When I read Cisco CCNP official guide, I found an explanation on how to calculate the cost of intra-area routes:

Step 1. Finds all subnets inside the area, based on the stub interfaces listed in the Type 1 LSAs and based on any Type 2 Network LSAs.

Step 2. Runs SPF to find all possible paths through the area’s topology, from itself to each subnet.

Step 3. Calculates the OSPF interface costs for all outgoing interfaces in each route, picking the lowest-total-cost route for each subnet as the best route.

My question is, is finding all possible paths one of SPF algorithm's functions? I thought all possible paths is implicitly showed by LSDB, SPF algorithm's mission is just creating a SPF tree, and get the shortest path to each subnet which are leaves of this tree. Or here the author want to express the meaning that SPF traverses all possible paths and find the shortest path.

Thanks for any answer.

When I read Cisco CCNP official guide, I found an explanation on how to calculate the cost of intra-area routes:

1. Find all networks inside the area, based on the stub interfaces listed in the Type 1 LSAs and based on any Type 2 Network LSAs.
2. Run SPF to find all possible paths through the area’s topology, from itself to each network.
3. Calculate the OSPF interface costs for all outgoing interfaces in each route, picking the lowest-total-cost route for each network as the best route.

My question is: is finding all possible paths one of SPF algorithm's functions? I thought all possible paths is implicitly shown by LSDB, SPF algorithm's mission is just creating a SPF tree, and get the shortest path to each network which are leaves of this tree. Or here the author want to express the meaning that SPF traverses all possible paths and find the shortest path.