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An Internet Protocol address (IP address) is a numerical label assigned to a device that participates in a computer network that uses the internet for communication, such as a printer or computer. The IP address has two functions, network interface identification and location addressing. IP addresses have been defined as a 32-bit number system known as Internet Protocol Version 4 (IPv4) which is still in use today. But, with the limited availability of addresses, a new version was developed in 1995, using 128 bits and was standardized in 1998.
An IP address consists of binary numbers usually stored in text files that are displayed in readable form, for example, 172.16.254.1 would be an IPv4 address and 2001:db8:0:1234:567:8:1 would be an IPv6 address.
An IPv4 address has 32 bits which limits the amount of available addresses to 4,294,967,296. Eighteen million private networks and 270 million multicast addresses are reserved in IPv4. The IPv4 consists of 4 numbers ranging from 0 – 255, separated by dots. Each number represents 8 bits of the address.
The early method of an IP address proved inadequate as more networks were developed, so in 1981 classful network architecture was introduced. This allowed for a larger number of individual network assignments. This system is now obsolete and was replaced in 1993 with Classless Inter-Domain Routing (CIDR), which was based on variable length subnet masking (VLSM) to allow allocation and routing based on arbitrary length prefixes. Today this concept is limited as the default configuration of some network software and hardware components.
The IPv4 private address originally was designed to communicate with all internet hosts and the IP address be assigned to a particular device. But, it was not necessary as private networks developed and public address space needed to be conserved. Computers that were not connected to the internet and only communicated with like devices did not need a global IP address, so these addresses did not need to be coordinated with an IP address registry. Today these networks connect to the internet by network address translation (NAT). Most home routers automatically use a default address in the range of 192.168.0.0 through 192.168.0.255.
IPv4 address exhaustion means the supply of unallocated IPv4 addresses available have been depleted. As of February 3, 2011, the last five blocks were allocated, except for a small amount of space reserved to transition to the IPv6 system.
In 1995 IPv6 was introduced to replace the rapidly diminishing IPv4 addresses. The address size was increased from 32 bits to 128 bits, which mathematically will increase the address space to sufficiently provide 3.403 x 10 to the 38th power of unique address. It will not provide the quantity on its own, but it will allow for efficient collection of routing prefixes to occur, resulting in the smallest possible allocation for hosts, which amounts to the square of the entire IPv4 IP addresses. It also makes it possible to automatically change the routing prefix of entire networks, without requiring internal redesign or renumbering. Although modern desktops and servers include support for IPv6, it is not yet widely deployed in other devices such as home routers, voice over IP, and multimedia equipment.
IPv6 private addresses are set aside and referred to as unique local address (ULA). Early designs were called site-local addresses, but the poorly defined addressing policy created uncertainty in the routing so it was abandoned and not to be used in the new systems. An address starting with fe80 is called a link-local address. These addresses are for communication with the link only and are automatically generated by the operating system for each network interface. This will provide instant and automatic connectivity for any IPv6 host. If several hosts connect to a common hub, they have a communication path through their link-local IPv6 address that is used in the lower layers of the IPv6 network. Private IP address prefixes cannot be routed on the public internet.
The assignment of an IP address to a host is either a new address at the time of booting, or a permanently fixed configuration of the hardware or software. When a computer’s IP address is assigned newly each time, it is known as a dynamic IP address.
A static IP address is manually assigned to a computer by an administrator. In some cases the administrator will use a Dynamic Host Configuration Protocol (DHCP) server which will assign the same IP address to a particular computer, allowing the static IP address to be configured centrally without having to configure each computer manually.
The dynamic IP addressing system is mostly used to assign the address on LAN and broadband networks using DHCP servers. This avoids the burden of assigning specific static addresses to each device on a network. It will also allow many devices to share address space on a network even if only a few will be online at the same time. Desktop operating systems use dynamic IP configuration so the user does not have to manually enter any settings to connect to a network. Dialup and some broadband networks use another dynamic addressing protocol called Point-to-Point Protocol. This is a direct link between two networks.
A sticky dynamic IP address is a term used by cable and DSL subscribers to describe a dynamically assigned IP address that will seldom change. Modems fall within the parameters of this term because the modem will stay powered for long periods of time and the IP address will simply be renewed. If the modem is turned off, and it is powered back up again, the IP address will most likely be the same.
Firewalls perform internet protocol blocking to protect networks from unauthorized access, which is common on the internet. If an IP address is blocked by a client using a proxy server or a network address translation, blocking one IP address may also block many individual computers.
Multiple client devices can share the same IP address because they are part of a shared hosting web server, an IPv4 network address translator (NAT), or using a proxy server acting as an intermediate agent on the behalf of its customer. In this case the originating IP address might be hidden from the server receiving a request.
Most commonly NAT is used in home networks and takes place typically in a router, which the computer that is connected to the router would have a private IP address and the router has a public address to communicate with the internet. This allows several computers to share the one public IP address.