Mac OS X: Sharing a Shared Connection
How I shared my G5’s Internet access, which in turn is shared from my iMac server over FireWire, to a Windows computer.
Posted on 2004-09-05 00:46 by Jørn Støylen [permalink]
My girlfriend just moved in with me. She has a PC with Windows XP Home Edition, and needs Internet access. However, my options are fairly limited because of my rather special network setup at home. I’m writing this article in case anyone else runs into the same problems I did, in the hope that it might help them (you?) out.
See, I started out with one computer, an iMac DV SE. This served me faithfully for about three years. When OS X came out, I didn’t hesitate to install it. I even set it up as a server, and registered at no-ip.com to get domain names.
Then I got a dual processor G5, and decided that I wanted to use the iMac as a firewall also. The trouble was, the iMac has only one Ethernet plug. But then I read about IP over FireWire at Oreilly’s MacDevCenter, which turned out to be a godsend, although I initially had some trouble getting it to work. (It was in beta, and only available as a download from Apple’s Developer site.) When Panther was released, IP over FireWire was built in.
Tinkering with all the innards of OS X through the Terminal was a bit of a pain, especially with the firewall, so I finally got Mac OS X Server, and everything got so much easier.
Since the iMac’s Ethernet port is already in use to connect to the router, the best option I have for connecting the Windows box would be to share the G5’s Internet access through its Ethernet port, since that port is not in use.
Setting this up on the G5 was easy enough. It requires setting up the Ethernet as a network port in the Network System Preferences pane, and then setting up this port as a shared Internet connection in the Sharing preferences pane. Just make sure the port where the G5 gets its Internet access is on top; if it’s not, reorder the ports by drag-and-drop:
I set it up using DHCP with manual address, the same thing I’d done with the FireWire connection on the iMac. IP addresses in the 192.168.0.0 range are reserved for private internets (see RFC 1918). The iMac used the IP address 192.168.2.1, the G5 end of the FW connection used 2.2, so the Ethernet on the G5 got 2.3, and then I tried getting the Windows box to use DHCP. It got an IP address, but that was all. No Internet access, and pinging the other addresses didn’t work; the requests timed out.
Ciaran offered to help me figure it out, something which I gladly accepted since I’m not very proficient in the ways of TCP/IP, and even less proficient with Windows. (Windows computers and I have a kind of mutual allergy toward eachother. I can’t stand working on Windows boxes, and whenever I try to fix one, I invariably make it worse.)
I won’t go into detail about our troubleshooting process, but I’ll provide you with the solution: It was a case of subnet confusion on the G5. When traffic to and from the Windows box went through the G5, the G5 got confused as to where it should go next, since both its connections was on the same subnet. Simply changing the IP address of the shared Ethernet port on the G5 to 192.168.3.1 and using 3.2 for the Windows box (setting it up manually) made it all work as it should.
And here’s the complete home network setup, complete with iMac, G5 and Windows PC, living happily together!
The only downside to this setup is that the G5 must be running for the Windows box to have Internet access. I should investigate the possibility of using a hub instead. This will be a project for the future.
I’m even able to access the Windows box by hitting Cmd-K (or selecting Go -> Connect to Server�) in Finder, entering smb://192.168.3.2 and providing my girlfriend’s user name. After the initial confusion and trouble, and with the aid of a kind online friend, it looks like it’s going to be a peaceful coexistence.
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