How to Bridge Two Ethernet Ports on Mac OS X

Question

How can I bridge two wired ethernet interfaces on Mac OS X (e.g. the current MacPro comes with two ethernet ports)?

Googling turned up (e.g. this Apple forum post and this openvpn post) that this is fairly easy on Linux (using the brctl command) and under Windows (via Network Connections > right-click > Bridge Connections), but how is it done under Mac OS X?

BTW: There also doesn't seem to be a macport for brctl ('port search brctl' didn't turn up any results)

Note: I don't want to have 'internet sharing', which creates a new network (by handing out network addresses in a new range). I want to really 'bridge' two interfaces so to keep the same network subnet.

Answer 1

If you want to build a real Ethernet bridge (Layer 2 bridge) on Mac OS X, answer is, you simply can't without third-party software. That's just the way it is, there is nothing in the kernel or in userspace to do this.

The only software I know capable of doing this is IPNetRouterX, which is not free. Never tried it myself.

Answer 2

This post claims to get it working, using a special script (tap-up-down.sh) he found on a mailing list: http://blog.acmelab.org/2008/07/20/mac-os-x-openvpn-bridge-ssh-tunnel-vpn-goodness/

I'm having the same problem: I set up a bridged OpenVPN on a linux server, and am trying to get on to its network from a OSX client. I haven't tried the link above myself, but I'd be interested if anyone else has tried it.

Answer 3

I found a way that seems to work.

1. Open System Preferences
2. Click on Sharing
3. Click on the lock and type in your password to unlock the preference pane (if this applies)
4. Click on Internet Sharing (the text and not the box)
5. Select "Airport" from the "Share your connection from:" drop-down menu
6. Check the checkbox next to "Ethernet" in the "To computers using:" list
7. Lock the preference pane (if this applies)
8. Plug the ethernet cable into the computer
9. Test out the internet connection

In the Network preference pane, the ethernet should be a yellow circle and should say "Self-assigned IP address", this is normal, and ignore it. I tested it with different sites and it looks like it worked. I'm not sure about BitTorrent programs (though, I'm pretty sure there it would work if a web browser works). I don't know about the port forwarding, maybe someone else can figure that part out.

Answer 4

As far as I can read, you are looking for the link aggregation. Go to System Preferences -> Network -> then select the small cog in the bottom left side (next to the + and -) and choose Manage Virtual Interfaces -> select the + in the bottom left and choose New link aggregate. Then you select the two wired interfaces and call it whatever you like. After that it will appear in the network list as one network interface.

Answer 5

a bit late, but this feature is called "bond" in OS X: see

networksetup -h | grep -i bond
networksetup -isBondSupported <hardwareport>
networksetup -createBond <bondname> <hardwareport1> <hardwareport2> <...>
networksetup -deleteBond <bonddevicename>
networksetup -addDeviceToBond <hardwareport> <bonddevicename>
networksetup -removeDeviceFromBond <hardwareport> <bonddevicename>
networksetup -listBonds
networksetup -showBondStatus <bonddevicename>

Answer 6

I concur with James W.

My situation is that my ISP provides me a WiFi/wired router. The router is upstairs, near my wife's workstation. My work area is two floors below - no option to pull Cat5/6 cables from the router to my workstation. I have a Mac mini OS X 10.5 (which has a built-in WiFi adapter and a built-in wired ethernet adpater and a two PCs in my work area, both with built-in wired ethernet, but no WiFi adapters. I also have a mini-switch for wired ethernet.

My only solution (without buying more hardware -- which goes against my cheap-a__ bastard grain) for connecting my work area to the internet is to use the WiFi connection that my Mac gives me. The question then becomes: what option should I choose for extending that connection to the pair of PCs?

The obvious answer is to use Mac's nice little Internet Connection Sharing (ICS) function. However, I run a bit torrent client on one of my PCs, which I wish to make available to the internet via port-forwarding through my ISP router -- it's how you "pay back" for the benefit that I'm reaping, right, citizens? This means that simple ICS won't do the trick, since I would then need to port-forward through my Mac as well (which, incidentally, I have a difficult time learning how to do, even when consulting Google to tap y'all's smart brians).

An elegant solution would be to bridge the connection through the Mac, right? So that my PC is on the same network as the ISP router (whose port-forwarding functions are built-in and easily managed).

How to do it? As James W says, is it true that there' a sole solution (which costs $100)? Say it ain't so, Joe!