I was able to successfully set everything up.
Write-down for everyone else, including pitfalls I identified.

Use case

I want the ar750 to bridge connected devices to the rest of my home network. I identified “Access Point” network mode as what should serve my intent.

Setup

  • AR750 has Firmware v3.105.
  • Modem: Fritz!Box 7590 with default settings, DHCP assignment etc.
  • The modem sits at 192.168.178.1
  • AR750 gets assigned 192.168.178.29 in that subnet. In the default network mode, it seems to bridge everything into the 192.168.8.x subnet. This works but e.g. won’t work with mdns of the 192.168.178.x subnet which is a problem already

AP approach & analysis

Upon entering AP mode, I encounter the situation described in above post 2h ago. More details:

  • My router tells me the AR750 is assigned 192.168.178.29
  • My test client device is connected via LAN port and shows that it is assigned 192.168.8.33, with 192.168.8.1 as DNS + AP. Here lies a pitfall: my device still thinks it sits in the 192.168.8.x subnet. This must be resolved on my side. I was able to do so via disconnecting and reconnecting the LAN connection, please not that this means in the system settings. Disconnecting the LAN plug in itself probably won’t work on it’s own. More technically, the system has to refresh its DNS lease, in the process of DHCP network reconfiguration. Try different methods for achieving this. For WLAN, I suppose one should “forget” the AP + set it up again if you’re on a smartphone or something.
    • The ar750 software actually points this out to the user. I imagine, a direct How-To on setting up the connection on client devices again could be useful, as it appears the device is bricked until then.

Alas, everything works as intended now

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