Configuring Dropping Behavior With Red And Wred; Dropping Behavior Overview - Juniper JUNOSE SOFTWARE FOR E SERIES 11.3.X - QUALITY OF SERVICE CONFIGURATION GUIDE 2010-09-22 Configuration Manual

CHAPTER 4
Configuring Dropping Behavior with RED
and WRED

Dropping Behavior Overview

Copyright © 2010, Juniper Networks, Inc.
This chapter provides information for configuring dropping behavior using RED and WRED
on the E Series router.
QoS topics are discussed in the following sections:
Dropping Behavior Overview on page 25
RED and WRED Overview on page 26
Configuring RED on page 27
Example: Configuring Average Queue Length for RED on page 28
Example: Configuring Dropping Thresholds for RED on page 28
Example: Configuring Color-Blind RED on page 29
Configuring WRED on page 30
Example: Configuring Different Treatment of Colored Packets for WRED on page 32
Example: Defining Different Drop Behavior for Each Traffic Class for WRED on page 32
Example: Configuring WRED and Dynamic Queue Thresholds on page 33
Monitoring RED and WRED on page 35
Drop profiles control the dropping behavior of a set of egress queues. They define the
range within the queue where random early detection (RED) operates, the maximum
percentage of packets to drop, and sensitivity to bursts of packets. Weighted random
early detection (WRED) is an extension to RED that enables you to assign different RED
drop profiles to each color of traffic.
The purpose of RED and WRED is to signal end-to-end protocols, such as TCP, that the
router is becoming congested along a particular egress path. The intent is to trigger TCP
congestion avoidance in a random set of TCP flows before congestion becomes severe
and causes tail dropping on a large number of flows. Tail dropping can lead to TCP
slow-starts, and tail dropping on a large number of flows results in global synchronization.
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