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Managing Congestion by Setting Packet Loss Priority for Different Traffic Flows

By default, the least significant bit of the CoS value sets the packet loss priority (PLP) value. For example, CoS value 000 is associated with PLP low, and CoS value 001 is associated with PLP high. In general, you can change the PLP by configuring a behavior aggregate (BA) or multifield classifier, as discussed in Understanding How Behavior Aggregate Classifiers Prioritize Trusted Traffic and Overview of Assigning Service Levels to Packets Based on Multiple Packet Header Fields.

However, on Juniper Networks M320 Multiservice Edge Routers, MX Series 5G Universal Routing Platforms, and T Series Core Routers and EX Series switches that do not have tricolor marking enabled, the loss priority can be configured by setting the PLP within a multifield classifier or by behavior aggregate (BA) classifier. This setting can then be used by the appropriate drop profile map and rewrite rule.

On M320 routers and T Series routers with Enhanced II Flexible PIC Concentrators (FPCs) and tricolor marking enabled, you can set the PLP with a BA or multifield classifier, as described in Configuring Behavior Aggregate Classifiers and Using Multifield Classifiers to Set Packet Loss Priority.

On T Series routers with different Packet Forwarding Engines (non-Enhanced Scaling and Enhanced Scaling FPCs), you can configure PLP bit copying for ingress and egress unicast and multicast traffic. To configure, include the copy-plp-all statement at the [edit class-of-service] hierarchy level.

The following example shows a two-step procedure to override the default PLP settings on M320 routers.

The first part of this example specifies that while the DSCP code points are 110, the loss priority is set to high; however, on M320 routers, overriding the default PLP this way has no effect.

  1. Configure the classifier name and specify it as type as DSCP.
  2. Specify the forwarding class

For M320 routers, use the following procedure to configure a multifield classifier that sets the PLP.

  1. Under the firewall statement, 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.