The Linksys VPN routers BEFVP41 and BEFSX41 are great devices for setting up LAN to LAN VPNs quickly and easily. The VP41 allows up to 70 VPN links, the SX41, 2
In a static IP environment setting up the VPN links is straightforward. Go to the VPN tab on the router setup and follow the Linksys instructions on creating the VPN
For sites with one or both (or multiple) dynamic IP addresses, it is only slightly more complex.
Firstly go to www.dyndns.org, register there(FREE) and (preferably from the site that has a dynamic IP address) create an account name for your dynamic IP address location for example: companyname.dyndns.org. If you have multiple dynamic IP sites, register one for each of them.
At the Linksys VPN router at the dynamic IP site click on the Advanced tab and select the DDNS tab. Enter the details of your Dyndns account, click Apply and you are set to go. This gives you a Fully Qualified Domain Name which you can use for your VPN. When the IP address of the dynamic location changes, it updates dyndns and there is no (minimal?) interruption in your VPN link.
This is also useful for anything else, for example if you want to run remote desktop or terminal services or a web server.
Thereafter it is a case of creating the VPN tunnels on both routers (REMEMBER to click Apply when you have entered all the details BEFORE you click on Connect!) - at the dynamic IP site router, connect to the static IP address of the other router, at the static address site, use the Dyndns FQDN to resolve the address of the dynamic site.
A very useful tip - make sure you have strong passwords on both routers and then enable remote management. In this way you then have access to the routers from anywhere and you can work on setting up the tunnel on both routers simultaneously. While you are setting it up, you might have to get someone at the dynamic IP site to look at the router's status page to tell you what the then current IP address is, so you can get in there and set up the DDNS
NOTE: to access the router, use http:\\IP address OR FQDN:8080 this will give you your remote router's logon (Only if remote management is turned on)