Sharing a Mac Internet Connection Through Airport

I just solved a networking problem on my Macs after hours of trying. For the benefit of others, I’ll describe here the problem and the solution.

Setup

Cable modem from ISP, network cable to a firewall, the private end of the firewall via network cable on to a switch. Pretty basic, I guess. No wireless base stations or anything. Just an iMac connected via network cable to the switch.

Problem

Share the iMac’s network cable connection through its Airport wireless capability. The client is a MacBook Pro. Basically, I just want to get Internet access on my laptop via the iMac. Sounds simple, but hey, it took me half a day and plenty of research to figure out.

Useful pieces of information gathered during this adventure

  1. Turning on Internet Connection Sharing (ICS) will start a DHCP server.
  2. Turning on ICS will create a full Airport network (not a computer-to-computer network).
  3. Turning on ICS will create a new network configuration for 10.0.2.1, which I understand is the same address as the Airport base stations use.

Solution

  1. On the iMac, set the Airport network to “Use DHCP with manual address” and set the IP to 10.0.2.1. Set the DNS servers to the ones recommended by your ISP. Apply.
  2. On the iMac, go to Sharing|Internet and choose AirPort Options. Enable WEP encryption (I chose 40-bit with a 5 character password). The default network name is your computer name. I added a postfix to the network name (“-ics”) so I can distinguish it from the computer-to-computer network. Apply.
  3. Now start sharing your Built-in Ethernet connection to computers using Airport. As I mentioned previously, this will create the new network and also start a DHCP server.
  4. On the MacBook, set the Airport network to “Use DHCP”. Leave all fields blank.
  5. On the MacBook, connect to the newly created network, which should be named “hostname-ics” if you followed my naming advice earlier. Watch the network configuration. Eventually it shows the IP 10.0.2.2.

That’s it. You should now have access to your other machines on your private network, but also to Internet.

This Post Has 5 Comments

  1. Chris

    Thank You, THANK YOU!!!!!!!!!!!!!!!!! x 10,000,000,000
    Your solution worked first go!!! Apple’s site needs this info I think!!

  2. aman

    am trying to use the Airport to connect to my Ipod. :-S
    doesn’t work!
    IS this configurable only for mac-to-mac?

    your reply is appreciated!
    thanks

  3. andrew

    You can just turn internet sharing in your sharing preferences and create a wireless network that acts like a normal router. You took a long route to get to the same spot. Its built into the OS.

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    I constantly spent my half an hour to read this blog’s posts
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  5. david morris

    Well, there are large number of people who are searching for the same problem they face. The solution you have shared will help them to resolve this issue.

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