IP address
An Internet Protocol address (IP address) is a numerical label such as 192.0.2.1 that is assigned to a device connected to a computer network that uses the Internet Protocol for communication.[1][2] IP addresses serve two main functions: network interface identification, and location addressing.
Internet Protocol version 4 (IPv4) defines an IP address as a 32-bit number.[2] However, because of the growth of the Internet and the depletion of available IPv4 addresses, a new version of IP (IPv6), using 128 bits for the IP address, was standardized in 1998.[3][4][5] IPv6 deployment has been ongoing since the mid-2000s.
IP addresses are written and displayed in human-readable notations, such as 192.0.2.1 in IPv4, and 2001:db8:0:1234:0:567:8:1 in IPv6. The size of the routing prefix of the address is designated in CIDR notation by suffixing the address with the number of significant bits, e.g., 192.0.2.1/24, which is equivalent to the historically used subnet mask 255.255.255.0.
The IP address space is managed globally by the Internet Assigned Numbers Authority (IANA), and by five regional Internet registries (RIRs) responsible in their designated territories for assignment to local Internet registries, such as Internet service providers (ISPs), and other end users. IPv4 addresses were distributed by IANA to the RIRs in blocks of approximately 16.8 million addresses each, but have been exhausted at the IANA level since 2011. Only one of the RIRs still has a supply for local assignments in Africa.[6] Some IPv4 addresses are reserved for private networks and are not globally unique.
Network administrators assign an IP address to each device connected to a network. Such assignments may be on a static (fixed or permanent) or dynamic basis, depending on network practices and software features. Some jurisidications consider IP addresses to be personal data.
Function
An IP address serves two principal functions: it identifies the host, or more specifically its network interface, and it provides the location of the host in the network, and thus the capability of establishing a path to that host. Its role has been characterized as follows: "A name indicates what we seek. An address indicates where it is. A route indicates how to get there."[2] The header of each IP packet contains the IP address of the sending host and that of the destination host.
IP versions
Two versions of the Internet Protocol are in common use on the Internet today. The original version of the Internet Protocol that was first deployed in 1983 in the ARPANET, the predecessor of the Internet, is Internet Protocol version 4 (IPv4).
By the early 1990s, the rapid exhaustion of IPv4 address space available for assignment to Internet service providers and end-user organizations prompted the Internet Engineering Task Force (IETF) to explore new technologies to expand addressing capability on the Internet. The result was a redesign of the Internet Protocol which became eventually known as Internet Protocol Version 6 (IPv6) in 1995.[3][4][5]
IPv6 technology was in various testing stages until the mid-2000s when commercial production deployment commenced.
Today, these two versions of the Internet Protocol are in simultaneous use. Among other technical changes, each version defines the format of addresses differently. Because of the historical prevalence of IPv4, the generic term IP address typically still refers to the addresses defined by IPv4. The gap in version sequence between IPv4 and IPv6 resulted from the assignment of version 5 to the experimental Internet Stream Protocol in 1979, which however was never referred to as IPv5.
Other versions v1 to v9 were defined, but only v4 and v6 ever gained widespread use. v1 and v2 were names for TCP protocols in 1974 and 1977, as there was no separate IP specification at the time. v3 was defined in 1978, and v3.1 is the first version where TCP is separated from IP. v6 is a synthesis of several suggested versions, v6 Simple Internet Protocol, v7 TP/IX: The Next Internet, v8 PIP — The P Internet Protocol, and v9 TUBA — Tcp & Udp with Big Addresses.[7]
Subnetworks
IP networks may be divided into subnetworks in both IPv4 and IPv6. For this purpose, an IP address is recognized as consisting of two parts: the network prefix in the high-order bits and the remaining bits called the rest field, host identifier, or interface identifier (IPv6), used for host numbering within a network.[1] The subnet mask or CIDR notation determines how the IP address is divided into network and host parts.
The term subnet mask is only used within IPv4. Both IP versions however use the CIDR concept and notation. In this, the IP address is followed by a slash and the number (in decimal) of bits used for the network part, also called the routing prefix. For example, an IPv4 address and its subnet mask may be 192.0.2.1 and 255.255.255.0, respectively. The CIDR notation for the same IP address and subnet is 192.0.2.1/24, because the first 24 bits of the IP address indicate the network and subnet.
Public address
A public IP address is a globally routable unicast IP address, meaning that the address is not an address reserved for use in private networks, such as those reserved by RFC 1918, or the various IPv6 address formats of local scope or site-local scope, for example for link-local addressing. Public IP addresses may be used for communication between hosts on the global Internet.
In a home situation, a public IP address is the IP address assigned to the home's network by the ISP. In this case, it is also locally visible by logging into the router configuration.[31]
Most public IP addresses change, and relatively often. Any type of IP address that changes is called a dynamic IP address. In home networks, the ISP usually assigns a dynamic IP. If an ISP gave a home network an unchanging address, it is more likely to be abused by customers who host websites from home, or by hackers who can try the same IP address over and over until they breach a network.[31]
Address translation
Multiple client devices can appear to share an IP address, either because they are part of a shared web hosting service environment or because an IPv4 network address translator (NAT) or proxy server acts as an intermediary agent on behalf of the client, in which case the real originating IP address is masked from the server receiving a request. A common practice is to have a NAT mask many devices in a private network. Only the public interface(s) of the NAT needs to have an Internet-routable address.[32]
The NAT device maps different IP addresses on the private network to different TCP or UDP port numbers on the public network. In residential networks, NAT functions are usually implemented in a residential gateway. In this scenario, the computers connected to the router have private IP addresses and the router has a public address on its external interface to communicate on the Internet. The internal computers appear to share one public IP address.
Law
In March 2024, the Supreme Court of Canada decided that IP addresses were protected private information under the Canadian Charter of Rights and Freedoms, with police searches requiring a warrant in order to obtain them.[33] IP addresses are considered personal data by the European Commission and are protected by the General Data Protection Regulation.[34]
Diagnostic tools
Computer operating systems provide various diagnostic tools to examine network interfaces and address configuration. Microsoft Windows provides the command-line interface tools ipconfig[35] and netsh and users of Unix-like systems may use ifconfig, netstat, route, lanstat, fstat, and iproute2 utilities to accomplish the task.[36]