Understanding Cos Classifiers; Behavior Aggregate Classifiers - Juniper JUNOS OS 10.4 - FOR EX REV 1 Manual

Understanding CoS Classifiers

Behavior Aggregate Classifiers

Copyright © 2010, Juniper Networks, Inc.
Packet classification associates incoming packets with a particular class-of-service
(CoS) servicing level. Classifiers associate packets with a forwarding class and loss
priority and assign packets to output queues based on the associated forwarding class.
There are two general types of classifiers:
Behavior aggregate (BA) classifiers
Multifield (MF) classifiers
You can configure both a BA classifier and an MF classifier on an interface. If you do this,
the BA classification is performed first and then the MF classification. If the two
classification results conflict, the MF classification result overrides the BA classification
result.
NOTE: When a source media access control (MAC) address is learned, the
frame that contains the source MAC address is always sent out on queue 0
while egressing from the network interface, irrespective of the classifier
applied to the ingress interface.
On Juniper Networks EX8200 Ethernet Switches, you can specify BA classifiers for bridged
multidestination traffic and IP multidestination traffic. The BA classifier for multicast
packets is applied to all interfaces on the EX8200 switch.
This topic describes:
Behavior Aggregate Classifiers on page 3381
Multifield Classifiers on page 3383
The behavior aggregate classifier maps a CoS value to a forwarding class and loss priority.
The forwarding class determines the output queue. The loss priority is used by a scheduler
to control packet discard during periods of congestion.
There are three types of BA classifiers:
Differentiated Services Code Point (DSCP) for IP DiffServ
IP precedence bits
IEEE 802.1p CoS bits
BA classifiers are based on fixed-length fields, which makes them computationally more
efficient than MF classifiers. Therefore core devices, which handle high traffic volumes,
are normally configured to perform BA classification.
Chapter 113: Class of Service (CoS)—Overview
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