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So I have a home network without internet, and permission to use the neighbours wifi. However, not all devices on the LAN have a wifi card, so I would like to share/proxy the wifi network to the wired LAN.

On Mac there is a feature called "internet sharing" that seems to be made for this purpose. I've successfully used it in the past to do the inverse(share ethernet to ad-hoc wifi).

However, it doesn't work out of the box.

If I connect a computer directly to my Mac, it seems to obtain an IP from the bootp on my Mac. Internet on the connected PC doesn't work though.

On the LAN setup, I'm not even sure how this is supposed to work. I only faintly remember than in Windows XP there is this option called something like "this computer connects to the internet via another computer in this network".

The network contains a mix of Mac, Windows 7 and Linux computers. Any advice how to make this work?

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Unfortunately, "doesn't work" isn't a helpful problem description. Does it get a default gateway? Can it ping its default gateway? Does it get a name server? Does name resolution work? Can it traceroute out by IP? And so on. It helps an awful lot to know the simplest thing that doesn't work and which simple things do work. That really helps to pinpoint the problem. – David Schwartz Dec 13 '12 at 17:58
Like if someone said "I can't take my car to work". Well, can you open the door? When you turn the key, does it click? Or crank? Or start? What happens when you put it in drive? With such a vague problem description, all anyone can tell you is that something is broken. But knowing exactly how far you get, the first thing that doesn't work, and what happens when you try it, we can at least point out the likely problems that would cause that specific step to fail in that specific way. – David Schwartz Dec 13 '12 at 17:59
what works is not having a router in the network. It works for now by using a switch instead of a router. So the remaining question is, can internet sharing coexists with a router? It seems my Mac now plays the role of router. – Pepijn Dec 13 '12 at 18:12
It shouldn't make any difference how the Mac gets its Internet connection, unless perhaps the IP addresses on the two networks conflict. – David Schwartz Dec 13 '12 at 18:28
The problem is that when I use a router, computers get their DHCP from the router. With the switch, they get it from my Mac. So when using a router, I need to tell either the client or the router to use my Mac for connecting to the internet. – Pepijn Dec 13 '12 at 19:18

I'm a little confused as to what exactly is going on, but you did mention sharing on your Mac. Which version of OS X are you using? In 10.8 (Mountain Lion) the Internet Connection Sharing menu is in the "Sharing" preference pane. You can find this in the System Preferences.

The Sharing Preference Pane, with internet connection sharing selected

As you can see, you can select where your Mac gets its connection from - in your case, the Neighbours Wi-Fi - and you can share it to computers through a number of other options. From what I can gather, ethernet is the one you want. Make sure the "Internet Sharing" checkbox is ticked!!

As was said by David Schwartz you will want to disable the DHCP assignment setting in your router, so that the Mac can assign all of the IP addresses.

Hopefully this should be enough to get something going for you.

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