Which of these statements about penultimate hop popping are true? (Choose three)

A.
It is used only for directly connected subnets or aggregate routes

B.
It can only be used with LDP.

C.
It is only used when two or more labels are stacked.

D.
It enables the Edge LSR to request a label pop operation from Its upstream neighbors

E.
It is requested through TDP using a special label value that is also called the implicit-null value.

F.
It is requested through LDP using a special label value that is also called the implicit-null value.

Explanation:

In order to implement penultimate hop popping, the edge LSR requests a label pop operation from
its upstream neighbor via LDP or TDP using a special implicit-null label. This label has a value of 3
for LDP and 1 for TDP.