I set up an IPSec/Xauth (RSA) server with LibreSwan on a server. My Android device (a Pixel 2 XL with Android 8.1) actually connects fine when I manually start the VPN connection, and it does tunnel me through the server.
However, when I configure it to be "Always-on" it doesn't seem to work. To be precise:
- IKE and SA establishment succeeds
- Android reaches to connectivitycheck.gstatic.com and appears to succeed
- I see occasional NAT-keepalive packets
- But (most importantly!) no ESP packets are ever sent by my Android device!
Has anyone encountered this issue before? Even details on how the behaviour of Always-on VPNs differ from regular ones would be very helpful.
I did see this question here, asked back in 2014: Always-on VPN sends no traffic
Unfortunately for me, his problem went away when he updated to lollipop.