What is the advantage of weighted random early detection (WRED), and how do I know if my line card can support WRED?
A. For congestion avoidance on output scheduling, the Catalyst 6500 (Cat6K) Switch supports WRED on some egress queues. Each queue has a configurable size and threshold. Some have WRED. WRED is a congestion-avoidance mechanism which randomly drops packets with a certain IP precedence when the buffers reach a defined threshold filling. WRED is a combination of two features: tail drop and random early detection (RED). The early Catalyst operating system (CatOS) implementation of WRED only set the max-threshold, while the min-threshold was hard-coded to 0%. Note that the drop probability for a packet is always non-null, as they always are above the min-threshold. This behavior is corrected in CatOS 6.2 and later. WRED is a very useful congestion-avoidance mechanism for when the traffic type is TCP-based. For other types of traffic, RED is not very efficient because RED takes advantage of the windowing mechanism that is used by TCP to manage congestion. Refer to the Understanding the Queue
Related Questions
- Can I enabled Weighted Random Early Detection (WRED) and Low Latency Queueing (LLQ), or Class Based Weighted Fair Queueing (CBWFQ) at the same time?
- What is the advantage of weighted random early detection (WRED), and how do I know if my line card can support WRED?
- How can I monitor Weighted Random Early Detection (WRED) and see it actually taking effect?
