UDLD is Unidirectional Link Detection protocol.
A connect is considered unidirectional when the interface is up on both sides but one of the sides is not accepting parcels sent by the inaccessible side whereas the farther side still gets parcels sent by the nearby side. Layer 2 convention works with Layer 1 instruments to decide the physical connect status. UDLD identifies personalities of neighbors and closing down misconnected ports. It trades convention parcels between the neighbors. Both gadgets on the interface must back UDLD and have it empowered.
When empowered, each switch harbour will have the port’s claim device/port ID within the UDLD bundles and the neighbor’s device/port IDs seen by UDLD on that harbour. Neighbor ports ought to see their own device/port ID within the gotten bundles. In case the neighbor doesn’t see their claim device/port ID for a indicated term of time, the connect is considered unidirectional.
When UDLD kicks within the taking after support message is shown for the influenced port(s):
UDLD-3-DISABLE: Unidirectional link detected on port 1/2. Port disabled
Port remains shut down unless manually re enabled.
There are two operational modes:
- Normal
- Aggressive
Normal
In this state, on the off chance that a bi-directional harbour times out with the UDLD data, no activity is taken by UDLD. The harbour state gets stamped as undetermined and the harbour carries on concurring to its STP state.
Aggressive
In this state, when a bi-directional harbour times out on UDLD data, UDLD tries to re-establish the state of the harbour. In the event that unsuccessful, the harbour is put into err disable state.
Additional detections included are:
- Port is stuck (one side neither transmits nor receives however the link is up on both sides)
- Link is up on one side and down on the other
Aging Time
When a harbour, running UDLD, doesn’t get UDLD parcels from a neighbor harbour for a term of the hold time it’ll be matured out and be decided as unidirectional. The shorter the interim, the quicker the location will be.
Message interval is 15 seconds by default. Fast enough to detect unidirectional link before a forwarding loop occurs.
Configuration
UDLD is globally disabled.
Enable globally:
Enable UDLD on an interface:
Reset an interface disabled by UDLD:
Or you can shutdown the interface and re enable the interface with no shutdown
Verify
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