CompTIA’s Network+ certification Study Guide part 33 is a globally-recognized, vendor neutral exam that has helped over 235,000 IT professionals reach further and higher in their careers. The 2009 Network+ exam (N10-004) is a major update with more focus on security and wireless aspects of networking. Our new study guide has been updated accordingly with focus on network, systems, and WAN security and complete coverage of today’s wireless networking standards. | 306 CHAPTER 7 TCP IP and Routing you recall there are some instances when information is broadcast on a network. Imagine broadcasts to and from 16 million hosts. The network would come to a grinding halt from all that traffic. Therefore although a company may have a Class A network ID it will segment divide that network to avoid having 16 million hosts per network. This process of segmenting is called subnetting. Each segment or subnet must have a unique identifier so that traffic can be sent to the correct location. Because the network ID is a fixed number assigned by the InterNIC a method was devised to subdivide the assigned network ID by borrowing bits from the host address space not the network address space. An assigned Class A network assigns the network ID using only the first octet. A subnetted Class A network might use bits from the second and third octets to create new subnetworks. Although it s theoretically possible to use any host octet bits in practice they are always used starting from the left-most host address space bit moving to the right. In other words we take the high-order host address bits first. Table shows the resulting number of subnets and number of host bits used when subnetting a Class A network. The process is identical to extend the number of subnets on a Class A network beyond 256 by taking additional host address bits from the next octet where and y are used for network and only z is left for host addresses . This process is similar for Class B and Class C networks as well although the number of subnets and hosts will vary. We can identify the number of bits used for the network by notating how many total bits counting left to right are used in the network address. From there we can calculate how many bits remain for host addresses. A Class A Table Subnets Using Host ID Bits Number of Subnets Number of Host Bits Used in Network ID Binary network ID in bold 0 0 1-2 1 01000010 . .
