What will happen when the link between R1 and R3 fails in regards to R4’s path to 10.1.5.0/24.?

Study the exhibit carefully. Assume that all the links in this nerwork are internal OSPF links. What will happen when the link between R1 and R3 fails in regards to R4’s path to 10.1.5.0/24.?

A.
R1 and R3 will each originate a new router (type 1) LSA, indicating they are no longer connected. When R4 receives these two LSA’s, it will run SPF and find the alternate path through R2.

B.
R4’s OSPF database and routing table will not be afffected, since R4 will not have a route to 10.1.5.0/24. It wil only have default routes originated by the ABRs, R2 and R3.

C.
R3 will generate a new summary (type3) LSA and flood it into Area 1. R4, on receiving this LSA, will run SPF and find an alternate path to 10.1.5.0/24 via R2.

D.
R3 will generate a new summary (type3) LSA and flood it into Area 1. R4’s route to 10.1.5.0/24 via R2 will not be affected by this new information, since it will be using the path through R2 whether or not the link between R1 and R3 is up.

Explanation:
ABR summary LSA type3 into stub

Depending on the point where a network is sourced, there are various types of routes that could be present in a OSPF domain.
When there are multiple routes to a particular network in a OSPF domain, the type of the route influences the route that is selected and installed by the router in the routing table.
In OSPF, routes that are learned by a router from OSPF sources within the same area are known as inta-area routes.
Routes that originate from an OSPF router in a different area are considered as inter-area routes.
Certain networks could belong to a domain outside OSPF, which could then be redistributed into the OSPF by an Autonomous System Boundary Router (ASBR).
Such routes are considered external routes.
They can be further divided into external type-1 or external type-2 routes, depending on how they are advertised while being redistributing on the ASBR.
The difference between these two types is the way in which the metric for the route is calculated.
OSPF-running routers use these criteria to select the best route to be installed in the routing table:

1. Intra-area routes.
2. Inter-area routes.
3. External Type-1 routes.
4. External Type-2 routes.
B) If there are multiple routes to a network with the same route type, the OSPF metric calculated as cost based on the bandwidth is used for selecting the best route.
The route with the lowest value for cost is chosen as the best route.
C) If there are multiple routes to a network with the same route type and cost, it chooses all the routes to be installed in the routing table, and the router does equal cost load balancing across multiple paths.