Fujitsu PRIMERGY BX900 User Manual page 24

UDLD (UnDirectional Link Detection)
UDLD is a lightweight protocol that can be used to detect and disable one-way connections before they
create dangerous situations such as Spanning Tree loops or other protocol malfunctions.
The protocol's main goal is to advertise the identities of all the capable devices attached to the same
LAN segment and to collect the information received on the ports of each device to determine if the
Layer 2 communication is happening in the appropriate fashion. UDLD was implemented to help correct
certain assumptions made by other protocols, and in particular to help the Spanning Tree Protocol to
function properly so as to avoid the creation of dangerous Layer 2 loops. It has been available on most
Cisco Systems switches for several years.
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