Supported Platforms
Configuring CoS Tail-Drop Profiles
You can configure an interpolated weighted random early detection (WRED) tail-drop profile to control packet drop characteristics for different traffic loss priorities.
 | Note: You cannot enable WRED on multidestination (multicast) queues. You can enable WRED only on unicast queues. Also, do not enable WRED on lossless traffic flows. Use priority-based flow control (PFC) to prevent packet loss on lossless forwarding classes. |
Interpolated means that the switch creates a smooth drop curve from a drop start point to a drop end point, with a maximum drop rate that is reached at the drop end point.
The drop start point is the average queue fill level when the WRED algorithm starts to drop packets. Before the drop start point, no packets are scheduled to drop. Specify the drop start point using the first of two fill-level statements.
The drop end point is the average queue fill level at which all subsequently arriving packets are dropped. When the queue fill levels falls below the drop end point, packets begin to be forwarded again. (At the drop end point, the packet drop probability becomes 100 percent.) Specify the drop end point using the second of two fill-level statements.
The minimum drop rate is always 0. Specify the minimum drop rate using the first of two drop-probability statements. The maximum drop rate is the drop probability when the average queue fill level reaches the drop end point. Specify the maximum drop rate using the second of two drop-probability statements.
The drop rate is zero until the queue fill level reaches the drop start point. As the queue continues to fill, packets drop in smooth linear curve until the queue reaches the drop end point, when packets drop at the maximum drop rate. If the queue fills beyond the drop end point, all packets that match the drop profile are dropped.
To configure a tail-drop profile using the CLI:
- Name the drop profile and set the drop start point, drop
end point, minimum drop rate, and maximum drop rate for the drop profile:
[edit class-of-service]
user@switch# set drop-profile drop-profile-name interpolate fill-level percentage fill-level percentage drop-probability 0 drop-probability percentage
