Cisco Systems 3750E manual Policing and Marking, 36-8

Chapter 36 Configuring QoS

Understanding QoS

The policy map can contain the police and police aggregate policy-map class configuration commands, which define the policer, the bandwidth limitations of the traffic, and the action to take if the limits are exceeded.

To enable the policy map, you attach it to a port by using the service-policyinterface configuration command.

You can apply a nonhierarchical policy map to a physical port or an SVI. However, a hierarchical policy map can only be applied to an SVI. A hierarchical policy map contains two levels. The first level, the VLAN level, specifies the actions to be taken against a traffic flow on the SVI. The second level, the interface level, specifies the actions to be taken against the traffic on the physical ports that belong to the SVI. The interface-level actions are specified in the interface-level policy map.

For more information, see the “Policing and Marking” section on page 36-8. For configuration information, see the “Configuring a QoS Policy” section on page 36-45.

Policing and Marking

After a packet is classified and has a DSCP-based or CoS-based QoS label assigned to it, the policing and marking process can begin as shown in Figure 36-4.

Policing involves creating a policer that specifies the bandwidth limits for the traffic. Packets that exceed the limits are out of profile or nonconforming. Each policer decides on a packet-by-packet basis whether the packet is in or out of profile and specifies the actions on the packet. These actions, carried out by the marker, include passing through the packet without modification, dropping the packet, or modifying (marking down) the assigned DSCP of the packet and allowing the packet to pass through. The configurable policed-DSCP map provides the packet with a new DSCP-based QoS label. For information on the policed-DSCP map, see the “Mapping Tables” section on page 36-12. Marked-down packets use the same queues as the original QoS label to prevent packets in a flow from getting out of order.

Note All traffic, regardless of whether it is bridged or routed, is subjected to a policer, if one is configured. As a result, bridged packets might be dropped or might have their DSCP or CoS fields modified when they are policed and marked.

You can configure policing on a physical port or an SVI. For more information about configuring policing on physical ports, see the “Policing on Physical Ports” section on page 36-9. When configuring policy maps on an SVI, you can create a hierarchical policy map and can define an individual policer only in the secondary interface-level policy map. For more information, see the “Policing on SVIs” section on page 36-10.

After you configure the policy map and policing actions, attach the policy to an ingress port or SVI by using the service-policyinterface configuration command. For configuration information, see the “Classifying, Policing, and Marking Traffic on Physical Ports by Using Policy Maps” section on page 36-51, the “Classifying, Policing, and Marking Traffic on SVIs by Using Hierarchical Policy Maps” section on page 36-55, and the “Classifying, Policing, and Marking Traffic by Using Aggregate Policers” section on page 36-61.

Catalyst 3750-E and 3560-E Switch Software Configuration Guide

36-8 OL-9775-02