Episode 09      NAT Routers Part 1: Client Firewalls

 

Most NAT Routers are installed so that a single, low-cost Internet connection can be shared between 2 or more personal computers. However, a NAT router can be a great help even if only one computer is in use, because every NAT router functions as a "firewall" gateway, allowing the user of that single computer to request web pages or begin dialogs with other servers all over the Internet, but discarding every incoming request from Internet-based processes that want to begin an unanticipated dialog.

 

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Episode 08     The “Seven-Layer” Vocabulary of Modern Internetworking

In the movies constituting our Ethernet series, and especially in the Internet movie entitled: “Ethernet Delivers the Internet,” we’ve shown how a message can originate anywhere in the world, can be sliced up and formatted inside IP packets, which can then be encapsulated and removed from various types of framing to traverse the entire world and end up at the doorstep of our local network. In a typical home-office or small-office environment, our local DSL modem or cable modem delivers that information to our local router inside an Ethernet frame, on a tiny little subnet managed and owned by our Internet service provider that only knows about one IP address for all of our computers. Other movies published at AskMisterWizard.com explain how our small local router asserts the additional intelligence necessary so that our local network can have more IP addresses and send that packet to one computer within our premises.

Experience has shown, however, that just getting the message to the right computer on our network is not sufficiently precise to allow real and useful work.

 

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Episode 07     Ethernet Delivers the Internet

Most home-office or small-office situations bring the Internet into the local network through an Ethernet connection, leading to a basic router, interfaced with a DSL modem or a cable modem.

In order to understand the way Ethernet brings us the Internet, we have to take a little diversion into the concept of messages within messages.



Let me call your attention to a common, ordinary envelope. The outside of the envelope contains destination address and source address after the usual pattern that has been established for many, many years. In this case, the envelope is addressed to the Smith family, of 140 East Lilac, in Sunol, California. And, of course, the source address is placed in the upper left-hand corner according to well-established conventions.

It turns out that when a postman delivers this envelope to the Smith family according to this postal address, he’s performing a function that’s pretty similar to the way Ethernet delivers frames using Ethernet addresses.

Our example will get a little more interesting as we open up the envelope and see what’s inside. Of course, opening the envelope and looking inside is something that the postman will generally not do. He’s only concerned with the address on the outside of the envelope.

 

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