Cisco WS-SUP32-GE-3B Software Configuration Guide - Page 553

Chapter 38 Configuring PFC QoS Understanding How PFC QoS Works For policy map classes that include both an aggregate and a microflow policer, PFC QoS responds to an out-of-profile status from either policer and, as specified by the policer, applies a new DSCP value or drops the packet. If both policers return an out-of-profile status, then if either policer specifies that the packet is to be dropped, it is dropped; otherwise, PFC QoS applies a marked-down DSCP value. Note To avoid inconsistent results, ensure that all traffic policed by the same aggregate policer has the same trust state. With a PFC3B, policing uses the Layer 2 frame size. You specify the bandwidth utilization limit as a committed information rate (CIR). You can also specify a higher peak information rate (PIR). Packets that exceed a rate are "out of profile" or "nonconforming." In each policer, you specify if out-of-profile packets are to be dropped or to have a new DSCP value applied to them (applying a new DSCP value is called "markdown"). Because out-of-profile packets do not retain their original priority, they are not counted as part of the bandwidth consumed by in-profile packets. If you configure a PIR, the PIR out-of-profile action cannot be less severe than the CIR out-of-profile action. For example, if the CIR out-of-profile action is to mark down the traffic, then the PIR out-of-profile action cannot be to transmit the traffic. For all policers, PFC QoS uses a configurable global table that maps the internal DSCP value to a marked-down DSCP value. When markdown occurs, PFC QoS gets the marked-down DSCP value from the table. You cannot specify marked-down DSCP values in individual policers. Note • Policing with the conform-action transmit keywords supersedes the ingress LAN port trust state of matched traffic with trust DSCP or with the trust state defined by a trust policy-map class command. • By default, the markdown table is configured so that no markdown occurs: the marked-down DSCP values are equal to the original DSCP values. To enable markdown, configure the table appropriately for your network. • When you apply both ingress policing and egress policing to the same traffic, both the input policy and the output policy must either mark down traffic or drop traffic. PFC QoS does not support ingress markdown with egress drop or ingress drop with egress markdown. Understanding Port-Based Queue Types Port-based queue types are determined by the ASICs that control the ports. The following sections describe the queue types, drop thresholds, and buffers that are supported on the Catalyst 6500 series switch LAN modules: • Ingress and Egress Buffers and Layer 2 CoS-Based Queues, page 38-20 • Ingress Queue Types, page 38-21 • Egress Queue Types, page 38-22 • Module to Queue Type Mappings, page 38-23 OL-11439-03 Catalyst Supervisor Engine 32 PISA Cisco IOS Software Configuration Guide, Release 12.2ZY 38-19