Which kind of ports or where do UDLD apply

[Maivoko]

Which kind of ports or where do UDLD apply

To detect unidirectional link?

[Meheretab Mengistu]

Most of the time, UDLD is used for fiber ports as there could be failure in one-direction. It could also be configured on Ethernet ports.

HTH,
Meheretab

[Leo Laohoo]

Use UDLD on fibre optic ports. Never use UDLD on copper ports.

[Maivoko]

if using on optic fiber port, 

should it apply on root port or designated port ? access switch only or both distribution layer and access switch or core + distribution layer or access switch?

where should it apply?

[Leo Laohoo]

If used on fibre optic port, configure both ends with UDLD.  

If one end does not support UDLD then don't configure it on the other end.  

[Maivoko]

do you mean that configured this at core switch root port and designated port
and distribution layer root port and designated port and access switch layer root port and designated port all ports if supported?

[Leo Laohoo · Accepted solution]

If UDLD is supported in the local and remote device (on the fibre optic ports), then enable it.  If not, disable UDLD. 

And for goodness sake, DO NOT enable auto-recovery function when UDLD disables a port.  It is counter-productive!

[Maivoko]

i find that UDLD is not enabled in etherchannel in real practice of an ISP company.
not easy to find a scenario to apply CCNP knowledge in real practice
it seems most security commands only works when using one cable uplink to core switch for small bandwidth

i guess only access switch can be applied