This article constitutes section 1, part C, chapter 5 of the CIW Website design manager course briefly covers: Internet Addressing

Internet Addressing

To ensure that each host on the Internet has a unique IP address, a central authority called the International Corporation of Assigned Names and Numbers (ICANN) issues all Internet addresses.

Most Internet addresses contain a network portion and a host portion. The network portion precedes the host portion. Internet addresses are specified as four fields seperated by full stops. These are typically written in dotted decimal notation. Each field has a value from 0 to

In this example the network portion is 208.158.21 and the host portion is 110. The network portion is determined by the class of the address.

Internet Addressing Classes

Internet addresses are divided into five classes: A, B, C, D and E to provide structure. These classes are shown below:

Address Classes internet Addressing


IP Internet Addressing Rules

Internet addresses must follow several guideline to function correctly. Not all addresses within the above ranges may be used.

Loopback Address

The loopback address 127. This is often assigned the name localhost. An Internet address cannot use the loopback address. This address allows a client and server on the same host to communicate with each other. This is ideal for testing and troubleshooting.

Broadcast Address

The broadcast address is 255. All network hosts can receive messages from this address.  The address is known as a limited broadcast and is used  for configuration at boot up. In the earlier IP example will broadcast to all hosts on the local network.

Reserved IP Addressing

ICANN has reserved three blocks of IP addresses for private networks:

  • to
  • to
  • to

Networks normally isolated from the Internet may use reserved addresses.

Subnet Masks

A subnet mask is a 32-bit number (like an IP address) with a one-to-one correlation to each bit of the IP address.

The subnet mask server two main purposes:

  • Distinguish the network and host portions of an IP address
  • Specify whether a destination address is local or remote

The following shows the default subnet masks for the first three classes: Class A Class B Class C

Class D and E do not have hosts, and therefore do not need subnet masks.

This section on Internet Addressing is like the rest of the course, in that, it only provides a brief overview of each element to give the webmaster a working knowledge of the technology.

Much of this section focuses on the terminology used in the field of internet addressing. And familiarity with the wording and context are important in understanding how it all pieces together.

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