A virtual link is a logical connection between two OSPF routers that belong to different areas but share a common border with a transit area. A virtual link allows an OSPF router to participate in the backbone area (Area 0) even if it is not physically connected to it. This way, the OSPF network can maintain connectivity and routing consistency across all areas. A virtual link is configured between the OSPF router IDs of the two routers that need to be connected to the backbone area123.
Option A is incorrect because a stub area is an area that does not receive external routes from other autonomous systems or other OSPF areas. A stub area can only transit traffic to and from the backbone area, and it cannot be used as a transit area for a virtual link12.
Option B is incorrect because a virtual link does not change the IP address space of the networks that it connects. A virtual link is transparent to the IP layer and only affects the OSPF routing protocol. To connect two networks that have overlapping private IP address space, other solutions such as NAT or VPN are required12.
Option C is incorrect because a virtual link cannot merge two existing Area 0s through a nonbackbone area. A virtual link can only extend an existing Area 0 through a nonbackbone area. If there are two separate Area 0s in an OSPF network, they cannot be merged by a virtual link, and the network is considered to be partitioned. A partitioned network can cause routing loops and inconsistencies, and it should be avoided12. References: 1: Configure OSPF Connection in a Virtual Link Environment, 2: How to configure OSPF Virtual Link, 3: Understand OSPF Areas and Virtual Links