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Using Multifield Classifiers to Set Packet Loss Priority

This topic describes how to use and configure multifield classifiers to set the loss priority of incoming or outgoing packets.

Multifield classifiers take action on incoming or outgoing packets, depending on whether the firewall rule is applied as an input filter or an output filter. When tricolor marking (TCM) is enabled, Juniper Networks M320 Multiservice Edge Routers and T Series Core Routers support four multifield classifier packet loss priority (PLP) designations: low, medium-low, medium-high, and high.

To configure the PLP for a multifield classifier, include the loss-priority statement in a policer or firewall filter that you configure at the at the [edit firewall] hierarchy level:

The inputs (match conditions) for a multifield classifier are one or more of the six packet header fields: destination address, source address, IP protocol, source port, destination port, and DSCP. The outputs for a multifield classifier are the forwarding class and the loss priority (PLP). A multifield classifier sets the forwarding class and the PLP for each packet entering or exiting the interface with a specific destination address, source address, IP protocol, source port, destination port, or DSCP.

In the following sample procedure, the forwarding class expedited-forwarding and PLP medium-high are assigned to all IPv4 packets with the or source address.

To use the classifier in this sample procedure, you must configure the settings for the expedited-forwarding forwarding class at the [edit class-of-service forwarding-classes queue queue-number expedited-forwarding] hierarchy level. For more information, see Understanding How Forwarding Classes Assign Classes to Output Queues.

  1. Under the firewall statement, specify the protocol family as IPv4 (inet) and specify a name for the filter.
  2. Specify the term name and match criteria you want to look for in incoming packets.
  3. Specify the action you want to take when a packet matches the conditions.
  4. Verify your configuration.
  5. Save your configuration.