Classifying Packets by Behavior Aggregate

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The behavior aggregate (BA) classifier maps a class-of-service (CoS) value 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.

The types of BA classifiers are based on which part of the incoming packet the classifier examines:

Differentiated Services code point (DSCP) for IP DiffServ
DSCP for IPv6 DiffServ
IP precedence bits
MPLS EXP bits
IEEE 802.1p CoS bits
IEEE 802.1ad drop eligible indicator (DEI) bit

Unlike multifield (MF) classifiers (which are discussed in Classifying Packets Based on Various Packet Header Fields), BA classifiers are based on fixed-length fields, which makes them computationally more efficient than multifield (MF) classifiers. For this reason, core devices are normally configured to perform BA classification, because of the higher traffic volumes they handle.

In most cases, you need to rewrite a given marker (IP precedence, DSCP, IEEE 802.1p, IEEE 802.1ad, or MPLS EXP settings) at the ingress node to accommodate BA classification by core and egress devices. For more information about rewrite markers, see Rewriting Packet Header Information.

For M-series routing platforms, four classes can forward traffic independently. For M320 and T-series platforms, eight classes can forward traffic independently. Therefore, you must configure additional classes to be aggregated into one of these classes. You use the BA classifier to configure class aggregation.

Note: For a specified interface, you can configure both an MF classifier and a BA classifier without conflicts. Because the classifiers are always applied in sequential order, the BA classifier followed by the MF classifier, any BA classification result is overridden by an MF classifier if they conflict. For more information about MF classifiers, see Classifying Packets Based on Various Packet Header Fields.

To configure BA classifiers, you can include the following statements at the [edit class-of-service] hierarchy level of the configuration:



[edit class-of-service]

classifiers {


(dscp | dscp-ipv6 | exp | ieee-802.1 | ieee-802.1ad | inet-precedence) classifier-name {

import (classifier-name | default);



forwarding-class class-name {



loss-priority level {

code-points [ aliases ] [ 6-bit-patterns ];
}


}


}


}

interfaces {



interface-name {



unit logical-unit-number {



classifiers {
(dscp | dscp-ipv6 | exp | ieee-802.1 | ieee-802.1ad | inet-precedence)
(classifier-name | default);
}


}


}


}

routing-instances routing-instance-name {



classifiers {
exp (classifier-name | default);
}


}

This chapter discusses the following topics:

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