervisor Engine 6-E, Supervisor Engine 6L-E, Catalyst 4900M, and Catalyst 4948E
support the qos account layer-all encapsulation command which accounts for Layer 1 headers of
20 bytes (12 bytes preamble + 8 bytes IPG) and Layer 2 headers in policing features.
By default, on Supervisor Engine V-10GE and earlier supervisor engines, policer or shaping
computation involves only IP payload information. You can include Layer 2 lengths and any
overhead with the qos account layer2 encapsulation command.
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.
With the Supervisor Engine V-10GE (WS-X4516-10GE), 8192 policers are supported on
ingress and on egress.
With all other supervisor engines, 1024 policers are supported on ingress and on egress.
The accuracy of the policer configured is +/- 1.5 percent.
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.
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 defined.
Greater than 100,000 flows can be microflow policed.
On an interface configured for QoS, all traffic received or sent using 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 using the interface is classified, policed, and marked according to the policy map attached to
the VLAN (configured on the VLAN interface) to which the 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.
For 2 rate 3 colors (2r3c) policers, if no explicit violation-action is specified, the exceed-action is
used as the violate-action.
After you configure the policy map and policing actions, attach 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 page 37-28 and the “Creating Named Aggregate Policers”
section on page 37-26.