Using Your MacBook as a Local WiFi Access Point
· 5 min read

Using Your MacBook as a Local WiFi Access Point

#macOS #network
Table of Contents

The Problem

I needed my MacBook Air M2 (Sonoma) to broadcast its own WiFi network, being a WiFi server instead of a client. Not to share an internet connection, just to create a local wireless network so other devices could connect to it and talk to each other. Think local development and setting up a private LAN without carrying a router.

macOS has a built-in Internet Sharing feature (documentation), but it’s designed to share an existing internet connection (like Ethernet or Bluetooth tethering) over another network (such as WiFi).

On a MacBook with only a WiFi card and no wired connection, creating a standalone access point is not straightforward.

Attempt 1: Native Internet Sharing (Silent failure)

So I did follow the documentation and the internet’s recommendations. I went to System Settings → General → Sharing → Internet Sharing and enabled everything:

  • Picked a source connection (let’s say Thunderbolt)
  • Selected “To computers using:” Wi-Fi
  • Set the network name and password
  • Kept my WiFi on, but not connected to any network
  • Turned the toggle on
  • Accepted the warning popup

Everything appeared enabled. No error messages. No warnings. But the WiFi network simply never appeared. Not on my phone, not on any other device. macOS accepted the configuration but silently refused to actually broadcast the signal.

Internet sharing is enabled, but not wifi is broadcasted
Internet sharing is enabled, but not wifi is broadcasted (it should be displayed here as we will see later)

The reason: macOS Internet Sharing is built to share an existing (i.e. activated, up) connection, not blindly bridge one network stack to another. Without an active upstream connection that the system recognizes as active, the underlying service doesn’t actually bring up the access point, even though the UI lets you enable everything.

The hack: Faking a connection with a loopback interface

The solution came from a gist by @zhuhuilin: macOS Internet Sharing Without Internet Connection1.

The trick is to create a new network service on the loopback interface (lo0). macOS only checks that the network service has an IP address (which is apparently how it determines whether a connection is active) before allowing Internet Sharing. It doesn’t verify that the connection reaches the real internet. By assigning a static IP to lo0 and registering it as a network service, macOS happily accepts it as a valid source.

The gist provides the exact commands to run in Terminal:

curl -L https://gist.github.com/zhuhuilin/01656866b3e73a677a434c21183b40d2/raw/setup-adhoc-network.sh | bash
Running zhuhuilin's setup script
Running zhuhuilin's setup script

This will automatically:

  • Find your active internet connection
  • Create a new network service (named AdHoc) on lo0
  • Assign the Mac the IP 10.10.10.1 on this new service
  • Save state for safe removal
MacOS Settings window with the Internet Sharing configured with the AdHoc interface
Internet Sharing configured with the AdHoc interface, just need to enable it now

Then you can select this AdHoc service as your source in Internet Sharing. Once configured, macOS actually brings up the WiFi access point, and devices can see and connect to it.

The WiFi should be enabled on MacOS to have the beacon activated. But it should not be connected to any networks.

Keeping wifi enabled and seeing the shared network broadcasted
WiFi is enabled, and is showing the "Internet Sharing" on Channel 11

Changing the DHCP range

By default, macOS Internet Sharing assigns connected devices to the 192.168.2.0/24 range. I needed mine to be 192.168.68.0/24 to match my existing setup.

After some digging, I found that you can override the default DHCP range with three defaults write commands targeting the system NAT preferences:

# Set the starting IP address
sudo defaults write /Library/Preferences/SystemConfiguration/com.apple.nat NAT -dict-add SharingNetworkNumberStart 192.168.68.2
# Set the last IP address
sudo defaults write /Library/Preferences/SystemConfiguration/com.apple.nat NAT -dict-add SharingNetworkNumberEnd 192.168.68.254
# Set the netmask as /24
# -> This isn't automatic and is necessary!
sudo defaults write /Library/Preferences/SystemConfiguration/com.apple.nat NAT -dict-add SharingNetworkMask 255.255.255.0

After running these and restarting Internet Sharing, connected devices received IPs in the 192.168.68.x range — exactly what I needed.

Settings seems to cache these parameters. Quit the Settings application before applying them, then reactivate Internet Sharing.

The whole thing works reliably once the loopback trick is in place. The AdHoc service survives reboots, and the DHCP range sticks as long as you don’t reset the NAT preferences. The one thing to keep in mind: if you do have an actual upstream connection available (Ethernet, USB tethering), you can use that directly as the Internet Sharing source and skip the loopback hack entirely, it’s only needed when you want to have an access point from macOS without internet.

Footnotes

  1. I made a backup of Zhuhuilin’s scripts here ↩

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