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Networks, Internets, and the Internet

One computer on its own is a beautiful thing — a technical marvel. But it's good to communicate. Link two or more computers together using network cards and cables (or a wireless setup) and you have a local area network (LAN). All the computers on the network can share data and e-mail as well as access shared resources like printers, modems, or broadband Internet connections. Link two or more LANs together and you have a wide area network (WAN). For example, you might link two offices in different locations with a dedicated leased line.

An internet (note the small "i") is a network of networks. Information from any computer in any given network can travel over the internet to any computer on any other network, with the internet acting as a sort of common carrier. Think of an internet as a highway system linking local road systems together.

The Internet (note the capital "I") is a global internet. All computers on the Internet communicate using standard protocols so that information from any computer on the Internet can reach any other computer on the Internet. Here the trouble comes: Until you connect with a public network, you are reasonably safe from external threats. Hooking up to the public Internet is like publishing your name, address, and phone number and saying, "Hey look, we have computers here."

A Brief History of the Internet

In 1969, the Internet originated as a government run military network, the ARPAnet.  Later, colleges and universities that contracted with the military for research were connected.  Later still it was opened up to computer networking professionals and hobbyists.  These people were all assumed to be “insiders” who understood the rules of the game, and security was not considered to be necessary.  During twenty years that followed other large research and commercial networks were created and tied into the ARPAnet.  By 1994 the ARPAnet was turned over to a consortium of non-profit organizations (InterNIC, and IANA) and public corporations (ATT, UUNet, and Network Solutions) to be run as a commercial network.

The protocols that run and define internet operations all assume that we will play by the rules.  E-mail is sent in the clear, or unencrypted, which means all the information we transmit via e-mail is accessible to anyone with the knowledge and the means to intercept and read it.   Web forms you fill out on the Internet may not be encrypted either.   There are other hazards that exist, simply because when the Internet was created, no one foresaw the size and scope that it would evolve into.  Security was added to the Internet as the need for it arose, some web sites are secure, while others are not.  For the most part, the safe assumption for you to make is nothing is secure, unless you have explicit information to the contrary.

Packets

Information typically travels across networks in packets. A packet is a chunk of data plus an address and other information that tells the network where to deliver that data. Everything going over the Internet is broken down into packets: Web pages, e-mail, downloads, everything. Think of it like taking a circus on the road. You can't take the whole circus in one vehicle. You have to break it up, package it into separate vehicles, tell each vehicle where it's going, and put the circus back together when all the vehicles arrive at their destination. Like vehicles on a road, packets share physical connections and travel in streams. Big data is broken down into a series of packets and reassembled at the destination. As packets travel over the Internet, they are effectively exposed to eavesdropping by the public.

Ports and IP Addresses

Each computer on a network is assigned a unique number called an IP address. The IP address uniquely defines that computer on the network and provides directions for packets to reach their destinations. IP addresses work a lot like a street addresses. Part of the address identifies the network segment of the destination computer and part of the address identifies the actual computer.

While an IP address refers to a computer and the network segment on which that computer exists, the individual applications on that machine must also be identifiable. Think of it like an apartment number attached to the street address; the street address denotes the apartment building, and the apartment number denotes the actual apartment. The IP address denotes the computer, and the port number denotes the program on that computer. Each program on a computer that must send and receive data over the network is assigned a special port number. When packets of information are received at a particular port number, the computer knows which application gets the packet. For example, port 80 is the port for Web servers (which host the Web sites you use your Web browser to explore), and port 25 is the port that is used to send e-mail. Packets are addressed to a specific port at a specific IP address.

Firewalls

A firewall blocks traffic over specified ports. This doesn't mean that you can't access services on other people's computers, just that outsiders can't get into yours. Some firewalls examine the packets that flow in and possibly out of the network to make sure that they are legitimate; they can also filter out suspicious packets. Firewalls hide the identities of computers within your network to make it harder for criminal hackers to target individual machines.

Servers

A server is really just another computer attached to a network but one that is designated to perform some special function, such as share a printer, store files, or deliver Web pages. Remember that if your notebook or desktop computer is connected to the Internet, it is also a kind of server and, without a firewall, is capable of receiving unwanted traffic from the Internet.

(Special Thanks to Microsoft for some of the content on this page) 

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