Now the engineer wants to realize the loopback address of R1 to R4. Which of the following operations can meet this requirement?

As shown in the figure, an engineer uses 4 routers to test branch network interoperability. Among them, R1, R2, and R3 in branch 1 deploy OSPF to achieve network interoperability. R2, R3, and R4 in branch 2 deploy IS-S to achieve network interoperability.

Now the engineer wants to realize the loopback address of R1 to R4. Which of the following operations can meet this requirement?
A . In the OSFF process and the IS-IS process of R2, respectively advertise the default route
B . No configuration is required
C . Advertise the default route only in the IS-IS process of R2
D . Advertise the default route only in the OSPF process of R2

Answer: A