Slope policies

General Information

Slope policies are applied to access ports, network ports, and network daughter cards.

Slope policies define weighted RED (WRED) slope characteristics for buffer pools. Low-priority and high-priority slopes are specified when you configure a slope policy. If a slope policy is not explicitly specified, a default policy is applied.

Each buffer pool supports a high-priority, a low-priority RED slope, an Exceed Slope, and a HighPlus Slope. The high-priority RED slope manages access to the shared portion of the buffer pool for the high-priority or in-profile packets. The low-priority RED slope manages access to the shared portion of the buffer pool for low-priority or out-of-profile packets. The Exceed slope handles the exceeded profile traffic congestion control at the pool and megapool level. The Exceed slope is only used for exceed profile traffic when it is not shutdown. The defaults for the Exceed slope parameters should be set so that they are lower than the low slope in the slope hierarchy. Finally, the HighPlus Slope handles the inplus profile traffic congestion control. A HighPlus Slope policy can be applied to pool-per-queue queues in an egress queue group template, which in turn can be applied at a network egress port. The HighPlus Slope is also supported in a slope policy applied to the egress WRED megapool. The values for the HighPlus Slope parameters should be set so that they are higher than the High Slope in the slope hierarchy. By default, the Low, High, Exceed, and HighPlus slopes are initially disabled.

A RED slope is a graph with an X (horizontal) and Y (vertical) axis. The X axis plots the percentage of shared buffer utilization, from 0 to 100%. The Y axis plots the probability of packet discard marked from 0 to 1. The slope is defined as four sections, as shown in the following figure.

Figure 50-1: RED slope characteristics

Section A is (0, 0) to (start-avg, 0). For this part of the slope, the packet discard value is always zero, which prevents the RED function from discarding packets when the shared buffer average utilization falls between 1 and start-avg.

Section B is (start-avg, 0) to (max-avg, max-prob). This part of the slope is linear where packet discard probability increases from zero to max-prob.

Section C is (max-avg, max-prob) to (max-avg, 1). This part of the slope shows the instantaneous increase of packet discard probability from max-prob to one. A packet discard probability of one results in an automatic discard of the packet.

Section D is (max-avg, 1) to (100%, 1). On this part of the slope, the shared buffer average utilization value of max-avg to 100% results in a packet discard probability of one.