It took me a while to figure out why many of my self-hosted services were intermittently failing to connect on my phone after updating to Android 17. I eventually figured out there's a new ACCESS_LOCAL_NETWORK permission which means the "Nearby devices" permission is now required to access devices on the same network subnet. For an avid self-hoster, this can be quite a bit.
I had my DNS configured so my public-facing server resolved to a local IP address when on my LAN. This meant that my web, immich, xmpp, NTP, jellyfin and DoH servers all resolved to a local IP address on wifi. On Android 17, it all broke without warning. No error messages. No asking for extra permissions. Just silent packet dropping.
I've solved it by configuring my public-facing services to resolve to my external (static) IP address, even when inside the network. I couldn't make any internal services resolve to the external address (SMB, CUPS etc) because they are (obviously) not bound to my WAN interface.
I get why the change was made. A lot of apps were snooping around people's networks to gather intel. A potentially massive privacy violation.
Has anyone else had this issue? Is this the cleanest solution?
It works but I wouldn't call it the cleanest solution, more a workaround. As far as I know only apps targeting SDK 37 are affected, older apps still get the permission implicitly. So the proper way would be to just grant "Nearby devices" to the apps that need it e.g. Immich or Jellyfin and if an app doesn't ask for it that's actually a bug and worth reporting, because it should request the permission as soon as the server resolves to a local IP. I also find the "Nearby Devices" title a bit misleading for apps that only need it to reach your own server, but on the other side it gives a somehow proper hint what the permission actually allows.