Cisco Catalyst 2960 Software Configuration Manual page 615

Hide thumbs Also See for Catalyst 2960:

Table of Contents

Configuring UDLD

This chapter describes how to configure the UniDirectional Link Detection (UDLD) protocol on the

2960, 2960-S, or 2960-C switch. Unless otherwise noted, the term switch refers to a standalone switch

and to a switch stack

For complete syntax and usage information for the commands used in this chapter, see the command

reference for this release.

This chapter consists of these sections:

Understanding UDLD

UDLD is a Layer 2 protocol that enables devices connected through fiber-optic or twisted-pair Ethernet

cables to monitor the physical configuration of the cables and detect when a unidirectional link exists.

All connected devices must support UDLD for the protocol to successfully identify and disable

unidirectional links. When UDLD detects a unidirectional link, it disables the affected port and alerts

you. Unidirectional links can cause a variety of problems, including spanning-tree topology loops.

Modes of Operation

UDLD supports two modes of operation: normal (the default) and aggressive. In normal mode, UDLD

can detect unidirectional links due to misconnected ports on fiber-optic connections. In aggressive mode,

UDLD can also detect unidirectional links due to one-way traffic on fiber-optic and twisted-pair links

and to misconnected ports on fiber-optic links.

In normal and aggressive modes, UDLD works with the Layer 1 mechanisms to learn 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 down misconnected ports. When you enable both autonegotiation and UDLD, the Layer 1 and

Layer 2 detections work together to prevent physical and logical unidirectional connections and the

malfunctioning of other protocols.

Understanding UDLD, page 24-1

Configuring UDLD, page 24-3

Displaying UDLD Status, page 24-7

Catalyst 2960 and 2960-S Switches Software Configuration Guide, Release 15.0(1)SE

C H A P T E R

Show Quick Links

Chapters

Table of Contents

Catalyst 2960-s