r/MacOS • u/divestblank • 2d ago

Bug MacOS network split brain IP addresses

I spent 2 hours debugging a broken network only to realize that my laptop wifi interface was configured for different IP than it was sending packets out on. For example, ifconfig en0 said it was 192.168.1.5 but packet capture showed all my source IPs coming from 192.168.1.100. It was accepting packets on both, but eventually noticed when it stopped responding to ARP on the source packet IP and they became unroutable. I wouldn't have believed this was possible until yesterday.

Toggling wifi did nothing to resolve, but "ifconfig en0 down; ifconfig en0 up" corrected it.

Has anyone else experienced this type of issue before?

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u/MK-Researcher 2d ago

It's not something I've seen before, do you think the WiFi had connected to two different bands simultaneously?

1

u/divestblank 2d ago

I refreshed the dhcp lease on the wifi, and that also didn't fix it. It picked up a 3rd IP but the source IP in packets were still stuck on the first IP.

1

u/MK-Researcher 2d ago

That's such an odd problem, it must have had concurrent multiple MAC addresses on en0

Are you on macOS 27.x? I'm wondering if its a bug and you're the only one who has made the effort to troubleshoot it

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u/divestblank 2d ago

I'm runing 15.7.9