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An Internet Protocol address (IP address) is a numerical label such as that is connected to a
computer network A computer network is a set of s sharing resources located on or provided by . The computers use common s over to communicate with each other. These interconnections are made up of technologies, based on physically wired, optical, and wire ...
that uses the
Internet Protocol The Internet Protocol (IP) is the network layer In the seven-layer OSI model The Open Systems Interconnection model (OSI model) is a conceptual model A conceptual model is a representation of a system, made of the composition of concept C ...
for communication.RFC 760, ''DOD Standard Internet Protocol'', DARPA, Information Sciences Institute (January 1980). Updated by . An IP address serves two main functions: network interface
identification Identification or identify may refer to: Art and entertainment *Identify (album), ''Identify'' (album) by Got7 *''Kill Command'', 2016 film, also known as ''Identify'' *Identify (song), "Identify" (song) *Identification (album), by Benjamin Ingr ...
and location
addressing In computing, an address space defines a range of discrete addresses, each of which may correspond to a network host, peripheral device, disk sector, a computer data storage, memory cell or other logical or physical entity. For software programs to ...
.
Internet Protocol version 4 Internet Protocol version 4 (IPv4) is the fourth version of the Internet Protocol The Internet Protocol (IP) is the principal communications protocol in the Internet protocol suite for relaying datagrams across network boundaries. Its routi ...

Internet Protocol version 4
(IPv4) defines an IP address as a
32-bit 32-bit microcomputers are computers in which 32-bit microprocessors are the norm. Range for storing integers A 32-bit register can store 232 different values. The range (computer programming), range of integer values that can be stored in 32 bi ...
number. However, because of the growth of the
Internet The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a ''internetworking, network of networks'' that consist ...

Internet
and the depletion of available IPv4 addresses, a new version of IP (
IPv6 Internet Protocol version 6 (IPv6) is the most recent version of the Internet Protocol (IP), the communication protocol, communications protocol that provides an identification and location system for computers on networks and routes traffic ...

IPv6
), using 128 bits for the IP address, was standardized in 1998.
IPv6 deploymentDeployment of Internet Protocol Version 6 (IPv6 Internet Protocol version 6 (IPv6) is the most recent version of the Internet Protocol (IP), the communication protocol, communications protocol that provides an identification and location system ...
has been ongoing since the mid-2000s. IP addresses are written and displayed in
human-readable 220px, ISBN represented as EAN-13 bar code showing both human-readable and machine-readable data A human-readable medium or human-readable format is any encoding of data Data are units of information Information can be thought of as ...
notations, such as in IPv4, and in IPv6. The size of the routing prefix of the address is designated in
CIDR notation Classless Inter-Domain Routing (CIDR ) is a method for allocating IP addresses and for IP routing. The Internet Engineering Task Force introduced CIDR in 1993 to replace the previous classful network addressing architecture on the Internet ...
by suffixing the address with the number of significant bits, e.g., , which is equivalent to the historically used
subnet mask A subnetwork or subnet is a logical subdivision of an IP network The Internet protocol suite, commonly known as TCP/IP, is the set of communications protocol A communication protocol is a system of rules that allows two or more entit ...
. The IP address space is managed globally by the
Internet Assigned Numbers Authority The Internet Assigned Numbers Authority (IANA) is a standards organization that oversees global IP address allocation, Autonomous system (Internet), autonomous system number allocation, DNS root zone, root zone management in the Domain Name Sys ...
(IANA), and by five regional Internet registries (RIRs) responsible in their designated territories for assignment to local Internet registries, such as
Internet service provider An Internet service provider (ISP) is an organization that provides a myriad of services for accessing, using, or participating in the Internet The Internet (or internet) is the global system of interconnected computer networks that ...
s (ISPs), and other
end user In product development, an end user (sometimes end-user) is a person who ultimately uses or is intended to ultimately use a product. The end user stands in contrast to users who support or maintain the product, such as sysop A sysop (; an abbrev ...
s. 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. Some IPv4 addresses are reserved for
private network In Internet networking, a private network is a computer network A computer network is a set of s sharing resources located on or provided by . The computers use common s over to communicate with each other. These interconnections are mad ...
s and are not globally unique.
Network administrator A network administrator is the person designated in an organization whose responsibility includes maintaining computer infrastructures with emphasis on local area networks A local area network (LAN) is a computer network that interconnects co ...
s 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.


Function

An IP address serves two principal functions: it identifies the host, or more specifically its
network interface Network interface may refer to: * Network interface controller A network interface controller (NIC, also known as a network interface card, network adapter, LAN adapter or physical network interface, and by similar terms) is a computer hardware ...
, 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." The
header Header may refer to: Computers and engineering * Header (computing)In information technology, header refers to supplemental data placed at the beginning of a block of data being stored or transmitted. In data transmission, the data following the h ...
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 Advanced Research Projects Agency Network (ARPANET) was the first wide-area packet-switching network with distributed control and one of the first networks to implement the Internet protocol suite, TCP/IP protocol suite. Both technologies ...
, the predecessor of the Internet, is
Internet Protocol version 4 Internet Protocol version 4 (IPv4) is the fourth version of the Internet Protocol The Internet Protocol (IP) is the principal communications protocol in the Internet protocol suite for relaying datagrams across network boundaries. Its routi ...

Internet Protocol version 4
(IPv4). The rapid exhaustion of IPv4 address space available for assignment to
Internet service providers#REDIRECT Internet service provider {{Redirect category shell, 1= {{R from other capitalisation ...
and end-user organizations by the early 1990s, prompted the
Internet Engineering Task Force The Internet Engineering Task Force (IETF) is an open standards organization, which develops and promotes voluntary Internet standards, in particular the technical standards that comprise the Internet protocol suite (TCP/IP). It has no formal ...
(IETF) to explore new technologies to expand the addressing capability on the Internet. The result was a redesign of the Internet Protocol which became eventually known as
Internet Protocol Version 6 Internet Protocol version 6 (IPv6) is the most recent version of the Internet Protocol (IP), the communication protocol, communications protocol that provides an identification and location system for computers on networks and routes traffic a ...

Internet Protocol Version 6
(IPv6) in 1995. 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 The Internet Stream Protocol (ST) is a family of experimental protocols first defined in Internet Experiment Note IEN-119 in 1979, and later substantially revised in RFC 1190 (ST-II) and RFC 1819 (ST2+). The protocol uses the version number 5 in t ...
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 The Transmission Control Protocol (TCP) is one of the main protocols of the Internet protocol suite The Internet protocol suite, commonly known as TCP/IP, is the set of s used in the and similar s. The current foundational protocols in th ...
in 1974 and 1977, as there was to 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''.


Subnetworks

IP networks may be divided into
subnetwork A subnetwork or subnet is a logical subdivision of an IP network. Updated by RFC 6918. The practice of dividing a network into two or more networks is called subnetting. Computers that belong to the same subnet are addressed with an identical ...
s in both
IPv4 Internet Protocol version 4 (IPv4) is the fourth version of the Internet Protocol The Internet Protocol (IP) is the network layer communications protocol A communication protocol is a system of rules that allows two or more entities of a ...
and
IPv6 Internet Protocol version 6 (IPv6) is the most recent version of the Internet Protocol (IP), the communication protocol, communications protocol that provides an identification and location system for computers on networks and routes traffic ...
. 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. The
subnet mask A subnetwork or subnet is a logical subdivision of an IP network The Internet protocol suite, commonly known as TCP/IP, is the set of communications protocol A communication protocol is a system of rules that allows two or more entit ...
or
CIDR notation Classless Inter-Domain Routing (CIDR ) is a method for allocating IP addresses and for IP routing. The Internet Engineering Task Force introduced CIDR in 1993 to replace the previous classful network addressing architecture on the Internet ...
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 and , respectively. The CIDR notation for the same IP address and subnet is , because the first 24 bits of the IP address indicate the network and subnet.


IPv4 addresses

An IPv4 address has a size of 32 bits, which limits the
address space In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithm of an algorithm (Euclid's algorithm) for calculating the greatest common ...
to (232) addresses. Of this number, some addresses are reserved for special purposes such as
private network In Internet networking, a private network is a computer network A computer network is a set of s sharing resources located on or provided by . The computers use common s over to communicate with each other. These interconnections are mad ...
s (~18 million addresses) and
multicast address A multicast address is a logical identifier for a group of host A host is a person responsible for guests at an event or for providing hospitality during it. Host may also refer to: Places *Host, Pennsylvania, a village in Berks County P ...
ing (~270 million addresses). IPv4 addresses are usually represented in
dot-decimal notationDot-decimal notation is a presentation format for numerical data. It consists of a string of decimal numbers, using the full stop The full stop ( Commonwealth English), period ( North American English) or full point is a punctuation mark. It is ...
, consisting of four decimal numbers, each ranging from 0 to 255, separated by dots, e.g., . Each part represents a group of 8 bits (an
octet Octet may refer to: Music * Octet (music) In music, an octet is a musical ensemble consisting of eight Musical instrument, instruments or voices, or a musical composition written for such an ensemble. Octets in classical music Octets in Europea ...
) of the address. In some cases of technical writing, IPv4 addresses may be presented in various
hexadecimal In mathematics and computing, the hexadecimal (also base 16 or hex) numeral system is a Numeral system#Positional systems in detail, positional numeral system that represents numbers using a radix (base) of 16. Unlike the decimal system repres ...
,
octal The octal numeral system, or oct for short, is the radix, base-8 number system, and uses the Numerical digit, digits 0 to 7, that is to say 10 represents 8 in decimal and 100 represents 64 in decimal. However, English uses a Base 10, base-10 num ...

octal
, or
binary Binary may refer to: Science and technology Mathematics * Binary number In mathematics and digital electronics, a binary number is a number expressed in the base-2 numeral system or binary numeral system, which uses only two symbols: ty ...
representations.


Subnetting history

In the early stages of development of the Internet Protocol, the network number was always the highest order octet (most significant eight bits). Because this method allowed for only 256 networks, it soon proved inadequate as additional networks developed that were independent of the existing networks already designated by a network number. In 1981, the addressing specification was revised with the introduction of
classful network 300px, Map of the prototype Internet in 1982, showing 8-bit-numbered networks (ovals) only, interconnected by routers (rectangles). A classful network is a network address A network address is an identifier for a node or host on a telecommun ...
architecture. Classful network design allowed for a larger number of individual network assignments and fine-grained subnetwork design. The first three bits of the most significant octet of an IP address were defined as the ''class'' of the address. Three classes (''A'', ''B'', and ''C'') were defined for universal
unicast image:unicast.svg, Unicast is data transmission from a single sender (red) to a single receiver (green). Other devices on the network (yellow) do not participate in the communication. In computer networking, unicast is a One-to-one (communication ...

unicast
addressing. Depending on the class derived, the network identification was based on octet boundary segments of the entire address. Each class used successively additional octets in the network identifier, thus reducing the possible number of hosts in the higher order classes (''B'' and ''C''). The following table gives an overview of this now-obsolete system. Classful network design served its purpose in the startup stage of the Internet, but it lacked
scalability Scalability is the property of a system to handle a growing amount of work by adding resources to the system. In an economic An economy (from Greek language, Greek οίκος – "household" and νέμoμαι – "manage") is an area of th ...
in the face of the rapid expansion of networking in the 1990s. The class system of the address space was replaced with
Classless Inter-Domain Routing Classless Inter-Domain Routing (CIDR ) is a method for allocating IP address An Internet Protocol address (IP address) is a numerical label such as that is connected to a computer network that uses the Internet Protocol for communication.R ...
(CIDR) in 1993. CIDR is based on variable-length subnet masking (VLSM) to allow allocation and routing based on arbitrary-length prefixes. Today, remnants of classful network concepts function only in a limited scope as the default configuration parameters of some network software and hardware components (e.g. netmask), and in the technical jargon used in network administrators' discussions.


Private addresses

Early network design, when global end-to-end connectivity was envisioned for communications with all Internet hosts, intended that IP addresses be globally unique. However, it was found that this was not always necessary as private networks developed and public address space needed to be conserved. Computers not connected to the Internet, such as factory machines that communicate only with each other via
TCP/IP The Internet protocol suite, commonly known as TCP/IP, is the set of communications protocol A communication protocol is a system of rules that allows two or more entities of a communications system 400px, Communication system A commu ...
, need not have globally unique IP addresses. Today, such private networks are widely used and typically connect to the Internet with
network address translation#REDIRECT Network address translation Network address translation (NAT) is a method of mapping an IP address space In computing, an address space defines a range of discrete addresses, each of which may correspond to a network host, peripheral dev ...
(NAT), when needed. Three non-overlapping ranges of IPv4 addresses for private networks are reserved. Updated by . These addresses are not routed on the Internet and thus their use need not be coordinated with an IP address registry. Any user may use any of the reserved blocks. Typically, a network administrator will divide a block into subnets; for example, many home routers automatically use a default address range of through ().


IPv6 addresses

In IPv6, the address size was increased from 32 bits in IPv4 to 128 bits, thus providing up to 2128 (approximately ) addresses. This is deemed sufficient for the foreseeable future. The intent of the new design was not to provide just a sufficient quantity of addresses, but also redesign routing in the Internet by allowing more efficient aggregation of subnetwork routing prefixes. This resulted in slower growth of
routing table In computer networking A computer network is a set of computers sharing resources located on or provided by Node (networking), network nodes. The computers use common communication protocols over digital signal, digital Interconnection, inter ...

routing table
s in routers. The smallest possible individual allocation is a subnet for 264 hosts, which is the square of the size of the entire IPv4 Internet. At these levels, actual address utilization ratios will be small on any IPv6 network segment. The new design also provides the opportunity to separate the addressing infrastructure of a network segment, i.e. the local administration of the segment's available space, from the addressing prefix used to route traffic to and from external networks. IPv6 has facilities that automatically change the routing prefix of entire networks, should the global connectivity or the
routing policy A routing protocol specifies how routers communicate with each other to distribute information that enables them to select routes between nodes In general, a node is a localized swelling (a "knot") or a point of intersection (a Vertex (graph theor ...
change, without requiring internal redesign or manual renumbering. The large number of IPv6 addresses allows large blocks to be assigned for specific purposes and, where appropriate, to be aggregated for efficient routing. With a large address space, there is no need to have complex address conservation methods as used in CIDR. All modern desktop and enterprise server operating systems include native support for
IPv6 Internet Protocol version 6 (IPv6) is the most recent version of the Internet Protocol (IP), the communication protocol, communications protocol that provides an identification and location system for computers on networks and routes traffic ...

IPv6
, but it is not yet widely deployed in other devices, such as residential networking routers,
voice over IP Voice over Internet Protocol (VoIP), also called IP telephony, is a method and group of technologies for the delivery of voice communications and multimedia Multimedia is a form of communication that ...
(VoIP) and multimedia equipment, and some
networking hardware Networking hardware, also known as network equipment or computer networking devices, are electronic devices which are required for communication and interaction between devices on a computer network A computer network is a group of computer ...
.


Private addresses

Just as IPv4 reserves addresses for private networks, blocks of addresses are set aside in IPv6. In IPv6, these are referred to as
unique local address A unique local address (ULA) is an Internet Protocol version 6 Internet Protocol version 6 (IPv6) is the most recent version of the Internet Protocol (IP), the communication protocol, communications protocol that provides an identification and ...
es (ULAs). The routing prefix is reserved for this block, which is divided into two blocks with different implied policies. The addresses include a 40-bit
pseudorandom A pseudorandom sequence of numbers is one that appears to be statistically randomA numeric sequence is said to be statistically random when it contains no recognizable patterns or regularities; sequences such as the results of an ideal dice, dice ...
number that minimizes the risk of address collisions if sites merge or packets are misrouted. Early practices used a different block for this purpose (), dubbed site-local addresses. Obsoleted by . However, the definition of what constituted a ''site'' remained unclear and the poorly defined addressing policy created ambiguities for routing. This address type was abandoned and must not be used in new systems. Addresses starting with , called
link-local address In computer network A computer network is a group of computers that use a set of common communication protocols over digital signal, digital interconnections for the purpose of sharing resources located on or provided by the Node (networking) ...
es, are assigned to interfaces for communication on the attached link. The addresses are automatically generated by the operating system for each network interface. This provides instant and automatic communication between all IPv6 hosts on a link. This feature is used in the lower layers of IPv6 network administration, such as for the
Neighbor Discovery Protocol The Neighbor Discovery Protocol (NDP), or simply Neighbor Discovery (ND), is a protocol of the Internet protocol suite used with IPv6, Internet Protocol Version 6 (IPv6). It operates at the link layer of the Internet model, and is responsible for ...

Neighbor Discovery Protocol
. Private and link-local address prefixes may not be routed on the public Internet.


IP address assignment

IP addresses are assigned to a host either dynamically as they join the network, or persistently by configuration of the host hardware or software. Persistent configuration is also known as using a static IP address. In contrast, when a computer's IP address is assigned each time it restarts, this is known as using a dynamic IP address. Dynamic IP addresses are assigned by network using
Dynamic Host Configuration Protocol The Dynamic Host Configuration Protocol (DHCP) is a network management protocol used on Internet Protocol The Internet Protocol (IP) is the network layer In the seven-layer OSI model The Open Systems Interconnection model (OSI model) i ...
(DHCP). DHCP is the most frequently used technology for assigning addresses. It avoids the administrative burden of assigning specific static addresses to each device on a network. It also allows devices to share the limited address space on a network if only some of them are online at a particular time. Typically, dynamic IP configuration is enabled by default in modern desktop operating systems. The address assigned with DHCP is associated with a ''lease'' and usually has an expiration period. If the lease is not renewed by the host before expiry, the address may be assigned to another device. Some DHCP implementations attempt to reassign the same IP address to a host, based on its
MAC address A media access control address (MAC address) is a unique identifier A unique identifier (UID) is an identifier An identifier is a name that identifies (that is, labels the identity of) either a unique object or a unique ''class'' of objects, ...
, each time it joins the network. A network administrator may configure DHCP by allocating specific IP addresses based on MAC address. DHCP is not the only technology used to assign IP addresses dynamically.
Bootstrap Protocol The Bootstrap Protocol (BOOTP) is a computer network A computer network is a set of computer A computer is a machine that can be programmed to Execution (computing), carry out sequences of arithmetic or logical operations automaticall ...
is a similar protocol and predecessor to DHCP.
Dialup Dial-up Internet access is a form of Internet access that uses the facilities of the public switched telephone network (PSTN) to establish a connection to an Internet service provider (ISP) by dialing a telephone number on a conventional telephone ...
and some
broadband networks The ideal telecommunication network has the following characteristics: broadband, ''multi-media'', ''multi-point'', ''multi-rate'' and economical implementation for a diversity of services (multi-services). The Broadband Integrated Services Digital ...
use dynamic address features of the
Point-to-Point Protocol In computer network A computer network is a set of computer A computer is a machine that can be programmed to Execution (computing), carry out sequences of arithmetic or logical operations automatically. Modern computers can perform ...
. Computers and equipment used for the network infrastructure, such as routers and mail servers, are typically configured with static addressing. In the absence or failure of static or dynamic address configurations, an operating system may assign a link-local address to a host using stateless address autoconfiguration.


Sticky dynamic IP address


Address autoconfiguration

Address block is defined for the special use of link-local addressing for IPv4 networks. Updated by . In IPv6, every interface, whether using static or dynamic addresses, also receives a link-local address automatically in the block . These addresses are only valid on the link, such as a local network segment or point-to-point connection, to which a host is connected. These addresses are not routable and, like private addresses, cannot be the source or destination of packets traversing the Internet. When the link-local IPv4 address block was reserved, no standards existed for mechanisms of address autoconfiguration. Filling the void,
Microsoft Microsoft Corporation is an American multinational corporation, multinational technology company, technology corporation which produces Software, computer software, consumer electronics, personal computers, and related services. Its best-know ...

Microsoft
developed a protocol called Automatic Private IP Addressing (APIPA), whose first public implementation appeared in
Windows 98 Windows 98 is an operating system An operating system (OS) is system software System software is software designed to provide a platform for other software. Examples of system software include operating systems (OS) like macOS, Linux, And ...
. APIPA has been deployed on millions of machines and became a
de facto standard A de facto standard is a custom or convention Convention may refer to: * Convention (norm), a custom or tradition, a standard of presentation or conduct ** Treaty, an agreement in international law * Convention (meeting), meeting of a (usually la ...
in the industry. In May 2005, the
IETF The Internet Engineering Task Force (IETF) is an open standards organization A standards organization, standards body, standards developing organization (SDO), or standards setting organization (SSO) is an organization whose primary functi ...
defined a formal standard for it.


Addressing conflicts

An IP address conflict occurs when two devices on the same local physical or wireless network claim to have the same IP address. A second assignment of an address generally stops the IP functionality of one or both of the devices. Many modern
operating system An operating system (OS) is system software System software is software designed to provide a platform for other software. Examples of system software include operating systems (OS) like macOS, Linux, Android (operating system), Android and Mi ...

operating system
s notify the administrator of IP address conflicts. When IP addresses are assigned by multiple people and systems with differing methods, any of them may be at fault. If one of the devices involved in the conflict is the
default gateway A default gateway is the node In general, a node is a localized swelling (a "knot A knot is an intentional complication in Rope, cordage which may be practical or decorative, or both. Practical knots are classified by function, including hitche ...
access beyond the LAN for all devices on the LAN, all devices may be impaired.


Routing

IP addresses are classified into several classes of operational characteristics: unicast, multicast, anycast and broadcast addressing.


Unicast addressing

The most common concept of an IP address is in
unicast image:unicast.svg, Unicast is data transmission from a single sender (red) to a single receiver (green). Other devices on the network (yellow) do not participate in the communication. In computer networking, unicast is a One-to-one (communication ...

unicast
addressing, available in both IPv4 and IPv6. It normally refers to a single sender or a single receiver, and can be used for both sending and receiving. Usually, a unicast address is associated with a single device or host, but a device or host may have more than one unicast address. Sending the same data to multiple unicast addresses requires the sender to send all the data many times over, once for each recipient.


Broadcast addressing

Broadcasting Broadcasting is the distributionDistribution may refer to: Mathematics *Distribution (mathematics) Distributions, also known as Schwartz distributions or generalized functions, are objects that generalize the classical notion of functi ...
is an addressing technique available in IPv4 to address data to all possible destinations on a network in one transmission operation as an ''all-hosts broadcast''. All receivers capture the network packet. The address is used for network broadcast. In addition, a more limited directed broadcast uses the all-ones host address with the network prefix. For example, the destination address used for directed broadcast to devices on the network is . IPv6 does not implement broadcast addressing and replaces it with multicast to the specially defined all-nodes multicast address.


Multicast addressing

A
multicast address A multicast address is a logical identifier for a group of host A host is a person responsible for guests at an event or for providing hospitality during it. Host may also refer to: Places *Host, Pennsylvania, a village in Berks County P ...
is associated with a group of interested receivers. In IPv4, addresses through (the former
Class D Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differently f ...
addresses) are designated as multicast addresses. IPv6 uses the address block with the prefix for multicast. In either case, the sender sends a single
datagram A datagram is a basic transfer unit associated with a packet-switched network In telecommunication Telecommunication is the transmission of information Information can be thought of as the resolution of uncertainty; it answers the ques ...
from its unicast address to the multicast group address and the intermediary routers take care of making copies and sending them to all interested receivers (those that have joined the corresponding multicast group).


Anycast addressing

Like broadcast and multicast,
anycast Anycast is a network addressing In computing, an address space defines a range of discrete addresses, each of which may correspond to a network host, peripheral device, disk sector, a computer data storage, memory cell or other logical or physical ...

anycast
is a one-to-many routing topology. However, the data stream is not transmitted to all receivers, just the one which the router decides is closest in the network. Anycast addressing is a built-in feature of IPv6. In IPv4, anycast addressing is implemented with
Border Gateway Protocol Border Gateway Protocol (BGP) is a standardized exterior gateway protocol The Exterior Gateway Protocol (EGP) was a routing protocol A routing protocol specifies how routers communicate with each other to distribute information that enables ...
using the shortest-path
metric Metric or metrical may refer to: * Metric system, an internationally adopted decimal system of measurement Mathematics * Metric (mathematics), an abstraction of the notion of ''distance'' in a metric space * Metric tensor, in differential geomet ...
to choose destinations. Anycast methods are useful for global load balancing and are commonly used in distributed
DNS The Domain Name System (DNS) is the hierarchical and Decentralised system, decentralized naming system used to identify computers, Internet#Applications_and_services, services, and other resources reachable through the internet or other intern ...

DNS
systems.


Geolocation

A host may use
geolocation software In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes and development of both computer hardware , hardware and software ...
to deduce the
geographic position A geographic coordinate system (GCS) is a coordinate system associated with position (geometry), positions on Earth (geographic position). A GCS can give positions: *as Geodetic coordinates, spherical coordinate system using latitude, long ...
of its communicating peer.


A public IP address is a globally routable unicast IP address, meaning that the address is not an address reserved for use in

private network In Internet networking, a private network is a computer network A computer network is a set of s sharing resources located on or provided by . The computers use common s over to communicate with each other. These interconnections are mad ...
s, such as those reserved by , 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 An Internet service provider (ISP) is an organization that provides a myriad of services for accessing, using, or participating in the Internet. Internet service providers can be organized in various forms, such as commercial, community-owned, ...

ISP
. In this case, it is also locally visible by logging into the router configuration. 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's 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.


Firewalling

For security and privacy considerations, network administrators often desire to restrict public Internet traffic within their private networks. The source and destination IP addresses contained in the headers of each IP packet are a convenient means to discriminate traffic by
IP address blocking IP address blocking is a configuration of a network service that blocks requests from hosts with certain IP addresses. IP address blocking is commonly used to protect against brute force attacks and to prevent access by a disruptive address. ...
or by selectively tailoring responses to external requests to internal servers. This is achieved with
firewall Firewall may refer to: * Firewall (computing) In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes and development ...
software running on the network's gateway router. A database of IP addresses of restricted and permissible traffic may be maintained in blacklists and
whitelist Whitelisting (also referred to as allow-listing) is the practice of explicitly allowing some identified entities access to a particular privilege, service, mobility, access or recognition. It is the opposite of Blacklist (computing), blacklisting. ...
s, respectively.


Address translation

Multiple client devices can appear to share an IP address, either because they are part of a
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environment or because an IPv4
network address translator Network address translation (NAT) is a method of mapping an IP address space In computing, an address space defines a range of discrete addresses, each of which may correspond to a network host, peripheral device, disk sector, a computer data sto ...
(NAT) or
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proxy server
acts as an
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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. The NAT device maps different IP addresses on the private network to different TCP or UDP
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s on the public network. In residential networks, NAT functions are usually implemented in a
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. 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.


Diagnostic tools

Computer operating systems provide various diagnostic tools to examine network interfaces and address configuration.
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