WebBuilding

Foundations

Internet

Summary

The internet is the worldwide network of networks that carries data between computers using a shared set of rules, the Internet Protocol suite or TCP/IP. It grew out of ARPANET, a U.S. research network that sent its first message on October 29, 1969, and switched to TCP/IP on January 1, 1983. The World Wide Web is one service that runs on top of it. ITU estimated in November 2025 that about 6 billion people, 74% of the world's population, were online in 2025.

Web Building Encyclopedia · Foundations · Last reviewed October 22, 2026 · 10 min read

What the internet is

The internet is a network of networks. Separately run networks agree to pass data to one another using one shared set of rules, so a computer on any of them can reach a computer on any other. In the words of Tim Berners-Lee: “The Internet (‘Net) is a network of networks. Basically it is made from computers and cables.”1

The data travels in packets. A packet is a small block of data with a destination address on it. A long message is cut into many packets, which can take different routes and are put back together at the other end. The Internet Protocol, or IP, defined in RFC 791 in September 1981, describes how these blocks, which it calls datagrams, are carried from a source to a destination.2

An RFC (Request for Comments) is a numbered document in the series where the internet’s technical standards are published. Today the Internet Engineering Task Force (IETF), founded in 1986, publishes its technical documents as RFCs. Its stated goal is to make the internet work better.3

On October 24, 1995, the U.S. Federal Networking Council passed a resolution defining the word “Internet.” Its definition has three parts: one global address space based on IP, support for communication using the TCP/IP protocol suite or its successors, and high-level services built on top of that infrastructure.4

The rules are arranged in layers, each doing one job and relying on the layer below. RFC 1122, the October 1989 standard for internet hosts, describes four:5

  • Link layer. The protocol a computer uses to talk to the network it is directly attached to.
  • Internet layer. IP, which carries data from the source computer to the destination computer, across as many networks as it takes.
  • Transport layer. Protocols such as TCP (Transmission Control Protocol), which provide end-to-end communication between programs on the two computers.
  • Application layer. The top layer, where the programs people use exchange their data.

ARPANET, the first network, 1969

The internet grew out of ARPANET, a network funded by the U.S. Defense Department’s Advanced Research Projects Agency (ARPA, now DARPA).67 DARPA describes it as “a pioneering network for sharing digital resources among geographically separated computers.”7

The ideas came first. The Internet Society’s history, which Kleinrock co-wrote, says Leonard Kleinrock published the first paper on packet switching theory in July 1961.4 J.C.R. Licklider wrote memos in 1962 about his Intergalactic Network concept, and Paul Baran at RAND and Donald Davies at Britain’s National Physical Laboratory worked on packet networks in parallel with Kleinrock.8

In 1968 ARPA hired the company BBN to build the network’s first routers.7 They were called Interface Message Processors, or IMPs, and the Computer History Museum notes that they evolved into today’s routers.8 A router is a device that passes packets from one link of a network to the next.

On April 7, 1969, Steve Crocker at UCLA wrote “Host Software,” the first Request for Comments.98 BBN installed the first IMP at UCLA in September 1969 and connected the first host computer to it. The Stanford Research Institute (SRI) became the second node about a month later.4

At 10:30 p.m. on October 29, 1969, Charley Kline, a student programmer working under Kleinrock at UCLA, tried to log in to SRI’s computer, where Bill Duvall was the programmer at the other end. The letters “l” and “o” arrived, then the system crashed. The full login worked about an hour later.10 An IEEE plaque at UCLA records it as the first ARPANET message, and Vint Cerf calls it the first connection between two computers on the network.1112

Four host computers were connected by the end of 1969. The network’s first host-to-host protocol, the Network Control Protocol (NCP), was finished in December 1970.4 According to the Computer History Museum, Ray Tomlinson wrote a program for sending email over ARPANET in 1972.13 In October 1972 Robert Kahn organized a large public demonstration of the network at the International Computer Communication Conference.4

TCP/IP: Cerf and Kahn’s network of networks

ARPANET was a single network. ARPA was also funding networks that sent packets over radio and by satellite, and RFC 801 later explained that ARPANET’s original host-to-host protocol was not adequate for those networks.14

Robert Kahn joined ARPA’s Information Processing Techniques Office in 1972 and asked Vinton Cerf, then at Stanford University, to work with him on new communication protocols.15 Kahn’s starting idea was open-architecture networking: independent networks, each built in its own way, joined by a common protocol.4 Their first written version circulated in September 1973.4

In May 1974 the journal IEEE Transactions on Communications published their paper, “A Protocol for Packet Network Intercommunication.” It described a transmission control program, or TCP, that sent and received messages for the programs running on each host computer, and it gave a special name to the machine joining two networks: a GATEWAY.16 The paper set out to handle problems that still matter, including different packet sizes, failed transmissions, sequencing, flow control and end-to-end error checking.16

A detailed specification followed in December 1974 as RFC 675, by Cerf, Yogen Dalal and Carl Sunshine, titled “Specification of Internet Transmission Control Program.”17 On November 22, 1977, a demonstration linked three different networks, the Packet Radio network, the Packet Satellite network and ARPANET.12 The Computer History Museum describes messages traveling from a van in the San Francisco Bay Area across the country and through a satellite link.13

The first TCP did two jobs at once: moving packets between networks and managing the conversation between two computers. In August 1977 Jon Postel argued in a note called IEN 2 for a separate internetwork protocol to handle addressing and routing, with TCP kept as an end-to-end protocol between hosts.18 TCP was later split into two protocols, TCP and IP.19

The lasting definitions came in September 1981: RFC 791 for IP, edited by Postel at the University of Southern California’s Information Sciences Institute for DARPA, and RFC 793 for TCP, also by Postel.220 RFC 791 fixed addresses at 32 bits.2 TCP’s standard was replaced in August 2022 by RFC 9293, which obsoletes RFC 793.21

Flag day: January 1, 1983

In November 1981 Postel published RFC 801, a plan for moving ARPANET from NCP to TCP/IP. Its goal was a complete switch by January 1, 1983, after which NCP would be removed from service and every service would be TCP-based.14 The switch took place on that date.422 Cerf has written that on January 1, 1983, “the Internet was operationally born.”12 An IEEE milestone plaque also dates the internet’s operational launch by DARPA to 1983.19

The same year ARPANET split in two: a public research network and a separate military network called MILNET.22 In November 1983 Paul Mockapetris published RFC 882, which introduced the Domain Name System (DNS), the naming system that lets people use domain names instead of numeric host addresses.23 The Computer History Museum says DNS was introduced across the internet in 1984.22

NSFNET and the move to commercial networks

In 1981 the National Science Foundation (NSF) funded CSNET to give university computer scientists network access.6 It then built NSFNET to connect academic researchers to its new supercomputer centers.24

Sources differ on NSFNET’s start. NSF dates the launch to 1986, and an NSF history article says the network went online that year at 56,000 bits per second.246 Merit Network, which later ran the backbone, says NSFNET was launched in 1985 and first linked six supercomputer centers over a 56 Kbps backbone.25 The Internet Society’s history dates the NSFNET program to 1985, when Dennis Jennings came to NSF to lead it for a year, and says Steve Wolff took it over in 1986.4

In late 1987 NSF chose Merit, with MCI, IBM and the State of Michigan, to rebuild the backbone. The new T1 network, running at about 1.5 megabits per second, began service on July 1, 1988, and traffic on it grew by more than 20% per month.256 NSF says that in 1991 the NSFNET backbone became the first national internet network to run at 45 megabits per second, and the move to that faster T3 network was completed in 1992.625

NSF counts about 2,000 computers connected in 1986 and more than 2 million by 1993.24 ARPANET itself formally shut down in 1990.264

Commercial services grew in parallel. UUNET was founded in 1987 to sell access to UUCP and Usenet newsgroups. In 1988 the Corporation for National Research Initiatives connected MCI Mail to the internet, which the Computer History Museum calls the start of commercial internet services in the United States.22

A law of October 23, 1992, Public Law 102-476, allowed NSF to support access to computer networks “which may be used substantially for purposes in addition to research and education,” as long as those extra uses helped the networks serve research and education.27

In 1995 NSF awarded contracts for three network access points, where networks meet to exchange traffic, and decommissioned the NSFNET backbone in April.6 Merit’s account says the backbone’s peering sessions were switched off on April 25, 1995, and its nodes were shut down one by one the next night. By then it reached more than 50,000 networks, against 217 at launch.25 The Internet Society’s history puts the NSFNET program’s funding at $200 million from 1986 to 1995.4

In 1998 NSF’s direct role ended, and the U.S. Commerce Department reached an agreement with ICANN over oversight of domain name registration.6

The internet and the web are different things

The World Wide Web is one service that runs on the internet, not the internet itself. Berners-Lee describes the web as “an abstract (imaginary) space of information,” while the internet is the network of computers and cables underneath it.1

The internet came first. Berners-Lee says he invented the web when the internet had already existed for a decade and a half, and places the first web page at the end of 1990, at CERN.1 Email over ARPANET is older than the web by almost two decades.13

When someone opens a page on your site, the layers work together:

  1. Name lookup. The browser asks DNS for the numeric IP address behind your domain name.23
  2. Connection. The browser opens a connection to that address. With HTTP/1.1 and HTTP/2 this is a TCP connection.28 HTTP/3, published in June 2022, uses QUIC instead, a newer transport protocol that runs over UDP.2829
  3. Routing. Routers pass the packets from network to network. Independently run networks, called autonomous systems, tell each other which addresses they can reach using the Border Gateway Protocol (BGP).30
  4. The web layer. Only now does HTTP, the web’s own protocol, come in: the browser requests the page and the web server sends it back.

So your domain name, its DNS records and your server’s IP address are internet infrastructure. The pages, links and HTTP requests are the web layer that sits on top.

Addresses, from IPv4 to IPv6

Every device reachable on the internet needs an IP address. The 32-bit addresses fixed by RFC 791 allow 2 to the power of 32 combinations, about 4.3 billion.2 That version is called IPv4.

It was not enough. On February 3, 2011, the Internet Assigned Numbers Authority (IANA) handed out its last blocks of IPv4 addresses to the five Regional Internet Registries, and the Number Resource Organization announced that the free pool of IPv4 addresses was fully depleted.31

The successor, IPv6, increases the address size from 32 bits to 128 bits. Its current standard is RFC 8200, published in July 2017, which replaced RFC 2460.32 The Number Resource Organization noted in 2011 that IPv6 address space had been available since 1999.31

Who uses the internet today

The International Telecommunication Union (ITU) publishes global estimates of internet use in its yearly Facts and Figures reports. In its Facts and Figures 2025 release of November 17, 2025, ITU estimated that about 6 billion people, about three-quarters of the world’s population, used the internet in 2025, and that 2.2 billion people remained offline.33 ITU’s statistics page puts the share at 74% of the world’s population, up from 60% in 2020.34 As of October 2026, these 2025 estimates are the latest global figures on ITU’s statistics page.34

Group (ITU, 2025 estimates)Share using the internet
World74%
High-income countries94%
Low-income countries23%
Urban areas85%
Rural areas58%

Sources: ITU press release and statistics page.3334

ITU also reports that mobile broadband coverage is nearly universal, and that 5G reaches more than half of the world’s population and makes up more than a third of mobile broadband subscriptions.35 A typical user in a high-income country generates nearly eight times as much mobile data as a typical user in a low-income country.33

Timeline

  1. ITU estimates that about 6 billion people use the internet in 202533
  2. RFC 9293 replaces RFC 793 as the TCP standard21
  3. RFC 8200 becomes the current IPv6 specification32
  4. IANA hands out its last IPv4 address blocks31
  5. U.S. Federal Networking Council adopts a definition of "Internet"4
  6. NSF decommissions the NSFNET backbone6
  7. Public Law 102-476 lets NSF support networks also used for purposes beyond research and education27
  8. ARPANET formally shuts down26
  9. NSFNET's T1 backbone begins service25
  10. RFC 882 introduces the Domain Name System23
  11. ARPANET switches from NCP to TCP/IP4
  12. RFC 791 (IP) and RFC 793 (TCP) are published2
  13. Demonstration links three networks: Packet Radio, Packet Satellite and ARPANET12
  14. Cerf and Kahn publish "A Protocol for Packet Network Intercommunication"16
  15. First ARPANET message sent from UCLA to SRI10

What it means for your website

You never configure TCP/IP to run a website, but several internet-level facts shape how your site reaches people.

  • Your domain is a pointer to an IP address. Connecting a domain to a host means editing DNS records so the name leads to your server’s address.23 Our DNS glossary entry and our guide to domains and hosting explain where those records live and who controls them.
  • Ask your host about IPv6. The free pool of new IPv4 addresses ran out in 2011.31 A host that gives your site both an IPv4 and an IPv6 address lets it reach visitors on either kind of network.
  • Distance still counts. Each request can cross several networks between your server and the visitor.30 Pick a host with servers near most of your customers, or put a CDN in front of the site so copies of your pages are served from closer by.
  • Build for slower connections too. ITU estimates that 58% of people in rural areas were online in 2025, against 85% in cities, and that 2.2 billion people were still offline.33 If your customers include rural or lower-income areas, keep pages light so they load on weak mobile signals.
  • Know which layer failed. When a site is unreachable, the cause is often at the internet layer (an expired domain or wrong DNS record) rather than in the site itself. Our guide to how a website works walks through each piece.

The web you publish on sits on top of all of this. Moving your site to a new host changes your server’s IP address, but not your domain, which is why the DNS step comes up in every migration.

See also

References

  1. Frequently asked questions by the Press, Tim BL. Tim Berners-Lee, W3C. accessed October 22, 2026.
  2. RFC 791: Internet Protocol. Jon Postel (ed.), Information Sciences Institute, for DARPA, RFC Editor. 1981-09. accessed October 22, 2026.
  3. Introduction to the IETF. Internet Engineering Task Force. accessed October 22, 2026.
  4. A Brief History of the Internet (Leiner, Cerf, Clark, Kahn, Kleinrock, Lynch, Postel, Roberts, Wolff). Internet Society. accessed October 22, 2026.
  5. RFC 1122: Requirements for Internet Hosts, Communication Layers. R. Braden (ed.), Internet Engineering Task Force, RFC Editor. 1989-10. accessed October 22, 2026.
  6. NSF Shapes the Internet's Evolution. David Hart, U.S. National Science Foundation. accessed October 22, 2026.
  7. ARPANET. Defense Advanced Research Projects Agency (DARPA). accessed October 22, 2026.
  8. Internet History of 1960s. Computer History Museum. accessed October 22, 2026.
  9. RFC 1: Host Software. Steve Crocker, UCLA, RFC Editor. 1969-04-07. accessed October 22, 2026.
  10. The Day the Infant Internet Uttered its First Words. Leonard Kleinrock, UCLA. accessed October 22, 2026.
  11. Milestones: Birthplace of the Internet, 1969. IEEE History Center, Engineering and Technology History Wiki. accessed October 22, 2026.
  12. Vint Cerf's top moments from 50 years of the Internet. Vint Cerf, Google Blog. 2019-10-29. accessed October 22, 2026.
  13. Internet History of 1970s. Computer History Museum. accessed October 22, 2026.
  14. RFC 801: NCP/TCP Transition Plan. Jon Postel, Information Sciences Institute, RFC Editor. 1981-11. accessed October 22, 2026.
  15. TCP/IP. Defense Advanced Research Projects Agency (DARPA). accessed October 22, 2026.
  16. A Protocol for Packet Network Intercommunication (Vinton G. Cerf and Robert E. Kahn), IEEE Transactions on Communications, vol. COM-22, no. 5, pp. 637-648. IEEE, copy hosted by Boston University. 1974-05. accessed October 22, 2026.
  17. RFC 675: Specification of Internet Transmission Control Program. Vinton Cerf, Yogen Dalal and Carl Sunshine, RFC Editor. 1974-12. accessed October 22, 2026.
  18. IEN 2: Comments on Internet Protocol and TCP. Jon Postel, Internet Experiment Note, RFC Editor history archive. 1977-08-15. accessed October 22, 2026.
  19. Milestones: Transmission Control Protocol (TCP) Enables the Internet, 1974. IEEE History Center, Engineering and Technology History Wiki. accessed October 22, 2026.
  20. RFC 793: Transmission Control Protocol. Jon Postel, RFC Editor. 1981-09. accessed October 22, 2026.
  21. RFC 9293: Transmission Control Protocol (TCP). W. Eddy (ed.), Internet Engineering Task Force, RFC Editor. 2022-08. accessed October 22, 2026.
  22. Internet History of 1980s. Computer History Museum. accessed October 22, 2026.
  23. RFC 882: Domain Names, Concepts and Facilities. P. Mockapetris, Information Sciences Institute, RFC Editor. 1983-11. accessed October 22, 2026.
  24. Birth of the Commercial Internet. NSF Impacts, U.S. National Science Foundation. accessed October 22, 2026.
  25. 20th Anniversary of First National High-Speed Network. Merit Network. 2008-07-01. accessed October 22, 2026.
  26. Internet History of 1990s. Computer History Museum. accessed October 22, 2026.
  27. 42 U.S.C. 1862: Functions (subsection g, Support of access to computer networks). United States Code, 2010 edition, U.S. Government Publishing Office. accessed October 22, 2026.
  28. RFC 9114: HTTP/3. M. Bishop (ed.), Internet Engineering Task Force, RFC Editor. 2022-06. accessed October 22, 2026.
  29. RFC 9000: QUIC: A UDP-Based Multiplexed and Secure Transport. J. Iyengar and M. Thomson (eds.), Internet Engineering Task Force, RFC Editor. 2021. accessed October 22, 2026.
  30. RFC 4271: A Border Gateway Protocol 4 (BGP-4). Y. Rekhter, T. Li and S. Hares (eds.), Internet Engineering Task Force, RFC Editor. 2006-01. accessed October 22, 2026.
  31. IPv6 adoption at critical phase. Number Resource Organization. 2011-02-03. accessed October 22, 2026.
  32. RFC 8200: Internet Protocol, Version 6 (IPv6) Specification. S. Deering and R. Hinden, Internet Engineering Task Force, RFC Editor. 2017-07. accessed October 22, 2026.
  33. Global number of Internet users increases, but disparities deepen key digital divides. International Telecommunication Union. 2025-11-17. accessed October 22, 2026.
  34. Statistics. ITU Telecommunication Development Sector, International Telecommunication Union. accessed October 22, 2026.
  35. Measuring digital development: Facts and Figures 2025. ITU Telecommunication Development Sector, International Telecommunication Union. 2025-11. accessed October 22, 2026.

Web Building Encyclopedia. First published October 22, 2026. Last reviewed October 22, 2026. Every fact on this page is linked to a source we opened. Spotted an error? Write to [email protected].