Fortigate IPSEC site to site VPN with DSL modem

Hi,

first off, I would upgrade to v5.4.4 which is way more stable than the old v5.4.1. Avoid headaches if you can.

Then, there are 2 ways to create a tunnel:

1- use dyndns names on both HQ and branch, and a standard site-to-site VPN.

2- use only one side with dyndns name and a dial-up VPN.

I recommend using the first option. Use the VPN wizard (what else) to create a site-to-site VPN with Fortigate devices. The remote gateway is a 'dynamic host'. Use main mode, and choose your encryption as you like it.

Always specify the remote and the local subnet in phase2.

The wizard will create the correct static route and 2 policies for you. Review and adjust (!) or even delete one of them.

All of this is pretty straightforward and very well documented. Have a look at the Cookbook (cookbook.fortinet.com) for an example setup.