How to use 2nd Ethernet port in "bridge" mode

Discussion in 'Mac Pro' started by Killerbob, Jul 26, 2014.

  1. Killerbob macrumors 6502a

    Jan 25, 2008
    I have been trying to use my Thunderbolt Display Ethernet port as an extension to my network, which my nMP is connecting to. The TBD is connected to my nMP, and I thought I could use the Ethernet port for my laptops etc., connecting to the network. As it turns out I can't. I can setup Internet Sharing, creating an Internet "bridge" between Ethernet 1 (on the nMP), and the Display Ethernet - that is not what I need!

    What about the 2nd Ethernet port on the nMP. Can I not use that for my purpose? Can I not connect to my network, in addition to Internet using that?

    I checked int he Sharing Preferences, and I see no logical way to do this, but it CANNOT be impossible. We are talking about making a simple bridge between two Ethernet ports in the same machine...
  2. sebseb macrumors 6502


    May 24, 2014
    The ethernet port on the back of the TBD is only an ethernet to thunderport adaptor, therefore no, you can not connect your laptop! That port in an input, not output! It's like saying can I get sound out of Microphone Jack! Something that even software can't fix!

    And about the 2 ethernet ports on the Mac Pros, those are also inputs, so I don't think you could use one as input and the other as output.
  3. brand macrumors 601


    Oct 3, 2006
    Clearly you do not know how Ethernet works.
  4. h9826790 macrumors G4


    Apr 3, 2014
    Hong Kong
    I don't have TBD, can't tell, but for the Ethernet port, that should be very simple.

    In system preferences, go to sharing, turn on internet sharing. And then choose the internet source, also which port you want to share.

    Screen Shot 2014-07-27 at 14.36.25.jpg

    It seems you've already try this, which part not work?
  5. goMac macrumors 603

    Apr 15, 2004
    Ethernet is ethernet. There is no direction to it.

    If there was, then you couldn't upload and download from the same connection.
  6. Killerbob thread starter macrumors 6502a

    Jan 25, 2008
    When I use "Internet Sharing" the laptop only gets internet. It is not connected to the network, but rather a small unique network is created between the nMP and the laptop, giving access to internet and nothing else - the laptop even gets an IP address different from what my DHCP server is handing out.

    This happens/works whether I use the TBD or the 2nd port on the nMP.

    If there was a "Network Sharing" option in addition to the "Internet Sharing" one in "Sharing" preferences, that would probably do what I need...
  7. h9826790 macrumors G4


    Apr 3, 2014
    Hong Kong
    So, you want to connect your laptop to the Mac Pro's intranet (local network), right?

    In this case, I believe that you need the server app. It's a pay apps from the Appstore, it can make your Mac Pro work as a DCHP server to provide IP to another computer to access your local network. Since it's a pay function from Apple, I doubt if there is a way to achieve the same thing without any 3rd party software.
  8. Killerbob thread starter macrumors 6502a

    Jan 25, 2008
    The Mac Pro should NOT provide DHCP services, my router is already doing just that. The Mac Pro should ONLY work as a dumb switch. It is much more to provide Internet, and it does that well. When it provides Internet Sharing it is working as a DHCP service, creating a subnet. I just need it to give access to an existing network.
  9. Alrescha macrumors 68020

    Jan 1, 2008
  10. dyn macrumors 68030

    Aug 8, 2009
    As I've explained in your other thread you really should use the Time Capsule switch or an additional one if you ran out of ports. Running it the way you want either requires creating a bridge (see the post above me) or using internet sharing (not recommended due to NAT behind NAT) and they both come with problems. For one you need to keep the MP running whenever you want to use the network on the other machine.
  11. Killerbob thread starter macrumors 6502a

    Jan 25, 2008

    In the other thread I focused on getting this to work with the TBD. That I have given up on, and now I am trying to get this working via the nMP. What you are saying is that it is not possible to connect to the Network via the 2nd port in the nMP either. That is very disappointing, and I think Apple is wrong is preventing this. I do say preventing, as it is not technically difficult - it is more work to allow for internet sharing that letting the nMP work as a switch.

    I'll try the bridge method. Is the reversal just rebooting?
  12. DPUser macrumors 6502a

    Jan 17, 2012
    Is there a reason you can't just run a another ethernet cable from your switch to your laptop or, better yet, use a wireless connection?
  13. Killerbob thread starter macrumors 6502a

    Jan 25, 2008
    Both my Time Capsules are full, and WiFi is too slow. I am editing photos and videos off the NAS, and the WiFi connection simply isn't good enough. I know I could buy another switch, but don't understand why is should be necessary, when I have two unused Ethernet connections on the network (TBD and nMP)...
  14. chrfr macrumors 604

    Jul 11, 2009
    Well, this isn't how networks are intended to be set up; Ethernet networks are not generally daisy chained. A switch will perform better, and allow your laptop to be on the network even if your Pro is not.
  15. dyn macrumors 68030

    Aug 8, 2009
    It's the exact same thing. Both are merely network cards in a computer. Connecting different computers is not something that you should do with network cards, you need a switch for that. That doesn't mean you can't do it (because you can with things like internet sharing and bridging), it just means that it isn't a very good solution.

    Simply put:
    • a network card is only used to connect the computer to the network
    • a switch is used to connect different computers to each other.
  16. rei101 macrumors 6502a

    Dec 24, 2011

    I have my iMac and my old Mac Pro connected via ethernet to each other. I do renders in the iMac and the Mac Pro used as a server and for extra computing when rendering.

    I can log via screen sharing to the Mac Pro and surf the web if I need to install something but I believe is via wi-fi the internet connection. The file transfer is ethernet. The mac pro has no monitor.

    And the second ethernet port in the Mac Pro has a different function than the first one, I do not recall why.
  17. DigitalVT macrumors member


    Jul 16, 2010
  18. goMac macrumors 603

    Apr 15, 2004
    Errrr no. This isn't true at all. Ethernet is totally intended to be daisy chained. That's how the "web" works. If you do a trace route, you're probably "daisy chained" to about 15-30 machines between you an through your ISP. All a managed switch is is basically a miniature computer running DHCP and a TCP/IP switch, so even if poster got a stack he's still just daisy chaining into a computer. The whole internet is just a bunch of machines daisy chained to another.

    This is one of the reasons the Mac Pro ships with a second ethernet port. It's not uncommon for businesses to pipe the internet into one end of a server, and then pipe the network connection for everyone else out the other. That let's you do more managed DHCP, caching, filtering, etc. Again, all totally normal with ethernet.

    Performance would be just fine. Maybe slightly/imperceptibly faster than a managed switch due to a better CPU than what you would find in most switches. Even Cisco gear usually has pretty low end CPUs. They used to use PowerPCs, dunno if they still are. AirPort Base Stations might still be ARM CPUs running Linux. So again, any switch you use is still a computer one daisy chains to. All an ethernet switch is, is a low end computer running everything attached in a bridge mode.

    That said, there are several other reasons I wouldn't do this (none of which are "ethernet isn't meant to do this!")

    If you're not running the Mac Pro as a server, letting your Mac Pro sleep or turn off will interrupt your connection. Or if you use boot camp, you'll suddenly have no connection. Also, not being able to figure out how to set this up is a problem.

    A good gigabit switch is $20-$30. With all the time you've spent trying to figure it out in this thread, just buying a switch seems like a better use of your time. This sort of configuration is really for people who want to run the Mac Pro as a server and ensure continuous uptime. It's not meant for someone who doesn't want to do tech support on their Mac Pro all the time.
  19. chrfr macrumors 604

    Jul 11, 2009
    Bad wording on my part. In general, networks aren't intended to be set up with regular workstations operating as switches.
    A cheap gigabit switch will do what's needed, with far less hassle.
  20. Killerbob thread starter macrumors 6502a

    Jan 25, 2008
    I hear what you're all saying, however; I live in Greenland and a decent gigabit switch is USD100, at least, and it'll take a few days, if not a week, to get here. Also, my nMP is on all the time, at least when I am home.

    Finally, I k now a switch is the correct way to go, but I don't want another box on the desk. I have a TBD and an nMP, both with unused ports, and I just can't believe it is such a big deal. Internet I can get via WiFi, but connecting to my network is obviously impossible without Terminal:confused:

    I will find myself an old TC, I probably have one lying around, and sort it out.
  21. dyn macrumors 68030

    Aug 8, 2009
    The problem in your post is the wrong use of terminology as well as the use of uncommon terminology. Daisy chaining is mostly seen as something different than how you connect devices to a network. In this case daisy chaining is a network topology meaning that you connect things in series (sequence).

    This is not how the web works. If the web worked like that it would mean that only 1 device has to be defunct in order to bring down the entire internet. The internet is set up like a web just so it can avoid this scenario. Only small parts can be brought down, not the entire internet. The web is more like a star-based and/or mesh topology. Networking books talk about star topology btw.

    What you are describing here is a SOHO router. A switch is nothing but a device that connects two ports together. It only has a bunch of those ports (4, 5, 8, 16, 24, 48). A layer 2 switch can even create virtual networks. A layer 3 switch can do some basic routing. Most managed switches are layer 2 switches and thus do nothing with tcp/ip nor dhcp!

    Also, a switch general only lays a physical connection. Whatever is on top is controlled by other devices such as routers.

    The correct terminology here is devices or nodes, not machines since not everything connected is a machine. Same thing for calling a switch a miniature computer. By doing so you are also saying that a modern vacuum cleaner is a miniature computer. And again, the internet is not daisy chained.

    Not true at all. The only reason a Mac Pro ships with a second network card is for LACP: having a reliable network connection by using 2 network cards. If one fails, the other takes over.

    The piping of a connection is not something you do through a server. That's what routers and firewalls are for. They can be dedicated boxes with the same hardware as a server, a virtual machine or special dedicated boxes (special as in specialised hardware that is able to handle encrypted connections, package handling and so on). You're using the wrong terminology here!

    A device that does this is usually called a UTM but in no means do you need to have 1 machine do all this. Usually they are scattered over multiple machines for added reliability. These services can also be run over other protocols than ethernet.

    That highly depends on the workload of the machine. There is a thread on this forums regarding the Thunderbolt bridge functionality in OS X Mavericks which discusses this. Both are done entirely in software and thus heavily rely on the workload of the machine. A switch works differently. It is not meant for a vast amount of computing tasks, it is only meant to do 1 thing and it does that in hardware. That's why you don't need that much computing power and why switches can be a lot faster than an ordinary computer. The biggest difference is that in case of a computer most things will be done via software which causes a higher cpu usage. A switch has to do it all via the hardware so it uses a lot of hardware offloading. Usually they are faster than a pc. It also shows that it isn't the cpu in a switch that is doing all the work.

    They are absolutely not like a computer, not even remotely. A computer is more hardware + software whereas a switch is mostly hardware. They are also designed to do one thing, not doing generic tasks like a computer. Any modern vacuum cleaner could be called a computer with your definition!

    Bootcamp has nothing to do with that. What you mean here is that any kind of reboot will lead to connection loss (due to the software actually making the connection not being active thus there is no connection being made). When you want to switch between Windows and OS X you need to reboot. IN that case you'll also have to setup the bridge in both OS X and Windows else it will only work if one of them is booted.

    Depends on the definition of "good" but for this case you are absolutely right. A cheap gigabit switch will get the job done with less fuss and time lost than using any computer to do the task. Since the setup is easier it also means troubleshooting is easier and you're set for the future. If you use the second network card you'll be able to connect 1 more device but what if you need to connect another? If you buy a switch you don't have that problem.

    Nope, it is meant for people who think they know networking but in reality have no idea (aka people who implement crappy solutions instead of doing it properly). Anybody who actually knows networking will only do this as a temporary solution (i.e. emergency). Too much work, too much disadvantages to ever use it.

    Network cards in a computer were never designed to be used like that. And that is the exact reason why using one for something like this is difficult.

    Word of advice: it's fine if you want to dumb down the networking principles but at least use the proper terminology and leave out things that have nothing to do with the setup discussed here (such as dhcp, bootcamp, daisy chaining, etc.). And yes, Apple calls it an ethernet port but in reality it is a network card which is also much easier to understand (ethernet??? network...ah!).
  22. deconstruct60 macrumors 604

    Mar 10, 2009
    Huh? CPUs in dedicated switches/router gear don't handle the base network traffic. If want it filtered/shaped perhaps a bit, but a simple switch is primarily just as big crossbar where packets are just shuffled to the correct address. The CPU doesn't have to decode or do anything.

    In larger gear the "CPU" is really general core attached to a ASIC or FPGA (custom logic). The low level network stuff is all custom logic. The CPU is primarily for the management interface and admin stuff.

    Packet forwarding from one phy interface to another shouldn't need a full fledge general purpose CPU. The CPU generally isn't going to "speed it up". If anything it probably will be slow down since the switch logic here is being implemented in software and not a fix function logic circuit. (e.g., CPUs handling TCP/IP packet headers doesn't speed them up. )

    I suspect the GUI interface for "Internet sharing" is set to deal with arbitrary networks ( hence get a whole new sub net ) being plugged into the "other" socket. Essentially, the Mac as relatively (versus most entry models), super expensive router/switch.

    If it is really just a one other machine it is really just a edge (or point-to-point) link and simply just have to forward everything. [ If the software bridge ifconfig create isn't forwarding the DCHP requests then may have to explicitly tag the edge/ptp link to the laptop as being that. Should automagically figure out it is an edge but may not. ]
  23. goMac macrumors 603

    Apr 15, 2004
    A hub would be a dumb multi-broadcaster. A switch has some sort of management on board, whether that is smart or dumb, to decide where to send a packet, as opposed to just broadcasting the packet across all the ports. This requires some sort of decoding even though it's not tearing apart the packet or anything.

    You can get a dumb switch, a smart switch, or an enterprise switch, but they all have some sort of logic built in for how to route packets which requires some sort of CPU and some sort of software, whether that is burned into a ROM or in firmware.

    Do they even make ethernet hubs any more? I haven't seen one in a long time. They probably do, but switches are probably cheap enough no one needs hubs.
  24. HenryAZ macrumors 6502a


    Jan 9, 2010
    South Congress AZ
    A basic switch maintains in memory a table of MAC addresses and which port they go to. That is the "management" or "decoding". When a frame arrives, it switches it over to the correct destination port. If the destination MAC address is not already in memory, then the switch does flood all the ports to see which one replies. After that, it is maintained in the switching table. Each port is its own collision domain and has full wire speed.

    A hub represents a single collision domain, where everything is broadcast and the total bandwidth is shared across all ports.

    Management interfaces with additional functions can be added on top of these basic capabilities.
  25. dyn macrumors 68030

    Aug 8, 2009
    That reminds me of my networking teacher: "a hub is as intelligent as a drop of solder". It just drops everything it receives everywhere.

    No. Hubs were really dumb devices. Current networks do things that require the use of a switch, even the small networks at home (hubs can't do everything that the gigabit ethernet standard requires).

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