The interconnection of branches of a company through the internet is a frequent requirement. Such communication has often private character, but the communication through the internet is a communication through a public network, thus it is public. It is possible to create a tunnel between branche networks through the internet so it is transparent.

The first possibility is the use of the GRE tunnel or other similar means. The internet as a communication mean is seamless for users in a network, and by such tunnel it is possible to interconnect networks which have addresses inaccessible from internet. The drawback of that solution is, that the communication could be intercepted.

The most suitable solution is enciphering of the communication by the widely used standard. IPsec is such a standard. It works as a usual tunnel between networks or hosts but is is secured. Moreover it enables secure communication between network and road warriors with dynamic IP addresses. This could be dialed networks or workers which connect to the internet from many places. All of then could work as if they were connected to the internal network.