Service, please! Manage multiple Mac network interfaces’ priority
Six Colors reader Philip asked some specific networking questions that centered on this dilemma:
How does the choice between using Ethernet vs. Wi-Fi get made? Does one particular transaction solely use Ethernet or Wi-Fi, or can it be a mixture of the two?
Home, home on the range of choices
One of the joys of the modern Mac is that you can attach all sorts of networks to it, and macOS just figures it out. Gone are the days of installing drivers or digging deep into network configuration settings. Just plug a cable into the right jack where the other end is connected to an Ethernet hub, an iPhone with Personal Hotspot enabled, or even another Mac. You can add Wi-Fi to the mix, too. (This is called multihoming.)
There are reasons you might want multiple connections configured:
- You prefer the performance of Ethernet in your home or office and plug in a laptop (or luggable Mac mini) when you’re in a fixed location. When you detach the cable for travel or another location, Wi-Fi kicks in.
- Your Internet connection is flaky, and you want to have a backstop in place, like keeping your iPhone connected over USB.
- You use a lot of bandwidth over the local network, and multiple interfaces increase your maximum throughput.
Philip noted a particular case: his household Wi-Fi works fine for nearly all purposes, but when they try to use Zoom or other live video sessions, they often receive a message about an unstable connection.
First things first
Fortunately, you can prioritize which network connection gets used via Set Service Order. You may have never used this option or find it hard to find due to reorganization over the years. It’s always been in the Network pane in System Preferences or Settings Settings, but the icon used to access it has shifted from a gear under the left-hand interface list to a More … button in the same location to its current System Settings More … button to the right and below the interface list.
Here’s how you use this old feature:
- Go to System Settings > Network.
- Control-click/right-click any network interface or click the More button under the interface list.
- Choose Set Service Order from the menu.
- In the Service Order dialog, you see a list of all network interfaces. Drag these into the order you want them used.
- Click OK.
Note that VPN and Firewall appear in the Network settings pane, but because they aren’t network interfaces, they do not show up in the Service Order dialog box.
What you’re telling macOS through this ordering is which network interface to consult first. It doesn’t take into account which of them are currently active. Nor is it precisely responsive to flakiness: an unreliable network set first, as long as it appears to have an active connection, will still be the preferential destination of your data packets.
You can shut down a flaky connection via the Network pane, too: Control-click/right-click an interface and choose Make Service Inactive. Use the same process to Make Service Active when you want it back in the fray.
If you’re curious about how much data passes through your various multihomed interfaces, you used to be able to do so via Apple’s included app Network Utility. Unfortunately, that app has been discontinued, but DEVONtechnologies created its own version called Neo Network Utility, which packages the same Unix network tools behind a friendly interface.
In NNU’s Info tab, you can choose an interface from the popup menu and then look at the Transfer Statistics sections to see how much data has transited in and out. (I believe this is reset whenever you restart your Mac.) In my case, as you can see in the figures, the Ethernet connection carries the vast majority of all data from my machine—under 2% passed over my Wi-Fi link.
For more in-depth details, you might like
I have written extensively about networking, particularly for the Mac, for decades. Most recently, I’ve kept three Take Control Books up-to-date:
- Take Control of Wi-Fi Networking and Security, which is focused on Wi-Fi but has a lot of general information about DHCP/NAT and other network issues
- Take Control of Apple Screen and File Sharing, which explains setting up remote access into your network to access screen and servers
- Take Control of Untangling Connections, a surprisingly popular book that deciphers the hardware side of Thunderbolt, USB, Ethernet, and other standards
[Got a question for the column? Anyone can email glenn@sixcolors.com. Six Colors subscribers can also use /glenn in our Discord community.]
[Glenn Fleishman is a printing and comics historian, Jeopardy champion, and serial Kickstarterer. His latest books are Six Centuries of Type & Printing (Aperiodical LLC) and How Comics Are Made (Andrews McMeel Publishing).]
If you appreciate articles like this one, support us by becoming a Six Colors subscriber. Subscribers get access to an exclusive podcast, members-only stories, and a special community.