An IP address ( Internet Protocol address ) is a unique number that devices use in order to identify and communicate with each other on a computer network utilizing the Internet Protocol standard ( IP ). Any participating network device — including routers , computers , time-servers, printers, internet fax machines, and some telephones — must have its own unique address.
An IP address can also be thought of as a street address or a phone number but for a computer or other network device on the internet. Just as each street address and phone number uniquely identifies a building or telephone, an IP address can uniquely identify a specific computer or other network device on a network.
Main article: Domain Name System
A network lookup service, the Domain Name System , provides the ability to map domain names to a specific IP address. The purpose of domains is that humans better remember names than arbitrary strings of numbers. It also allows an entity to change its IP addresses or reassign them without having to notify anyone except their DNS server.
Another reason for DNS is to allow, for example, a web site to be hosted on multiple servers (each with its own IP address) which allows for rudimentary load balancing .
For example, www.wikipedia.org resolves to 126.96.36.199 .
Dynamic vs. static IP addresses
There are two methods to assigning IP addresses to computers: static and dynamic.
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Static IP addresses are used to identify semi-permanent devices on a network and their IP addresses are constant. Servers are the primary users of static IP addresses.
Dynamic IP addresses are issued to identify non-permanent devices. Clients are the primary user of dynamic IP addresses. Internet Service Providers (ISP) can use dynamic allocation so that they can reuse addresses when they have more customers than connections to the internet (particularly prevalent in dial-up access ).
Dynamic IP address allocation requires a server to listen for requests and then assign an address. Addresses can be assigned at random or through some policies based on need. The most common protocol used to assign dynamically is Dynamic Host Configuration Protocol (DHCP). DHCP also includes a "lease time" which determines how long the requester can use that address before having to make another request. This allows for addresses to be reclaimed if the requester goes off line.
It is also common to use dynamic allocation for private networks . Since private networks rarely have an address shortage, one policy could be to assign the same address to the same computer on each request or assign the lease time to a ridiculous length of time. These two methods simulate static IP address assignment.
Main article: Internet Assigned Numbers Authority
IP addresses are allocated by a Regional Internet Registry (RIR) which are delegated to the five RIRs by the Internet Assigned Numbers Authority . IP addresses are allocated in blocks to an organization/business which are then suballocated to other organizations.
For example, en.wikipedia.org resolves to 188.8.131.52 which belongs to the 184.108.40.206 - 220.127.116.11 block operated by AGIS . This block belongs to the 18.104.22.168 - 22.214.171.124 block operated by American Registry for Internet Numbers (the RIR for North America ).
Since IP address blocks are assigned to RIRs, which are geographically distributed, it is somewhat possible to geolocate an IP address based on its registration.
Subnetworks are used to further divide networks.
The Internet Protocol has two primary versions in use. Each version has its own defintion of an IP address. Because of its prevalence, "IP address" typically refers to those defined by IPv4 .
IP version 4
Main article: IPv4#Addressing
IPv4 uses 32- bit (4 byte ) addresses which limits the address space to 4,294,967,296 possible unique addresses. However, many are reserved for special purposes such as private networks (~18 million addresses) or multicast addresses (~1 million addresses). This reduces the number of addresses that can be allocated as public Internet addresses and as the number of addresses available is consumed, an IPv4 address shortage appears to be inevitable in the long run. This limitation has helped stimulate the push towards IPv6 , which is currently in the early stages of deployment and is currently the only contender to replace IPv4.
IP version 5
What would be considered IPv5 existed only as an experimental non-IP real time streaming protocol called ST2, described in RFC 1819 . In keeping with standard UNIX release conventions, all odd-numbered versions are considered experimental, and this version was never intended to be implemented; the protocol was not abandoned. RSVP has replaced it to some degree.
IP version 6
Main article: IPv6#Addressing
In IPv6 , the new (but not yet widely deployed) standard protocol for the Internet, addresses are 128 bits wide, which, even with generous assignment of netblocks, should suffice for the foreseeable future. In theory, there would be exactly 2 128 , or about 3.403 ? 10 38 unique host interface addresses. That translates into 340,282,366,920,938,463,463,374,607,431,768,211,456 addresses. If the earth were made entirely out of 1 cubic millimeter grains of sand, then you could give a unique address to each grain in 300 million planets the size of the earth. This large address space will be sparsely populated, which makes it possible to again encode more routing information into the addresses themselves.
A version 6 address is written as eight 4-digit hexadecimal numbers separated by colons. For readability, addresses may be shortened in two ways. Within each colon-delimited section, leading zeroes may be truncated. Secondly, one string of zeroes (and only one) may be replaced with two colons (::). For example, all of the following addresses are equivalent:
Global unicast IPv6 addresses are constructed as two parts: a 64-bit routing part followed by a 64-bit host identifier.
Netblocks are specified as in the modern alternative for IPv4: network number, followed by a slash, and the number of relevant bits of the network number (in decimal). Example: 12AB::CD30:0:0:0:0/60 includes all addresses starting with 12AB00000000CD3.
IPv6 has many improvements over IPv4 other than just bigger address space, including autorenumbering and mandatory support for IPsec
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