Episode 10 Segment 1

NAT Routers Part 2: Connecting 2 or more PCs to the Internet through a single Internet Address

( Internet Connection Sharing )


During the 1990s, as millions of small businesses and families all over the world discovered the Internet, demand for Internet Addresses surpassed the expectations of even the most enthusiastic Internet proponents of previous decades. Unfortunately, - "real" - Internet Addresses are a limited commodity, and back in the early days of the Internet, before it became clear that they would one day be of immense value, huge blocks of these Addresses were irretrievably allocated to a few influential universities, corporations, and government institutions. Billions more IP addresses were lost to inefficient allocation schemes as Internet architects tried to allocate address blocks in patterns that could help them clarify the logical locations of (and boundaries between) separate networks.

Back in the early days, people requesting Internet access got to choose between a "Class A" arrangement (with 16,000,000 Internet Addresses), a "Class B" arrangement (with 65,000 addresses), or a "Class C" arrangement (with 256 Internet Addresses).

Those days are gone forever. As the last blocks of Internet Addresses have been gobbled up, even "Class C" network access is now too expensive for small businesses, and the price is unthinkable for all but the wealthiest of families.

If you've already seen the AskMisterWizard.com movie entitled "Class C Commercial-Grade Internet Services", then you know that even this smallest of traditional arrangements can provide addressing for as many as 33 million communicating processes simultaneously running on as many as 253 different computers. That's a LOT of networking power!

A few years ago, as the first - "Internet Service Providers" ( ISPs ) opened their virtual doors for business, they all purchased blocks of address space and made plans to sell addresses, one by one, to families and individuals all over the world. By purchasing tens of thousands of IP addresses in a single block and then leasing single addresses, month-by-month, to individual homes and small businesses, they expected to be able to generate handsome profits. In fact, they even concocted schemes to lease access to more addresses than they actually owned, by gambling that most of their customers would switch their computers off when not in use. By keeping careful track of computers that were not active from moment to moment, and dynamically allocating addresses from a carefully managed "pool", they knew they might meet the likely demands of 20,000 homes with only 10,000 addresses. This practice has come to be known as "dynamic IP addressing, and it's the cause of some extra complexity and related challenges for small businesses and families using the Internet. (The opposite of - "dynamic IP addressing" - is - "static IP addressing". You can learn more about static and dynamic IP addressing from other movies here at AskMisterWizard.com).

The customers of these ISPs ended up with just a single Internet address, with the implicit expectation that they would connect just one computer. As you will soon see, however, that single Internet address has hidden power to support all of the computers that an individual household might ever want: as many as 253 of them!

Episode 10 Segment 2


This movie builds on the concepts discussed in two other movies that are available from AskMisterWizard.com. They are:

"Simple Routers for Small Networks Part 1: Client Firewalls", (explaining operation of a "NAT" router to protect a single PC),


"Class C Commercial-Grade Internet Services" (explaining extension of IP addressing beyond individual computers to communicate with as many as 130,000 separate processes per computer).

If these concepts are unfamiliar to you, then you should watch those two movies before proceeding.

You may also find it useful to review our movie entitled "Ethernet Delivers the Internet" to become comfortable with the way your ISP encapsulates IP protocol packets inside Ethernet frames for compatibility with your network equipment.

All of these movies introduce the subject of - "routers", with particular attention to the subject of - "network address translation", or - NAT.

Episode 10 Segment 3
In - this - movie, we will now examine the way Network Address Translation permits connection of additional computers, all sharing the single, low-cost Internet Address made available by your Internet Service Provider. The - "good news" - is that routers supporting NAT are available at very low cost, and they help you beat those Internet Service Providers at their own game! Low-cost NAT routers can easily arrange simultaneous Internet access for three or four separate computers, and we'll show you how you can even expand beyond that: (the theoretical limit permits as many as 253 separate computers, running as many as 130,000 simultaneous, communicating processes)!

Episode 10 Segment 4


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After you install a NAT router as described in the other movies that we've just mentioned, you will probably notice that several Ethernet connections are provided. (Most low-cost NAT routers provide 5 or more RJ45 jacks for ethernet connections. One of these will be labeled - ISP - or - "Wide AreaNetwork" (WAN). That one must be connected to your DSL or cable - "modem". The others expand your Local Area Network (LAN) for your use through a built-in ethernet hub or switch. If your router provides only two RJ45 jacks for ethernet connections, you will have to provide your own hub or switch for expansion).

You can immediately connect your additional computers into these extra ethernet connectors. If you run out of connectors, you can insert additional ethernet hubs or switches as described in other AskMisterWizard.com movies from our - "Ethernet" - series.

Episode 10 Segment 5


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As you connect ethernet - "patch" - cables between your additional computers and the ethernet connectors of your router, you should see the associated - "link lights" - illuminate, one by one, indicating proper ethernet connection. If any link light fails to activate as expected, you may need to tinker a bit with the connectors or cable, swapping with a - "crossover" - cable or activating - "crossover" - switches if necessary.

Once each link light is illuminated, you will be able to use any communicating applications that rely only on ethernet protocols.

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