Forwarding Classes Overview
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 best effort 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 Juniper Networks M Series Multiservice Edge Routers (except the M320), you can configure up to four forwarding classes, one of each type: expedited forwarding (EF), assured forwarding (AF), best effort (BE), and network control (NC).
The Juniper Networks M320 Multiservices Edge Routers and Juniper Networks T Series Core Routers support 16 forwarding classes, enabling 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 routers, you can configure high or low loss priority. On the following routers you can configure high, low, medium-high, or medium-low loss priority:
- Juniper Networks J Series Services Router interfaces
- M320 routers and T Series routers with Enhanced II Flexible PIC Concentrators (FPCs)
- T640 routers with Enhanced Scaling FPC4s
For more information, see the J Series router documentation and Policer Overview.
