UDLD
This is the more common way to prevent ULD Failures, enabling ULD.
- ULD: Unidirectional Link Detection.
This feature has two modes:
-
Normal: Detect a fiber port that’s miss-cabled. Maybe port 1 and port 2 (four fibers total) got mixed up.
-
Aggressive: Detect one way traffic on both fiber, and twisted pair.
From Cisco:
- On fiber-optic or twisted-pair links, one of the ports cannot send or receive traffic.
- On fiber-optic or twisted-pair links, one of the ports is down while the other is up.
- One of the fiber strands in the cable is disconnected.
Requirements
- Both devices need this feature turned on.
- Both sides need the same mode (normal or aggressive)
Global
udld enable
Per Interface
interface 1
udld enable
Verification
sw1# show udld neighbors
Port Device Name Device ID Port ID Neighbor State
---- ----------- --------- ------- --------------
Gi0/0 91YBLF6S1KI 1 Gi0/0 Bidirectional
Capture
Reference
Layer 2 Configuration Guide, Cisco IOS XE 17.16.x (Catalyst 9500 Switches)