Packet Loss Priority Configuration Overview
Loss priority settings help determine which packets are dropped from the network during periods of congestion. The software supports multiple packet loss priority (PLP) designations: low and high. (In addition, medium-low and medium-high PLPs are supported when you configure tricolor marking, as discussed in Configuring Tricolor Marking.) You can set PLP by configuring a behavior aggregate or multifield classifier, as discussed in Setting Packet Loss Priority and Configuring Multifield Classifiers.
 | Note: 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. |
A drop-profile map examines the loss priority setting of an outgoing packet: high, medium-high, medium-low, low, or any.
Obviously, low, medium-low, medium-high, and high are relative terms, which by themselves have no meaning. Drop profiles define the meanings of the loss priorities. In the following example, the low-drop drop profile defines the meaning of low PLP as a 10 percent drop probability when the fill level is 75 percent and a 40 percent drop probability when the fill level is 95 percent. The high-drop drop profile defines the meaning of high PLP as a 50 percent drop probability when the fill level is 25 percent and a 90 percent drop probability when the fill level is 50 percent.
In this example, the scheduler includes two drop-profile maps, which specify that packets are evaluated by the low-drop drop profile if they have a low loss priority and are from any protocol. Packets are evaluated by the high-drop drop profile if they have a high loss priority and are from any protocol.
