A server is a computer or device on a network that manages network resources. Servers are often dedicated and they perform only their server tasks.
D (Network and subnet parts) . When using classful IP addressing concepts as described in Chapter 13, Analyzing Subnet Masks, addresses have three parts: network, subnet, and host. For addresses in a single classful network, the network parts must be identical for the numbers to be in the same network.
That system is known as CIDR notation. CIDR IP addresses consist of two groups of numbers, which are also referred to as groups of bits. The most important of these groups is the network address, and it is used to identify a network or a sub-network (subnet). The lesser of the bit groups is the host identifier.