Configuring Forwarding Classes

It is helpful to think of forwarding classes as output queues. In effect, the end result of classification is the identification of an output queue for a particular packet. For a classifier to assign an output queue to each packet, it must associate the packet with one of the following forwarding classes:

• Expedited forwarding (EF)—Provides a low loss, low latency, low jitter, assured bandwidth, end-to-end service.
• Assured forwarding (AF)—Provides a group of values you can define and includes four subclasses: AF1, AF2, AF3, and AF4, each with three drop probabilities: low, medium, and high.
• Best effort (BE)—Provides no service profile. For the BE forwarding class, loss priority is typically not carried in a class-of-service (CoS) value, and random early detection (RED) drop profiles are more aggressive.
• Network control (NC)—This class is typically high priority because it supports protocol control.

For M-series platforms (except the M320 platform), you can configure up to four forwarding classes, one of each type: EF, AF, BE, and NC.

For M320 and T-series platforms, 16 forwarding classes are supported, thus allowing you to classify packets more granularly. For example, you can configure multiple classes of EF traffic: EF, EF1, and EF2. The software supports up to eight output queues; therefore, if you configure more than eight forwarding classes, you must map multiple forwarding classes to single output queues. For more information, see Configuring Up to 16 Forwarding Classes.

By default, the loss priority is low. On most platforms, you can configure high or low loss priority. On the following platforms you can configure high, low, medium-high, or medium-low loss priority:

• J-series Services Routers interfaces with Frame Relay encapsulation
• T-series and M320 platforms with Enhanced II Flexible PIC Concentrators (FPCs)
• T640 platforms with Enhanced Scaling FPC4

For more information, see Classifying Frame Relay Traffic and Configuring Two-Rate Tricolor or Four-Color Marking.

To configure CoS forwarding classes, include the following statements at the [edit class-of-service] hierarchy level of the configuration:

class-of-service {

    forwarding-classes {

        class class-name queue-num queue-number priority (high | low);

        queue queue-number class-name priority (high | low);

    }

    interfaces {

        interface-name {

            unit logical-unit-number {

                forwarding-class class-name;

            }

        }

    }

    restricted-queues {

        forwarding-class class-name queue queue-number;

    }

}

This chapter discusses the following topics:

• Default Forwarding Classes
• Configuring Forwarding Classes
• Assigning a Forwarding Class to an Interface
• Overriding Fabric Priority Queuing
• Configuring Up to 16 Forwarding Classes
• Configuring Up to Eight Forwarding Classes