IP Addressing.  In order for computers to send messages to each other over the internet there needs to be some way for them to locate each other.  The addresses associated with the IP - Internet Protocol are used to locate different machines from routers to computers on the internet.  IP Addressing are 32 bits as shown in the next figure.

 Part of the IP address represents the network, part of it represents the host number for the device on this network. They are grouped into four groups of eight or octets as represented in the following diagram.

 IP addressing defines five address classes: A, B, C, D and E.  Classes D and E are for specialized devices.  Class D is used for multicast groups, Class E is reserved for experimental use.  Classes A, B and C are used more commonly for network addresses.  The majority of networks are numbered using class B and C addresses.

 Class Format Prefix Length Higher Order Bits Address Range Number of Hosts (no subnets) A N.H.H.H 8 bits 0 1.0.0.0 to 126.0.0.0 (256)3 - 2 = 16,777,214 B N.N.H.H 16 bits 10 128.0.0.0 to 191.255.0.0 (256)2 > 65,534 C N.N.N.H 24 bits 110 192.0.0.0 to 223.255.255.0 254

 What the table attempts to imply is that Class A addresses are network and host portions are configured as illustrated in the following.

 For class B the addresses are likely to look like.

 For class C the addresses are of the following form.

 So if you think about the proliferation of computers and LANs on the internet there is the very basic problem of just locating the LANs and all of their machines that are internet capable.  From the classes of addresses how many networks you can locate and how many machines.  The following table is theoretical numbers because some of the addresses are reserved for other purposes.

 Theoretical Numbers Class Number of Network Addresses Number of Computer Addresses A 256 (256)3 - 2= 16,777,214 B (256)2 = 65,563 (256)2 - 2 = 65,561 C (256)3 = 16,777,216 256 - 2 = 254