Internet access can improve people's life quality by helping them to reduce and overcome the poverty and educational gaps. However, most rural communities in the world, specially in underdeveloped countries, do not have access to the Internet. Delay/Disruption Tolerant Networking (DTN) is a recent low-cost technology now being used to provide connectivity to rural towns were some transportation means periodically arrive. DTNs can be implemented to connect communities to Internet, since this technology takes advantage of the existing people's transportation infrastructure using it to move packets and messages to and from Internet. This paper proposes a DTN mathematical optimization model that maximizes the availability probabilities of the paths from sources to destinations. We also present an opportunistic forwarding algorithm that takes into account the availability probability of a node's neighbors to decide if a node should forward a message or store the message until a node with a higher availability probability contacts it. This algorithm was tested in five different scenarios and in all of them it found a path to the destination.