Configuring Udld - Cisco Catalyst 4500 series Administration 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, see 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 a command is not in the Catalyst 4500 Series Switch Command Reference, you can locate it in the
Cisco IOS library. See 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_28731-01
About UDLD, page 32-1
Default UDLD Configuration, page 32-4
Configuring UDLD on the Switch, page 32-4
Displaying UDLD Link Status, page 32-9
C H A P T E R
Software Configuration Guide—Release IOS XE 3.6.0E and IOS 15.2(2)E
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32-1