Alias: application gateway HTTP proxy HTTP proxy Web proxy Web proxy A proxy is a computer that is located at the boundary between the internal network of the company and the Internet and connects to a computer on the Internet as a “”proxy”” of the internal computer. Also, server software with such functions. When the proxy server receives an access request from the internal computer to the outside, it requests itself as the connection source, and when the response comes back, it proceed to the internal computer. When viewed from an external server or the like, the proxy seems to be connected and it is possible to conceal the existence of the internal computer and its address to some extent. Since the proxy operates at the application layer, it is necessary to prepare for each protocol and application such as for mail, for web. Usually, in the case of simply proxy or the like, it refers to an HTTP proxy (Web proxy) that relays HTTP communication for Web browsing. In principle, you can not use it unless you explicitly make settings via a proxy to web browsers etc, but there are also ways to make all accesses automatically (forcibly) via a proxy through setting of communication devices in the network, It is called “”transparent proxy””. Main functions / roles The proxy has a cache function that saves the data of the external server once acquired in its own storage (external storage device), and when there is an acquisition request to the same data again, it substitutes the data stored by the proxy In some cases. This not only reduces the load on the external server but also alleviates the congestion of communication lines connecting the inside and outside. In addition, since it is possible to grasp the data circulating inside and outside at the application level, it is necessary to set undesirable connection destinations and perform filtering to refuse relaying from the inside and to prevent unauthorized data such as viruses from entering from outside It may also act like a firewall to detect / deter. When internal networks are operated with an address system (private address) independent of the Internet and others, some have functions to simultaneously perform internal and external address conversion, such as NAT and NAPT. Public proxy Some proxies are installed on the Internet instead of network boundaries, some proxies accept client connections from the outside, and are called “”public proxies”” (open proxies). Since the connection source is the IP address of the proxy server, it is often used when you want to conceal its own IP address to the connection destination or want to change the country / region / organization etc of the connection source. In Japan it is sometimes referred to as a “”skewer”” in secret code, and passing through a public proxy is called “”sticking a skewer””. Forward Proxy and Reverse Proxy Usually, in the case of proxy etc., it refers to “”forward proxy”” which is placed on the client side network and relays the connection to the server on behalf of the client. Meanwhile, one that accepts connections from the client on behalf of the server on the server side network and provides functions such as proxy transmission (caching) of files and encryption and other functions (offloading), load balancing (load balancing) There is also called “”reverse proxy”” (reverse proxy).