Traffic Classes

A traffic class is a systemwide collection of buffers, queues, and bandwidth that you can allocate to provide a defined level of service to packets in the traffic class.

A traffic class corresponds to what the IETF DiffServ working group calls a traffic class in RFC 2597—Assured Forwarding PHB Group (June 1999).

Traffic classes are global to the router. Packets are:

• Classified into a traffic class on ingress or egress
• Queued on fabric queues that are specific to the traffic class
• Queued on the egress line module on queues that are specific to the traffic class
• Scheduled for transmission

Input policies classify packets into the traffic class; the fabric carries the packets to an egress line module in a fabric queue that is specific to the traffic class; the packets are placed into traffic class-specific queues on the egress line module; and the scheduler schedules the packets for transmission.

Best-Effort Forwarding

The router has a default traffic class called best-effort. You cannot delete this class. You can add the best-effort class to a traffic-class group. The router assigns packets to the best-effort class in each of the following cases:

• You do not create any other traffic classes.
• Packets are not classified into a traffic class.
• Packets arrive at an egress line module that has no queues allocated for their traffic class.

Configuring a Traffic Class

To configure a traffic class:

1. Create a traffic class and enter Traffic Class Configuration mode.

host1(config)#traffic class low-loss1

host1(config-traffic-class)#

2. (Optional) For ERX-1440 routers, specify the relative weight for queues in the traffic class in the fabric.

host1(config-traffic-class)#fabric-weight 12

3. (Optional) Specify strict-priority scheduling across the fabric.

host1(config-traffic-class)#fabric-strict-priority

fabric-strict-priority

• Use to specify strict-priority scheduling across the fabric for queues in the traffic class.
• If multiple traffic classes are strict priority, the fabric weight determines which class gets more bandwidth.
• Example

host1(config-traffic-class)#fabric-strict-priority

• Use the no version to delete the strict-priority setting.

fabric-weight

• Use to specify the relative weight for queues in the traffic class in the fabric.
• Fabric weight controls the bandwidth of fabric queues associated with the traffic class. It does not control the weight of egress queues associated with the traffic class.
• The weight value is in the range 1-63. Zero is not a valid weight.
  

  NOTE: The fabric-weight command works only with ERX-1440 routers.

  
  
• Example

host1(config-traffic-class)#fabric-weight 12

• Use the no version to set the fabric to the default weight value, 8.

traffic-class

• Use to configure a traffic class and enter Traffic Class Configuration mode.
• The traffic class name can be up to 32 characters. It cannot include spaces.
• The router supports up to eight global traffic classes.
• Each traffic class can appear in only one traffic-class group. If not explicitly added to a traffic-class group, the traffic class is considered to be ungrouped.
• Example

host1(config)#traffic class low-loss1

host1(config-traffic-class)#

• Use the no version to delete a specified traffic class.