IPv4 addressing

IPv4 addressing
9.2.3 This page will discuss IPv4 addressing.


A router uses IP to forward packets from the source network to the destination network. The packets must include an identifier for both the source and destination networks. A router uses the IP address of the destination network to deliver a packet to the correct network. When the packet arrives at a router connected to the destination network, the router uses the IP address to locate the specific computer on the network. This system works in much the same way as the national postal system. When the mail is routed, the zip code is used to deliver it to the post office at the destination city. That post office must use the street address to locate the final destination in the city.

Every IP address also has two parts. The first part identifies the network where the system is connected and the second part identifies the system. As is shown Figure , each octet ranges from 0 to 255. Each one of the octets breaks down into 256 subgroups and they break down into another 256 subgroups with 256 addresses in each. By referring to the group address directly above a group in the hierarchy, all of the groups that branch from that address can be referenced as a single unit.

This kind of address is called a hierarchical address, because it contains different levels. An IP address combines these two identifiers into one number. This number must be a unique number, because duplicate addresses would make routing impossible. The first part identifies the system's network address. The second part, called the host part, identifies which particular machine it is on the network.

IP addresses are divided into classes to define the large, medium, and small networks. Class A addresses are assigned to larger networks. Class B addresses are used for medium-sized networks, and Class C for small networks. The first step in determining which part of the address identifies the network and which part identifies the host is identifying the class of an IP address.

The Interactive Media Activity will require students to identify the different classes of addresses.

The next page will provide more information about Class A, B, C, D, and E IP addresses.