Udld (Global Configuration) - Cisco Catalyst 2950 Command Reference Manual

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Chapter 2 Cisco IOS Commands

udld (global configuration)

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. Use the no form of this command to
disable aggressive or normal mode UDLD on all fiber-optic ports.
Syntax Description
aggressive
enable
message time
message-timer-interval
Defaults UDLD is disabled on all fiber-optic interfaces.
The message timer is set at 60 seconds.
Command Modes
Global configuration
Command History Release
12.0(5.2)WC(1)
12.1(6)EA2
Usage Guidelines Use the udld global configuration command to enable UDLD only on fiber-optic ports.
In normal mode, if UDLD is in the advertisement or in the detection phase and all the neighbor cache
entries are aged out, UDLD restarts the link-up sequence to resynchronize with any potentially
out-of-sync neighbors.
If you enable aggressive mode, when all the neighbors of a port have aged out either in the advertisement
or in the detection phase, UDLD restarts the link-up sequence to resynchronize with any potentially
out-of-sync neighbor. UDLD shuts down the port if, after the fast train of messages, the link state is still
undetermined. Use aggressive mode on point-to-point links where no failure between two neighbors is
allowed. In this situation, UDLD probe packets can be considered as a heart beat whose presence
guarantees the health of the link. Conversely, the loss of the heart beat means that the link must be shut
down if it is not possible to re-establish a bidirectional link.
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.
78-11381-05
udld {aggressive | enable | message time message-timer-interval}
no udld {aggressive | enable | message time}
Enable UDLD in aggressive mode on all fiber-optic interfaces.
Enable UDLD in normal mode on all fiber-optic interfaces.
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 from 7 to 90 seconds.
Modification
This command was first introduced.
The udld enable global configuration command was changed to udld
(global configuration).
Catalyst 2950 Desktop Switch Command Reference
udld (global configuration)
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