Which of the following statements about penultimate hop popping are true? (Multiple Choice)
A . It is used only for directly connected subnets or aggregate routes.
B . It can only be used with LD
D . It is only used when two or more labels are stacked.
E . It enables the Edge LSR to request a label pop operation from its upstream neighbors.
F . It is requested through LDP using a special label value that is also called the implicit-null value.
Answer: DE