The TCP/IP Guide  9  TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)       9  TCP/IP Internet Layer (OSI Network Layer) Protocols            9  Internet Protocol (IP/IPv4, IPng/IPv6) and IP-Related Protocols (IP NAT, IPSec, Mobile IP)                 9  Internet Protocol Version 4 (IP, IPv4)                      9  IP Addressing                           9  IP Addressing Concepts and Issues

IP Addressing Overview and Fundamentals 1 2 3 IP Basic Address Structure and Main Components: Network ID and Host ID

Now that we have looked at the general issues and characteristics associated with IP addresses, it's time to get past the introductions and dig into the “meat” of our IP address discussion. Let's start by looking at the physical construction and size of the IP address and how it is referred to and used.

At its simplest, the IP address is just a 32-bit binary number: a set of 32 ones or zeroes. At the lowest levels computers always work in binary and this also applies to networking hardware and software. While different meanings are ascribed to different bits in the address as we shall soon see, the address itself is just this 32-digit binary number.

Humans don't work too well with binary numbers, because they are long and complicated, and the use of only two digits makes them hard to differentiate. (Quick, which of these is larger: 11100011010100101001100110110001 or 11100011010100101001101110110001? J) For this reason, when we use IP addresses we don't work with them in binary except when absolutely necessary.

The first thing that humans would naturally do with a long string of bits is to split it into four eight-bit octets (or bytes, even though the two aren't technically the same), to make it more manageable. So, 11100011010100101001101110110001 would become “11100011 - 01010010 - 10011101 - 10110001”. Then, we could convert each of those octets into a more manageable two-digit hexadecimal number, to yield the following: “E3 - 52 - 9D - B1”. This is in fact the notation used for IEEE 802 MAC addresses, except that they are 48 bits long so they have six two-digit hex numbers, and they are usually separated by colons, not dashes as I used here.

IP Addressing Overview and Fundamentals 1 2 3 IP Basic Address Structure and Main Components: Network ID and Host ID