iOS attempts to route user IP traffic over WiFi connections which aren't yet active

Originator:mo
Number:rdar://31907827 Date Originated:2017-04-30
Status:New Resolved:
Product:iOS Product Version:iOS 10.3.1 [14E304]
Classification:Bug Reproducible:Always
 
Area:
CFNetwork Framework

Summary:
While iOS is attempting to connect to a WiFi hotspot (either because it is configured to connect to all, or because it's one that it has previously connected to), but it has not yet established a reliable connection to the Internet, the status bar will not display a WiFi icon. However, iOS will still attempt to route traffic over this non-functioning connection in preference to cellular data.

Steps to Reproduce:
1. Ensure the device has good cellular and WiFi connectivity.
2. Launch an application which is heavily network-dependent, such as Snapchat or Messenger.
3. Move just outside of the range of the WiFi network, such that the WiFi indicator in the status bar will be hidden.
4. Compose and attempt to send a message, or perform some similar network action (e.g., browsing a website)
5. Note that the connection will stall, and the WiFi indicator is still not present in the status bar.
6. Swipe up to display Control Center and disable WiFi.
7. The network activity in the application will immediately become unblocked.

Expected Results:
While a connection via WiFi has not been fully established, this network interface would remain invisible to applications and no user traffic would be routed through it.

Actual Results:
Traffic attempts to be routed through the WiFi interface even though the OS is aware that reliable connectivity is not (yet) available.

Version:
iOS 10.3.1 [14E304]

Notes:
This does not appear to be a recent regression — it's existed throughout iOS 10, and possibly earlier releases.

Configuration:
iPhone SE 64GB, Three UK & WiFi

Attachments:

Comments


Please note: Reports posted here will not necessarily be seen by Apple. All problems should be submitted at bugreport.apple.com before they are posted here. Please only post information for Radars that you have filed yourself, and please do not include Apple confidential information in your posts. Thank you!