A router forwards packets from the originating network to the destination network using the IP protocol. The packets must include an identifier for both the source and destination networks. Using the IP address of destination network, a router can 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 particular computer connected to that network. This system works in much the same way as the national postal system. When the mail is routed, it must first be delivered to the post office at the destination city using the zip code. That post office then must locate the final destination in that city using the street address. This is a two-step process.

Accordingly, every IP address has two parts. One part identifies the network where the system is connected, and a second part identifies that particular system on the network. 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.

Interactive Media Activity Drag and Drop: Identifying Address Classes After completing this activity, the student will be able to identify all the details within the different internet address classes.

   

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