Cisco NM-8B-U User Guide - Page 32

Feature Overview 16- and 36-Port Ethernet Switch Module for Cisco 2600 Series, Cisco 3600 Series, and Cisco 3700 Series • Policing determines whether a packet is in or out of profile according to the configured policer, and the policer limits the bandwidth consumed by a flow of traffic. The result of this determination is passed to the marker. For more information, see the "Policing and Marking" section on page 34. • Marking evaluates the policer and configuration information for the action to be taken when a packet is out of profile and decides what to do with the packet (pass through a packet without modification, mark down the DSCP value in the packet, or drop the packet). For more information, see the "Policing and Marking" section on page 34. Actions at the egress interface include queueing and scheduling: • Queueing evaluates the CoS value and determines which of the four egress queues in which to place the packet. • Scheduling services the four egress queues based on their configured WRR weights. Figure 15 Basic QoS Model Actions at ingress Classification Policing In profile or out of profile Mark Classifies the packet based on the ACL. Determines if the packet is in profile or out of profile based on the policer associated with the filter. Based on whether the packet is in or out of profile and the configured parameters, determines whether to pass through, mark down, or drop the packet. The DSCP and CoS are marked or changed accordingly. Actions at egress Queuing and scheduling Based on the CoS, determines into which of the egress queues to place the packet, then services the queues according to the configured weights. 60979 Classification Classification is the process of distinguishing one kind of traffic from another by examining the fields in the packet. Classification occurs only on a physical interface basis. No support exists for classifying packets at the VLAN or the switched virtual interface level. You specify which fields in the frame or packet that you want to use to classify incoming traffic. Classification Based on QoS ACLs You can use IP standard or IP extended ACLs to define a group of packets with the same characteristics (class). In the QoS context, the permit and deny actions in the access control entries (ACEs) have different meanings than with security ACLs: • If a match with a permit action is encountered (first-match principle), the specified QoS-related action is taken. • If no match with a permit action is encountered and all the ACEs have been examined, no QoS processing occurs on the packet. • If multiple ACLs are configured on an interface, the packet matches the first ACL with a permit action, and QoS processing begins. Cisco IOS Release 12.2(2)XT, 12.2(8)T, and 12.2(15)ZJ 32