UDLD is used to prevent STP loops, therefore it L2 protocol and it does not run on the L3 interfaces. If you have router with a switch ports on the router, then you might have it
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. It is not used to prevent STP loops. It is supported on some of the etherswitch daughter cards. I don't have any fiber terminating on the chassis SFP ports so I'm not sure if it's supported there.
This document explains how the Unidirectional Link Detection (UDLD) protocol can help to prevent forwarding loops and blackholing of traffic in switched networks.
Just to give some more information about UDLD, whenever the switch detects a unidirectional link in the layer 2 LAN switching environment, it prefers to block the port completly(send it to err-disabled) rather than allowing the unidirectional flow of information. It has no use in the layer 3 environment.
Thanks.
Getting Started
Find answers to your questions by entering keywords or phrases in the Search bar above. New here? Use these resources to familiarize yourself with the community:
