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Wireless device (internet of things device, like wireless printer) creates a wifi network. The device has ip 10.0.0.1 and does not have acces to the internet.

The DHCP server on the device sets the option "Offer Router (3)" as itself (see screenshot): screenshot of wireshark capture

Would it be of any benefit to disable offering this option?

I am thinking of disabling it because this option is misleading and it might solve some connectivity problems like some android phones identify the network as having no internet and route all traffic through mobile network.

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    That will probably happen anyway. The phone will always try to connect to the internet – Ron Trunk Jul 31 '18 at 12:21
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Would it be of any benefit? No.

Traffic intended for a network outside of your subnet would die at the printer since there are no other connected networks, but the Android phones have to be told to stay connected even though there is no internet. The phone connects to Wi-Fi expecting internet and then it should ask you if it should stay connected since it didn't find it.

Any local traffic is handled perfectly fine with/without a default gateway, so no benefit to disabling it. Your problem is the phones not finding internet that they desperately want to be connected to and disabling the gateway won't satisfy that internet hunger.

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Setting an DHCP option 3 is indeed useless (apart if there is more than 1 IP on the printer).

In my opinion, you're 100% correct, disabling this option will remove the default route on connected devices.

Then, behavior will really depend on the device. Few years ago (it may have changed now), Apple IOS was keeping the Cellular Internet connection active with no gateway on the WIFI (what is expected in my opinion), but Android shut down the cellular as a WiFi network is detected (even without a gateway).

But in all cases, I don't see any reason for the printer to send such a option (maybe because they left the default configuration of the dhcp-server they put in their printer)..

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