UDLD – Unidirectional Link Detection
(UDLD) is a Cisco proprietary protocol used to detect unidirectional links. A unidirectional link occurs when a link is operational in one direction but not in the other, potentially causing issues in network topologies like spanning tree.
Enabling UDLD Globally (This enables UDLD on all fiber-optic interfaces):
# conf t
# udld enable
Enabling Aggressive UDLD Globally (This enables aggressive UDLD mode globally, which is more proactive in detecting and shutting down unidirectional links.):
# conf t
# udld aggressive
Enabling UDLD on an Interface:
# conf t
# interface <interface-id>
# udld port
Enabling Aggressive UDLD on an Interface:
# conf t
# interface <interface-id>
# udld port aggressive
Viewing UDLD Information:
# show udld neighbors
Viewing UDLD Status for a Specific Interface:
# show udld <interface-id>
Use UDLD to detect and prevent unidirectional links, which can cause network issues. Enable globally or per interface, and use aggressive mode for more proactive detection. Monitor using show udld neighbors.