How do I check my UDLD status?

To display the UDLD status for the specified port or for all ports, use the show udld [interface-id] privileged EXEC command. For detailed information about the fields in the command output, see the command reference for this release.

What is UDLD error?

UDLD Overview This can occur when the link is up on both sides, but one side is not receiving packets, or when wiring mistakes occur, causing the transmit and receive wires to not be connected to the same ports on both ends of a link.

What is unidirectional link failure?

Unidirectional links are the links for which either one of the transmission path has failed but not both. Cisco implementations have different mechanisms to detect unidirectional links and avoided the impact caused by them.

What causes port to go err disabled?

The Errdisable error disable feature was designed to inform the administrator when there is a port problem or error. The reasons a catalyst switch can go into Errdisable mode and shutdown a port are many and include: Duplex Mismatch. Loopback Error.

What is UDLD STP?

Unidirectional Link Detection (UDLD) is one of two major features (UDLD and loop guard) in Cisco Switches to prevent Layer 2 loops. Spanning-Tree Protocol (STP) resolves redundant physical topology into a loop-free, tree-like forwarding topology via blocking one or more ports.

Is UDLD Cisco proprietary?

UDLD is a Cisco-proprietary protocol but HP, Extreme Networks, and AVAYA all have a similar feature calling it by a different name. HP calls theirs Device Link Detection Protocol (DLDP).

Which command would you use to determine if a port has been error-disabled?

When a port is in error-disabled state, it is effectively shut down and no traffic is sent or received on that port. The port LED is set to the orange color and, when you issue the show interfaces command, the port status shows as Errdisabled.

How do I enable the UDLD port on fiber interfaces?

Use the udld port command in interface-configuration mode to enable UDLD on other interface types. This example shows how to enable UDLD on all fiber interfaces: Displays the administrative and operational UDLD status. Enables UDLD on the interface or enables UDLD in aggressive mode on the interface.

What is the Cisco UDLD protocol?

In order to detect the unidirectional links before the forwarding loop is created, Cisco designed and implemented the UDLD protocol. UDLD is a Layer 2 (L2) protocol that works with the Layer 1 (L1) mechanisms to determine the physical status of a link.

What happens when a port is shut down by UDLD?

Port shutdown by UDLD remains disabled until it is manually reenabled, or until errdisable timeout expires (if configured). UDLD can operate in two modes: normal and aggressive. In normal mode, if the link state of the port was determined to be bi-directional and the UDLD information times out, no action is taken by UDLD.

What determines the hold time for the port in UDLD?

The hold time for the port is dictated by the remote port and depends on the message interval at the remote side. The shorter the message interval, the shorter the hold time and the faster the detection. Recent implementations of UDLD allow configuration of message interval.