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?
Routing between two interfaces on the same NIC takes nanoseconds. You wouldn't notice a performance difference.
When I first set it up, I didn't have a static IP address, so it would not be great when it changed. I also want my server to remain reachable locally if my internet goes down. I had different firewall/ACL rules for wifi too. For example, some of my internal websites only prompt for a login if you're outside the network.
IPv6 has been awesome here. I have my server and clients on different /64 subnets in the same /48 block. The nearby devices on Android assumes only the same /64 is local.