Didn't find this on Google so I thought I'd see if anyone here knew.

I have a LAN with Windows clients and a Linux 2.4.18 kernel (Mandrake MNF) server. My server is currently the router for the LAN also DHCP, firewall, proxy (squid) and squidGuard server.

I know that my distro came with freeswan, a VPN server.

My company has 2 other locations and we'd like to make a WAN so we can have a Intranet site and make files available to them.

The problem is that my LAN here, uses ADSL and only can have a dynamic IP address. So is it even possible to use this server as a VPN server? Before, I tried to use IPtables to open a port number to a internal Webserver, but all that did was make us lose our Internet connection. So that's why I thought maybe VPN would be good. Any thoughts?

Thanks in advance.

You need a public hostname for your VPN gateway.
To achieve this, register at a service like DynDNS and put a script for updating your IP address in /etc/ppp/ip-up.d/
That script can call any of the dynamic DNS clients; I use ez_ipupdate. Have a look at the DynDNS website for these.

There is also a pretty good documentation on how to set up VPNs with FreeS/WAN and Windows clients:

http://www.jacco2.dds.nl/networking/freeswan-l2tp.html


However, beside this you must configure your firewall to accept IPsec protocols and the tunneled connections.

... so it IS possible. Thank you for the excellent and detailed answer, ricstirato. I will try that.

Dont' call it excellent until you tried ;-)