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New Member

UDLD concept

Dear,

can anyone tell me what UDLD is?

what is its function? and how does it work?

8 REPLIES
Cisco Employee

Re: UDLD concept

Hi Vishal,

UDLD is a L2 protocol meant to tackle unidirectional links, which is interface is up on both sides, but one side is not receiving what other side is sending.

When link is unidirectional STP BPDUs are lost > forwarding loop > network down > need for UDLD.

It is a High level echo-based protocol, need to be supported & enabled on both sides of the link.

The simplified idea of how it works is this

Hope this gives the info you were looking for.

Riccardo

Cisco Employee

UDLD concept

UDLD concept

If two devices, A and B, are connected via a pair of optical fibers, one used for sending from A to B and other for sending from B to A, the link is bidirectional (two-way). If one of these fibres is broken, the link has become one-way or unidirectional. The goal of the UDLD protocol is to detect a broken bidirectional link

This is a very helpful protocol to protect the network from loops.  It helped me on at least one occasion where a wan fiber turned out to be unidirectional.

Cisco Employee

UDLD concept

Vishal,

thank you for asking questions and then disappearing without further feedbacks.

R

Cisco Employee

UDLD concept

Hello Riccardo,

That happens sometimes. I suggest to take it easily and with a certain degree of generous gentlemanhood It is beyond our level to go around begging people for feedback or ratings.

Best regards,

Peter

Cisco Employee

UDLD concept

Hi Peter,

it is not a matter of ratings but courtesy.

You ask a question to a community and you get an answer from good willing people.

A mere thanks will do.

PS: I am not upset at all 

New Member

UDLD concept

hi riccardo,

apology for not replying, what if someone couldn't be online

...than u for replying my question.....

Cisco Employee

UDLD concept

Hi Vishal,

I am sorry to have reacted somewhat prematurely. You know, it happens sometime that people here give great answers, often much better than in expensive textbooks, but the person who originally asked never comes back again. Riccardo deserves all the credit and I am sure he did not mean his post maliciously. Of course I accept your reasons and apologize for my own comment if it was inppropriate.

Thank you for coming back and letting us know, and huge thanks goes also to Riccardo for his tireless help on CSC!

Best regards,

Peter

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