Cisco 3845 Software Guide - Page 492

Understanding QoS Chapter 27 Configuring QoS • The QoS features to apply to the classified traffic. These include the set or police commands for input policy maps or the bandwidth, priority, queue-limit or shape average commands for output policy maps. Note A packet can match only one traffic class within a traffic policy. If a packet matches more than one traffic class in the traffic policy, the first traffic class defined in the policy is used. To configure more than one match criterion for packets, you can associate multiple traffic classes with a single traffic policy. Step 3 Attach the traffic policy to a target, which can be an interface or an EFP service instance. Use the service-policy interface configuration command to attach the policy map to a target and to specify if the policy should be applied to packets that enter or leave the target. For example, entering the service-policy output policy1 interface configuration command attaches all the characteristics of the traffic policy named class1 to the interface. Entering the service-policy output policy1 service instance configuration command attaches all the characteristics of the traffic policy named class1 to the EFP service policy. All packets leaving the target are evaluated according to the criteria specified in the traffic policy class1. You cannot attach traffic policies to interfaces on which an EFP service instance is configured. Note If you enter the no policy-map policy-map-name global configuration command to delete a policy map that is attached to an interface or service instance, a warning message appears that lists any interfaces from which the policy map is being detached. The policy map is then detached and deleted. For example: Warning: Detaching Policy test1 from Interface GigabitEthernet0/1 Hierarchical QoS Hierarchical QoS configuration involves traffic classification, policing, queuing, and scheduling. You can create a hierarchy by associating a class-level policy map with a VLAN-level policy map, by associating that VLAN-level policy map with a physical-level policy map, and by attaching the physical-level policy map to a port or EFP. You can omit hierarchical levels, but the order of levels (class level, VLAN level, and then physical level) must be preserved. You can configure three QoS levels in the hierarchy: • Class level-You configure this level of the hierarchy by matching CoS, DSCP, IP precedence, MAC ACLs, IP ACLs, QoS groups, discard-class, or MPLS EXP bits in the packet by using the match {access-group name | cos [inner] cos-list | discard-class value | dscp dscp-list | ip precedence ip-precedence-list | mpls experimental exp-list} | qos-group value class-map configuration command. At the class level, you can use policy-map class configuration commands to: - Configure policer drops by using the police cir or police cir percent command. - Configure tail drop policies by using the queue-limit command. - Modify the traffic class by setting Layer 2 and Layer 3 QoS fields by using the set commands. - Configure scheduling by using the bandwidth or the priority command. - Configure traffic shaping by using the shape command. 27-4 Cisco ME 3800X and 3600X Switch Software Configuration Guide OL-23400-01