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Have you ever wondered about how the internet actually works, but don't have a great deal of technical knowledge? No problem, you've come to the right place. I will attempt to explain the basics of how the internet works without getting too technical. To do so, we will step through the network diagram above. But first, it's important to understand the following three points.

First of all, it is important to understand that the internet is nothing more than a term used to describe a massive world wide network of computers connected together for the purpose of sharing content. Every computer or network device connected to the internet has two things true about it, a physical connection is established via a physical cable or a wireless device and it has software necessary to interpret/send/receive the various internet protocols. The protocol refers to the way in which data is transferred from one device to the next. For instance, web page viewing uses a different protocol than sending email. Fortunately, software does all of this automatically for us, so we don't need to understand the underlying technology. But, we do need to understand the high level basics of what is going on.

Another thing to understand is that viewing websites may be what most people think about when they think of the internet, but it's not the only thing to do on the internet. However, since it's the most common thing to do, that's what we'll discuss here. It's also important to understand here that a webpage is nothing more than a collection of text files, stored somewhere on a web server. We'll talk more about that later.

The final point is that in order to understand the basics of the internet you really have to understand the basics of a computer network, because that's really all the internet is.
Important Terminology Referenced in This Article
LAN -Local Area Network - A localized internal collection of devices all connected together inside one home or one building of an organization.

Internet - or World Wide Web - The collection and connection of all internal networks together to form one huge world wide network for sharing information across all homes and organizations connected.

Switches/Routers/Modems/Wireless Access Points - Devices on a computer network that perform various functions related to physically connecting computers together and routing traffic in between one computer and another.

IP Address - Internet Protocol Address - A unique set of numbers assigned to every single device on a network that functions much like a street address on a house. It lets every other device on the network know where to find the device assigned that number.

Server - A powerful computer that is used to serve some function on a computer network. Servers perform various functions, such as hosting web pages, hosting network printers, hosting file shares, handing out IP address, and much more.

DNS - Domain Name Service - A service, typically running from a server that matches and translates names to IP addresses.

DHCP - Dynamic Host Configuration Protocol - A service, typically running from a server that assigns each network device its own unique IP address.

Web Browser - A piece of software used to access websites. The most common browsers include IE (Internet Explorer), Chrome, Firefox, and Safari.

URL - Uniform Resource Locator - Name used to point to a website. This is what you type in to get to a website or what pops up when you search for a website. A URL looks something like "www.website.com".
Understanding What Happens When a Website is Opened
We will now step through what happens when someone opens a website in order to get a conceptual view of how the internet works. You can use the network diagram above for a pictorial reference.

1. The end user opens a web browser and types in a URL, which is the name of the website they are wanting to see.

2. The URL request is sent through their LAN to their internet service provider.

3. The internet service provider then sends the URL requested to an external DNS server, which is either hosted by them or by who ever provides their internet access.

4. The external DNS server then matches the URL up with the external IP Address assigned to the LAN hosting that website and the request is then sent on to that network.

5. The network hosting that website accepts the request and then sends it to its own internal DNS server.

6. The internal DNS server matches the URL requested to the internal IP address of the actual web server where the files making up the website are physically stored.

7. The request is then sent to the web server and the web server packages up the files that make up the website requested.

8. The website that is all packaged up now makes the return trip in reverse all the way back to the computer that originally made the request.

9. The web browser on that computer then interprets the text files full of computer code sent to it by the web server hosting the site and displays them as a graphic website.

This is a high level overview of how the internet works and each of these main steps can be broken down into hundreds of sub steps. But, that would get much too technical for this particular explanation.

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Have you ever wondered about how the internet actually works, but don't have a great deal of technical knowledge? No problem, you've come to the right place. I will attempt to explain the basics of how the internet works without getting too technical. To do so, we will step through the network diagram above.

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How the internet works - inc discussion of TCP/IP

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How the internet works - inc discussion of TCP/IP

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Even though the Internet is still a young technology, it's hard to imagine life without it now. Every year, engineers create more devices to integrate with the Internet. This network of networks crisscrosses the globe and even extends into space. But what makes it work?

To understand the Internet, it helps to look at it as a system with two main components. The first of those components is hardware. That includes everything from the cables that carry terabits of information every second to the computer sitting in front of you.

Other types of hardware that support the Internet include routers, servers, cell phone towers, satellites, radios, smartphones and other devices. All these devices together create the network of networks. The Internet is a malleable system -- it changes in little ways as elements join and leave networks around the world. Some of those elements may stay fairly static and make up the backbone of the Internet. Others are more peripheral.

These elements are connections. Some are end points -- the computer, smartphone or other device you're using to read this may count as one. We call those end points clients. Machines that store the information we seek on the Internet are servers. Other elements are nodes which serve as a connecting point along a route of traffic. And then there are the transmission lines which can be physical, as in the case of cables and fiber optics, or they can be wireless signals from satellites, cell phone or 4G towers, or radios.

All of this hardware wouldn't create a network without the second component of the Internet: the protocols. Protocols are sets of rules that machines follow to complete tasks. Without a common set of protocols that all machines connected to the Internet must follow, communication between devices couldn't happen. The various machines would be unable to understand one another or even send information in a meaningful way. The protocols provide both the method and a common language for machines to use to transmit data.

We'll take a closer look at protocols and how information travels across the Internet on the next page.

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The Internet lets you transfer information around the world in seconds. But the pieces of your file may not all get there the same way. How does all that data get where it's supposed to go without getting lost?

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TCP /IP is end to end connection and transfer data around the internet (the 'IP' part of it). The TCP part sets rules to decide how to package it, fault correction and effective and secure.
TCP/IP has 4 layers link layer, internet layer, transport layer, application layer.
Application layer protocols: DNS, FTP, POP3, HTTP, SMTP etc
Application layer check for correct host, is it available, error recovery procedures

http://walkwidnetwork.blogspot.co.uk/2013/04/application-layer-internet-protocol.html

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An application layer protocol defines how application processes (clients and servers), running on different end systems, pass messages to each other. In particular, an application layer protocol defines:

The types of messages, e.g., request messages and response messages.

The syntax of the various message types, i.e., the fields in the message and how the fields are delineated.

The semantics of the fields, i.e., the meaning of the information that the field is supposed to contain;

Rules for determining when and how a process sends messages and responds to messages.

SMTP (Simple Mail Transfer Protocol):

One of the most popular network service is electronic mail (e-mail).

The TCP/IP protocol that supports electronic mail on the Internet is called Simple Mail Transfer Protocol (SMTP).

SMTP transfers messages from senders' mail servers to the recipients' mail servers using TCP connections.

Users based on e-mail addresses.

SMTP provides services for mail exchange between users on the same or different computers.

Following the client/server model:

SMTP has two sides: a client side which executes on a sender's mail server, and server side which executes on recipient's mail server.

Both the client and server sides of SMTP run on every mail server.

When a mail server sends mail (to other mail servers), it acts as an SMTP client.

When a mail server receives mail (from other mail servers) it acts as an SMTP server.

TELNET (Terminal Network):

TELNET is client-server application that allows a user to log onto remote machine and lets the user to access any application program on a remote computer.

TELNET uses the NVT (Network Virtual Terminal) system to encode characters on the local system.

On the server (remote) machine, NVT decodes the characters to a form acceptable to the remote machine.

TELNET is a protocol that provides a general, bi-directional, eight-bit byte oriented communications facility.

Many application protocols are built upon the TELNET protocol

Telnet services are used on PORT 23.

FTP (File Transfer Protocol):

FTP is the standard mechanism provided by TCP/IP for copying a file from one host to another.

FTP differs form other client-server applications because it establishes 2 connections between hosts.

Two connections are: Data Connection and Control Connection.

Data Connection uses PORT 20 for the purpose and control connection uses PORT 21 for the purpose.

FTP is built on a client-server architecture and uses separate control and data connections between the client and the server.

One connection is used for data transfer, the other for control information (commands and responses).

It transfer data reliably and efficiently.

Multipurpose Internet Mail Extensions (MIME):

It is an extension of SMTP that allows the transfer of multimedia messages.

If binary data is included in a message MIME headers are used to inform the receiving mail agent:

Content-Transfer-Encoding: Header alerts the receiving user agent that the message body has been ASCII encoded and the type of encoding used.

Content-Type: Header informs the receiving mail agent about the type of data included in the message.

POP (Post Office Protocol):

POP is also called as POP3 protocol.

This is a protocol used by a mail server in conjunction with SMTP to receive and holds mail for hosts.

POP3 mail server receives e-mails and filters them into the appropriate user folders. When a user connects to the mail server to retrieve his mail, the messages are downloaded from mail server to the user's hard disk.

HTTP (Hypertext Transfer Protocol):

This is a protocol used mainly to access data on the World Wide Web (www).

The Hypertext Transfer Protocol (HTTP) the Web's main application-layer protocol although current browsers can access other types of servers

A respository of information spread all over the world and linked together.

The HTIP protocol transfer data in the form of plain text, hyper text, audio, video and so on.

HTTP utilizes TCP connections to send client requests and server replies.

it is a synchronous protocol which works by making both persistent and non persistent connections.

Domain Name System (DNS):

To identify an entity, TCP/IP protocol uses the IP address which uniquely identifies the connection of a host to the Internet.

DNS is a hierarchical system, based on a distributed database, that uses a hierarchy of Name Servers to resolve Internet host names into the corresponding IP addresses required for packet routing by issuing a DNS query to a name server.

However, people refer to use names instead of address. Therefore, we need a system that can map a name to an address and conversely an address to name.

In TCP/IP, this is the domain name system.

DNS in the Internet: DNS is protocol that can be used in different platforms.

Domain name space is divided into three categories.

Generic Domain: The generic domain defines registered hosts according, to their generic behaviour. Each node in the tree defines a domain which is an index to the domain name space database.

Country Domain: The country domain section follows the same format as the generic domain but uses 2 characters country abbreviations (e.g., US for United States) in place of 3 characters.

Inverse Domain: The inverse domain is used to map an address to a name.

Overview of Services

Thanks
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Application Layer Protocols (DNS, SMTP, POP, FTP, HTTP)

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An application layer protocol defines how application processes (clients and servers), running on different end systems, pass messages to each other. In particular, an application layer protocol defines: The types of messages, e.g., request messages and response messages. The syntax of the various message types, i.e., the fields in the message and how the fields are delineated.

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TCP/IP Application Layer, Application Layer Protocols

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This Lesson explains TCP/IP Application Layer and Application Layer Protocols

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Application layer is the top layer of TCP/IP protocol. The Application layer includes all the processes that use Transport layer protocols to deliver data to the Internet layer. There are many application protocols, and new protocols are frequently added.

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The TCP/IP Guide - Application Layer (Layer 7)

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If you want to use this site for free, I'd be grateful if you could add the site to the whitelist for Adblock. To do so, just open the Adblock menu and select "Disable on tcpipguide.com". Or go to the Tools menu and select "Adblock Plus Preferences...". Then click "Add Filter..."

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Examples of Application layer interfaces for TCP/IP applications are Windows Sockets and NetBIOS. Windows Sockets provides a standard application programming interface (API) under Windows 2000. NetBIOS is an industry standard interface for accessing protocol services such as sessions, datagrams, and name resolution. More information on Windows Sockets and NetBIOS is provided later in this chapter.

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Who we are

The World Wide Web Consortium (W3C) is an international public-interest non-profit organization where Member organizations, a full-time staff, and the public work together to develop Web standards. Founded by Web inventor Tim Berners-Lee and led by President & CEO Seth Dobbs and a Board of Directors, the Web Consortium's mission is to lead the web to its full potential.

W3C's history

Web inventor Tim Berners-Lee founded the World Wide Web Consortium in 1994 to ensure the long-term growth of the Web. He remains W3C's Emeritus Director and Honorary Member of the Board of Directors.

From the start the World Wide Web Consortium (W3C) has been an international multi-stakeholder community where member organizations, a full-time staff, and the public work together to develop open web standards.
Read the W3C history
W3C Community

W3C's global standards constitute the toolkit for web solutions that scale, enabling innovators to solve hard problems, providing the proper foundations to meet requirements for accessibility, internationalization, privacy, and security on the web.

Standards that meet the varied needs of society are created not by one company but through the work of the Web Consortium community:

Members: More than 400 Members from around the world lead the development and implementation of standards.

Staff: W3C is a public-interest non-profit organization whose revenues come primarily from Membership dues. These and some grants support a staff of about 50 people.

Developers: Over 12,000 developers worldwide participate in the standards development.

Learn how W3C is led
W3C standard development process

The proven standards development process upheld at the Web Consortium promotes fairness and enables progress.

Our standards work is accomplished in the open, under the W3C Process Document and royalty-free W3C Patent Policy, with input from the broader community. Decisions are taken by consensus. Technical direction and Recommendations require review by W3C Members - large and small. The Advisory Board guides the community-driven enhancement of the Process Document. The Technical Architecture Group is our highest authority on technical matters.

International Participation

W3C conducts its work primarily in English. Organizations located all over the world and involved in many different fields join W3C as Members to participate in a vendor-neutral forum for the creation of Web standards. W3C Members and a dedicated full-time staff of experts have earned W3C international recognition for contributions to the Web. W3C's global efforts include:

Liaisons with national, regional and international organizations around the globe. These contacts help W3C maintain a culture of global participation in the development of the World Wide Web. W3C coordinates particularly closely with other organizations that are developing standards for the Web or Internet in order to enable clear progress.

The W3C Chapters Program, which promotes adoption of W3C recommendations among developers, application builders, and standards setters, and encourage inclusions of stakeholder organizations in the creation of future standards by joining W3C.

Translations of Web standards and other materials from dedicated volunteers in the W3C community. W3C also has a policy for authorized translations of W3C materials. Authorized W3C Translations can be used for official purposes in languages other than English.

Talks around the world in a variety of languages on Web standards by people closely involved in the creation of the standards.

W3C's Internationalization activity helps ensure that the Web is available to people.

Recognition

In orchestrating these activities, the Web Consortium has earned a reputation for fairness, quality, and efficiency.

Though not well-known by the general public, the Web Consortium has earned recognition for its global impact: the Boston Globe ranked W3C the most important achievement associated with MIT (the first W3C historical Host).

The Web Consortium's impact even extends beyond this planet: NASA regularly uses W3C standards in Mars and space exploration missions.

The organization has won three Emmy Awards: in 2016 for its work to make online videos more accessible with captions and subtitles, in 2019 for standardization of a Full TV Experience on the web, and again in 2022 for standardizingfont technology for custom downloadable fonts and typography for web and TV devices.

Organizational Structure

In administrative terms W3C has become its own legal entity since January 2023, moving to a public-interest non-profit organization after 28 years with an atypical organizational structure where legal and fiduciary roles were assumed by four host institutions across the planet. Read more about the W3C history.

In process terms, the W3C Process Document, Member Agreement, Patent Policy, and a few others documents establish the roles and responsibilities of the parties involved in the making of W3C standards.

The Process governs the standards-setting aspect of W3C. The Bylaws govern the operation of the corporation that supports the standards process and W3C's other efforts to pursue its mission.

Funding model

W3C sources of revenue include:

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This page introduces the World Wide Web Consortium, a multi-stakeholder member-organization which develops web standards in the open.

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Teacher Has Personalized Handshakes With Every Single One of His Students

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What are the differences between server-side and client-side programming?

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I've seen questions (mainly on Stack Overflow), which lack this basic knowledge. The point of this question is to provide good information for those seeking it, and those referencing to it. In...

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Differences between Client-side and Server-side Scripting

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Especially under the heading 'Bridging the Divide

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Do you ever wonder how the Internet really works? How do Web pages, e-mail and music move to and from your computer? Learn all about the amazing global network we call the World Wide Web.

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1 - Introduction & Web Architecture - new(1)

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© 2002 Rus Shuler @ Pomeroy IT Solutions, all rights reserved

Contents

1. Introduction

2. Where to Begin? Internet Addresses

3. Protocol Stacks and Packets

4. Networking Infrastructure

5. Internet Infrastructure

6. The Internet Routing Hierarchy

7. Domain Names and Address Resolution

8. Internet Protocols Revisited

9. Application Protocols: HTTP and the World Wide Web

10. Application Protocols: SMTP and Electronic Mail

11. Transmission Control Protocol

12. Internet Protocol

13. Bibliography

Introduction
How does the Internet work? Good question! The Internet's growth has become explosive and it seems impossible to escape the bombardment of www.com's seen constantly on television, heard on radio, and seen in magazines. Because the Internet has become such a large part of our lives, a good understanding is needed to use this new tool most effectively.
This whitepaper explains the underlying infrastructure and technologies that make the Internet work. It does not go into great depth, but covers enough of each area to give a basic understanding of the concepts involved. For any unanswered questions, a list of resources is provided at the end of the paper. Any comments, suggestions, questions, etc. are encouraged and may be directed to the author at rshuler@gobcg.com. Because the Internet is a global network of computers each computer connected to the Internet must have a unique address. Internet addresses are in the form nnn.nnn.nnn.nnn where nnn must be a number from 0 - 255. This address is known as an IP address. (IP stands for Internet Protocol; more on this later.)

The picture below illustrates two computers connected to the Internet; your computer with IP address 1.2.3.4 and another computer with IP address 5.6.7.8. The Internet is represented as an abstract object in-between. (As this paper progresses, the Internet portion of Diagram 1 will be explained and redrawn several times as the details of the Internet are exposed.)
If you connect to the Internet through an Internet Service Provider (ISP), you are usually assigned a temporary IP address for the duration of your dial-in session. If you connect to the Internet from a local area network (LAN) your computer might have a permanent IP address or it might obtain a temporary one from a DHCP (Dynamic Host Configuration Protocol) server. In any case, if you are connected to the Internet, your computer has a unique IP address.

If you're using Microsoft Windows or a flavor of Unix and have a connection to the Internet, there is a handy program to see if a computer on the Internet is alive. It's called ping, probably after the sound made by older submarine sonar systems. ¹ If you are using Windows, start a command prompt window. If you're using a flavor of Unix, get to a command prompt. Type ping www.yahoo.com. The ping program will send a 'ping' (actually an ICMP (Internet Control Message Protocol) echo request message) to the named computer. The pinged computer will respond with a reply. The ping program will count the time expired until the reply comes back (if it does). Also, if you enter a domain name (i.e. www.yahoo.com) instead of an IP address, ping will resolve the domain name and display the computer's IP address. More on domain names and address resolution later.

Protocol Stacks and Packets
So your computer is connected to the Internet and has a unique address. How does it 'talk' to other computers connected to the Internet? An example should serve here: Let's say your IP address is 1.2.3.4 and you want to send a message to the computer 5.6.7.8. The message you want to send is "Hello computer 5.6.7.8!". Obviously, the message must be transmitted over whatever kind of wire connects your computer to the Internet. Let's say you've dialed into your ISP from home and the message must be transmitted over the phone line. Therefore the message must be translated from alphabetic text into electronic signals, transmitted over the Internet, then translated back into alphabetic text. How is this accomplished? Through the use of a protocol stack. Every computer needs one to communicate on the Internet and it is usually built into the computer's operating system (i.e. Windows, Unix, etc.). The protocol stack used on the Internet is refered to as the TCP/IP protocol stack because of the two major communication protocols used. The TCP/IP stack looks like this:

Protocol Layer

Comments

Application Protocols Layer

Protocols specific to applications such as WWW, e-mail, FTP, etc.

Transmission Control Protocol Layer

TCP directs packets to a specific application on a computer using a port number.

Internet Protocol Layer

IP directs packets to a specific computer using an IP address.

Hardware Layer

Converts binary packet data to network signals and back.
(E.g. ethernet network card, modem for phone lines, etc.)

If we were to follow the path that the message "Hello computer 5.6.7.8!" took from our computer to the computer with IP address 5.6.7.8, it would happen something like this:

1. The message would start at the top of the protocol stack on your computer and work it's way downward.

2. If the message to be sent is long, each stack layer that the message passes through may break the message up into smaller chunks of data. This is because data sent over the Internet (and most computer networks) are sent in manageable chunks. On the Internet, these chunks of data are known as packets.

3. The packets would go through the Application Layer and continue to the TCP layer. Each packet is assigned a port number. Ports will be explained later, but suffice to say that many programs may be using the TCP/IP stack and sending messages. We need to know which program on the destination computer needs to receive the message because it will be listening on a specific port.

4. After going through the TCP layer, the packets proceed to the IP layer. This is where each packet receives it's destination address, 5.6.7.8.

5. Now that our message packets have a port number and an IP address, they are ready to be sent over the Internet. The hardware layer takes care of turning our packets containing the alphabetic text of our message into electronic signals and transmitting them over the phone line.

6. On the other end of the phone line your ISP has a direct connection to the Internet. The ISPs router examines the destination address in each packet and determines where to send it. Often, the packet's next stop is another router. More on routers and Internet infrastructure later.

7. Eventually, the packets reach computer 5.6.7.8. Here, the packets start at the bottom of the destination computer's TCP/IP stack and work upwards.

8. As the packets go upwards through the stack, all routing data that the sending computer's stack added (such as IP address and port number) is stripped from the packets.

9. When the data reaches the top of the stack, the packets have been re-assembled into their original form, "Hello computer 5.6.7.8!"

Networking Infrastructure
So now you know how packets travel from one computer to another over the Internet. But what's in-between? What actually makes up the Internet? Let's look at another diagram:

Here we see Diagram 1 redrawn with more detail. The physical connection through the phone network to the Internet Service Provider might have been easy to guess, but beyond that might bear some explanation.
The ISP maintains a pool of modems for their dial-in customers. This is managed by some form of computer (usually a dedicated one) which controls data flow from the modem pool to a backbone or dedicated line router. This setup may be refered to as a port server, as it 'serves' access to the network. Billing and usage information is usually collected here as well.

After your packets traverse the phone network and your ISP's local equipment, they are routed onto the ISP's backbone or a backbone the ISP buys bandwidth from. From here the packets will usually journey through several routers and over several backbones, dedicated lines, and other networks until they find their destination, the computer with address 5.6.7.8. But wouldn't it would be nice if we knew the exact route our packets were taking over the Internet? As it turns out, there is a way...

Check It Out - The Traceroute Program

If you're using Microsoft Windows or a flavor of Unix and have a connection to the Internet, here is another handy Internet program. This one is called traceroute and it shows the path your packets are taking to a given Internet destination. Like ping, you must use traceroute from a command prompt. In Windows, use tracert www.yahoo.com. From a Unix prompt, type traceroute www.yahoo.com. Like ping, you may also enter IP addresses instead of domain names. Traceroute will print out a list of all the routers, computers, and any other Internet entities that your packets must travel through to get to their destination.

If you use traceroute, you'll notice that your packets must travel through many things to get to their destination. Most have long names such as sjc2-core1-h2-0-0.atlas.digex.net and fddi0-0.br4.SJC.globalcenter.net. These are Internet routers that decide where to send your packets. Several routers are shown in Diagram 3, but only a few. Diagram 3 is meant to show a simple network structure. The Internet is much more complex.
The Internet backbone is made up of many large networks which interconnect with each other. These large networks are known as Network Service Providers or NSPs. Some of the large NSPs are UUNet, CerfNet, IBM, BBN Planet, SprintNet, PSINet, as well as others. These networks peer with each other to exchange packet traffic. Each NSP is required to connect to three Network Access Points or NAPs. At the NAPs, packet traffic may jump from one NSP's backbone to another NSP's backbone. NSPs also interconnect at Metropolitan Area Exchanges or MAEs. MAEs serve the same purpose as the NAPs but are privately owned. NAPs were the original Internet interconnect points. Both NAPs and MAEs are referred to as Internet Exchange Points or IXs. NSPs also sell bandwidth to smaller networks, such as ISPs and smaller bandwidth providers. Below is a picture showing this hierarchical infrastructure.

This is not a true representation of an actual piece of the Internet. Diagram 4 is only meant to demonstrate how the NSPs could interconnect with each other and smaller ISPs. None of the physical network components are shown in Diagram 4 as they are in Diagram 3. This is because a single NSP's backbone infrastructure is a complex drawing by itself. Most NSPs publish maps of their network infrastructure on their web sites and can be found easily. To draw an actual map of the Internet would be nearly impossible due to it's size, complexity, and ever changing structure.
So how do packets find their way across the Internet? Does every computer connected to the Internet know where the other computers are? Do packets simply get 'broadcast' to every computer on the Internet? The answer to both the preceeding questions is 'no'. No computer knows where any of the other computers are, and packets do not get sent to every computer. The information used to get packets to their destinations are contained in routing tables kept by each router connected to the Internet.

Routers are packet switches. A router is usually connected between networks to route packets between them. Each router knows about it's sub-networks and which IP addresses they use. The router usually doesn't know what IP addresses are 'above' it. Examine Diagram 5 below. The black boxes connecting the backbones are routers. The larger NSP backbones at the top are connected at a NAP. Under them are several sub-networks, and under them, more sub-networks. At the bottom are two local area networks with computers attached.

When a packet arrives at a router, the router examines the IP address put there by the IP protocol layer on the originating computer. The router checks it's routing table. If the network containing the IP address is found, the packet is sent to that network. If the network containing the IP address is not found, then the router sends the packet on a default route, usually up the backbone hierarchy to the next router. Hopefully the next router will know where to send the packet. If it does not, again the packet is routed upwards until it reaches a NSP backbone. The routers connected to the NSP backbones hold the largest routing tables and here the packet will be routed to the correct backbone, where it will begin its journey 'downward' through smaller and smaller networks until it finds it's destination.
But what if you don't know the IP address of the computer you want to connect to? What if the you need to access a web server referred to as www.anothercomputer.com? How does your web browser know where on the Internet this computer lives? The answer to all these questions is the Domain Name Service or DNS. The DNS is a distributed database which keeps track of computer's names and their corresponding IP addresses on the Internet.

Many computers connected to the Internet host part of the DNS database and the software that allows others to access it. These computers are known as DNS servers. No DNS server contains the entire database; they only contain a subset of it. If a DNS server does not contain the domain name requested by another computer, the DNS server re-directs the requesting computer to another DNS server.

The Domain Name Service is structured as a hierarchy similar to the IP routing hierarchy. The computer requesting a name resolution will be re-directed 'up' the hierarchy until a DNS server is found that can resolve the domain name in the request. Figure 6 illustrates a portion of the hierarchy. At the top of the tree are the domain roots. Some of the older, more common domains are seen near the top. What is not shown are the multitude of DNS servers around the world which form the rest of the hierarchy.
When an Internet connection is setup (e.g. for a LAN or Dial-Up Networking in Windows), one primary and one or more secondary DNS servers are usually specified as part of the installation. This way, any Internet applications that need domain name resolution will be able to function correctly. For example, when you enter a web address into your web browser, the browser first connects to your primary DNS server. After obtaining the IP address for the domain name you entered, the browser then connects to the target computer and requests the web page you wanted.

If you're using Windows 95/NT and access the Internet, you may view your DNS server(s) and even disable them.

If you use Dial-Up Networking:
Open your Dial-Up Networking window (which can be found in Windows Explorer under your CD-ROM drive and above Network Neighborhood). Right click on your Internet connection and click Properties. Near the bottom of the connection properties window press the TCP/IP Settings... button.

If you have a permanent connection to the Internet:
Right click on Network Neighborhood and click Properties. Click TCP/IP Properties. Select the DNS Configuration tab at the top.

You should now be looking at your DNS servers' IP addresses. Here you may disable DNS or set your DNS servers to 0.0.0.0. (Write down your DNS servers' IP addresses first. You will probably have to restart Windows as well.) Now enter an address into your web browser. The browser won't be able to resolve the domain name and you will probably get a nasty dialog box explaining that a DNS server couldn't be found. However, if you enter the corresponding IP address instead of the domain name, the browser will be able to retrieve the desired web page. (Use ping to get the IP address prior to disabling DNS.) Other Microsoft operating systems are similar.

Internet Protocols Revisited
As hinted to earlier in the section about protocol stacks, one may surmise that there are many protocols that are used on the Internet. This is true; there are many communication protocols required for the Internet to function. These include the TCP and IP protocols, routing protocols, medium access control protocols, application level protocols, etc. The following sections describe some of the more important and commonly used protocols on the Internet. Higher level protocols are discussed first, followed by lower level protocols.
Application Protocols: HTTP and the World Wide Web
One of the most commonly used services on the Internet is the World Wide Web (WWW). The application protocol that makes the web work is Hypertext Transfer Protocol or HTTP. Do not confuse this with the Hypertext Markup Language (HTML). HTML is the language used to write web pages. HTTP is the protocol that web browsers and web servers use to communicate with each other over the Internet. It is an application level protocol because it sits on top of the TCP layer in the protocol stack and is used by specific applications to talk to one another. In this case the applications are web browsers and web servers.
HTTP is a connectionless text based protocol. Clients (web browsers) send requests to web servers for web elements such as web pages and images. After the request is serviced by a server, the connection between client and server across the Internet is disconnected. A new connection must be made for each request. Most protocols are connection oriented. This means that the two computers communicating with each other keep the connection open over the Internet. HTTP does not however. Before an HTTP request can be made by a client, a new connection must be made to the server.

When you type a URL into a web browser, this is what happens:

1. If the URL contains a domain name, the browser first connects to a domain name server and retrieves the corresponding IP address for the web server.

2. The web browser connects to the web server and sends an HTTP request (via the protocol stack) for the desired web page.

3. The web server receives the request and checks for the desired page. If the page exists, the web server sends it. If the server cannot find the requested page, it will send an HTTP 404 error message. (404 means 'Page Not Found' as anyone who has surfed the web probably knows.)

4. The web browser receives the page back and the connection is closed.

5. The browser then parses through the page and looks for other page elements it needs to complete the web page. These usually include images, applets, etc.

6. For each element needed, the browser makes additional connections and HTTP requests to the server for each element.

7. When the browser has finished loading all images, applets, etc. the page will be completely loaded in the browser window.

Check It Out - Use Your Telnet Client to Retrieve a Web Page Using HTTP

Telnet is a remote terminal service used on the Internet. It's use has declined lately, but it is a very useful tool to study the Internet. In Windows find the default telnet program. It may be located in the Windows directory named telnet.exe. When opened, pull down the Terminal menu and select Preferences. In the preferences window, check Local Echo. (This is so you can see your HTTP request when you type it.) Now pull down the Connection menu and select Remote System. Enter www.google.com for the Host Name and 80 for the Port. (Web servers usually listen on port 80 by default.) Press Connect. Now type

and press Enter twice. This is a simple HTTP request to a web server for it's root page. You should see a web page flash by and then a dialog box should pop up to tell you the connection was lost. If you'd like to save the retrieved page, turn on logging in the Telnet program. You may then browse through the web page and see the HTML that was used to write it.

Most Internet protocols are specified by Internet documents known as a Request For Comments or RFCs. RFCs may be found at several locations on the Internet. See the Resources section below for appropriate URL's. HTTP version 1.0 is specified by RFC 1945.
Application Protocols: SMTP and Electronic Mail
Another commonly used Internet service is electronic mail. E-mail uses an application level protocol called Simple Mail Transfer Protocol or SMTP. SMTP is also a text based protocol, but unlike HTTP, SMTP is connection oriented. SMTP is also more complicated than HTTP. There are many more commands and considerations in SMTP than there are in HTTP.
When you open your mail client to read your e-mail, this is what typically happens:

1. The mail client (Netscape Mail, Lotus Notes, Microsoft Outlook, etc.) opens a connection to it's default mail server. The mail server's IP address or domain name is typically setup when the mail client is installed.

2. The mail server will always transmit the first message to identify itself.

3. The client will send an SMTP HELO command to which the server will respond with a 250 OK message.

4. Depending on whether the client is checking mail, sending mail, etc. the appropriate SMTP commands will be sent to the server, which will respond accordingly.

5. This request/response transaction will continue until the client sends an SMTP QUIT command. The server will then say goodbye and the connection will be closed.

A simple 'conversation' between an SMTP client and SMTP server is shown below. R: denotes messages sent by the server (receiver) and S: denotes messages sent by the client (sender).
      This SMTP example shows mail sent by Smith at host USC-ISIF, to
      Jones, Green, and Brown at host BBN-UNIX.  Here we assume that
      host USC-ISIF contacts host BBN-UNIX directly.  The mail is
      accepted for Jones and Brown.  Green does not have a mailbox at
      host BBN-UNIX.

      -------------------------------------------------------------

         R: 220 BBN-UNIX.ARPA Simple Mail Transfer Service Ready
         S: HELO USC-ISIF.ARPA
         R: 250 BBN-UNIX.ARPA

         S: MAIL FROM:<Smith@USC-ISIF.ARPA>
         R: 250 OK

         S: RCPT TO:<Jones@BBN-UNIX.ARPA>
         R: 250 OK

         S: RCPT TO:<Green@BBN-UNIX.ARPA>
         R: 550 No such user here

         S: RCPT TO:<Brown@BBN-UNIX.ARPA>
         R: 250 OK

         S: DATA
         R: 354 Start mail input; end with <CRLF>.<CRLF>
         S: Blah blah blah...
         S: ...etc. etc. etc.
         S: .
         R: 250 OK

         S: QUIT
         R: 221 BBN-UNIX.ARPA Service closing transmission channel

This SMTP transaction is taken from RFC 821, which specifies SMTP.
Transmission Control Protocol
Under the application layer in the protocol stack is the TCP layer. When applications open a connection to another computer on the Internet, the messages they send (using a specific application layer protocol) get passed down the stack to the TCP layer. TCP is responsible for routing application protocols to the correct application on the destination computer. To accomplish this, port numbers are used. Ports can be thought of as seperate channels on each computer. For example, you can surf the web while reading e-mail. This is because these two applications (the web browser and the mail client) used different port numbers. When a packet arrives at a computer and makes its way up the protocol stack, the TCP layer decides which application receives the packet based on a port number.
TCP works like this:

When the TCP layer receives the application layer protocol data from above, it segments it into manageable 'chunks' and then adds a TCP header with specific TCP information to each 'chunk'. The information contained in the TCP header includes the port number of the application the data needs to be sent to.

When the TCP layer receives a packet from the IP layer below it, the TCP layer strips the TCP header data from the packet, does some data reconstruction if necessary, and then sends the data to the correct application using the port number taken from the TCP header.

This is how TCP routes the data moving through the protocol stack to the correct application.
TCP is not a textual protocol. TCP is a connection-oriented, reliable, byte stream service. Connection-oriented means that two applications using TCP must first establish a connection before exchanging data. TCP is reliable because for each packet received, an acknowledgement is sent to the sender to confirm the delivery. TCP also includes a checksum in it's header for error-checking the received data. The TCP header looks like this:

Notice that there is no place for an IP address in the TCP header. This is because TCP doesn't know anything about IP addresses. TCP's job is to get application level data from application to application reliably. The task of getting data from computer to computer is the job of IP.

Internet Protocol
Unlike TCP, IP is an unreliable, connectionless protocol. IP doesn't care whether a packet gets to it's destination or not. Nor does IP know about connections and port numbers. IP's job is too send and route packets to other computers. IP packets are independent entities and may arrive out of order or not at all. It is TCP's job to make sure packets arrive and are in the correct order. About the only thing IP has in common with TCP is the way it receives data and adds it's own IP header information to the TCP data. The IP header looks like this:

Above we see the IP addresses of the sending and receiving computers in the IP header. Below is what a packet looks like after passing through the application layer, TCP layer, and IP layer. The application layer data is segmented in the TCP layer, the TCP header is added, the packet continues to the IP layer, the IP header is added, and then the packet is transmitted across the Internet.

Wrap Up
Now you know how the Internet works. But how long will it stay this way? The version of IP currently used on the Internet (version 4) only allows 2 ³² addresses. Eventually there won't be any free IP addresses left. Surprised? Don't worry. IP version 6 is being tested right now on a research backbone by a consortium of research institutions and corporations. And after that? Who knows. The Internet has come a long way since it's inception as a Defense Department research project. No one really knows what the Internet will become. One thing is sure, however. The Internet will unite the world like no other mechanism ever has. The Information Age is in full stride and I am glad to be a part of it.
Rus Shuler, 1998
Updates made 2002 Below are some interesting links associated with some of the topics discussed. (I hope they all still work. All open in new window.)

http://www.ietf.org/ is the home page of the Internet Engineering Task Force. This body is greatly responsible for the development of Internet protocols and the like.

http://www.internic.org/ is the organization responsible for administering domain names.

http://www.nexor.com/public/rfc/index/rfc.html is an excellent RFC search engine useful for finding any RFC.

http://www.internetweather.com/ shows animated maps of Internet latency.

http://routes.clubnet.net/iw/ is Internet Weather from ClubNET. This page shows packet loss for various carriers.

http://navigators.com/isp.html is Russ Haynal's ISP Page. This is a great site with links to most NSPs and their backbone infrastructure maps.

The following books are excellent resources and helped greatly in the writing of this paper. I believe Stevens' book is the best TCP/IP reference ever and can be considered the bible of the Internet. Sheldon's book covers a much wider scope and contains a vast amount of networking information.

TCP/IP Illustrated, Volume 1, The Protocols.
W. Richard Stevens.
Addison-Wesley, Reading, Massachusetts. 1994.

Encyclopedia of Networking.
Tom Sheldon.
Osbourne McGraw-Hill, New York. 1998.

Although not used for writing this paper, here are some other good books on the topics of the Internet and networking:

Firewalls and Internet Security; Repelling the Wiley Hacker.
William R. Cheswick, Steven M. Bellovin.
Addison-Wesley, Reading, Massachusetts. 1994.

Data Communications, Computer Networks and Open Systems. Fourth Edition.
Fred Halsall.
Addison-Wesley, Harlow, England. 1996.

Telecommunications: Protocols and Design.
John D. Spragins with Joseph L. Hammond and Krzysztof Pawlikowski.
Addison-Wesley, Reading, Massachusetts. 1992.

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internet how does whitepaper topology addressing protocol stack infrastructure backbone dwight marion rus shuler

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A slightly technical whitepaper explaining what makes the Internet tick.

# data[].attributes.attachment_link.description
The Internet is the backbone of the Web, the technical infrastructure that makes the Web possible. At its most basic, the Internet is a large network of computers which communicate all together.

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A router is a networking device that forwards data packets between computer networks. Routers perform the traffic directing functions on the Internet. A data packet is typically forwarded from one router to another router through the networks that constitute an internetwork until it reaches its destination node.

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A deeper discussion

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A router (including a wireless router) is a specialized networking device connected to two or more networks running software that allows the router to move data from one network to another. Router functions in an Internet protocol based network operate at the network layer ( OSI Model's layer 3). The primary function of a router is to connect networks together and keep certain kinds of broadcast traffic under control. There are several companies that make routers: Cisco, Linksys, Juniper, Netgear, Nortel (Bay Networks), Redback, Lucent, 3Com, HP, Dlink and Belkin just to name a few.

Several networking exams (CCNA, CCNP, JNCIA, JNCIE) will test your ability to identify different types of network equipment. This network certification tutorial on routers focuses on identifying network routers, and explaining the functions of routers provide. This tutorial is not specific to any vendor's technology.

How Do Routers Work?

Let's use a home wireless router connected to a cable provider's internet network in a very simplified example.

1. The router powers on and loads it's OS from flash

2. The router loads the configuration file last saved to NVRAM and sets up the network interfaces and routing protocols it will run.

3. The router adds the network address and subnet for each interface to it's routing table along with the name of the interface itself.

4. The router has a simple static default route to send all non-local data out the network port connected to the cable company.

5. When the router receives a web page request from your computer, it checks the destination IP address against its routing table.

6. The bits forming the destination IP address in the IP packet are used as a hash key to point to the correct route, which in turn points to the correct network interface that the packet should be forwarded out of.

7. The router transmits the packet out the correct interface, to the next router, which repeats the process until the packet reaches the destination.

The process is mostly the same for any router.

CAVEAT: A small complication here. For home cable and wifi routers, the router is also acting as a "proxy" so the router does one thing that is NOT normal for a router out on the Internet somwehere: it changes the source IP address in the IP packet to it's own address.

Why do I need a Router?

Routers are used to connect networks together and routers perform the following network functions, whish you should be able to identify and describe on the Network+, CCNA or JNCP exam:
FUNCTIONS OF A ROUTER (identify and describe)

1. Restrict broadcasts to the LAN

2. Act as the default gateway.

3. Perform Protocol Translation (Wired Ethernet to Wireless/WiFi, or Ethernet to CATV)

4. Move (route) data between networks

5. Learn and advertise loop free paths

6. Calculate 'best paths' to reach network destinations.

Restrict Broadcasts to the LAN

Networks (especially Ethernet networks) use broadcast communication at the physical, datalink and network layer. Network layer broadcasts are transmissions sent to all hosts using the network layer protocol (usually Internet Protocol [IP] or IPX). Network broadcast communication is used to communicate certain kinds of information that makes the network function ( ARP, RARP, DHCP, IPX-SAP broadcasts etc.). Since several devices could attempt to transmit simultaneously and cause collisions, it is preferable to separate large sets of hosts into different broadcast domains using a switch, or router.

As the number of hosts on the network increases, the amount of broadcast traffic increases. If enough broadcast traffic is present on the network, then ordinary communication across the network becomes difficult.

To reduce broadcasts, a network administrator can break up a network with a large number of hosts into two smaller networks. Broadcasts are then restricted to each network, and the router performs as the 'default gateway' to reach the hosts on the other networks.

Act as the Default Gateway

Especially in today's networks, people want to use their computer to connect to the Internet. When your computer wants to talk to a computer on another network, it does so by sending your data to the default gateway. The default gateway is the local router connected to the same network your computer is connected to. The router serving as the default gateway receives your data, looks for the remote address of that far-off computer and makes a routing decision. Based on that routing decision, it forwards your data out a different interface that is closer to that remote computer. There could be several routers between you and the remote computer, so several routers will take part in handing off the packet, much like a fireman's bucket brigade.

Move (route) Data between Networks

Routers have the capability to move data from one network to another. This allows two networks managed by different organizations to exchange data. They create a network between them and exchange data between the routers on that network. Because a router can accept traffic from any kind of network it is attached to, and forward it to any other network, it can also allow networks that could not normally communicate with each other to exchange data. In technical terms, a token ring network and an ethernet network can communicate over a serial network. Routers make all this possible.

A router can take in an Ethernet frame, strip the ethernet data off, and then drop the IP data into a frame of another type such as SDH/SONET, PDH/T1, ATM, FDDI. In this way a router can also perform 'protocol conversion', provided it has the appropriate hardware and software to support such a function. The whole point, however, is to forward the data from the interface it receives data on, to another interface that retransmits the received data onto another interface serving another network.

Learn and Advertise Loop-Free Paths

Routers can only learn and advertise routes dynamically if they are using a routing protocol such as RIP, OSPF, EIGRP, IS-IS or BGP. Otherwise, a human has to configure the routes by hand, which is called static routing.

Routing moves data on a hop-by-hop basis, what is often called 'hot potato' routing. If a set of routers ends up passing the data around in a circle, without reaching the destination, it's calleda a 'routing loop'. Packets get handed off around the loop until they die of old age: their 'Time To Live' expires. Time To Live is a counter that is part of the IP datagram header. The Time To Live value is decremented as it passes through each router and eventually it reaches zero and is discarded.

Router Components & Parts

Since routers are just specialized computers, the have the same "parts" as other computers:

Central Processing Unit (CPU)

Flash Memory

Non-Volitile RAM

RAM

Network Interfaces

Console

Central Processing Unit: Runs special software called an "operating system" such as JunOS on Juniper routers, or Cisco IOS (Nexus OS) for Cisco routers. The operating system manages the router's components and provies all the logical networking functions of the router.

Flash Memory is where the operating system is stored, and in this respect, is like the hard disk drive in your computer. If you use a Solid State Disk Drive (SSD), then your computer uses Flash RAM, just like the router does.

Non-Volitile RAM: This is additional memory for storing the backup or startup version of the operating system being used. The router will boot from this memory and load all it's programs from here.

RAM: When the router starts up, the operating system is loaded into RAM. Once the router finishes starting up, it begins to calculate its own routes and, if configured to do so, learns network routes from other routers via RIP (v1 and v2), OSPF, EIGRP, IS-IS or BGP. RAM is also used for caching ARP tables, routing tables, routing metrics and other data that can speed up the process of forwarding of packets.

Network Interfaces: Routers always have lots of network interfaces. The operating system contains 'drivers' that allow the operating sytem to access the network hardware in the interface modules. Routers will learn which networks are configured on which ports as they start up. After that, they will 'learn' routes from other routers they are connected to, and learn which interface to transmit packets on to reach a remote network destination.

Console: Last, but not least, is the console. In "Ye Olden Days" managing and configuring a router was performed at the console of individual devices, as was most troubleshooting and diagnostics. Network certification exams will contain a large selection of questions on the configuration and troubleshooting commands you can issue from the console. However, manufacturers are rapidly doing away with a console on each device and building management systems for managing large numbers of network devices from a centralized location.

More IP Routing Tutorials

Routing | Routing Protocols | Routing vs. Routed Protocols | Default Route | Default Gateway | Routing Protocol Convergence | Interior vs. Exterior Gateway Protocols (IGP/EGP)| Dynamic vs. Static Routing | Distance Vector vs. Link State Routing Protocols

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# data[].attributes.attachment_link.description
A router (including a wireless router) is a specialized networking device connected to two or more networks running software that allows the router to move data from one network to another. Router functions in an Internet protocol based network operate at the network layer ( OSI Model's layer 3).

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interactivity, user content, information sharing, cloud computing. Blogs, Wikis, Tumblr, blogs. Positive information, negative information, Twitter, bi-directional communication

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How websites move information to enable internet and web functionality

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How websites move information to enable internet and web functionality

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cloud storage (google drive)
online storage (youtube, online applications (sound recorders, anywhere where you have an account and make things)
bit torrent
file sharing
reddit /Tumblr etc
Browser
Download speeds

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A very detailed overview of Web architecture is here

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A very detailed overview of Web architecture is here

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Introduction to Web ArchitectureChhorn Chamnap

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https://www.techopedia.com/definition/30409/website-architecture

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http://firstmonday.org/article/view/2125/1972#p4

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The web today is a growing universe of interlinked web pages and web apps, teeming with videos, photos, and interactive content. What the average user doesn't see is the interplay of web technologies and browsers that makes all this possible.

Over time web technologies have evolved to give web developers the ability to create new generations of useful and immersive web experiences. Today's web is a result of the ongoing efforts of an open web community that helps define these web technologies, like HTML5, CSS3 and WebGL and ensure that they're supported in all web browsers.

The color bands in this visualization represent the interaction between web technologies and browsers, which brings to life the many powerful web apps that we use daily.
Explore

Browsers & Technologies The Growth of the Internet
Credits

x

Credits

Made with some friends from the Google Chrome team

2011 & 2012 versions by Hyperakt and Vizzuality

2010 version by mgmt design and GOOD

Sources

Wikipedia, CanIUse.com, W3C, HTML5rocks.com and Mozilla Developer Network

Browser screenshots used in this infographic were sourced with best efforts from the web community.

# data[].attributes.attachment_link.description
Interactive infographic about the evolution of browsers and the web. This infographic features major web browsers since 1993 such as Mosaic, Netscape, Opera, Internet Explorer, Safari, Firefox, and Chrome, as well as key developments in web technologies such as HTML, CSS, and JavaScript.

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Application Layer:-

Application layer is most important as this is the only layer present at the top of OSI model and through which user can interact it. It provides services to the user.

Application Layer protocol:-

1. TELNET:

Telnet stands for telephone network.It helps in terminal emulation.It allows Telnet client to access the resources of Telnet server.It is used for managing the files on the internet.It is used for initial set up of devices like switches.Telnet command is a command that uses the Telnet protocol to communicate with a remote device or system.
Command

telnet [\\RemoteServer]
\\RemoteServer   : Specifies the name of the server to which you want to connect

2. FTP:

FTP stands for file transfer protocol. It is the protocol that actually lets us transfer files.It can facilitate this between any two machines using it. But FTP is not just a protocol but it is also a program.FTP promotes sharing of files via remote computers with reliable and efficient data transfer
Command

ftp machinename

3. TFTP:

The Trivial File Transfer Protocol (TFTP) is the stripped-down, stock version of FTP, but it's the protocol of choice if you know exactly what you want and where to find it. It's a technology for transferring files between network devices, and is a simplified version of FTP
Command

tftp [ options... ] [host [port]] [-c command]

4. NFS:

It stands for network file system.It allows remote hosts to mount file systems over a network and interact with those file systems as though they are mounted locally. This enables system administrators to consolidate resources onto centralized servers on the network.
Command

service nfs start

5. SMTP:

It stands for Simple Mail Transfer Protocol.It is a part of TCP/IP protocol.Using a process called "store and forward," SMTP moves your email on and across networks. It works closely with something called the Mail Transfer Agent (MTA) to send your communication to the right computer and email inbox.
Command

MAIL FROM:<mail@abc.com?

6. LPD:

It stands for Line Printer Daemon.It is designed for printer sharing.It is the part that receives and processes the request. A "daemon" is a server or agent.
Command

lpd [ -d ] [ -l ] [ -D DebugOutputFile]

7. X window:

It defines a protocol for the writing of graphical user interface-based client/server applications. The idea is to allow a program, called a client, to run on one computer. It is primarily used in networks of interconnected mainframes.
Command

Run xdm in runlevel 5

8. SNMP:

It stands for Simple Network Management Protocol.It gathers data by polling the devices on
the network from a management station at fixed or random intervals, requiring
them to disclose certain information.It is a way that servers can share information about their current state, and also a channel through which an administer can modify pre-defined values.
Command

snmpget -mALL -v1 -cpublic snmp_agent_Ip_address sysName.0

9. DNS:

It stands for Domain Name Service.Every time you use a domain name, therefore, a DNS service must translate the name into the corresponding IP address. For example, the domain name www.abc.com might translate to 198.105.232.4.
Command

ipconfig /flushdns

10. DHCP:

It stands for Dynamic Host Configuration Protocol (DHCP).It gives IP addresses to hosts.There is a lot of information a DHCP server can provide to a host when the host is registering for an IP address with the DHCP server.
Command

clear ip dhcp binding {address | * }

This article is contributed by Kritka. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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Protocols in Application Layer - GeeksforGeeks

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Application layer is most important as this is the only layer present at the top of OSI model and through which user can interact it. It provides services to the user. 1.

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Web 2.0 technologies
Most of the technologies used in delivering web 2.0 are rich Web technologies, such as Adobe Flash, Microsoft Silverlight and JavaScript (in addition to Ajax, RSS and Eclipse).  Web 2.0 applications are often based on the decentralized download methodology that made BitTorrent so successful, in which each downloader of content is also a server, sharing the workload and making heavily demanded content more accessible that it would be in the centralized model where demand can lead to overwhelmed servers and pages.
https://whatis.techtarget.com/definition/Web-20-or-Web-2

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4.3. Key underlying Web 2.0 technologies

AJAX stands for asynchronous Javascript and XML, and is one of the key visible building box in popular Web 2.0 technologies. Ajax is a mixture of several technologies that integrate Web page presentation, interactive data exchange between client and server, client side scripts, and asynchronous updates of server response. The Ajax intermediary sits on the client side sending requests to a server and updating the page asynchronously. A key component of the open standards–based AJAX is the Application Programmer Interface called XMLHttpRequest (XHR) that scripting languages use to exchange data between a client and a Web server. The data is often in XML format but can be HTML, text, Javascript arrays, or even a few customized formats. Likewise, the scripting language does not have to be Javascript. XHR is not a protocol extension and was not introduced in any formal manner, rather, it was a feature of Microsoft’s ActiveX extended to other platforms.

The key purpose of Ajax is to let scripts act as HTTP (or HTTPS) clients and send/receive data from Web servers using a variety of common HTTP methods (GET, HEAD, POST, PUT, DELETE, and OPTIONS are supported currently). Thus, Ajax can be used for dynamic layout and reformatting of a Web page, reduce the amount of reloading needed by sending a request for just a small portion, and interact on demand with the server. The responses from the server are handled asynchronously by the browser without having to keep the user’s attention frozen. Numerous popular dynamic Web applications, such as maps, use XHR.

Similarly, Flash objects can offer similar functionality in that once downloaded they can communicate asynchronously with a server. Consequently, YouTube videos can begin playing before the whole movie has been received: the user downloads a compact flash object which downloads a small prefix of the video and begins playing it out while asynchronously fetching the remainder of the video. Supporting Flash requires an appropriate Adobe plug–in to be installed, although user penetration of this plug–in is in the high ninety percentiles. Toolkits exist allowing Internet applications to be written in a high level language and then rendered either as Flash objects or pages with Ajax components, meaning that it may be helpful to sometimes think of Flash and Ajax merely as object code. Ajax apps are typically easier for the researcher to reverse–engineer and understand for measurement purposes than the Shockwave Flash (SWF) format. Currently, Flash is mostly used for rendering rich embedded objects (video, audio, games): few entire applications which store and recall data are implemented in Flash.
https://firstmonday.org/article/view/2125/1972#p4

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How to Make a Social Media App - Build Your Own Social App in 2019

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How to create a social media application: essential features of social network app, MVP and other steps of social media app development, metrics for social media application.