IP Address Basics
What is IP
An IP address is a number that uniquely identifies every host on an IP network. IP addresses operate at the Network layer of the TCP/IP protocol stack, so they are independent of lower-level Data Link layer MAC addresses, such as Ethernet MAC addresses.
IP addresses are 32-bit binary numbers, which means that theoretically, a maximum of something in the neighborhood of 4 billion unique host addresses canexist throughout the Internet. However, due to the enormous growth of the Internet and the resulting depletion of the address space, a new addressing system (IPv6), using 128 bits for the address, was developed. You’d think that would be enough, but TCP/IP places certain restrictions on how IP addresses are allocated. These restrictions severely limit the total number of usable IP addresses, and today, about half of the total available IP addresses have already been assigned. The Internet Assigned Numbers Authority (IANA) manages the IP address space allocations globally. IANA works in cooperation with five Regional Internet Registries (RIRs) to allocate IP address blocks to Local Internet Registries (Internet service providers) and other entities. However, new techniques for working with IP addresses have helped to alleviate this problem, and a new standard for 128-bit IP addresses (known as IPv6) is on the verge of winning acceptance.
Understanding IP Adress
IP stands for Internet Protocol, and its primary purpose is to enable communications between networks. As a result, a 32-bit IP address actually consists of two parts:
The network ID (or network address) identifies the network on which a host computer can be found.
The host ID (or host address) identifies a specific device on the network indicated by the network ID.
Most of the complexity of working with IP addresses has to do with figuring out which part of the complete 32-bit IP address is the network ID and which part is the host ID. The original IP specification uses a system called address classes to determine which part of the IP address is the network ID and which part is the host ID. A newer system, known as classless IP addresses (IP6) is rapidly taking over the address classes system.
IPv4 addresses are usually represented in dot-decimal notation (four numbers, each ranging from 0 to 255, separated by dots, e.g. 188.8.131.52). Each part represents 8 bits of the address, and is therefore called an octet. In less common cases of technical writing, IPv4 addresses may be presented in hexadecimal, octal, or binary representations. When converting, each octet is usually treated as a separate number. In dotted-decimal notation, each group of eight bits, known as an octet, is represented by its decimal equivalent. For example, consider the following
binary IP address:
The dotted-decimal equivalent to this address is:
Here, 192 represents the first eight bits (11000000), 168 the second set of eight bits (10101000), 136 the third set of eight bits (10001000), and 28 the last set of eight bits (00011100). This is the format in which you’ll usually see IP addresses represented.