Answer to Question 1
Subnetworks offer several advantages. Subnets allow networks with different topologies to be supported. For example, a router can connect an Ethernet subnet with a token ring subnet. Subnets also resolve the problem of the physical limitations of a network's capacity. An Ethernet network can only accommodate so many devices. Through subnetting, the physical limitations of an Ethernet LAN are overcome. If a network becomes too large, management and configuration can become quite complicated, if not impossible. Subnets allow a greater number of hosts to be provided for and more easily managed over the entire enterprise. Another advantage of subnets is that they can reduce traffic. Reducing traffic improves the overall performance of the network, allowing for faster response.
Answer to Question 2
In practice, most businesses that use TCP/IP refer to each separate network in the enterprise as a subnet. Rather than have one very large network, with hundreds or thousands of hosts, most organizations segment or subdivide a single network address through a process call subnetting. With subnetting, a single network identifier is subdivided into multiple uniquely identified segments, which is why we call this subdivision a subnet. Subnetting is accomplished by borrowing bits from the host portion of an IP address and reassigning those bits for use as network address identifiers. In order to subnet, something called a subnet mask is used. Subnet masks use binary ones to represent the network portion of an address and zeros to represent the host portion. Before describing how subnetting and submasking work, let's examine a few advantages of the subnetwork architecture.