As shown in the following figure, which of the following ensures that the two routers can establish
an IS-IS neighbor relationship?
A . The type of the two routers can keep the default settings.
B . The type of the two routers must be Level-1.
C . The IS-IS process IDs of the two routers must be the same as each other.
D . The type of one router can be Level-1-2, and that of the other can be Level-1.
Answer: A