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RED Drop Profiles Overview on ACX Series Routers

 

You can configure two parameters to control congestion at the output stage. The first parameter defines the delay-buffer bandwidth, which provides packet buffer space to absorb burst traffic up to the specified duration of delay. When the specified delay buffer becomes full, packets with 100 percent drop probability are dropped from the head of the buffer.

The second parameter defines the drop probabilities across the range of delay-buffer occupancy, supporting the random early detection (RED) process. When the number of packets queued is greater than the ability of the router to empty a queue, the queue requires a method for determining which packets to drop from the network. To address this, Junos OS provides the option of enabling RED on individual queues.

Depending on the drop probabilities, RED might drop many packets long before the buffer becomes full, or it might drop only a few packets even if the buffer is almost full.

A drop profile is a mechanism of RED that defines parameters that allow packets to be dropped from the network. Drop profiles define the meanings of the loss priorities.

Note

The ACX6360 router does not support drop profiles.

When you configure drop profiles, there are two important values: the queue fullness and the drop probability. The queue fullness represents a percentage of the memory used to store packets in relation to the total amount that has been allocated for that specific queue. Similarly, the drop probability is a percentage value that correlates to the likelihood that an individual packet is dropped from the network.

The ACX5448 router supports configuring drop profiles (to specify different drop behavior) for loss-priority low, medium-high and high for tcp protocol, as well as for non-tcp protocol. Priority setting (either strict-priority or low) for a particular queue does not affect WRED behavior. The default behavior for any queue is to have tail drops. There are two fill levels supported on the ACX5448 router and the first fill level for drop probability should be zero.

Note

The ACX5448 router does not support interpolate drop-probability and supports only the discrete method.

You specify drop probabilities at the [edit class-of-service drop-profiles drop profile-name fill-level percentage drop-probability percentage;] class-of-service (COS) configuration hierarchy and reference them in each scheduler configuration. For each scheduler, you can configure four drop profiles as high-tcp, medium-high-tcp, low-tcp, non-tcp. Two fill levels can be specified in each drop-profile map. The drop probability associated with the least fill level must be set as zero, otherwise the CLI command will be rejected during commit check.