VPN is a virtual intra-organization network constructed via a public line of telecommunications carriers and a communication service that can construct such a network It is used for connection between sites in the enterprise network, You can communicate with a remote location such as communication inside the company’s network. It was a service that was provided by telephone line (voice call service) in the past and was a service that connects the extension telephone of a large company having a base all over the country via the public network. Recently, it refers to a connection service between sites of data communication exclusively, and refers to a service that connects an enterprise LAN to each other through a backbone network of a communication carrier. In the past, a dedicated line was introduced between each site to communicate directly, but by “”sharing”” in the backbone of the carrier, it is possible to connect between bases at low cost. In the backbone, data of various enterprises will flow, but since the data is strictly protected and managed by authentication and encryption, the risk of interference, leakage, eavesdropping etc. is low. Recently, “”Internet VPN”” that uses the Internet for the backbone has appeared, and it can be used at a lower cost than the usual VPN service, but in terms of the nature of the Internet, securing of security and communication quality is based on the communication network It becomes more difficult than using.