Configuring Multifield Classifiers - Juniper ACX1000 Configuration Manual

ACX Series Universal Access Router Configuration Guide
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Configuring Multifield Classifiers

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Figure 56: How a Classifier Works
In Junos OS, you configure a multifield classifier with a firewall filter and its associated
match conditions. This enables you to use any filter match criteria to locate packets that
require classification. From a CoS perspective, multifield classifiers (or firewall filter rules)
provide the following services:
Classify packets to a forwarding class and loss priority. The forwarding class determines
the output queue. The loss priority is used by schedulers in conjunction with the random
early discard (RED) algorithm to control packet discard during periods of congestion.
Police traffic to a specific bandwidth and burst size. Packets exceeding the policer
limits can be discarded, or can be assigned to a different forwarding class, to a different
loss priority, or to both.
NOTE: You police traffic on input to conform to established CoS parameters,
setting loss handling and forwarding class assignments as needed. You shape
traffic on output to make sure that router resources, especially bandwidth,
are distributed fairly. However, input policing and output shaping are two
different CoS processes, each with their own configuration statements.
Understanding How Behavior Aggregate Classifiers Prioritize Trusted Traffic on page 950
Configuring Multifield Classifiers on page 892
This topic describes how you configure multifield classifiers.
Multifield classifiers classify packets to a forwarding class and loss priority based on the
filter match criteria. Multifield classification is usually done at the edge of the network
for packets that do not have valid or trusted behavior aggregate code points.
If you configure both a behavior aggregate (BA) classifier and a multifield classifier, BA
classification is performed first; then multifield classification is performed. If they conflict,
any BA classification result is overridden by the multifield classifier.
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