Cisco 10000 Series User Manual

11-14
Cisco 10000 Series Router Quality of Service Configuration Guide
OL-7433-09
Chapter 11 Managing Packet Queue Congestion
Controlling Congestion Using Weighted Random Early Detection
The minimum threshold indicates the minimum number of packets allowed in the queue. When the
average queue length reaches the minimum threshold, WRED randomly drops some packets with the
specified DSCP, IP precedence, or discard-class value. Valid minimum threshold values are from 1 to
16,384. This option is not available on the PRE3 for the random detect discard-class command.
The maximum threshold indicates the maximum number of packets allowed in the queue. When the
average queue length exceeds the maximum threshold, WRED drops all packets with the specified
DSCP, IP precedence, or discard-class value. Valid maximum threshold values are from the value of the
min-threshold to 1.
The maximum probability denominator is the drop rate. It specifies the denominator for the fraction of
packets dropped when the average queue depth is at the maximum threshold. For example, if the
denominator is 512, 1 out of every 512 packets is dropped when the average queue is at the maximum
threshold. Valid values are from 1 to 65,535. The default value is 10.
For information about the behavior of the random-detect command on the various PRE processor cards,
see the
“WRED Drop Profiles” section on page 11-14 and the “WRED Aggregate Drop Profiles” section
on page 11-17.
WRED Drop Profiles
A WRED drop profile specifies DSCP, IP precedence, discard-class, or ATM CLP values, which WRED
uses to determine the drop probability of packets.
Table 11-5 lists the commands used to configure a packet drop policy. The behavior of these commands
depends on the PRE installed in the router as the following describes:
• On the PRE2, the random-detect command specifies the default profile for the queue.
Ta b l e 11-4 WRED Drop Mode Commands
Command Description
random-detect dscp-based min-thresh-value
max-thresh-value
mark-probability-denominator-value
Drops packets based on a DSCP value. This
option is available on the PRE2, PRE3, and
PRE4.
random-detect prec-based min-thresh-value
max-thresh-value
mark-probability-denominator-value
Drops packets based on an IP precedence
value. This option is available on the PRE2,
PRE3, and PRE4.
random-detect discard-class-based
min-thresh-value max-thresh-value
mark-probability-denominator-value
Drops packets based on a discard-class value.
This option is available on the PRE2, PRE3,
and PRE4.
Note The min-thresh-value option is not
available on the PRE3 for this
command.
random-detect atm-clp-based min-thresh-value
max-thresh-value
mark-probability-denominator-value
Drops packets based on an ATM cell loss
priority (CLP) value. This option is available
on the PRE2, PRE3, and PRE4.
random-detect cos cos-value min-thres-value
max-thresh-value mark-probability-denominator
Drops packets based on the CoS bit value of
the packet. This option is available on the
PRE3, and PRE4.

Cisco 10000 Series Specifications

General

Brand	Cisco
Model	10000 Series
Category	Network Router
Language	English