[c-nsp] UDLD ?

[Tim Stevenson]

GE/10G can detect a physical unidirectional fiber link itself, UDLD 
is not necessary to detect this type of failure.

UDLD is needed for exactly the case you mention, or for cases where 
one side of the link is "braindead" but does not bring the physical 
link down (ie, software problem).


HTH,
Tim


At 07:57 AM 6/30/2009, Peter Rathlev stated:

>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
>
>
>
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Tim Stevenson, tstevens at cisco.com
Routing & Switching CCIE #5561
Technical Marketing Engineer, Cisco Nexus 7000
Cisco - http://www.cisco.com
IP Phone: 408-526-6759
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