Cisco IE-3000-8TC Software Configuration Guide - Page 691

Chapter 36 Configuring QoS Configuring Standard QoS Standard QoS Configuration Guidelines Before beginning the QoS configuration, you should be aware of this information in these sections: • "QoS ACL Guidelines" section on page 36-31 • "Policing Guidelines" section on page 36-31 • "General QoS Guidelines" section on page 36-32 QoS ACL Guidelines These are the guidelines with for configuring QoS with access control lists (ACLs): • If you use QoS ACLs for classification, you can use the sdm prefer qos global configuration command to set the Switch Database Management (SDM) feature to the QoS template. SDM configures system resources to support the maximum number of access control entries (ACEs). For more information on the SDM templates, see Chapter 10, "Configuring SDM Templates." • It is not possible to match IP fragments against configured IP extended ACLs to enforce QoS. IP fragments are sent as best-effort. IP fragments are denoted by fields in the IP header. • Only one ACL per class map and only one match class-map configuration command per class map are supported. The ACL can have multiple ACEs, which match fields against the contents of the packet. • A trust statement in a policy map requires multiple TCAM entries per ACL line. If an input service policy map contains a trust statement in an ACL, the access-list might be too large to fit into the available QoS TCAM and an error can occur when you apply the policy map to a port. Whenever possible, you should minimize the number of lines in a QoS ACL. Policing Guidelines These are the policing guidelines: • The port ASIC device, which controls more than one physical port, supports 256 policers (255 user-configurable policers plus 1 policer reserved for system internal use). The maximum number of user-configurable policers supported per port is 63. Policers are allocated on demand by the software and are constrained by the hardware and ASIC boundaries. You cannot reserve policers per port; there is no guarantee that a port will be assigned to any policer. • Only one policer is applied to a packet on an ingress port. Only the average rate and committed burst parameters are configurable. • You can set the policing rate only in 1-Mb/s increments. If you try to set a policing rate at less than1 Mb/s, the switch prompts you for a correct value. • On a port configured for QoS, all traffic received through the port is classified, policed, and marked according to the policy map attached to the port. On a trunk port configured for QoS, traffic in all VLANs received through the port is classified, policed, and marked according to the policy map attached to the port. • If you have EtherChannel ports configured on your switch, you must configure QoS classification, policing, mapping, and queueing on the individual physical ports that comprise the EtherChannel. You must decide whether the QoS configuration should match on all ports in the EtherChannel. OL-13018-03 Cisco IE 3000 Switch Software Configuration Guide 36-31