UDLD vs STP loop guard

Unanswered Question
Jun 24th, 2007

Hi everyone.. i have some trouble about those two technics. Sometimes i confused them.

What is the reason about using UDLD on a STP blocking port (port has been blocked after STP convergence) to detect the unidirectionality of the link and send errdisable msg?

I guess, the portis unidirectional since this port is on the blocking state !!!

So when it stopped receiving BPDU's, it must just get into the loop inconsistent state instead using UDLD.

Actually i don't really understand the purpose of using UDLD in the case of a blocking port not receiving BPDU's

I have this problem too.
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Edison Ortiz Sun, 06/24/2007 - 10:11

You will see the benefit of UDLD when using fiber connections instead of copper connections.

Usually in a fiber connection, you have 2 physical cables for transmit and receive while with copper you only have one.

If one of those physical cables break, you may have strange results in the connection and UDLD will detect such condition, once it does - it will shutdown the port.

This behavior has nothing to do with the STP port blocking services.

farellfolly Mon, 06/25/2007 - 02:15

Thx for your explanation.

I've been confused since i read a CCDA note information telling that UDLD can be used together with STP loop guard to enforces STP loop avoidance (for instance for loops occuring when a blocked port moves to forwarding state when it stopped receiving BPDUs)

farellfolly Mon, 06/25/2007 - 09:26

Thx, i alread have both them. But i wanted to be fixed by somebody else.


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