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I'm on the latest iPhone (13 Pro Max) (iOS 15.2.1) and connected to my carrier's LTE network. I opened an application, which then requested access to my local network.

I'm wondering how this is possible and what this means. How can an application request LAN access when I'm not on my LAN? Does anyone know what might have happened?

For context, I'm connected to Bell's network.

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  • It sounds like you just need a list of iOS permissions and what they mean. Like makeuseof.com/iphone-ipad-permissions-how-do-they-work How is this possible? Because the app wants this permission and asks for it. It's a permission so it does not need a network to connect to, and without LAN access, it cannot tell that it is not connected to a network. Nothing has "happened". It's just an app asking for permissions.
    – schroeder
    Commented Jan 30, 2022 at 13:38
  • If you are not connected to your WiFi network it is likely requesting access to is the carrier's LTE network, which can carry data (though likely not a quickly) just like a WiFi network. You can see what apps can (and have) used LTE data under Settings > Cellular Commented Jan 30, 2022 at 14:50
  • @schroeder The app in question would have had no reason to ask to be connected to the local carrier network. This is the same permission that is triggered if I were to connect my phone to a proxy server on my network. It isn't something that should just "happen", at the very least, it's suspicious. Commented Jan 30, 2022 at 15:17
  • @SteveChambers Right, my question is what is the reason an app would want to connect to the carrier's LTE network.. This is not a networking app. It would have had no reason to connect to LTE lan. I think I'll just have to dig further on when exactly iOS apps request this Commented Jan 30, 2022 at 15:18
  • You didn't specify the app so we are guessing here but many apps will access the network as many retrieve info from the internet (weather, etc) the dev's website (Dropbox, 1Password, etc.) and the list goes on. If you can't or won't share the app then your only recourse is the app's developer: ask them what the app is doing. Commented Jan 30, 2022 at 21:35

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The prompt was introduced in iOS 14 to inform and empower users when apps are possibly interacting with networks in a way that could potentially let the app harvest information about other devices on that network.

I.e. an app that connects to your A/C unit on your WiFi network is an app you as a user would expect and allow having that access. However a single player, offline game would not be expected to do that - it could potentially be harvesting information in order to fingerprint (identify) the user for the purpose of maximising ad revenue or even trying to exploit security holes in local devices such as routers and printers. With iOS 14 and newer the user is given the option of allowing or not allowing that type of network access.

There's really no contradiction in the app requesting this permission even when you're not connected to such a local network at the moment. The app would have no way of knowing before hand that this is the case.

Giving it permission to access the local network doesn't mean that it can actually do that right now - but it has permission to try. Note also that unless you revoke the permission, it could try again later when you actually are connected to such a local network.

Also you should note that "Local network" might mean something entirely different than what you think. It doesn't as such mean LAN as in "my home network connecting my WiFi router, printer, AppleTV, etc. with cables". Instead the definition is a bit technical:

When you connect a computer to any type of network, this is usually expressed within the operating system as something called a "network interface". Network interfaces cover many different types of networking technologies ranging from various types of physical signals, hardware options, networking protocols, etc.

In this context, a "Local network" is specially a network interface using the IP protocol (i.e. IP addresses are used) that is broadcast-capable. The latter means that it is possible to send/receive data on the network without a specific recipient (i.e. possible for more than one recipient).

This means that for example standard WiFi connections and Ethernet connections are considered a "Local network". However for example a VPN connection might not be considered a "Local network" (these are typically point-to-point connections).

Note also that even though a WiFi connection can be considered a "Local network" - it is not every interaction with the WiFi connection that is covered by that prompt. If an app only requires Internet access it can do so through your local network without requiring this permission. However, if the app specifically contacts a another device on your local network, or it tries to send multicast packets (data sent to a group of devices) or broadcast packets (data sent to all devices on the network) - then that will require this "Local network" permission. Similarly if the apps tries to receive multicast or broadcast data, that also requires the "Local network" permission. An app can receive data on the local network specifically addresses to itself without the permission.

The end result is that an app that tries to scan your network for devices using broadcast or simply brute-force will require this permission - whereas an app that only connects to Internet-based services or offers a service on the local network for others to use, will not require this permission.

Note that apps that themselves use the relatively popular Bonjour protocol to discover services will require the "Local network" permission - whereas if the app asks iOS that it wants to print something using AirPlay will not require the permission, even though that means that iOS uses Bonjour to locate those printers. The difference is that the app does not receive the Bonjour data directly, and as such it does not pose the same risk of data harvesting.

If you want the full technical details behind this feature, you can refer to Apple's WWDC video introducing the feature to developers and to the "Local Network Privacy FAQ" for app developers.

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