Comments on: How do I make my Mac Mini do bridging over wireless instead of NAT?

Question: How do I make my Mac Mini do bridging over wireless instead of NAT?

procrastination — Thu, 02 Oct 2008 15:26:27 -0800

How do I use my Mac Mini to share its ethernet network connection over the wireless connection, but in a way that NAT is not used? In other words, how do I make my Mac Mini do bridging over the wireless connection?

Here is my network setup:

Cable Modem -> Router (IP 192.168.0.1)

Router connects to two desktop Macs:

Router -> Upstairs Mac (192.168.0.6)
Router -> Downstairs Mac (192.168.0.50)

I want to use the downstairs mac as a wireless access point. I have done this using Internet Sharing, which works fine *except* that devices on the wireless get a 10.0.0.* address. Computers on the 10.0.0.* net, like my laptop and iPhone, and cannot see the shared services of the upstairs mac, such as iTunes and iChat over Bonjour.

The problem seems to be that the mac with the wireless connection automatically uses NAT, and I can't figure out how to make it just do bridging. I would like for devices that connect to the wireless to get a 192.168.0.* address, and be able to route across the mac mini to get IP addresses from the router by DHCP.

Can anyone tell me how to do that? I am perfectly comfortable with the command line, but am just not sure how to configure it.

By: mmascolino

mmascolino — Thu, 02 Oct 2008 19:56:36 -0800

I'll preface this as saying I don't have a Mac to try this on but if there is an option to disable the DHCP server on the Downstair's Mac then it should pass along a client's DHCP's address to the next device in the chain which would be your cable modem's router

By: Blazecock Pileon

Blazecock Pileon — Thu, 02 Oct 2008 22:06:13 -0800

Unfortunately my answer to your question was deleted, but I sent you a MeMail with one solution to bridging the Internet Sharing service.

By: TravellingDen

TravellingDen — Thu, 02 Oct 2008 22:06:22 -0800

Bridging is a no-go for a couple of reasons.
1) OSX does not include BSD bridging drivers for some reason.
2) Bridging wifi to ethernet is not as straightforward as it should be - most card drivers for PCs don't support it (you have to be able to spoof source addresses.)

Another way to put it is that wheras ethernet is ethernet... an access point is subtly different than a client.

That said - I hate saying "can't".. there's probably some obscure way to do this, and I will eventually figure it out.

Other ideas I've tossed around:

1) Use the mac as a router, and perhaps DHCP relay - and that's only if your DHCP server supports multiple subnets. Run a separate subnet behind the mac.

2) Rig up some kind of subnet + proxy-arp solution behind the mac.. not sure how the mac will accept overlapping network blocks though.

Bonjour works over link-local multicast addresses, not broadcast - you can probably rig that up somehow to span a few hops.