Changing default subnet no longer working?

[phillipross]

In the past I've been able to set the subnet via instructions at https://tart.run/faq/#changing-the-default-nat-subnet but this seems to have stopped working somewhere along the line. I'm running macOS 15.5 on an M3 and install tart and softnet via homebrew. Each time I upgrade tart the default subnet seems to increment by 1 and I'm no longer able to set it to a lower number. I'm getting concerned about hitting some kind of limit eventually 😅 Thanks for any hints or insights!

[edigaryev]

I've just checked and the FAQ entry instructions that you've mentioned still work for me on macOS Sequoia 15.5, even with --net-softnet.

1. How does the configuration look like in the end? Can be checked with sudo defaults read /Library/Preferences/SystemConfiguration/com.apple.vmnet.plist.
2. Which additional command-line arguments to you pass to tart run <VM name>?
3. You might also try removing the /var/db/dhcpd_leases file and running the VM again to see if that fixes the issue for you.

[phillipross]

Thanks for following up with this. When I was troubleshooting, I did write the value and then read it back to verify. In those cases, the value that I wrote would then be returned when I'd read it again. But then when I'd use the tart run to start a VM, the value would flip back to the previous value. I'd also been removing the dhcpd_leases file each time but the value would still flip back. I'd been testing exclusively with --net-softnet-allow=0.0.0.0/0 (as I need the VMs to be able to talk to each other).

Eventually I rebooted, and that seemed to fix the problem, and it's been working fine since then, but I've not attempted an upgrade of tart yet. I saw a new version of tart was just released so I'll test things again when I upgrade, but I'm hoping all of this was just intermittent MacOS Virtualization weirdness. I'll report back soonish to see if I run into the same thing again.

Thanks again!

[phillipross]

I'm happy to report that upgrading from tart v2.28.0 to v2.28.1 did NOT cause the subnet assignments to misbehave as before. I suspect I was bumping into some macOS weirdness where things were in a weird state. Thanks for the extra confirmation!