About Udld - Cisco Catalyst 4500 Series Configuration Manual

Configuring UDLD
This chapter describes how to configure UniDirectional Link Detection (UDLD) Ethernet on a Catalyst
switch.
This chapter includes the following major sections:
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Note For complete syntax and usage information for the switch commands used in this chapter, first look at
the Cisco Catalyst 4500 Series Switch Command Reference and related publications at this location:
http://www.cisco.com/en/US/products/hw/switches/ps4324/index.html
If the command is not found in the Catalyst 4500 Series Switch Command Reference, it will be found in
the larger Cisco IOS library. Refer to the Cisco IOS Command Reference and related publications at this
location:
http://www.cisco.com/en/US/products/ps6350/index.html

About UDLD

UDLD is a Layer 2 protocol that initializes devices connected through fiber-optic or twisted-pair
Ethernet cables. This protocol monitors a physical connection (such as wrong cabling) to detect
unidirectional links to avoid spanning-tree topology loops or silent drop traffic.
All connected devices must support UDLD for the protocol to successfully identify the unidirectional
links. When UDLD detects a unidirectional link, it can administratively shut down the affected port and
send you a warning message.
With UDLD, the time to detect a unidirectional link can vary from a few seconds to several minutes
depending on how the timers are configured. Link status messages are exchanged every couple of
seconds.
OL-25340-01
About UDLD, page 30-1
Default UDLD Configuration, page 30-4
Configuring UDLD on the Switch, page 30-4
Displaying UDLD Link Status, page 30-9
C H A P T E R
Software Configuration Guide—Release IOS XE 3.3.0SG and IOS 15.1(1)SG
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30-1