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New Member

UDLD errdisable port

when a port is errdisable by UDLD, are there commands to verify the switchport is ok?


Re: UDLD errdisable port


In IOS based switches, you can issue the command 'show interface status err-disabled' and it would display any ports in error disabled state. Alternatively, you could issue the same command without the keyword err-disabled to check the status of the port itself.

SW1#show int status ?

err-disabled Show interface error disabled state

inactive Show interface inactive state

module Limit display to interfaces on module

| Output modifiers

SW1#show int status

Port Name Status Vlan Duplex Speed Type

Fa0/1 connected 10 a-half a-10 10/100BaseTX

Fa0/2 connected 23 a-half a-10 10/100BaseTX

(output removed)

SW1#show int status err-disabled

You can see the 2nd command didn't generate any output as there's no port in err-disabled state.

Check out the link for more info on this command.



New Member

Re: UDLD errdisable port

Hi, this is catOS switch 5509/5505. When a port is errdisable by UDLD, the caused could be fiber cable, bad switchport or both. I am looking for a command to assure me the switchport is not the problem. maybe something at the firmware level. thanks.

Re: UDLD errdisable port

The UDLD protocol allows devices connected through fiber-optic or copper Ethernet cables (for example, Category 5 cabling) to monitor the physical configuration of the cables and detect when a unidirectional link exists. When a unidirectional link is detected, UDLD shuts down the affected port and alerts the user.

A unidirectional link occurs whenever traffic transmitted by the local device over a link is received by the neighbor but traffic transmitted from the neighbor is not received by the local device. For example, if one of the fiber strands in a pair is disconnected, as long as autonegotiation is active the link does not stay up. In this situation, the logical link is undetermined, and UDLD does not take any actions. If both fibers are working normally at Layer 1, then UDLD at Layer 2 determines whether those fibers are connected correctly and whether traffic is flowing bidirectionally between the correct neighbors.

I posts the UDLD explanation because knowing that the best way to isolate is move the same cable to another port with UDLD enabled, if the cable is the cause the UDLD will follow. In short, of running diagnostics on the line card by re-seating it, there is not command to see the health of the port. diagnostic is run at boot-up not online.

Please rate if it helps.

New Member

Re: UDLD errdisable port

Thanks Robert.

New Member

Re: UDLD errdisable port

Hi Bosolaza!

great explanation.i have understood the UDLD From U.