With a little bit of work, anyone can set up connection sharing and use their Mac’s Internet access as a gateway for their entire network. The steps outlined here apply to just about any kind of Internet connection whether it is DSL, Cable, Wireless, or dial-up. For the most part, the only connection with enough bandwidth to share is broadband. For that reason, we will look most specifically at DSL and Cable Internet access.

Broadband may be the way of the future, but for many, there are still too many limitations. Many DSL and Cable Modem providers supply broadband connections to customers but only provide a modem for the customer to use when connecting to the Internet. If they were to provide a router, customers would enjoy greater flexibility.

What’s wrong with a DSL/Cable modem?
Typically, modem access is intended for one computer at a time. The only difference between a dial-up modem and a broadband modem is the speed that it carries data. In either case, the modem is attached to one computer to allow that computer Internet access. There is no easy way attach multiple computers to that single modem.

This is great for broadband providers. They can easily guarantee you high speed access and an always on connection without much fear that you will be sucking down an excessive amount of data.

If you want to allow more than one computer to access the Internet at one time, your service provider will often require you to pay more, and will sell you an expensive router as part of the deal.

What’s so great about a router?
If you have several computers in your home, odds are you already have them networked. They may be connected through Ethernet cables, or wireless through one of the 802.11 solutions currently available.

When you add a router to your network, you simply take your existing Ethernet hub/switch or wireless access point and connect it to the router. The router becomes your networks gateway to the Internet. All data sent or received from the Internet now passes through the router and is sent to the appropriate host on your local area network. The router is simply the standalone device that connects your LAN to the Internet and routes the information to the correct locations.

Connection Sharing:
Many service providers only allow broadband access via modem. This simplifies administration on their end but seriously limits options available to customers who have more than one computer. Other service providers will allow you to connect multiple machines to the Internet, but typically charge accordingly.

Even with a single user modem, there are still options available. If you connect your Cable Modem to your Mac, you can turn that Mac into a software router that will share its connection with the rest of your LAN.

Connection Sharing has been around for a long time. In the past, it was possible to share a dial-up account with an entire network of computers. This was rarely ever done since there was simply not enough bandwidth for one user, let alone several.

With the release of OS X 10.2, Apple gave us access to some very powerful connection sharing tools that are built into the operating system. The steps below assume that your broadband modem connects to your computer via USB. If it in fact plugs into your Ethernet port, you will need to add a second Ethernet card to your Mac. That configuration is seriously more complicated and beyond the scope of this article. Our goal is to take a single user Internet connection such as DSL, Cable, Wireless Broadband, or Satellite Broadband and make it available to users on a local network.

You should be able to use any OS X 10.2 capable system to share your connection. The overhead on the system doing the sharing is minimal. When you decide which system will do the sharing, keep one very important point in mind. For the rest of the network to access the Internet at any given time, the Mac router must be turned on. If it is not, no routing will take place and, as a result, there will be no link to the Internet.

It is essential to get the Mac router tested and accessing the Internet by itself before continuing. There are many different types of broadband available today. Use your service provider’s documentation to configure your system per their specifications. There is no point in continuing until this Mac can access the Internet properly.

Step 2:
Once your Mac router can access the Internet, it’s time to make it start routing. Open the Sharing Preference Pane and click on the Internet tab. You will have an option called “Share the connection with other computers on Built-in Ethernet.” Once you check this box, you will see a warning like the one shown below.

Apple added this warning for good reason. The options we are activating are very powerful. Sharing your Internet connection with more than one computer could be in violation of the policies of your service provider. Neither Apple, nor I, will take responsibility for this system modification if your provider finds you in violation of their policies. That being said, lets continue!

Click OK on the message and hit the start button.

This simple check box is remarkably powerful. It activates some very powerful services that are built into OS X that are typically not used my most people. By checking that box, you have activated an industrial strength DHCP server that Apple has built into the core of the OS. The purpose of DHCP is to provide network addresses to other computers on the network that do not already have them. These computers use those network addresses to access the Internet.

You have also activated a NAT (Network Address Translation server). Its purpose is to take the IP address that your modem has been assigned by your provider and make it the gateway for an entirely new class of virtual IP address that the OS implements without you having to specify and configure.

Step 3:
The good news is that your Mac is already sharing its Internet connection with the rest of the computers on your LAN. Feel free to hop on one of your other Macs and see if you can access the Internet. If you can, great! Your work here is done, but odds are you will still not have access on your other computers. That is because, in many cases, the rest of the systems on your LAN will need to be configured to look for the network addresses that your Mac Router is distributing.

OS 9:
Make sure your computer is connected to your LAN via Ethernet. Then open the TCP/IP control panel. Set the Connect Via menu to Ethernet. Next set the Configure menu to “Using DHCP Server.” You can leave the rest of the fields blank in most cases. Just close the window and save the configuration when prompted.

OS X:
Open the Network Preference Pane. Select the TCP/IP tab and set the Configure menu to Using DHCP. The rest of the fields are usually best left blank. Click Apply Now. You should see an IP Address appear on screen with the words Provided by DHCP Server beneath it in parenthesis. This confirms that your Mac Router has provided the system network address. Try and load a web page in your browser. If your Mac Router is turned on, your client system should have Internet access.

Conclusion:
The steps behind this configuration are quite basic. Setting a similar connection share on a Windows system can be considerably more complicated and is extremely convoluted. This procedure may be difficult for a first time user who has no experience with networking, but for the mid-range and power-users, this information should get you up and running quickly.

The steps outlined here may be beyond the scope of beginner users. Experience with networking is not essential, but is extremely helpful. Apple has hidden away most of the technical side that trips up even the advanced users. We have been saved the trouble of configuring DHCP services and configuring the system for NAT, which on a UNIX based system can be very confusing. After all, that is why most of us chose the Mac in the first place.