haveing trouble understanding unidirectional links and its impact on spanning tree. consider the diagram attached. link B-C is unidirectional --- B can transmit to C, but not vice-versa.
i understand that B transitions to forwarding, but i don't see how a loop forms. that is, frames obviously can take path A-C. but can frames take path A-B-C? i thought because of unidirectionality, path A-B-C is not possible, and so switch B's designated port acts like it's blocking. where is the flaw in this arguement?
also, in what real-life scenoris does a unidirectional links occur? is it one of those 1 in 1000 situations?
finally, what is the difference between UDLD and loop guard? i read, for example, loop guard protects against software problems that cause STP failure, but i don't know what it means. your thoughts are appreciated.
thanks in advance.