Setting up a VPN between two sites for a small business to create a single network; although the interface will be different for every router, the functions are roughly the same.
1 – To build a VPN you need to know the IP address of the VPN terminator and the remote site, but unless the small business is paying for business-grade DSL they probably won’t have a static public IP address. Use a Dynamic DNS service to create a fully-qualified domain name instead.
2 – To create a site-to-site IPSec connection, first enable IPSec, then provide the fully-qualified domain name you set up in the DDNS tab. Now click Add to create a VPN tunnel.
3 – Set the Tunnel Type to IPSec, name the tunnel and fill in the dynamic DNS alias and the details of the local network to be connected to the VPN (here 192.168.1.0). Make sure both ends of the tunnel are set to use the same IKE encryption key methods, authentication (MD5 here) and encryption (Triple DES here).
4 – For a connection between two offices, make the VPN the default route so that all traffic from the LAN to the remote resources passes over it. Configure both ends of the VPN tunnel and enable it.