Configuring Udld; Understanding How Udld Works; Udld Overview - Cisco WS-SUP32-GE-3B - Supervisor Engine 32 Software Configuration Manual

Configuring UDLD

This chapter describes how to configure the UniDirectional Link Detection (UDLD) protocol on the
Catalyst 6500 series switches.
For complete syntax and usage information for the commands used in this chapter, refer to the
Note
Catalyst Supervisor Engine 32 PISA Cisco IOS Command Reference, Release 12.2ZY, at this URL:
http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2ZY/command/reference/cmdref.h
tml
This chapter consists of these sections:
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Understanding How UDLD Works

These sections describe how UDLD works:
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UDLD Overview

The Cisco-proprietary UDLD protocol allows devices connected through fiber-optic or copper (for
example, Category 5 cabling) Ethernet cables connected to LAN ports to monitor the physical
configuration of the cables and detect when a unidirectional link exists. When a unidirectional link is
detected, UDLD shuts down the affected LAN port and alerts the user. Unidirectional links can cause a
variety of problems, including spanning tree topology loops.
UDLD is a Layer 2 protocol that works with the Layer 1 protocols to determine the physical status of a
link. At Layer 1, autonegotiation takes care of physical signaling and fault detection. UDLD performs
tasks that autonegotiation cannot perform, such as detecting the identities of neighbors and shutting
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Understanding How UDLD Works, page 45-1
Default UDLD Configuration, page 45-3
Configuring UDLD, page 45-3
UDLD Overview, page 45-1
UDLD Aggressive Mode, page 45-2
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