BA Classifier Overview

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 classifiers (which are discussed in Multifield Classifier Overview), BA classifiers are based on fixed-length fields, which makes them computationally more efficient than multifield 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 Overview.

For Juniper Networks M Series Multiservice Edge Routers, four classes can forward traffic independently. For M320 Multiservice Edge Routers and T Series Core Routers, 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.

For MX Series Ethernet Services Routers and Intelligent Queuing 2 (IQ2) PICs, the following restrictions apply:

• You can only use multifield classifiers for IPv4 DSCP bits for virtual private LAN service (VPLS).
• You cannot use BA classifiers for IPv4 DSCP bits for Layer 2 VPNs.
• You cannot use BA classifiers for IPv6 DSCP bits for VPLS.
• You cannot use BA classifiers for IPv6 DSCP bits for Layer 2 VPNs.

For the 10-port 10-Gigabit Oversubscribed Ethernet (OSE) PICs, the following restrictions on BA classifiers apply:

• Multiple classifiers can be configured to a single logical interface. However, there are some restrictions on which the classifiers can coexist.

  For example, the DSCP and IP precedence classifiers cannot be configured on the same logical interface. The DSCP and IP precedence classifiers can coexist with the DSCP IPv6 classifier on the same logical interface. An IEEE 802.1 classifier can coexist with other classifiers and is applicable only if a packet does not match any of the configured classifiers. For information about the supported combinations, see Applying Classifiers to Logical Interfaces.

• If the classifiers are not defined explicitly, then the default classifiers are applied as follows:

  • All MPLS packets are classified using the MPLS (EXP) classifier. If there is no explicit MPLS (EXP) classifier, then the default MPLS (EXP) classifier is applied.
  • All IPv4 packets are classified using the IP precedence and DSCP classifiers. If there is no explicit IP precedence and DSCP classifiers, then the default IP precedence classifier is applied.
  • All IPv6 packets are classified using DSCP IPv6 classifier. If there is no explicit DSCP IPv6 classifier, then the default DSCP IPv6 classifier is applied.
  • If the IEEE 802.1p classifier is configured and a packet does not match any explicitly configured classifier, then the IEEE 802.1p classifier is applied.

Note: For a specified interface, you can configure both a multifield classifier and a BA classifier without conflicts. Because the classifiers are always applied in sequential order, the BA classifier followed by the multifield classifier, any BA classification result is overridden by an multifield classifier if they conflict. For more information about multifield classifiers, see Multifield Classifier Overview.

For MX Series routers and IQ2 PICs, the following restrictions on BA classifiers apply:

• IPv4 DSCP markings for VPLS are not supported (use multifield classifiers instead)
• IPv4 DSCP markings for Layer2 VPNs are not supported
• IPv6 DSCP markings for VPLS are not supported
• IPv6 DSCP markings for Layer2 VPNs are not supported