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## Refer to the exhibit. What is the OSPF cost to reach the West LAN 172.16.2.0/24 from East?​

• 782
• 74
• 128
• 65
 Explanation & Hint: Given the bandwidths: North to East = 64 Kbps North to West = 1544 Kbps West to East = 1544 Kbps and knowing that OSPF uses a default reference bandwidth of 100 Mbps (100,000 Kbps), we can calculate the OSPF cost for each segment: OSPF cost for North to East: `Cost = 100,000 / 64` OSPF cost for North to West: `Cost = 100,000 / 1544` OSPF cost for West to East (which is the reverse path of East to West and should have the same bandwidth and hence the same cost as North to West): `Cost = 100,000 / 1544` The OSPF cost to reach the West LAN from East would be the sum of the costs for East to North and North to West. However, since OSPF always chooses the path with the lowest cost, we would need to compare the cost of the direct East to West path with the cost of the East to North to West path to determine the actual OSPF cost to be used. Let’s calculate these costs. The calculated OSPF costs are as follows: The OSPF cost for the path from East to North to West is approximately 1627. The OSPF cost for the direct path from East to West (or West to East, since it’s the same) is approximately 65. Since OSPF chooses the path with the lowest cost, the cost to reach the West LAN 172.16.2.0/24 from East would be the cost of the direct path, which is the lower value of approximately 65. This matches the answer you’ve provided.

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