This document describes a L2TP/IPSec setup on a CentOS 6 server for use with Android ICS clients. As Openswan is reported having issues with Android ICS (byte 7 of ISAKMP NAT-OA Payload must be zero), this VPN setup is based on the ipsec-tools.
The setup was successfully tested with Android 4.0.3 and iOS 5.0.1 in this network scenario:
The following values are used in this document. You must adjust them according to your needs.