Ane of the greatest things well-nigh the Internet is that nobody really owns it. It is a global collection of networks, both big and small. These networks connect together in many dissimilar ways to form the single entity that we know as the
Cyberspace. In fact, the very name comes from this thought of interconnected networks.


Since its offset in 1969, the Internet has grown from four host calculator systems to tens of millions. Withal, just considering nobody owns the Internet, it doesn’t hateful information technology is non monitored and maintained in dissimilar ways. The Internet Society, a not-turn a profit group established in 1992, oversees the formation of the policies and protocols that define how we use and interact with the Cyberspace.

In this article, yous will learn nearly the basic underlying structure of the Internet. Yous volition learn about domain name servers, network access points and backbones. But first you lot volition learn about how your figurer connects to others.



A Hierarchy of Networks

Every reckoner that is continued to the Internet is part of a network, even the ane in your home. For example, you may use a modem and dial a local number to connect to an
Internet Service Provider
(Isp). At work, yous may be role of a
local area network
(LAN), but yous most likely still connect to the Internet using an Internet access provider that your visitor has contracted with. When you lot connect to your ISP, you go function of their network. The ISP may then connect to a larger network and get part of their network. The Internet is simply a network of networks.

Most large communications companies have their own dedicated backbones connecting various regions. In each region, the company has a
Point of Presence
(Pop). The POP is a place for local users to admission the company’south network, oftentimes through a local phone number or dedicated line. The astonishing thing hither is that at that place is no overall controlling network. Instead, in that location are several high-level networks connecting to each other through
Network Access Points
or NAPs.





When you connect to the Internet, your computer

becomes function of a network.





A Network Example

Here’s an example. Imagine that Company A is a big ISP. In each major city, Company A has a Pop. The POP in each urban center is a rack total of modems that the ISP’south customers dial into. Visitor A leases fiber optic lines from the phone company to connect the POPs together (see, for example, this UUNET Data Heart Connectivity Map).

Imagine that Company B is a corporate ISP. Visitor B builds large buildings in major cities and corporations locate their Cyberspace server machines in these buildings. Company B is such a large visitor that information technology runs its ain fiber optic lines between its buildings so that they are all interconnected.

In this organisation, all of Company A’s customers can talk to each other, and all of Visitor B’southward customers can talk to each other, but there is no way for Company A’southward customers and Visitor B’s customers to intercommunicate. Therefore, Company A and Company B both agree to connect to NAPs in various cities, and traffic between the two companies flows between the networks at the NAPs.

In the real Internet, dozens of big Internet providers interconnect at NAPs in diverse cities, and trillions of bytes of data flow between the individual networks at these points. The Cyberspace is a drove of huge corporate networks that concur to all intercommunicate with each other at the NAPs. In this fashion, every computer on the Internet connects to every other.



Bridging The Divide

All of these networks rely on NAPs, backbones and
routers
to talk to each other. What is incredible nigh this process is that a bulletin can exit one reckoner and travel halfway across the world through several different networks and arrive at some other computer in a fraction of a second!

The routers determine where to send data from 1 computer to another. Routers are specialized computers that send your letters and those of every other Net user speeding to their destinations along thousands of pathways. A router has two separate, but related, jobs:

  • It ensures that information doesn’t get where information technology’s not needed. This is crucial for keeping large volumes of data from clogging the connections of “innocent bystanders.”
  • It makes sure that information does make it to the intended destination.

In performing these ii jobs, a router is extremely useful in dealing with ii separate computer networks. It joins the two networks, passing information from i to the other. It also protects the networks from one another, preventing the traffic on one from unnecessarily spilling over to the other. Regardless of how many networks are fastened, the basic operation and function of the router remains the same. Since the Internet is one huge network made up of tens of thousands of smaller networks, its use of routers is an absolute necessity. For more information, read How Routers Work.




Backbones

The
National Science Foundation
(NSF) created the kickoff high-speed courage in 1987. Called
NSFNET, it was a T1 line that connected 170 smaller networks together and operated at 1.544 Mbps (one thousand thousand bits per second). IBM, MCI and Merit worked with NSF to create the courage and adult a T3 (45 Mbps) backbone the following year.

Backbones are typically fiber optic trunk lines. The trunk line has multiple fiber optic cables combined together to increase the capacity. Fiber optic cables are designated OC for optical carrier, such as OC-iii, OC-12 or OC-48. An OC-3 line is capable of transmitting 155 Mbps while an OC-48 can transmit ii,488 Mbps (ii.488 Gbps). Compare that to a typical 56K modem transmitting 56,000 bps and you see just how fast a modern courage is.

Today there are many companies that operate their ain high-chapters backbones, and all of them interconnect at various NAPs around the globe. In this manner, everyone on the Net, no matter where they are and what company they utilise, is able to talk to anybody else on the planet. The unabridged Cyberspace is a gigantic, sprawling understanding between companies to intercommunicate freely.



Internet Protocol: IP Addresses

Every auto on the Internet has a unique identifying number, called an
IP Accost. The IP stands for
Net Protocol, which is the linguistic communication that computers employ to communicate over the Internet. A protocol is the pre-divers way that someone who wants to utilize a service talks with that service. The “someone” could be a person, just more than oftentimes it is a reckoner program like a Web browser.

A typical IP accost looks like this:


216.27.61.137

To make information technology easier for the states humans to remember, IP addresses are normally expressed in decimal format equally a
dotted decimal number
similar the one above. But computers communicate in binary form. Look at the same IP address in binary:


11011000.00011011.00111101.10001001

The four numbers in an IP address are called
octets, because they each accept eight positions when viewed in binary course. If you lot add together all the positions together, you become 32, which is why IP addresses are considered 32-scrap numbers. Since each of the 8 positions can have two unlike states (1 or nil), the total number of possible combinations per octet is 2
8

or 256. And so each octet tin incorporate any value between zero and 255. Combine the iv octets and you get 2
32

or a possible iv,294,967,296 unique values!

Out of the almost iv.3 billion possible combinations, sure values are restricted from use as typical IP addresses. For example, the IP accost 0.0.0.0 is reserved for the default network and the address 255.255.255.255 is used for broadcasts.

The octets serve a purpose other than but separating the numbers. They are used to create
classes
of IP addresses that can be assigned to a particular business, government or other entity based on size and demand. The octets are split into ii sections:
Cyberspace
and
Host. The Net section always contains the first octet. Information technology is used to place the network that a computer belongs to. Host (sometimes referred to as
Node) identifies the bodily estimator on the network. The Host section always contains the last octet. There are five IP classes plus certain special addresses. You can learn more about IP classes at What is an IP address?.



Net Protocol: Domain Name System

When the Internet was in its infancy, it consisted of a small number of computers hooked together with modems and telephone lines. You could simply make connections by providing the IP address of the computer yous wanted to establish a link with. For example, a typical IP accost might be 216.27.22.162. This was fine when there were only a few hosts out there, but information technology became unwieldy as more and more systems came online.

The kickoff solution to the problem was a simple text file maintained by the Network Information Center that mapped names to IP addresses. Soon this text file became so large information technology was too cumbersome to manage. In 1983, the University of Wisconsin created the
Domain Name System
(DNS), which maps text names to IP addresses automatically. This way you only demand to remember http://reckoner.howstuffworks.com/index.htm, for example, instead of HowStuffWorks.com’s IP address.



Uniform Resource Locators

When you apply the Spider web or ship an due east-postal service message, y’all use a domain name to practise it. For instance, the
Uniform Resource Locator
(URL) “http://computer.howstuffworks.com/” contains the domain name howstuffworks.com. So does this e-mail accost: [email protected]. Every fourth dimension you use a domain name, you utilise the Cyberspace’s DNS servers to translate the human-readable domain name into the machine-readable IP address. Check out How Domain Proper noun Servers Work for more in-depth information on DNS.

Elevation-level domain names, also chosen first-level domain names, include .COM, .ORG, .NET, .EDU and .GOV. Within every acme-level domain there is a huge list of second-level domains. For example, in the .COM first-level domain there is:

  • HowStuffWorks
  • Yahoo
  • Microsoft

Every name in the .COM top-level domain must be unique. The left-most word, like www, is the host proper name. Information technology specifies the proper noun of a specific automobile (with a specific IP address) in a domain. A given domain can, potentially, comprise millions of host names as long as they are all unique within that domain.

DNS servers accept requests from programs and other name servers to catechumen domain names into IP addresses. When a request comes in, the DNS server can do one of four things with it:

  1. It can answer the request with an IP accost because it already knows the IP accost for the requested domain.
  2. It can contact another DNS server and try to find the IP address for the name requested. It may have to do this multiple times.
  3. Information technology can say, “I don’t know the IP address for the domain you requested, but here’s the IP address for a DNS server that knows more than than I do.”
  4. It can return an mistake message because the requested domain name is invalid or does not exist.



A DNS Example

Let’due south say that you type the URL http://estimator.howstuffworks.com/ into your browser. The browser contacts a DNS server to become the IP accost. A DNS server would start its search for an IP address by contacting 1 of the
root DNS servers. The root servers know the IP addresses for all of the DNS servers that handle the top-level domains (.COM, .NET, .ORG, etc.). Your DNS server would ask the root for world wide web.howstuffworks.com, and the root would say, “I don’t know the IP address for www.howstuffworks.com, only hither’s the IP accost for the .COM DNS server.”

Your proper name server then sends a query to the .COM DNS server asking it if it knows the IP address for world wide web.howstuffworks.com. The DNS server for the COM domain knows the IP addresses for the proper name servers handling the http://computer.howstuffworks.com/ domain, so information technology returns those.

Your proper noun server then contacts the DNS server for http://computer.howstuffworks.com/ and asks if it knows the IP address for http://reckoner.howstuffworks.com/. Information technology really does, then it returns the IP address to your DNS server, which returns information technology to the browser, which can so contact the server for http://computer.howstuffworks.com/ to go a Spider web folio.

One of the keys to making this piece of work is redundancy. In that location are multiple DNS servers at every level, and then that if one fails, in that location are others to handle the requests. The other key is caching. One time a DNS server resolves a request, it caches the IP address it receives. Once it has made a request to a root DNS server for whatever .COM domain, it knows the IP address for a DNS server treatment the .COM domain, so it doesn’t accept to problems the root DNS servers again for that information. DNS servers tin can do this for every request, and this caching helps to keep things from bogging down.

Even though information technology is totally invisible, DNS servers handle billions of requests every mean solar day and they are essential to the Cyberspace’south smooth operation. The fact that this distributed database works and so well and and then invisibly solar day in and day out is a testimony to the design. Exist sure to read How Domain Name Servers Work for more than information on DNS.



Clients and Servers

Internet
servers
make the Internet possible. All of the machines on the Net are either servers or
clients. The machines that provide services to other machines are servers. And the machines that are used to connect to those services are clients. There are Web servers, e-mail servers, FTP servers and and so on serving the needs of Cyberspace users all over the world.

When yous connect to http://estimator.howstuffworks.com/ to read a page, you are a user sitting at a customer’s machine. You are accessing the HowStuffWorks Spider web server. The server automobile finds the page you requested and sends it to you lot. Clients that come to a server machine do so with a specific intent, and then clients straight their requests to a specific software server running on the server machine. For example, if you are running a Web browser on your machine, information technology will want to talk to the Web server on the server car, not the email server.

A server has a static IP address that does not modify very often. A domicile car that is dialing upward through a modem, on the other hand, typically has an IP address assigned past the Internet access provider every time you punch in. That IP address is unique for your session — information technology may be different the side by side time you dial in. This way, an Isp but needs i IP address for each modem it supports, rather than one for each client.



Ports

Any server automobile makes its services available using numbered ports — 1 for each service that is bachelor on the server. For case, if a server machine is running a Web server and a file transfer protocol (FTP) server, the Web server would typically be bachelor on port 80, and the FTP server would be available on port 21. Clients connect to a service at a specific IP accost and on a specific port number.

One time a customer has connected to a service on a particular port, it accesses the service using a specific protocol. Protocols are frequently text and but describe how the client and server volition have their conversation. Every Spider web server on the Net conforms to the
hypertext transfer protocol (HTTP). You lot tin can learn more than about Internet servers, ports and protocols past reading How Web Servers Work.

Networks, routers, NAPs, ISPs, DNS and powerful servers all make the Internet possible. Information technology is truly amazing when you realize that all this information is sent around the earth in a matter of milliseconds! The components are extremely important in mod life — without them, there would be no Internet. And without the Internet, life would exist very different indeed for many of u.s.a..

For more than information on the structure of the Net and related topics, check out the links on the adjacent page.



Lots More than Information

Related HowStuffWorks Manufactures

  • How Domain Name Servers Piece of work
  • How Bits and Bytes Work
  • How Web Servers Work
  • How Routers Piece of work
  • How Routing Algorithms Work
  • How LAN Switches Work
  • How Ethernet Works
  • How CGI Scripts Work
  • How Firewalls Work
  • How Home Networking Works
  • What are IP Classes?
  • What is a packet?
  • Where are all the Internet domain names registered and maintained?
More Great Links
  • NetworkComputing.com: All About IP Addresses
  • BIND – the software that implements most proper noun servers
  • Domain proper noun registries around the earth
  • WhatIs.com Cyberspace Terms
  • The Original HTTP as defined in 1991
  • Colby.edu: The Anatomy of a URL
  • IANA
  • Network Solutions
  • University of Toronto: The HTTP Protocol
  • Ohio Land: RFC 1340 – Assigned numbers
  • GaryKessler.net: Setting up your own DNS
  • Yahoo! Directory: Security