Cisco 3845 Software Guide - Page 502

Understanding QoS Chapter 27 Configuring QoS When you configure a 2-rate policer, you configure the committed information rate (CIR) for updating the first token bucket, and you also configure the peak information rate (PIR) at which the second token bucket is updated. If you do not configure a PIR, the policer is a standard 1-rate, 2-color policer. For 2-rate, 3-color policing, you can then choose to set actions to perform on packets that conform to the specified CIR and PIR (conform-action), packets that conform to the PIR, but not the CIR (exceed-action), and packets that exceed the PIR value (violate-action). • If you set the CIR value equal to the PIR, a traffic rate that is less than or equal to the CIR is in the conform range. Traffic that exceeds the CIR is in the violate range. • If you set the PIR greater than the CIR, a traffic rate less than the CIR is in the conform range. A traffic rate that exceeds the CIR but is less than or equal to the PIR is in the exceed range. A traffic rate that exceeds the PIR is in the violate range. • If you do not configure a PIR, the policer is configured as a 1-rate, 2-color policer. Setting the burst sizes too low can reduce throughput in situations with bursty traffic. Setting burst sizes too high can allow too high a traffic rate. Note The switch supports byte counters for byte-level statistics for conform, exceed, and violate classes in the show policy-map interface privileged EXEC command output. Use the service-policy input interface configuration command to attach the policy map to a physical port or EFP service instance to make it effective. For more information, see the "Attaching a Service Policy to an Interface or EFP" section on page 27-56. Policing is done only on received traffic, so you can only attach a policer to an input service policy. See the "Configuring a Policy Map with 1-Rate, 2-Color Policing" section on page 27-34 for configuration examples. You can use the conform-action, exceed-action, and violate-action policy-map class configuration commands or the conform-action, exceed-action, and violate-action policy-map class police configuration commands to specify an action when the packet conforms to or exceeds the specified traffic rates. Conform, exceed, and violate actions are to drop the packet, to send the packet without modifications, to set a new CoS, DSCP, or IP precedence value, or to set a QoS group value for classification at the egress. You can simultaneously configure multiple conform, exceed, and violate actions for each service class. Marking You can use packet marking in input policy maps to set or modify the attributes for traffic belonging to a specific class. For example, you can change the CoS value in a class or set IP DSCP or IP precedence values for a specific type of traffic. These new values are then used to determine how the traffic should be treated. You can also use marking to assign traffic to a QoS group within the switch. Traffic marking is typically performed on a specific traffic type at the ingress port. The marking action can cause the CoS, DSCP, or precedence bits to be rewritten or left unchanged, depending on the configuration. This can increase or decrease the priority of a packet in accordance with the policy used in the QoS domain so that other QoS functions can use the marking information to judge the relative and absolute importance of the packet. The marking function can use information from the policing function or directly from the classification function. 27-14 Cisco ME 3800X and 3600X Switch Software Configuration Guide OL-23400-01