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Saturday 3 August 2013

Native Android VPN to a Cisco Router

Getting IPSec VPN connectivity between two devices is always a painful experience, somewhat akin to a root canal. So I eventually roused up the courage and decided to try and get Android 4.x native VPN  to connect to a Cisco 877 at home. A few four-letter words and some blasphemy later, I finally had success!

The below example should help anyone else having problems getting this working.

Topology
The topology is drawn below. Its very simple, consisting of:
  • A Cisco 877 running 12.4(24)T1 (advanced IP services), attached to an ADSL line on the public side, with a LAN in RFC1918 space internally. A simple NAT configuration is configured between public and private.
  • An Android phone (in my case a galaxy S3 running 4.1.2 stock) with a 3G SIM. My carrier runs CG-NAT yet the setup still works.