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New Member

testing UDLD

hi all

is there a way to test UDLD on my switches ?

4 REPLIES
New Member

Re: testing UDLD

I am not really sure what you want to test.

I asume you know the "show udld " command.

If you use UDLD on copper interfaces, it may be hard to simulate.

If you have a fiber connection between 2 devices - let's say with a SC or LC connector - you may be able to to unplug only one of the two fibers. Then you should see an UDLD error message on one of the 2 devices.

Make sure to use "errdisable recovery cause udld" to bring the link up again.

Cisco Employee

Re: testing UDLD

Hello,

For copper interfaces, the UDLD normal mode would not be effective - I suggest using the UDLD Aggressive mode for copper links.

As to the testing - Frank has suggested a way to test the fiber interface. To test a copper interface, simply use a single unmanaged switch or a hub - place it between your two switches running UDLD. When you disconnect one switch, the second will stop receiving UDLD packets while having the interface still up/up and it will react appropriately.

Best regards,

Peter

New Member

Re: testing UDLD

hi there

thanks for that

1 question, im gathering you can only use udld between switches, would it not work on normal access ports, as the pc would not send back the message ?

Cisco Employee

Re: testing UDLD

Hello,

After a port comes up, the UDLD starts sending packets but until it receives a response it does not do anything further. It just sends packets. The UDLD essentially waits for a peer to discover itself, and it will react only to a loss of a previously discovered peer.

Starting an UDLD against a PC is both harmless and useless. The PC will never respond to UDLD packet so the UDLD on the switch will wait for an UDLD peer on that port that will never appear.

Best regards,

Peter

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