[c-nsp] UDLD ?

[Peter Rathlev]

On Tue, 2009-06-30 at 09:59 -0400, Jeff Fitzwater wrote: 
> We have had a few strange unidirectional link problems and I thought  
> that I could detect them using UDLD.   So I thought I knew how it  
> worked.   I
... 
> I thought that breaking on side of the fiber would only bring down one  
> end LINK since the other still thought it was connected.
> 
> I then disabled the UDLD and disconnect the fiber again and still had  
> both ends show link failure.

Just tried this between a 3560 12.2(35)SE5 and a 2970 12.2(25)SEC2 with
the same symptoms as you describe; disconnecting one fiber doesn't
trigger UDLD but does give link down in both ends. This is also contrary
to what I expected.

UDLD is useful in another case though: Media converters and EoMPLS
xconnected ports are transparent to UDLD but might not have link
poisoning enabled. With UDLD you would discover the loss of connectivity
to the neighbor even though the link doesn't go down.

As long as the link actually goes down the UDLD isn't needed anyway. :-)

Regards,
Peter