Internet Addresses
Every interface on an internet must have a unique Internet address (also called an IP address). These
addresses are 32-bit numbers. Instead of using a flat address space such as 1, 2, 3, and so on, there is a
structure to Internet addresses.
These 32-bit addresses are normally written as four decimal numbers, one for each byte of the address. This
is called dotted-decimal notation. For example, the class B address of the author's primary system is
140.252.13.33.
The easiest way to differentiate between the different classes of addresses is to look at the first number of a
dotted-decimal address.
It is worth reiterating that a multihomed host will have multiple IP addresses: one per interface.
Since every interface on an internet must have a unique IP address, there must be one central authority for
allocating these addresses for networks connected to the worldwide Internet. That authority is the Internet
Network Information Center, called the InterNIC. The InterNIC assigns only network IDs. The assignment
of host IDs is up to the system administrator.
There are three types of IP addresses: unicast (destined for a single host), broadcast (destined for all hosts on
a given network), and multicast (destined for a set of hosts that belong to a multicast group).