If each Ethernet link has been manually assigned an OSPF cost of 4 and each end of a serial link has a cost of 15, what is the total cost from R1's routing table to reach the network 10.45.0.0/24?

To determine the total cost from R1's routing table to reach the network 10.45.0.0/24, we need to consider the costs associated with all the links involved in the path from R1 to that network.

Each Ethernet link has a manually assigned OSPF cost of 4, and each end of a serial link has a cost of 15. If R1 needs to reach the destination network through one or more of these links, the total cost will be the sum of the costs of all the links in the path.

For example, if the path consists of one serial link and two Ethernet links, the calculation would be as follows:

• Cost of the serial link (15)

• Cost of the first Ethernet link (4)

• Cost of the second Ethernet link (4)

Adding these together gives: 15 + 4 + 4 = 23.

This method of summing the costs of all involved links reflects the OSPF algorithm's principle of finding the lowest cost path. Because of this accurate summation of link costs, the option indicating a total cost of 23 aligns with the principles of OSPF routing protocols.