An
Internet Protocol address (
IP address) is a numerical label assigned to each device (e.g., computer, printer) participating in a
computer networkA computer network, often simply referred to as a network, is a collection of hardware components and computers interconnected by communication channels that allow sharing of resources and information....
that uses the
Internet ProtocolThe Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...
for communication. An IP address serves two principal functions: host or network interface
identificationThe function of identification is to map a known quantity to an unknown entity so as to make it known. The known quantity is called the identifier and the unknown entity is what needs identification. A basic requirement for identification is that the Id be unique. Ids may be scoped, that is, they...
and location
addressingIn computing, a logical address is the address at which an item appears to reside from the perspective of an executing application program....
. Its role has been characterized as follows: "
A nameA hostname is a label that is assigned to a device connected to a computer network and that is used to identify the device in various forms of electronic communication such as the World Wide Web, e-mail or Usenet...
indicates what we seek. An address indicates where it is. A route indicates how to get there."
The designers of the Internet Protocol defined an IP address as a
32-bitThe range of integer values that can be stored in 32 bits is 0 through 4,294,967,295. Hence, a processor with 32-bit memory addresses can directly access 4 GB of byte-addressable memory....
number and this system, known as
Internet Protocol Version 4Internet Protocol version 4 is the fourth revision in the development of the Internet Protocol and the first version of the protocol to be widely deployed. Together with IPv6, it is at the core of standards-based internetworking methods of the Internet...
(IPv4), is still in use today. However, due to the enormous growth of the
InternetThe Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...
and the predicted depletion of available addresses, a new addressing system (
IPv6Internet Protocol version 6 is a version of the Internet Protocol . It is designed to succeed the Internet Protocol version 4...
), using 128 bits for the address, was developed in 1995, standardized as RFC 2460 in 1998, and is being deployed worldwide since the mid-2000s.
IP addresses are binary numbers, but they are usually stored in text files and displayed in
human-readableA human-readable medium or human-readable format is a representation of data or information that can be naturally read by humans.In computing, human-readable data is often encoded as ASCII or Unicode text, rather than presented in a binary representation...
notations, such as 172.16.254.1 (for
IPv4Internet Protocol version 4 is the fourth revision in the development of the Internet Protocol and the first version of the protocol to be widely deployed. Together with IPv6, it is at the core of standards-based internetworking methods of the Internet...
), and 2001:db8:0:1234:0:567:8:1 (for
IPv6Internet Protocol version 6 is a version of the Internet Protocol . It is designed to succeed the Internet Protocol version 4...
).
The
Internet Assigned Numbers AuthorityThe Internet Assigned Numbers Authority is the entity that oversees global IP address allocation, autonomous system number allocation, root zone management in the Domain Name System , media types, and other Internet Protocol-related symbols and numbers...
(IANA) manages the IP address space allocations globally and delegates five regional Internet registries (RIRs) to allocate IP address blocks to
local Internet registriesA local Internet registry is an organization that has been allocated a block of IP addresses by a regional Internet registry , and that assigns most parts of this block to its own customers. Most LIRs are Internet service providers, enterprises, or academic institutions. Membership in an RIR is...
(
Internet service providerAn Internet service provider is a company that provides access to the Internet. Access ISPs directly connect customers to the Internet using copper wires, wireless or fiber-optic connections. Hosting ISPs lease server space for smaller businesses and host other people servers...
s) and other entities.
IP versions
Two versions of the Internet Protocol (IP) are in use: IP Version 4 and IP Version 6. Each version defines an IP address differently. Because of its prevalence, the generic term
IP address typically still refers to the addresses defined by
IPv4Internet Protocol version 4 is the fourth revision in the development of the Internet Protocol and the first version of the protocol to be widely deployed. Together with IPv6, it is at the core of standards-based internetworking methods of the Internet...
. The gap in version sequence between IPv4 and IPv6 resulted from the assignment of number 5 to the experimental Internet Stream Protocol in 1979, which however was never referred to as IPv5.
IPv4 addresses
In IPv4 an address consists of 32
bitA bit is the basic unit of information in computing and telecommunications; it is the amount of information stored by a digital device or other physical system that exists in one of two possible distinct states...
s which limits the
address spaceIn computing, an address space defines a range of discrete addresses, each of which may correspond to a network host, peripheral device, disk sector, a memory cell or other logical or physical entity.- Overview :...
to (2
32) possible unique addresses. IPv4 reserves some addresses for special purposes such as
private networkIn the Internet addressing architecture, a private network is a network that uses private IP address space, following the standards set by RFC 1918 and RFC 4193. These addresses are commonly used for home, office, and enterprise local area networks , when globally routable addresses are not...
s (~18 million addresses) or
multicast addressA multicast address is a logical identifier for a group of hosts in a computer network, that are available to process datagrams or frames intended to be multicast for a designated network service...
es (~270 million addresses).
IPv4 addresses are canonically represented in
dot-decimal notationDot-decimal notation is a presentation format for numerical data. It consists of a string of decimal numbers, each pair separated by a full stop ....
, which consists of four decimal numbers, each ranging from 0 to 255, separated by dots, e.g., 172.16.254.1. Each part represents a group of 8 bits (
octetAn octet is a unit of digital information in computing and telecommunications that consists of eight bits. The term is often used when the term byte might be ambiguous, as there is no standard for the size of the byte.-Overview:...
) of the address. In some cases of technical writing, IPv4 addresses may be presented in various
hexadecimalIn mathematics and computer science, hexadecimal is a positional numeral system with a radix, or base, of 16. It uses sixteen distinct symbols, most often the symbols 0–9 to represent values zero to nine, and A, B, C, D, E, F to represent values ten to fifteen...
,
octalThe octal numeral system, or oct for short, is the base-8 number system, and uses the digits 0 to 7. Numerals can be made from binary numerals by grouping consecutive binary digits into groups of three...
, or
binaryThe binary numeral system, or base-2 number system, represents numeric values using two symbols, 0 and 1. More specifically, the usual base-2 system is a positional notation with a radix of 2...
representations.
IPv4 subnetting
In the early stages of development of the Internet Protocol, network administrators interpreted an IP address in two parts: network number portion and host number portion. The highest order octet (most significant eight bits) in an address was designated as the
network number and the remaining bits were called the
rest field or
host identifier and were used for host numbering within a network.
This early method soon proved inadequate as additional networks developed that were independent of the existing networks already designated by a network number. In 1981, the Internet addressing specification was revised with the introduction of
classful networkA classful network is a network addressing architecture used in the Internet from 1981 until the introduction of Classless Inter-Domain Routing in 1993. The method divides the address space for Internet Protocol Version 4 into five address classes. Each class, coded in the first four bits of the...
architecture.
Classful network design allowed for a larger number of individual network assignments and fine-grained
subnetworkA subnetwork, or subnet, is a logically visible subdivision of an IP network. The practice of dividing a network into subnetworks is called subnetting....
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
unicastright|200pxIn computer networking, unicast transmission is the sending of messages to a single network destination identified by a unique address.-Addressing methodologies:...
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.
Historical classful network architecture
| Class |
Leading address bits (binary) |
Range of first octet (decimal) |
Network ID format |
Host ID format |
Number of networks |
Number of addresses per network |
| A |
000 |
0 - 127 |
a |
b.c.d |
27 = 128 |
224 = |
| B |
100 - 101 |
128 - 191 |
a.b |
c.d |
214 = |
216 = |
| C |
110 |
192 - 223 |
a.b.c |
d |
221 = |
28 = 256 |
Classful network design served its purpose in the startup stage of the Internet, but it lacked
scalabilityIn electronics scalability is the ability of a system, network, or process, to handle growing amount of work in a graceful manner or its ability to be enlarged to accommodate that growth...
in the face of the rapid expansion of the network in the 1990s. The class system of the address space was replaced with
Classless Inter-Domain RoutingClassless Inter-Domain Routing is a method for allocating IP addresses and routing Internet Protocol packets. The Internet Engineering Task Force introduced CIDR in 1993 to replace the previous addressing architecture of classful network design in the Internet...
(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.
IPv4 private addresses
Early network design, when global end-to-end connectivity was envisioned for communications with all Internet hosts, intended that IP addresses be uniquely assigned to a particular computer or device. However, it was found that this was not always necessary as
private networkIn the Internet addressing architecture, a private network is a network that uses private IP address space, following the standards set by RFC 1918 and RFC 4193. These addresses are commonly used for home, office, and enterprise local area networks , when globally routable addresses are not...
s 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, need not have globally unique IP addresses. Three ranges of IPv4 addresses for private networks were reserved in RFC 1918. These addresses are not routed on the Internet and thus their use need not be coordinated with an IP address registry.
Today, when needed, such private networks typically connect to the Internet through
network address translationIn computer networking, network address translation is the process of modifying IP address information in IP packet headers while in transit across a traffic routing device....
(NAT).
IANA-reserved private IPv4 network ranges
|
Start |
End |
No. of addresses |
| 24-bit Block (/8 prefix, 1 × A) |
10.0.0.0 |
10.255.255.255 |
|
| 20-bit Block (/12 prefix, 16 × B) |
172.16.0.0 |
172.31.255.255 |
|
| 16-bit Block (/16 prefix, 256 × C) |
192.168.0.0 |
192.168.255.255 |
|
Any user may use any of the reserved blocks. Typically, a network administrator will divide a block into
subnetsA subnetwork, or subnet, is a logically visible subdivision of an IP network. The practice of dividing a network into subnetworks is called subnetting....
; for example, many
home routersA residential gateway is a home networking device, used as a gateway to connect devices in the home to the Internet or other WAN.It is an umbrella term, used to cover multi-function networking computer appliances used in homes, which may combine a DSL or cable modem, a firewall, a consumer-grade...
automatically use a default address range of 192.168.0.0 - 192.168.0.255 (192.168.0.0/24).
IPv4 address exhaustion
IPv4 address exhaustion is the decreasing supply of unallocated
Internet Protocol Version 4Internet Protocol version 4 is the fourth revision in the development of the Internet Protocol and the first version of the protocol to be widely deployed. Together with IPv6, it is at the core of standards-based internetworking methods of the Internet...
(IPv4) addresses available at the
Internet Assigned Numbers AuthorityThe Internet Assigned Numbers Authority is the entity that oversees global IP address allocation, autonomous system number allocation, root zone management in the Domain Name System , media types, and other Internet Protocol-related symbols and numbers...
(IANA) and the
regional Internet registriesA regional Internet registry is an organization that manages the allocation and registration of Internet number resources within a particular region of the world...
(RIRs) for assignment to end users and
local Internet registriesA local Internet registry is an organization that has been allocated a block of IP addresses by a regional Internet registry , and that assigns most parts of this block to its own customers. Most LIRs are Internet service providers, enterprises, or academic institutions. Membership in an RIR is...
, such as Internet service providers. IANA's primary address pool was exhausted on February 3, 2011 when the last 5 blocks were allocated to the 5 RIRs.
APNICThe Asia Pacific Network Information Centre is the Regional Internet Registry for the Asia Pacific region.APNIC provides number resource allocation and registration services that support the global operation of the Internet...
was the first RIR to exhaust its regional pool on 15 April 2011, except for a small amount of address space reserved for the transition to IPv6, intended be allocated in a restricted process
IPv6 addresses
The rapid exhaustion of IPv4 address space, despite conservation techniques, prompted the
Internet Engineering Task ForceThe Internet Engineering Task Force develops and promotes Internet standards, cooperating closely with the W3C and ISO/IEC standards bodies and dealing in particular with standards of the TCP/IP and Internet protocol suite...
(IETF) to explore new technologies to expand the Internet's addressing capability. The permanent solution was deemed to be a redesign of the Internet Protocol itself. This next generation of the Internet Protocol, intended to replace IPv4 on the Internet, was eventually named
Internet Protocol Version 6Internet Protocol version 6 is a version of the Internet Protocol . It is designed to succeed the Internet Protocol version 4...
(IPv6) in 1995 The address size was increased from 32 to 128
bitA bit is the basic unit of information in computing and telecommunications; it is the amount of information stored by a digital device or other physical system that exists in one of two possible distinct states...
s or 16
octetAn octet is a unit of digital information in computing and telecommunications that consists of eight bits. The term is often used when the term byte might be ambiguous, as there is no standard for the size of the byte.-Overview:...
s. This, even with a generous assignment of network blocks, is deemed sufficient for the foreseeable future. Mathematically, the new address space provides the potential for a maximum of 2
128, or about unique addresses.
The new design is not intended to provide a sufficient quantity of addresses on its own, but rather to allow efficient aggregation of subnet routing prefixes to occur at routing nodes. As a result, routing table sizes are smaller, and the smallest possible individual allocation is a subnet for 2
64 hosts, which is the square of the size of the entire IPv4 Internet. At these levels, actual address utilization rates will be small on any IPv6 network segment. The new design also provides the opportunity to separate the addressing infrastructure of a network segment — that is the local administration of the segment's available space — from the addressing prefix used to route external traffic for a network. IPv6 has facilities that automatically change the routing prefix of entire networks, should the global connectivity or the routing policy change, without requiring internal redesign or 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 not the need to have complex address conservation methods as used in
Classless Inter-Domain RoutingClassless Inter-Domain Routing is a method for allocating IP addresses and routing Internet Protocol packets. The Internet Engineering Task Force introduced CIDR in 1993 to replace the previous addressing architecture of classful network design in the Internet...
(CIDR).
Many modern desktop and enterprise server operating systems include native support for the IPv6 protocol, but it is not yet widely deployed in other devices, such as home networking routers,
voice over IPVoice over Internet Protocol is a family of technologies, methodologies, communication protocols, and transmission techniques for the delivery of voice communications and multimedia sessions over Internet Protocol networks, such as the Internet...
(VoIP) and multimedia equipment, and network peripherals.
IPv6 private addresses
Just as IPv4 reserves addresses for private or internal networks, blocks of addresses are set aside in IPv6 for private addresses. In IPv6, these are referred to as
unique local addressA unique local address is an IPv6 address in the block fc00::/7, defined in RFC 4193. It is the IPv6 counterpart of the IPv4 private address. Unique local addresses are available for use in private networks, e.g. inside a single site or organization, or spanning a limited number of sites or...
es (ULA). RFC 4193 sets aside the routing prefix fc00::/7 for this block which is divided into two /8 blocks with different implied policies The addresses include a 40-bit pseudorandom number that minimizes the risk of address collisions if sites merge or packets are misrouted.
Early designs used a different block for this purpose (fec0::), dubbed site-local addresses. However, the definition of what constituted
sites remained unclear and the poorly defined addressing policy created ambiguities for routing. This address range specification was abandoned and must not be used in new systems.
Addresses starting with fe80:, called
link-localA link-local address is an Internet Protocol address that is intended only for communications within the segment of a local network or a point-to-point connection that a host is connected to. Routers do not forward packets with link-local addresses....
addresses, are assigned to interfaces for communication on the link only. The addresses are automatically generated by the operating system for each network interface. This provides instant and automatic network connectivity for any IPv6 host and means that if several hosts connect to a common hub or switch, they have a communication path via their link-local IPv6 address. This feature is used in the lower layers of IPv6 network administration (e.g.
Neighbor Discovery ProtocolThe Neighbor Discovery Protocol is a protocol in the Internet Protocol Suite used with Internet Protocol Version 6 . It operates in the Link Layer of the Internet model and is responsible for address autoconfiguration of nodes, discovery of other nodes on the link, determining the Link Layer...
).
None of the private address prefixes may be routed on the public Internet.
IP subnetworks
IP networks may be divided into
subnetworkA subnetwork, or subnet, is a logically visible subdivision of an IP network. The practice of dividing a network into subnetworks is called subnetting....
s in both IPv4 and IPv6. For this purpose, an IP address is logically recognized as consisting of two parts: the
network prefix and the
host identifier, or
interface identifier (IPv6). The subnet mask or the CIDR prefix 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
Classless Inter-Domain RoutingClassless Inter-Domain Routing is a method for allocating IP addresses and routing Internet Protocol packets. The Internet Engineering Task Force introduced CIDR in 1993 to replace the previous addressing architecture of classful network design in the Internet...
(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 notationCIDR notation is a compact specification of an Internet Protocol address and its associated routing prefix. Classless Inter-Domain Routing is an Internet Protocol address allocation and route aggregation methodology used within the Internet addressing architecture that replaced the IPv4 classful...
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.
IP address assignment
Internet Protocol addresses are assigned to a host either anew at the time of booting, or permanently by fixed configuration of its hardware or software. Persistent configuration is also known as using a
static IP address. In contrast, in situations when the computer's IP address is assigned newly each time, this is known as using a
dynamic IP address.
Methods
Static IP addresses are manually assigned to a computer by an administrator. The exact procedure varies according to platform. This contrasts with dynamic IP addresses, which are assigned either by the computer interface or host software itself, as in
ZeroconfZero configuration networking , is a set of techniques that automatically creates a usable Internet Protocol network without manual operator intervention or special configuration servers....
, or assigned by a server using
Dynamic Host Configuration ProtocolThe Dynamic Host Configuration Protocol is a network configuration protocol for hosts on Internet Protocol networks. Computers that are connected to IP networks must be configured before they can communicate with other hosts. The most essential information needed is an IP address, and a default...
(DHCP). Even though IP addresses assigned using DHCP may stay the same for long periods of time, they can generally change. In some cases, a network administrator may implement dynamically assigned static IP addresses. In this case, a DHCP server is used, but it is specifically configured to always assign the same IP address to a particular computer. This allows static IP addresses to be configured centrally, without having to specifically configure each computer on the network in a manual procedure.
In the absence or failure of static or stateful (DHCP) address configurations, an operating system may assign an IP address to a network interface using state-less auto-configuration methods, such as
ZeroconfZero configuration networking , is a set of techniques that automatically creates a usable Internet Protocol network without manual operator intervention or special configuration servers....
.
Uses of dynamic addressing
Dynamic IP addresses are most frequently assigned on LANs and broadband networks by
Dynamic Host Configuration ProtocolThe Dynamic Host Configuration Protocol is a network configuration protocol for hosts on Internet Protocol networks. Computers that are connected to IP networks must be configured before they can communicate with other hosts. The most essential information needed is an IP address, and a default...
(DHCP) servers. They are used because it avoids the administrative burden of assigning specific static addresses to each device on a network. It also allows many devices to share limited address space on a network if only some of them will be online at a particular time. In most current desktop operating systems, dynamic IP configuration is enabled by default so that a user does not need to manually enter any settings to connect to a network with a DHCP server. DHCP is not the only technology used to assign dynamic IP addresses. Dialup and some broadband networks use dynamic address features of the
Point-to-Point ProtocolIn networking, the Point-to-Point Protocol is a data link protocol commonly used in establishing a direct connection between two networking nodes...
.
Sticky dynamic IP address
A
sticky dynamic IP address is an informal term used by cable and DSL Internet access subscribers to describe a dynamically assigned IP address that seldom changes. The addresses are usually assigned with the DHCP protocol. Since the modems are usually powered-on for extended periods of time, the address leases are usually set to long periods and simply renewed upon expiration. If a modem is turned off and powered up again before the next expiration of the address lease, it will most likely receive the same IP address.
Address autoconfiguration
RFC 3330 defines an address block, 169.254.0.0/16, for the special use in link-local addressing for IPv4 networks. In
IPv6Internet Protocol version 6 is a version of the Internet Protocol . It is designed to succeed the Internet Protocol version 4...
, every interface, whether using static or dynamic address assignments, also receives a local-link address automatically in the block fe80::/10.
These addresses are only valid on the link, such as a local network segment or point-to-point connection, that a host is connected to. 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,
MicrosoftMicrosoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...
created an implementation that is called Automatic Private IP Addressing (APIPA). Due to Microsoft's market power, APIPA has been deployed on millions of machines and has, thus, become a
de factoDe facto is a Latin expression that means "concerning fact." In law, it often means "in practice but not necessarily ordained by law" or "in practice or actuality, but not officially established." It is commonly used in contrast to de jure when referring to matters of law, governance, or...
standard in the industry. Many years later, the IETF defined a formal standard for this functionality, RFC 3927, entitled
Dynamic Configuration of IPv4 Link-Local Addresses.
Uses of static addressing
Some infrastructure situations have to use static addressing, such as when finding the
Domain Name SystemThe Domain Name System is a hierarchical distributed naming system for computers, services, or any resource connected to the Internet or a private network. It associates various information with domain names assigned to each of the participating entities...
(DNS) host that will translate domain names to IP addresses. Static addresses are also convenient, but not absolutely necessary, to locate servers inside an enterprise. An address obtained from a DNS server comes with a
time to liveTime to live is a mechanism that limits the lifespan of data in a computer or network. TTL may be implemented as a counter or timestamp attached to or embedded in the data. Once the prescribed event count or timespan has elapsed, data is discarded. In computer networking, TTL prevents a data...
, or caching time, after which it should be looked up to confirm that it has not changed. Even static IP addresses do change as a result of network administration (RFC 2072)
es
A
public IP address in common parlance is synonymous with a, globally routable unicast IP address.
Both IPv4 and IPv6 define address ranges that are reserved for
private networkIn the Internet addressing architecture, a private network is a network that uses private IP address space, following the standards set by RFC 1918 and RFC 4193. These addresses are commonly used for home, office, and enterprise local area networks , when globally routable addresses are not...
s and
link-local addressA link-local address is an Internet Protocol address that is intended only for communications within the segment of a local network or a point-to-point connection that a host is connected to. Routers do not forward packets with link-local addresses....
ing. The term public IP address often used exclude these types of addresses.
IP blocking and firewalls
Firewalls perform
Internet Protocol blockingIP blocking prevents the connection between a server/website and certain IP addresses or ranges of addresses. IP blocking effectively bans undesired connections from those computers to a website, mail server, or other Internet server....
to protect networks from unauthorized access. They are common on 's Internet. They control access to networks based on the IP address of a client computer. Whether using a
blacklistIn computing, a blacklist or block list is a basic access control mechanism that allows everyone access, except for the members of the black list . The opposite is a whitelist, which means allow nobody, except members of the white list...
or a whitelist, the IP address that is blocked is the perceived IP address of the client, meaning that if the client is using a
proxy serverIn computer networks, a proxy server is a server that acts as an intermediary for requests from clients seeking resources from other servers. A client connects to the proxy server, requesting some service, such as a file, connection, web page, or other resource available from a different server...
or
network address translationIn computer networking, network address translation is the process of modifying IP address information in IP packet headers while in transit across a traffic routing device....
, blocking one IP address may block many individual computers.
IP address translation
Multiple client devices can appear to share IP addresses: either because they are part of a shared hosting
web serverWeb server can refer to either the hardware or the software that helps to deliver content that can be accessed through the Internet....
environment or because an IPv4 network address translator (NAT) or
proxy serverIn computer networks, a proxy server is a server that acts as an intermediary for requests from clients seeking resources from other servers. A client connects to the proxy server, requesting some service, such as a file, connection, web page, or other resource available from a different server...
acts as an
intermediaryAn intermediary is a third party that offers intermediation services between two trading parties. The intermediary acts as a conduit for goods or services offered by a supplier to a consumer...
agent on behalf of its customers, in which case the real originating IP addresses might be hidden from the server receiving a
requestRequest may refer to:*a question*in computer science, a message sent between objects*in computer science, a request in Hypertext Transfer Protocol*ReQuest Dance Crew, a hip-hop dance crew from New Zealand*Request TV, a defunct pay-per-view service...
. A common practice is to have a NAT hide a large number of IP addresses in a
private networkIn the Internet addressing architecture, a private network is a network that uses private IP address space, following the standards set by RFC 1918 and RFC 4193. These addresses are commonly used for home, office, and enterprise local area networks , when globally routable addresses are not...
. Only the "outside" interface(s) of the NAT need to have Internet-routable addresses.
Most commonly, the NAT device maps TCP or UDP port numbers on the outside to individual private addresses on the inside. Just as a telephone number may have site-specific extensions, the port numbers are site-specific extensions to an IP address.
In small home networks, NAT functions usually take place in a
residential gatewayA residential gateway is a home networking device, used as a gateway to connect devices in the home to the Internet or other WAN.It is an umbrella term, used to cover multi-function networking computer appliances used in homes, which may combine a DSL or cable modem, a firewall, a consumer-grade...
device, typically one marketed as a "router". In this scenario, the computers connected to the router would have 'private' IP addresses and the router would have a 'public' address to communicate with the Internet. This type of router allows several computers to share one public IP address.
Diagnostic tools
Computer operating systems provide various diagnostic tools to examine their network interface and address configuration. Windows provides the
command-line interfaceA command-line interface is a mechanism for interacting with a computer operating system or software by typing commands to perform specific tasks...
tools
ipconfigipconfig in Microsoft Windows is a console application that displays all current TCP/IP network configuration values and can modify Dynamic Host Configuration Protocol DHCP and Domain Name System DNS settings....
and
netshIn software, netsh, or network shell, is a utility included in Microsoft's Windows NT line of operating systems beginning with Windows 2000. It allows local or remote configuration of network devices such as the interface....
and users of
Unix-likeA Unix-like operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification....
systems can use
ifconfigifconfig is a system administration utility in Unix-like operating systems to configure, control, and query TCP/IP network interface parameters from a command line interface or in system configuration scripts...
,
netstat,
route,
lanstat,
ifstat, or
iproute2 utilities to accomplish the task.
See also
- Address pool
In the context of the Internet addressing structure, an address pool is a set of Internet Protocol addresses available at any level in the IP address allocation hierarchy. At the top level, the IP address pool is managed by the Internet Assigned Numbers Authority...
- Classful network
A classful network is a network addressing architecture used in the Internet from 1981 until the introduction of Classless Inter-Domain Routing in 1993. The method divides the address space for Internet Protocol Version 4 into five address classes. Each class, coded in the first four bits of the...
- Geolocation
Geolocation is the identification of the real-world geographic location of an object, such as a radar, mobile phone or an Internet-connected computer terminal...
- Geolocation software
In computing, geolocation software is used to deduce the geolocation of another party. For example, on the Internet, one geolocation approach is to identify the subject party's IP address, then determine what country , organization, or user the IP address has been assigned to, and finally,...
- Hierarchical name space
The DNS Hierarchical Name Space is a map of how DNS servers determine what IP address to connect to given a URL-Registrars:Registrars, such as VeriSign, the operator of the .com and .net top-level domains, let any company, organization, or private individual register a TLD for any number of years...
- Hostname
A hostname is a label that is assigned to a device connected to a computer network and that is used to identify the device in various forms of electronic communication such as the World Wide Web, e-mail or Usenet...
: a human-readable alpha-numeric designation that may map to an IP address
- Internet service provider
An Internet service provider is a company that provides access to the Internet. Access ISPs directly connect customers to the Internet using copper wires, wireless or fiber-optic connections. Hosting ISPs lease server space for smaller businesses and host other people servers...
- IP address spoofing
In computer networking, the term IP address spoofing or IP spoofing refers to the creation of Internet Protocol packets with a forged source IP address, called spoofing, with the purpose of concealing the identity of the sender or impersonating another computing system.-Background:The basic...
- IP blocking
IP blocking prevents the connection between a server/website and certain IP addresses or ranges of addresses. IP blocking effectively bans undesired connections from those computers to a website, mail server, or other Internet server....
- IP Multicast
IP multicast is a method of sending Internet Protocol datagrams to a group of interested receivers in a single transmission. It is often employed for streaming media applications on the Internet and private networks. The method is the IP-specific version of the general concept of multicast...
- List of assigned /8 IPv4 address blocks
- MAC address
A Media Access Control address is a unique identifier assigned to network interfaces for communications on the physical network segment. MAC addresses are used for numerous network technologies and most IEEE 802 network technologies, including Ethernet...
- Ping
Ping is a computer network administration utility used to test the reachability of a host on an Internet Protocol network and to measure the round-trip time for messages sent from the originating host to a destination computer...
- Private network
In the Internet addressing architecture, a private network is a network that uses private IP address space, following the standards set by RFC 1918 and RFC 4193. These addresses are commonly used for home, office, and enterprise local area networks , when globally routable addresses are not...
- Provider-aggregatable address space
- Provider-independent address space
- Regional Internet Registry
A regional Internet registry is an organization that manages the allocation and registration of Internet number resources within a particular region of the world...
- African Network Information Center
AfriNIC is the regional Internet registry for Africa. Its headquarters are in Ebene City, Mauritius. Adiel Akplogan is the registry's chief executive officer...
- American Registry for Internet Numbers
The American Registry for Internet Numbers is the Regional Internet Registry for Canada, many Caribbean and North Atlantic islands, and the United States. ARIN manages the distribution of Internet number resources, including IPv4 and IPv6 address space and AS numbers. ARIN opened its doors for...
- Asia-Pacific Network Information Centre
The Asia Pacific Network Information Centre is the Regional Internet Registry for the Asia Pacific region.APNIC provides number resource allocation and registration services that support the global operation of the Internet...
- Latin American and Caribbean Internet Addresses Registry
The Latin America and Caribbean Network Information Centre is the Regional Internet Registry for the Latin American and Caribbean regions.LACNIC provides number resource allocation and registration...
- RIPE Network Coordination Centre
The Réseaux IP Européens Network Coordination Centre is the Regional Internet Registry for Europe, the Middle East and parts of Central Asia...
- Subnet address
A subnetwork, or subnet, is a logically visible subdivision of an IP network. The practice of dividing a network into subnetworks is called subnetting....
- Virtual IP address
virtual IP address is an IP address that is not connected to a specific computer or network interface card on a computer...
- WHOIS
WHOIS is a query and response protocol that is widely used for querying databases that store the registered users or assignees of an Internet resource, such as a domain name, an IP address block, or an autonomous system, but is also used for a wider range of other information. The protocol stores...