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bridge ethernet to airport in Imac

Discussion in 'Mac OS X Server, Xserve, and Networking' started by oracleofmist, Jun 6, 2008.

  1. macrumors newbie

    hello all,

    I currently am using an Imac with 10.4. I would like to be able to have a laptop connect wirelessly to my Imac and use the internet that the Imac receives via ethernet. Is there any way to bridge the two and if so how? thank you.
  2. macrumors G5


  3. macrumors newbie

    Very simple. So simple you're wrong as well as arrogant.
    Apple's Internet Sharing is NOT bridging (it uses SNAT).
    For the record MacOSX can't bridge. So if you're reading this after Googling for ethernet bridging on the Mac - stop - you can't.
    As a side note I'd like to know how VMWare Fusion does implement this as it would be a good place to start on an open source bridging kernel module.

    Before you say "but it does the same thing" - stop - it doesn't. There are several protocols which will not work either because of the NAT taking place or because they rely on broadcast or multicast on the local subnet. For example, TimeMachine will not be able to locate your Time Capsule (if you have one) over a shared connection because the rendezvous protocol (or at least to the extent which it is used in locating your Time Capsule) will not escape the local subnet. This can be worked around but as the average Mac user rightly expects stuff to "just work" this will be rather confusing for them.

    Ironically, Airport base stations do bridge ethernet (really bridge as in IEEE 802.1D) so why this is missing from Mac OS X as shipped on desktops, laptops and even Mac OS X Server beats me.

    If you didn't understand the above or if you're just interested in knowing more about this I just Googled up an interesting project trying to add this functionality to Mac OS X: http://www.glassechidna.com.au/2009/projects/mac-os-x/xbridge/xbridge-network-bridging-in-os-x/ although their conclusions on why they couldn't implement a "true" bridge are a bit off the mark - their explanation does not consider Proxy ARP as a means of working around switch limitations. This Linux forum post also contains a good general explanation of ethernet bridging for anyone wanting to better understand this and why Internet Sharing is NOT bridging: http://forums.gentoo.org/viewtopic.php?t=118180&highlight=bridge
  4. macrumors newbie

    WOW that was a bit harsh...
    You can however buy a ethernet bridge and connect to your router.

    Why do people have to get so excited? Relax people. A lot of people come on these forums for help, not to be ridiculed.
  5. macrumors 65816


    I have a 4 port Ethernet router at home with 3 computers and a laser printer connected. Would it be possible to connect an Airport Extreme to my current router to use both routers?
  6. macrumors 6502a


    You would definitely know about arrogance.

    Just because someone asks for bridging doesn't mean they need bridging. For what the OP was asking for, Internet Sharing should be adequate.

    There is no need to show everyone how large your Internet p*nis is. I'm a UNIX gray beard, and would be happy to show everyone how large I am and how many years before they were even born that I've been working on computers. However, I take the opportunities to help people with their questions because that's a lot more helpful.
  7. macrumors 6502a


    The short answer is "yes".

    From your Ethernet router, you can connect any of these:
    • Another Ethernet router (preferably in bridging mode)
    • An Ethernet hub or switch
    • A wireless access point
    • A wireless router (preferably in bridging mode)
    • An Airport Extreme (preferably in bridging mode)

    What is your ideal configuration? Please describe it in detail and we'll see if we can help you.
  8. macrumors 65816


    Thanks for the offer to help. My router is a D-Link 4 port Ethernet only. I have a Windows XP desktop, a Mac Leopard desktop, a Mac Snow Leopard desktop and a laser printer connected to it using all 4 ports. Once in awhile, I connect a Windows laptop, so I have to unplug an Ethernet cable to hook up the laptop. The laptop can do wireless, but I do not have a wireless network.

    Knowing that Apple products work well with not a lot of tweaking, I figured an Airport Extreme would work for me if it works as I hope. My thoughts are to run an Ethernet cable from the D-Link router to the Airport Extreme. I would lose a port on the D-Link, but I would gain 3 Ethernet ports on the Extreme and gain wireless capabilities for my laptop and maybe an Apple TV. If everything works that way, I would have 6 Ethernet ports and a wireless hub. I do not want my desktop computers connected wirelessly.

    I am not sure what you mean referring to "bridging".
  9. macrumors 6502a

    As others have said, though tenable, the solution is undesirable due to lack of true bridging. Hell, you can't even share said SNAT via WPA or WPA2-- you're stuck with WEP.

    A router would be a better choice.
  10. macrumors regular

    It is quite possible that Internet sharing would be adequate for the OP, but on reading the thread, I think that DaveWhitla was correct, although maybe he should have missed the "as well as arrogant" from his first sentence...
  11. macrumors regular

    Apart from being delivered over ethernet, what type of Internet connection is it ?

    If you have a single public IP address, then bridging is not suitable as you would need two public addresses and Internet Sharing would be your simplest method.

    If you have a router with a single ethernet port, then purchasing a wireless access point (or router, but not using the "WAN" port) with multiple LAN ports would be a better way of allowing multiple computers to access your existing router.

    You could also use the same hardware if you have multiple public IP addresses, however I would always suggest that at least a filtering bridge firewall is used, and unless you have IPv6 connectivity, NAT does make some things easier, although it can be a pain for some protocols...
  12. macrumors 65816


    My 4 port Ethernet router does not have wireless, so I am wondering if I can plug an Ethernet cable from the router to an Airport Express or Extreme to get wireless. I know that the computers plugged into the router will not be able to talk to a computer on the Airport, but that is OK.
  13. macrumors regular

    If you connect your 4 port router to the LAN side of your access point, not the WAN side....
  14. macrumors 65816


    Correct me if I am wrong.

    The Express only has a WAN so it would not function with my Ethernet only router.

    The Extreme can be plugged in to my Ethernet only router through the LAN port and the computers connected to the Ethernet only router and the computers plugged in to the Ethernet ports of the Extreme can talk to each other.
    What about my laptop and iPhone 4? Can they communicate with computers connected to each of these two routers?
  15. macrumors regular

    yes, the express would not be suitable, but the extreme would be.

    by connecting to the LAN port, any devices that connect to the WLAN will be on the same subnet as the LAN
  16. macrumors newbie

    Yes Aaron, having been around for a very long time I recognise it instantly. I'm fed up with a$$h0les who ridicule people like the OP for asking what they think is a stupid question. There is no such thing as a stupid question - by definition. I read "search first next time" and saw red - as frankly the individual I referred to as arrogant fits the definition perfectly and did the OP and wider Internet a disservice by belittling the OP and talking complete crap. People can attempt to speak for the OP all they like - it doesn't change that he asked for "bridging" and "bridging" in ethernet land has a very clear definition to which SNAT does not even remotely relate.

    Rather than post some inaccurate and valueless quip I provided a complete explanation with links to relevant further reading. Something Consultant should have tried.

  17. macrumors newbie

    Hi All:

    I joined simply to find a solution to this because it does not seem to have been answered...

    I'm looking to create what I believe is an "ethernet bridge" by using my new sparkly imac core i7 and a dusty old Airport Extreme that I've had lying around for 4 years. I want to do this because my computer is in my bedroom and my x-box is in the living room and I don't want to run 100' of ehternet cable to play online. My hope is that I can put the airport extreme in the living room, have it receive the wireless signal from the imac, and plug an ethernet cable between the xbox and airport extreme to play online.

    If this is possible can someone please post detailed instructions or links to the same?

    Thank you for ANY help!

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