Your network has a mixture of Fast Ethernet and Gigabit Ethernet links. What needs to be done to
ensure optimal data routing when using OSPF?

A.
Nothing. OSPF will determine the most optimal path for routing data by default.

B.
Adjust the hello and dead timers for more rapid detection of link failures.

C.
Increase the reference-bandwidth used to calculate the interface default metrics, on all routers
in your network.

D.
Set the priority values on every broadcast interface to ensure that the designated and backup
designated routers are the routers with the most processor and memory resources.

Explanation:
The default formula to calculate the cost for the OSPF metric is (108/BW). Therefore when using
default reference bandwidth (100M) to calculate ospf, Gi and Fa interfaces could have the same
cost (1). This problem can be fixed by configuring reference bandwidth to 1000M.

This is how to configure reference bandwidth to 1000Mbps:
Router(config)#router ospf 1Router(config-router)#auto-cost reference-bandwidth 1000