Linux Router with VPN on a Raspberry Pi

Rationale

This guide demonstrates how to set up a Raspberry Pi as an Open Source Linux router with a VPN tunnel.

I had decided against re-flashing a consumer router with an embedded firmware like OpenWrt, DD-WRT or Tomato because these devices were not intended to run alternate firmware.

Support for devices varies significantly depending on which one you have - sometimes down to the revision of the router. Integrating wireless into the device creates significant driver compatibility issues as certain wireless chipsets have better support than others (eg Broadcom and Marvell).

For wireless a separate access point was purchased Ubiquiti UniFi AP because it contains a Atheros AR9287 which is supported by ath9k and I was keen to avoid blob drivers.