Uni-Directional Link Detection detects links where either the transmit or receive path has failed. Used to monitor fibre-optic or twisted pair cabling for unidirectional links.
UDLD used periodic hello packets and uses the concept of echos to ensure neighbors are receiving UDLD the UDLD hellos.
Supports 2 modes of operations,
- Normal – Port is placed into undetermined state. Port is not shutdown.
- Aggressive – Tries to get echo by sending hellow 8 times. Then places the interface into errdisable.
Disabled by default,
SW1(config) # udld enabled
(fibre and copper)
SW1(config-if)# udld port aggressive
SW1# show udld neigh
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