If you come to this post, you probably got trouble with the defaut Cisco VPN client on your iphone. The fact that the Cisco VPN client disconnects automaticlly every time the iphone goes auto-lock is truly annoying.
By following these steps, you can keep Cisco VPN stay connected for an unlimited duration.
1) Jailbreak your iphone
2) Install SBSetting on cydia
3) Intall SBSetting VPN Toggle on cydia
1) Touch the VPN toggle on SBSetting panel to enable your VPN
2) Fill whatever something in "Password" field
3) Touch "Cancel" button
4) You notice that the VPN toggle is still incicating like activated, just touch it one more time
5) Fill your password correctly
6) It's done! Enjoy.
I think it's an iOS bug.