94 CHAPTER 6 TCP/IP and Routing UNDERSTANDING SUBNET MASKING Large networks are subdivided to create smaller subnetworks. This process of segmenting is called subnetting, and most networks are divided into segments called subnets. Supernetting is the process of combining smaller networks into one larger network. A subnet mask is a 32-bit number that is to shield or mask certain bits. The number of host IDs on a network is variable, but the network ID must be the same for all hosts on a segment. The underlying concept of subnets and subnet masking involves a binary process called bitwise ANDing. DID YOU KNOW? Bitwise ANDing simply means that we are performing the logical AND function on each bit. The simple AND statements can be expressed as shown here. Rather than a mathematical plus function, this is a comparison between two (or more) values. 0 + 0 = 0 0 + 1 = 0