I understand if two office are far away (eg. New York - California) apart you can use the internet to communicate using the routers but (with out internet) if Company ABC started with 20 users and all of them were in one building, during the years it grew from 20 to 110 employees and now the company is using two building distance less than 1,000 feet. They are using fiber optic to connect from one building to the other and each building has it own server one primary the other secondary. In case the primary fail (Hardware) the secondary take over using heartbeat technology.
My questions are:
1)What is the benefit having two sub net ( or more) ?
2)If you want to have more than one sub net and the router are far away between 150 to 900 feet, what type of interface you will use to connect the router(see example ablove)