Random-Detect - Cisco Catalyst 3750 Metro Command Reference Manual

Chapter 2 Catalyst 3750 Metro Switch Cisco IOS Commands

random-detect

Use the random-detect policy-map class configuration command to enable Weighted Random Early
Detection (WRED) in a hierarchical policy map attached to an enhanced-services (ES) port. Use the no
form of this command to return to the default settings.
Syntax Description
dscp-based
precedence-based
Defaults
WRED is disabled.
If you do not enter either the dscp-based or the precedence-based keyword, WRED uses the IP
precedence value (the default method) to calculate drop probability for the packet.
Command Modes
Policy-map class configuration
Command History Release
12.1(14)AX
12.2(25)EY
Usage Guidelines WRED is a congestion-avoidance mechanism that slows traffic by randomly dropping packets when
congestion exists. WRED reduces the chances of tail drop by selectively dropping packets when the
egress port begins to show signs of congestion. By dropping some packets early rather than waiting until
the queue is full, WRED does not drop large numbers of packets at once.
Use the random-detect command only in a hierarchical policy map attached to an ES port. You can use
this command only in class-level classes.
You must configure the bandwidth or the shape policy-map class configuration command before you
configure either the queue-limit or the random-detect policy-map class configuration command in a
class policy.
You can define a class policy to use either tail drop or WRED packet drop by using either the queue-limit
policy-map class configuration command or the random-detect policy-map class configuration
command, respectively. You cannot use the queue-limit and random-detect commands in the same
class policy, but they can be used in two class policies in the same policy map.
OL-9645-10
random-detect [dscp-based | precedence-based]
no random detect [dscp-based | precedence-based]
(Optional) Enable Differentiated Services Code Point (DSCP)-based WRED as
a drop policy. WRED uses the DSCP value (that is, the first six bits of the IP
type of service [ToS] byte) to calculate the drop probability.
(Optional) Enable IP precedence-based WRED as a drop policy. WRED uses
the IP precedence value to calculate the drop probability.
Modification
This command was introduced.
Hierarchical service policies can be attached to inbound traffic received on
an ES port.
Catalyst 3750 Metro Switch Command Reference
random-detect
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