2 ethernet ports on Mac - Using 1st for file sharing & 2nd for Internet connection

Hello there,
I wonder if anyone can help me with a specific setup.

I am running a 2013 iMac and 2 x 2008 Mac Pro desktops. Each of them already runs on a 100Mbps ethernet local network. The 2 Mac Pros are running OSX Lion, and the iMac is using Mountain Lion.

I need to add a connection between all three machines that will run at 1000Mpbs speeds for transfer of video files between them. I was considering a Gigabit ethernet switch for this specific task. As they run on the company's ethernet network connection for the internet here, I would like to keep these in place and add the gigabit connection to the 2nd port on the macs.

Is there a way of dividing traffic up in this way, so that the file sharing traffic uses one port (on the 'local-only' gigabit network through the switch) and the internet traffic uses the existing ethernet connection on the other port.

Any help or suggestions would be very welcome.

Thanks very much.

Kind regards,
- Ian

Short answer - no - you cannot have two independent ethernet connections with managed traffic flow in this way.

Any network traffic on a lan is controlled and managed by the router. If the router doesn't have a full gigabit backbone you will not get gigabit speeds.

The best way to do this is to get a fully gigabit capable router and use this as the DCHP server. Replacing your existing one. It's unclear if this is possible in your situation.

It's also worth nothing that the iMac has only a single ethernet port.

Thanks very much for the response.

The iMac has a thunderbolt display with a second ethernet port, which was what I was hoping to use for the other connection.

It seems likely that to get this connection working, I may have to get a gigabit switch/router, and run our internet into this and then connect all three machines to this switch.

Can anyone suggest a low cost product that would perform this function?

Also, I have tested out connecting the existing 100Mbps internet ethernet into one port on each of two machines, and linking them together using the other port on each, turning on file-sharing on both. It is worth noting that the existing ethernet also allows network file sharing.

When I turn on all connections, transfers run at 100Mbps and the machines are visible in the shared sidebar on both computers. Indicating that all traffic is being routed through the existing internet ethernet.

If I turn off the existing internet ethernet connection on one machine, the existing file sharing through the 100Mbps network is cut off, and it then runs all file transfers at 1000Mbps. At this point, I have been able to turn on Internet Sharing on the other machine, and daisy-chain the internet connection.

The problem at this point is that I still need to network with a large server at the company and this daisy-chained connection only shows the other mac that is directly connected to it. This would basically mean switched ethernet connections on and off, when I wanted to network for these different purposes.

My question regarding this is: If I ran 3 macs from a gigabit switch and connected the internet from our company network into this switch, is there any way that the three local macs could network with devices that reside on the company network?

Any help on getting any aspect of this working, would be amazing.

Thanks very much.
- Ian

My question regarding this is: If I ran 3 macs from a gigabit switch and connected the internet from our company network into this switch, is there any way that the three local macs could network with devices that reside on the company network?

Click to expand...

Yes, they could access the internet and get there IPs from the main company router i.e. all traffic would go through the gigabit switch to the 10/100 router and back.

There are ways to configure a second router on separate subnet, also ways to filter IP traffic and ways to create vlans. All are designed to separate all or some parts of a network. But all depend on the existing as well as new equipment, your access to it and your willingness to experiment. Invariably these things can take a lot of time to debug.

I've been thinking about this, and looking at my own posts, over thinking it.

A good quality gigagbit switch with all your Macs connected and the company network connected should be all you need.

Once a route is established auto-negotiation should take place and the transfer effectively becomes peer-to-peer. I.e. you should get gigabit speeds between machines connected through the gigabit switch/hub.

Hello again.
Thanks for your response. This reassures me that my latest thinking has a chance of working. The only thing about this that I would need to be sure of, would be that the company drives shared over the main 10/100 network, would be visible as shared on each of the macs. If this group is considered as kind of a subnet where the sharing does not work the same, this would make it very difficult to reach other (non video/media) assets within the company.

Is my concern clear here, and do you know that this is the case. The reason I am so unsure about it, is when I connect the machines together and share the internet connection, the daisy-chained machine no longer sees the network-shared volumes.

Thanks so much for responding.

Kind regards,
- Ian

If you're each just connected to a switch there's no separate DHCP, no separate subnet. You shouldn't have any issues connecting the the existing network