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Configure iPhone to see cell Internet and local non-Internet LAN at the same time? (self.networking)

submitted 23 hours ago* (last edited 23 hours ago) by CandleTiger to c/[email protected]

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I have an off-grid setup with a few devices on a local network that is not connected to the internet. I can tell my iPhone to use the non-internet wireless LAN to talk to those devices, OR I can tell it to use cellular data to talk to the Internet, but there’s no config on the iPhone side to let them be both live at the same time.

Is there any magic config on a wireless router e.g. certain DHCP settings or just disable DHCP, that will let the iPhone route to static 10.x IPs on the WLAN while the cellular internet is still active?

Any “advanced network settings” on the iPhone to manage multiple NICs?

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[–] [email protected] 3 points 17 hours ago (2 children)

Haven't tried this in a while (I've been off iPhone for 5years now), but iPhone used to allow this as follows:

If you join your home WiFi and have no default route set by dhcp, iPhone should tell you it has no internet and you can tell it to use the connection anyway.

The iPhone feature to "use 4g when WiFi is bad" should then solve for internet access and let you do both.

Just be aware you can't have split brain DNS, so internal LAN stuff will likely need to be accessed by ip address only, not DNS based.

[–] [email protected] 1 points 7 hours ago

Nice solution!

[–] CandleTiger 1 points 17 hours ago

I will try it, thanks

[–] [email protected] 2 points 17 hours ago (1 children)

You would need to set your gateway to the cell service and then add a static route for your local subnet that points to the local WiFi.

[–] CandleTiger 1 points 17 hours ago (1 children)

Yes, that l’s exactly what I’m asking for in this post — is there any actual exposed config on the iPhone, or any way to set up DHCP on the WiFi, that will convince the iPhone to use its own cell service as the gateway even while it’s connected to a WiFi?

[–] [email protected] 2 points 16 hours ago

You can't do that with dhcp

[–] [email protected] 2 points 17 hours ago

You might be able to set something like this up if you turn on tethering

[–] [email protected] 4 points 23 hours ago

That would be dual homing using both cell and wifi networking.

I don't think iOS can do this - and I'd be hard-pressed to make it happen on Android (honestly I don't think it can be done, maybe with root, even then, I'm not sure).

[–] [email protected] 3 points 23 hours ago (1 children)

Set-up a cellular modem on your network and set your phone to WiFi?

[–] CandleTiger 0 points 23 hours ago

😬