BFD confusion

Hi guys
I am reading BFD RFC and i am not able to get some points in it

1. What is the use of Discriminator field in BFD Control ?. It says it is
used to demultiplex control plane packets to their neighbor . i cant
understand what is called as demultiplex control plane packets to the
neighbors

2. BFD works on which layer . Is it a Layer 2 encapsulation or L3
encapsulation . or it s a L2.5 encapsulation.

3. Which address that BFD uses to communicate with its neighbor? RFC says it
is application specific and i am not getting the point exactly ?

Can some one shed some light on it ?

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