This document is a quick little how-to on GRE tunneling. If you're not familiar with the concept of IPIP tunneling, or encapsulation of packets inside other packets, then this is probably not for you. Please note, the diagram below is setup with the dialup in mind however the scripts show usage of eth0. It makes no difference if you have DSL or a cable modem and use eth0, or if you have dialup and use pppN.