INS_CWGE24MS2_REV–
10/05/16 PAGE 195
INSTALLATION AND OPERATION MANUAL
CWGE24MS2
TECH SUPPORT: 1.888.678.9427
UDLD
Introduction
The UDLD (UniDirectional Link Detection) protocol is used to detect and/or disable unidirectional
connections before they create dangerous situations such as Spanning Tree loops or other
protocol malfunctions.
The UDLD protocol was implemented to help correct certain assumptions made by other
protocols and in particular to help the STP to function properly so as to avoid the creation of
dangerous Layer 2 loops.
UDLD is meant to be a Layer 2 detection protocol that works on top of existing Layer 1 detection
mechanisms defined by the IEEE standards.
Network systems typically check for miss wiring or unidirectional problems at the physical layer.
The physical layer defines the actual physical components such as connectors and cables. So,
physical layer only checks for open lines or port malfunctions and would not detect a miss wired
systems.
But, UDLD performs mutual neighbor identification; in addition, it performs neighbor
acknowledgement on top of the Logical Link Control (LLC) layer and thus is able to discover logical
one-way miscommunication between neighbors even when either one of PHY layer mechanisms
has deemed the transmission medium bidirectional.
Notice:
The port blocked by UDLD can be recovered automatically or you can execute the CLI command,
“no shutdown”, in interface node. You can configure the recovery interval with CLI command,
“errdisable recovery interval VALUE”.
