Connection via Cable Modem

An exciting new trend is the delivery of Internet Services via your Cable TV supplier! They install a two-way coax splitter in your TV cable, and add a "cable modem." This delightful box has huge cooling fins and an ethernet connector. The cable company builds a subnet containing a bunch of these, and gives you a single IP Address from that subnet. It's truly wonderful.

"Wait! I have three computers!"

Networking hardware and software are so cheap today, that it isn't unusual to find a home or small business with an extensive LAN already. With a NAT between your small LAN and the cable modem, all of your computers share the single IP Address that the cable company loaned you.

Here we see three workstations and a local server sharing the cable Internet connection, using a single external IP Address!

The ethernet connection from the cable modem connects to the public ethernet on the PC running the NAT code. The private ethernet of the NAT is on your private LAN. Your devices use the NAT as their default gateway. The NAT talks through the cable modem to the cable company's router.

Customer Case Study

Cox Communications is the major cable TV supplier in Phoenix, Arizona. They are rolling out Internet services in beta test, and offered this to a major local proponent of the Internet. They knew that he would have a PC, but didn't expect his lab to look more like something at NASA. Instead of connecting a single PC to this new Internet hookup, he wanted to connect his whole net, but Cox had no provision for that. So, he uses one of our NATs. It looks like the single PC to Cox, but allows any of his machines to reach out into the bigger world.

As an interesting note in this Case Study, the customer needed a demand dial PPP connection to a local client of his, for special access to their private network. His NAT now has a modem in addition to the two ethernet adaptors. He has static routes to his client via the PPP facility, and a default route to the rest of the Internet via the cable modem. The PPP connection comes up by itself whenever he needs to access his client. All messages on the PPP connection use an IP Address from the dial-up client, while messages via Cox use a Cox IP Address.

This page was last modified on June 28, 1996.

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