How to use WiFi and Ethernet at the same time

Solution 1:

The solution was extremely simple.

1. Prioritize ethernet to be first.
2. Under System Preferences->Network Settings: where EN0 is Manually configured, leave the router field blank.

I thought the router field was required, so I filled it in. My Ethernet connection has a "router" per say, but it is not used to access general connections. By filling in that field, the Mac OS would automatically try to create a default route through the Ethernet NIC. This would redirect all miscellaneous traffic through the wrong router.

I also tried to delete this route in the routing tables before I found the solution to my problem. This would delete the route appropriately and allow the my software system to run correctly. However after around a minute or so, the route was re-added (as I later discovered) by the operating system. After the route was re-added the connections would fail, so I had to restart the process all over again. This fix proved to be unproductive.

I hope this helps someone with their networking issues.

Solution 2:

Mac OS X gives the default route to the highest-ranked, active interface. It doesn't have anything to do with bandwidth. To change interface rankings, go to System Preferences > Network, click the cog drop-down menu under the list of devices and select Set Service Order. Then drag to rearrange your interface rankings.

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For your case, set the limited network above the internet connection. OS X will attempt to route packets to the first interface. For packets meant for that network, it will work fine. For packets not meant for that network it will see that it doesn't have a gateway or route to the internet, and will route those to the next interface, which is internet connected.

If your smaller network does have routers or a gateway that you need to access, you'll have to edit your routing tables to tell OS X which IP addresses can be found on which networks.

But I believe in your case the simple solution of putting the smaller network at a higher priority will work.