UDLD

[alihassan1618]

Hi, Studying about Cisco Switching now a days and spending most of the time to dive into new Switching topic. well, i already ended up UDLD(unidirectional link detection) but this question again screwed me..!! 

Which statement is true when UDLD is configured on a link and the link is determined to be unidirectional?

A. The port remains up for a configured time interval and then error disables if the link remains unidirectional.
B. LLDP is enabled on the port.
C. The port sends a log message to the console.
D. The port is disabled immediately.<---- Right Answer

As far as i know UDLD is having 2 modes (Normal and Aggressive) and both of the mode having their one way of deal with, like Norma Mode will wait for expire 3 hold down timers.(by default timer is 15sec) which means 15+15+15 = 45 which is less then STP's timer (50). and at other hand in Aggressive Mode if one Echo Reply is not received then 8 consistent Echo will be sent on every second (15+1+1+1+1+1+1+1+1= 23sec), if all echo replies not received then link will determined as Unidirectional and putted into errdisable state. 

Please correct me if i'm wrong, because as per my knowledge and study Answer should be "A". 

Thanks in Advance. 

[luis_cordova · Accepted solution]

Hi @alihassan1618 

I think that in your explanation of the modes is the correct answer.
The question, in my opinion, asks what happens to the link when it is already determined that it is unidirectional, that is, when the time determined by the configured mode has already passed(45 ir 23 sec).

According to that understanding of the question, answer D would be correct, since the link is disabled after this time.

Regards

[alihassan1618]

hmm... i was also thinking the same but was little bit confused that's why posted the question for expert advice. Thanks a lot for your input luis cordova.