How can I automatically re-connect to a WiFi network?

Question

In this question I am asking about how to stop my WiFi from disconnecting.

If I won't find an answer to that, the next best thing is to get my phone to re-connect automatically. The disconnect reason is: "Class 3 frame received from nonassociated STA"

I am on a rooted device running cyanogen mod on Android 5.

I'm using AFWall+ and OpenVPN, if that is relevant. OpenVPN is set to re-connect automatically already, which works.

Due to AFWall+ blocking non-vpn traffic, whenever I connect to WiFi it says "There is no Internet connectivity, do you still want to connect? [Yes/No]", ticking the "Don't ask again" box has no effect.
This might be relevant and if the phone does automatically reconnect, I obviously don't want this pop-up to prevent an automated re-connect.

Answer 1

Your issue is caused by Captive Portal¹ Check kicking in and not permitted through by AFWall+. So if you can live without that auto-detection, you could simply disable it:

# check what the original setting is. Should give "1" for enabled, "0" for disabled
settings get global captive_portal_detection_enabled
# now let's disable it
settings put global captive_portal_detection_enabled 0
# if you want to re-activate it
settings put global captive_portal_detection_enabled 1

Implications:

• no more pop-ups when connecting to e.g. a hotel network using Captive Portal. Easy work-around: just open a web browser and navigate to any url, the portal should "capture" you for login
• no more x on the WiFi symbol – so you might miss the fact of not reaching any network until you try manually (e.g. by visiting some web page and ending up on the Captive Portal's login page)
• automatic re-connect to "known WiFis" should simply work.

I've used that trick myself when having set up AFWall+ in a quite restricting mode, and it worked for me. As you (OP) just confirmed in a comment on the question, it did the trick for you as well – despite the additional complication of a VPN.

See Captive Portal parameters for more details on manipulation.

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¹ _{for those who don't know what a "Captive Portal" is, please see Wikipedia}