IP address
Encyclopedia
An Internet Protocol address (IP address) is a numerical label assigned to each device (e.g., computer, printer) participating in a computer network
that uses the Internet Protocol
for communication. An IP address serves two principal functions: host or network interface identification
and location addressing
. 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 designers of the Internet Protocol defined an IP address as a 32-bit
number and this system, known as Internet Protocol Version 4
(IPv4), is still in use today. However, due to the enormous growth of the Internet
and the predicted depletion of available addresses, a new addressing system (IPv6
), 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-readable
notations, such as 172.16.254.1 (for IPv4
), and 2001:db8:0:1234:0:567:8:1 (for IPv6
).
The Internet Assigned Numbers Authority
(IANA) manages the IP address space allocations globally and delegates five regional Internet registries (RIRs) to allocate IP address blocks to local Internet registries
(Internet service provider
s) and other entities.
. 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.
In IPv4 an address consists of 32 bit
s which limits the address space
to (232) possible unique addresses. IPv4 reserves some addresses for special purposes such as private network
s (~18 million addresses) or multicast address
es (~270 million addresses).
IPv4 addresses are canonically represented in dot-decimal notation
, 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 (octet
) of the address. In some cases of technical writing, IPv4 addresses may be presented in various hexadecimal
, octal
, or binary
representations.
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 network
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
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
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 Routing
(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.
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 translation
(NAT).
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 192.168.0.0 - 192.168.0.255 (192.168.0.0/24).
(IPv4) addresses available at the Internet Assigned Numbers Authority
(IANA) and the regional Internet registries
(RIRs) for assignment to end users and local Internet registries
, 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. APNIC
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
The rapid exhaustion of IPv4 address space, despite conservation techniques, prompted the Internet Engineering Task Force
(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 6
(IPv6) in 1995 The address size was increased from 32 to 128 bit
s or 16 octet
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 2128, 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 264 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 Routing
(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 IP
(VoIP) and multimedia equipment, and network peripherals.
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-local
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 Protocol
).
None of the private address prefixes may be routed on the public Internet.
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 Routing
(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.
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.
, or assigned by a server using Dynamic Host Configuration Protocol
(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 Zeroconf
.
(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 Protocol
.
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.
, 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, Microsoft
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 facto
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.
(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 live
, 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)
Both IPv4 and IPv6 define address ranges that are reserved for private network
s and link-local address
ing. The term public IP address often used exclude these types of addresses.
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 blacklist
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 server
or network address translation
, blocking one IP address may block many individual computers.
environment or because an IPv4 network address translator (NAT) or proxy server
acts as an intermediary
agent on behalf of its customers, in which case the real originating IP addresses might be hidden from the server receiving a request
. A common practice is to have a NAT hide a large number of IP addresses in a private network
. 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 gateway
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.
tools ipconfig
and netsh
and users of Unix-like
systems can use ifconfig
, netstat, route, lanstat, ifstat, or iproute2 utilities to accomplish the task.
Computer network
A 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 Protocol
Internet Protocol
The 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 identification
Identification (information)
The 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 addressing
Logical address
In 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 name
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...
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-bit
32-bit
The 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 4
IPv4
Internet 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 Internet
Internet
The 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 (IPv6
IPv6
Internet 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-readable
Human-readable
A 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 IPv4
IPv4
Internet 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 IPv6
IPv6
Internet Protocol version 6 is a version of the Internet Protocol . It is designed to succeed the Internet Protocol version 4...
).
The Internet Assigned Numbers Authority
Internet Assigned Numbers Authority
The 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 registries
Local Internet Registry
A 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 provider
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...
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 IPv4IPv4
Internet 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
Bit
A 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 space
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 memory cell or other logical or physical entity.- Overview :...
to (232) possible unique addresses. IPv4 reserves some addresses for special purposes such as private network
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...
s (~18 million addresses) or multicast address
Multicast address
A 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 notation
Dot-decimal notation
Dot-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 (octet
Octet (computing)
An 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 hexadecimal
Hexadecimal
In 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...
, octal
Octal
The 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 binary
Binary numeral system
The 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 network
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...
architecture.
Classful network design allowed for a larger number of individual network assignments and fine-grained subnetwork
Subnetwork
A 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 unicast
Unicast
right|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.
| 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 scalability
Scalability
In 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 Routing
Classless Inter-Domain Routing
Classless 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 networkPrivate 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...
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 translation
Network address translation
In 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).
| 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 subnets
Subnetwork
A 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 routers
Residential gateway
A 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 4IPv4
Internet 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 Authority
Internet Assigned Numbers Authority
The 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 registries
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...
(RIRs) for assignment to end users and local Internet registries
Local Internet Registry
A 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. APNIC
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...
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
Internet Engineering Task Force
The 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 6
IPv6
Internet 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 bit
Bit
A 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 octet
Octet (computing)
An 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 2128, 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 264 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 Routing
Classless Inter-Domain Routing
Classless 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 IP
Voice over IP
Voice 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 addressUnique local address
A 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-local
Link-local address
A 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 Protocol
Neighbor Discovery Protocol
The 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 subnetworkSubnetwork
A 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 Routing
Classless Inter-Domain Routing
Classless 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 notation
CIDR notation
CIDR 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 ZeroconfZeroconf
Zero 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 Protocol
Dynamic Host Configuration Protocol
The 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 Zeroconf
Zeroconf
Zero 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 ProtocolDynamic Host Configuration Protocol
The 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 Protocol
Point-to-Point Protocol
In 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 IPv6IPv6
Internet 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, Microsoft
Microsoft
Microsoft 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 facto
De facto
De 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 SystemDomain name system
The 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 live
Time to live
Time 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 network
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...
s and link-local address
Link-local address
A 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
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....
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 blacklist
Blacklist (computing)
In 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 server
Proxy server
In 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 translation
Network address translation
In 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
Web 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 server
Proxy server
In 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 intermediary
Intermediary
An 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 request
Request
Request 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 network
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...
. 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 gateway
Residential gateway
A 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 interfaceCommand-line interface
A command-line interface is a mechanism for interacting with a computer operating system or software by typing commands to perform specific tasks...
tools ipconfig
Ipconfig
ipconfig 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 netsh
Netsh
In 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-like
Unix-like
A 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 ifconfig
Ifconfig
ifconfig 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 poolAddress poolIn 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 networkClassful 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...
- GeolocationGeolocationGeolocation 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 softwareGeolocation softwareIn 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 spaceHierarchical name spaceThe 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...
- HostnameHostnameA 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 providerInternet 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...
- IP address spoofingIP address spoofingIn 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 blockingIP 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....
- IP MulticastIP MulticastIP 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 addressMAC addressA 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...
- PingPingPing 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 networkPrivate 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...
- Provider-aggregatable address space
- Provider-independent address space
- Regional Internet RegistryRegional Internet RegistryA 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 CenterAfriNICAfriNIC 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 NumbersAmerican Registry for Internet NumbersThe 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 CentreAsia-Pacific Network Information CentreThe 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 RegistryLatin American and Caribbean Internet Addresses RegistryThe 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 CentreRIPE NCCThe Réseaux IP Européens Network Coordination Centre is the Regional Internet Registry for Europe, the Middle East and parts of Central Asia...
- African Network Information Center
- Subnet addressSubnetworkA 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 addressVirtual IP addressvirtual IP address is an IP address that is not connected to a specific computer or network interface card on a computer...
- WHOISWHOISWHOIS 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...