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Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
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Chapter 22      Configuring UDLD
    Configuring UDLD
Enabling UDLD Globally
Beginning in privileged EXEC mode, follow these steps to enable UDLD in the aggressive or normal 
mode and to set the configurable message timer on all fiber-optic interfaces on the switch: 
To disable UDLD globally, use the no udld enable global configuration command to disable normal 
mode UDLD on all fiber-optic ports. Use the no udld aggressive global configuration command to 
disable aggressive mode UDLD on all fiber-optic ports. 
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
udld {aggressive | enable | message time 
message-timer-interval}
Specify the UDLD mode of operation:
• aggressive—Enables UDLD in aggressive mode on all fiber-optic 
interfaces. 
• enable—Enables UDLD in normal mode on all fiber-optic 
interfaces on the switch. UDLD is disabled by default. 
An individual interface configuration overrides the setting of the 
udld enable global configuration command.
For more information about aggressive and normal modes, see the 
“Modes of Operation” section on page 22-1.
• message time message-timer-interval—Configures 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.
Note This command affects fiber-optic interfaces only. Use the udld 
interface configuration command to enable UDLD on other 
interface types. For more information, see the “Enabling UDLD 
on an Interface” section on page 22-6.
Step 3
end Return to privileged EXEC mode.
Step 4
show udld Verify your entries.
Step 5
copy running-config startup-config (Optional) Save your entries in the configuration file.