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Comment from E-mail:
I have 2 iMac's and would like to have a cable Internet access installed in my home. I would like both iMac's to be able to use the Internet connection; I currently have no network. How can I network both Mac's and have the cable Internet access installed as well?
Your situation is quite common.

First, I'd like to discuss the internet addressing scheme. There are a fixed number of permanent worldwide IP (Internet Protocol) addresses at present. They look like, composed of 4 numbers, each of which can be between 0 and 255. You will notice that these numbers are like phone numbers. Oddly enough, they work similarly to phone numbers.

Groups of these addresses have been allocated to companies and to countries of the world and to schools. But institutions commonly secure many more addresses than they actually need. This inefficiency makes the numbers in short supply. But every server of the world has to have an IP Address (internet phone number) of it's own in order to be reached by other computers.

You don't type in addresses like to your browser, although you could. Instead you type in domain names like www.woz.org. There is a system of invisible internet phone book computers that lookup the domain name (www.woz.org) and find the IP address ( for your computer. As a user you never see this.

If you have a server with it's own IP Address, you also need to specify other geeky information that is supplied by your network administrator. The server needs not only it's IP address, but also the IP address of a friendly 'internet phone book' computer, called a DNS (Domain Name Server). Both of these addresses come from your network administrator, as only proper entries will work. The server also needs something called a subnet mask, like, which is based on how large a block of IP addresses are available on your network. This number also must come from your network administrator.

A school might not want to hassle with all these geeky numbers on each computer. A few methods exist to make this simpler. The most common method is called DHCP (Dynamic Host Control Protocol). Any computer can request it's internet address information automatically by DHCP. That computer doesn't need to enter even a single geeky number (in most cases). This is a very popular method. Every computer in the school (except web servers, which need known, fixable, IP Addresses of their own in order to be reachable by users) can be set up identically, to get all their internet setup data via DHCP. The key to this DHCP process is that one special computer program or internet router (switching equipment) has to handle the DHCP allocation. It must be set up by the network administrator.

Another problem arises if a school has more computers than the size of it's IP Address block. There aren't enough addresses to go around simultaneously, even if they are assigned automatically via DHCP. In this case, the NAT (Network Address Translation) protocol is commonly used. It assigns 'phony' IP Addresses (from a few special blocks) that can't be routed to the internet but can be used internally. NAT is used in conjunction with the DHCP protocol. There is virtually no limit on the number of these that can be used, internally to your school or company. The computer program or router that handles the DHCP with NAT allocates these special phony addresses to any computer that requests IP Addresses via DHCP. This program or router translates each phony address into a real IP Address that can be routed and used on the internet. This way, a single IP Address can be shared among any number of computers. The NAT device keeps track of which computer each block of data really belongs to, and changes addresses of data passing through it in both directions.

You might be able to figure out that with DHCP (with or without NAT) you can't be sure of what IP Address your computer will have at any particular time. This prevents you from using it as a web server.

When you get a cable modem, you might get one or more real IP Addresses along with it. The network administrator of the cable company could tell you if it's not clear. Let's assume that you get only a single IP Address. You might be told by the cable company (network administrator) what your IP Address is. In that case you could use it for a single computer, even a web server, but then you couldn't use this address for anything else. So if you want your own server, which cable companies tend to frown on, you should try to get at least 2 IP Addresses. You can frequently buy additional ones for a monthly fee. Use one for your server and the other for the rest of your computers. Actually, in your case, two IP Addresses might be all you need ever, one for each iMac.

First, your cable modem will have an ethernet RJ-45 connector. You can buy a very inexpensive ethernet hub (10BaseT). This hub will have ethernet ports to run standard ethernet wires to your various computers and to the cable modem. If you had iMacDV computers you could use Apple's wireless AirPort instead of ethernet wires, but your iMacs won't work this way.

Let's assume that you have one real IP Address. You can set up one iMac to use this address, along with the other internet setup data as supplied by your cable company. That 'root' iMac can run a router program like IPNetRouter and supply DHCP and NAT to the other iMacs and any other computers. Each of them has to be configured to work with DHCP. This program does cost you money.

If you want to skip using a program on an iMac, 24 hours a day, for this important function, you can instead buy some inexpensive routers for around $300 that can do the DHCP and NAT tasks that you need and other things too. You can even buy the Apple AirPort Base Station which serves DHCP and NAT, even though you don't use the RF network part of the Base Station. In that case any friends that bring over laptops (Macs or PC's) set up for RF will be able to work on your RF network as well as your ethernet network. Future computers of your own could be set up to use this RF network too. To set up a router or Base Station you'll probably need a network guy on hand.

Comment from E-mail:
I wonder if you could give my 5th graders some words of encouragement. I teach several new immigrants to our country in my fifth grade class who especially love using the computers. One student, Eddie is actually teaching himself programing. Knowing that you have Ukranian roots I was wondering what you would tell them to do to get jobs later in the computer field. In addition, I was wondering if you ever are able to donate Macs to schools. We could really use a computer to make multimedia projects, but being an inner city school we don't get too many luxuries. Thank you for reading this. Just a reply would thrill my students to no end.
School is the most important thing that you will attend or belong to in your life, just as your brain is the most important and valuable thing that you have.

Look at all the problems in the world, in our country, in your own city, and even in your school. We adults have worked to make things work and to get along, but we have done far from a perfect job. You can learn in school a lot about the things we have done and our many mistakes and conflicts. From that, you can figure out better ways to do things in the future. You can also see products that we produce to make life nice, and you can learn the things that will enable you to make these things better, and to make new things as well. You may even find ways to solve problems without resulting in violence or wars.

So you are the ones that will make a better world than we, the older generation, have left you. That is the importance of school.

Don't forget that the world is very interesting and beautiful and fun. The best times of your life will be in your school years, with all your great friends. Don't make a mistake and do anything that would shorten this fun time of your life.

When other things seem like more fun, and lure you from studying, it's time to wake yourself up and avoid a big mistake of giving up on school.

I don't have to tell you how much easier life will probably be for you if you do well in school. You've heard that many times by now. You will all find some things in school that are very interesting to you and that you are drawn to. Those things will be very important in your life. If you work very hard on any particular thing, and try to be the best at it in the world, you will likely find that it leads to great success for you. If you do well in school you can become very successful at an early age and you will never regret it.


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