What is the OSPF cost for a FastEthernet interface operating at 100 mbps using the default reference bandwidth?

The OSPF cost for a FastEthernet interface can be calculated using the formula:

[ \text{Cost} = \frac{\text{Reference Bandwidth}}{\text{Interface Bandwidth}} ]

By default, the reference bandwidth for OSPF is set to 100 Mbps, which is 100,000 kbps. FastEthernet operates at 100 Mbps as well. Therefore, the cost calculation for a FastEthernet interface is:

[ \text{Cost} = \frac{100,000}{100} = 1 ]

This calculation shows that the OSPF cost for a FastEthernet interface, using the default reference bandwidth, is indeed 1. This value indicates a high-speed link, as lower costs are assigned to faster interfaces in OSPF routing. The rationale behind this is that OSPF utilizes cost as a metric to determine the most efficient path in a routing scenario, favoring paths with lower costs (indicating higher speed).

Understanding this concept is crucial for network professionals as it helps in implementing OSPF appropriately and optimizing routing decisions based on bandwidth and performance expectations.