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Mapping CoS Component Inputs to Outputs

Some CoS components map one set of values to another set of values. Each mapping contains one or more inputs and one or more outputs.

Figure 1 shows the components of the Junos OS CoS features, illustrating the sequence in which they interact.

Figure 1: Packet Flow Through CoS-Configurable ComponentsPacket Flow Through CoS-Configurable Components
Tip:

Component mapping enables you to define forwarding classes and packet loss priorities for various traffic flows and then map those forwarding classes to output queues with specific shaping and scheduling characteristics.

When you configure a mapping, you set the outputs for a given set of inputs, as shown in Table 1.

Table 1: CoS Mappings—Inputs and Outputs

CoS Mappings

Inputs

Outputs

Comments

classifiers

code-points

forwarding-classloss-priority

The map sets the forwarding class and PLP for a specific set of code points.

drop-profile-map

loss-priorityprotocol

drop-profile

The map sets the drop profile for a specific PLP and protocol type.

scheduler-maps

forwarding-class

scheduler

This map assigns a forwarding class to a specific scheduler.

rewrite-rules

forwarding-class loss-priority

code-points

The map sets the code points for a specific forwarding class and PLP.

Following are sample configurations for classifiers, drop-profile maps, scheduler maps, and rewrite rules.

In the following classifier sample configuration, packets with EXP bits 000 are assigned to the data-queue forwarding class with a low loss priority, and packets with EXP bits 001 are assigned to the data-queue forwarding class with a high loss priority.

See Configuring Behavior Aggregate Classifiers for more information on setting the forwarding class and loss priority for a specific set of code-point aliases and bit patterns

In the following drop-profile map sample configuration, the scheduler includes two drop-profile maps, which specify that packets are evaluated by the low-drop drop profile if they have a low loss priority and are from any protocol. Packets are evaluated by the high-drop drop profile if they have a high loss priority and are from any protocol.

See Determining Packet Drop Behavior by Configuring Drop Profile Maps for Schedulers for more information on mapping drop profiles to a scheduler.

In the following scheduler maps configuration sample, each of the default forwarding classes is mapped to a scheduler specifically designed for that forwarding class.

See Configuring Scheduler Maps for more information on mapping forwarding classes to schedulers.

In the following rewrite rule configuration sample, packets in the be forwarding class with low loss priority are assigned the EXP bits 000, and packets in the be forwarding class with high loss priority are assigned the EXP bits 001.

See Configuring Rewrite Rules for more information on setting the code-point aliases and bit patterns for specific forwarding classes and loss priorities as packets leave the device.