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I am trying to setup a Mac as a wireless access point to an existing network. Internet is shared from the Ethernet connection to AirPort, and AirPort is all setup. I can connect to it with a wireless device. However, when I try to access something on the Ethernet side of the network, I cannot access it. I note that the Mac is assigning my wireless device an IP address in the private range.

Small diagram:

Wireless device ---- Mac ----- Other computers on network

However, it works like this:

Wireless device ---- Mac ----|---- Other computers

I simply cannot see them.

The Mac can see the other computers.

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Someone will have to verify this, but I don't think the mac-as-a-wireless router function will also work with an intranet. The mac can see the local network but is not passing that info along. –  JNK Sep 14 '10 at 17:42
    
@JNK I can refute that. Mac-as-a-wireless-router is just like a Wi-Fi capable home gateway running NAT and DHCP. It definitely lets you get to anything on the upstream network, although most service discovery protocols will break because that kind of multicast doesn't go through NAT. –  Spiff Sep 14 '10 at 22:34
    
@Spiff - Then I'm glad you weighed in :) –  JNK Sep 14 '10 at 23:39
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1 Answer

up vote 3 down vote accepted

When Internet Sharing is on, your Mac is acting as a NAT gateway, not an Ethernet bridge, so it'll block most service discovery and local name resolution protocols such as Bonjour, which use non-routable multicasts (and some old-school bad ones like NetBIOS that use broadcasts). So if you're trying to browse for services on the far side of your Internet Sharing Mac, or if the app you're running automatically uses Bonjour to find other things to connect to, it'll fail.

From the wireless devices, can you ping devices on the far side of the Internet Sharing Mac using IP address?

Another thing to check: I believe Internet Sharing hard-codes its NAT private address range to 10.0.2.x/24. Make sure the network on the far side of your Internet Sharing machine is not using that same subnet, otherwise your Internet Sharing Mac's route table will likely get confused (to put it mildly).

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I can ping it, but I cannot access server shares via computer name or IP address. Also, I cannot connect to the wireless device from the Ethernet network either. The network on the far side is not using the same subnet either, it is a domain with a non-private ip address range. (the Mac is connected to the domain too) The files and such are on a Windows server, but one of the wireless devices is a Windows computer. –  eagle0042 Sep 14 '10 at 22:48
    
I don't have any experience with how well or how poorly Windows domain authentication and directory binding and file sharing go through any NATs. It would be interesting to fire up an HTTP server on one of those machines, with a simple front page that doesn't require authentication, and see if your wireless clients can connect to that. That might be an indication that NAT is working, but that Microsoft's suite of proprietary networking protocols aren't going through NAT very well. –  Spiff Sep 15 '10 at 14:40
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