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RED Drop Profiles Overview

 

A drop profile is a feature of the random early detection (RED) process that allows packets to be dropped before queues are full. Drop profiles are composed of two main values—the queue fullness and the drop probability. The queue fullness represents percentage of memory used to store packets in relation to the total amount that has been allocated for that queue. The drop probability is a percentage value that correlates to the likelihood that an individual packet is dropped from the network. These two variables are combined in a graph-like format.

A random number between 0 and 100 is calculated for each packet. This random number is plotted against the drop profile having the current queue fullness of that particular queue. When the random number falls above the graph line, the packet is transmitted onto the physical media. When the number falls below the graph line, the packet is dropped from the network.

Randomly dropped packets are counted as RED-dropped, while packets dropped for other reasons (100% probability) are counted as tail-dropped.

You specify drop probabilities in the drop profile section of the class-of-service (CoS) configuration hierarchy and reference them in each scheduler configuration. For each scheduler, you can configure multiple separate drop profiles, one for each combination of loss priority (low, medium-low, medium-high, or high) and IP transport protocol (TCP or non-TCP or any).

Note

For some SRX Series devices, tcp and non-tcp values are not supported; only the value “any” is supported. Actual platform support depends on the Junos OS release in your implementation.

You can configure a maximum of 32 different drop profiles.

To configure RED drop profiles, include the following statements at the [edit class-of-service] hierarchy level of the configuration:

Default Drop Profiles

By default, if you configure no drop profiles, RED is still in effect and functions as the primary mechanism for managing congestion. In the default RED drop profile, when the fill level is 0 percent, the drop probability is 0 percent. When the fill level is 100 percent, the drop probability is 100 percent.