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Catalyst 3560 Switch Command Reference
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Chapter 2 Catalyst 3560 Switch Cisco IOS Commands
udld
udld
Use the udld global configuration command to enable aggressive or normal mode in the UniDirectional
Link Detection (UDLD) and to set the configurable message timer time. Use the no form of the command
to disable aggressive or normal mode UDLD on all fiber-optic ports.
udld {aggressive | enable | message time message-timer-interval}
no udld {aggressive | enable | message}
Syntax Description
Defaults UDLD is disabled on all interfaces.
The message timer is set at 60 seconds.
Command Modes Global configuration
Command History
Usage Guidelines UDLD supports two modes of operation: normal (the default) and aggressive. In normal mode, UDLD
detects unidirectional links due to misconnected interfaces on fiber-optic connections. In aggressive
mode, UDLD also detects unidirectional links due to one-way traffic on fiber-optic and twisted-pair links
and due to misconnected interfaces on fiber-optic links. For information about normal and aggressive
modes, see the “Understanding UDLD” section in the software configuration guide for this release.
If you change the message time between probe packets, you are making a trade-off between the detection
speed and the CPU load. By decreasing the time, you can make the detection-response faster but increase
the load on the CPU.
This command affects fiber-optic interfaces only. Use the udld interface configuration command to
enable UDLD on other interface types.
You can use these commands to reset an interface shut down by UDLD:
• The udld reset privileged EXEC command to reset all interfaces shut down by UDLD
• The shutdown and no shutdown interface configuration commands
• The no udld enable global configuration command followed by the udld {aggressive | enable}
global configuration command to re-enable UDLD globally
aggressive Enable UDLD in aggressive mode on all fiber-optic interfaces.
enable Enable UDLD in normal mode on all fiber-optic interfaces.
message time
message-timer-interval
Configure the period of time between UDLD probe messages on ports that
are in the advertisement phase and are determined to be bidirectional. The
range is 1 to 90 seconds.
Release Modification
12.1(19)EA1 This command was introduced.
12.2(25)SEC The range for the message-timer-interval was changed from 7 to 90 seconds
to 1 to 90 seconds.
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