Agency services technology is a very old technology, is in the early stage of the use of internet technology. General way to implement agent technology installed on the server proxy service software, let it become a proxy server, enabling agent technology. Commonly used agent technology into forward proxy, reverse proxy and transparent proxy. This article is aimed at these three agents to explain some basic principles and specific scope, to facilitate a deeper understanding of agency services technology.
First, the forward proxy (Forward Proxy)
Under normal circumstances, if not specified, the default agent technology say that forward proxy technology. About the concept of forward proxy as follows:
Forward proxy (forward) is a user in the client [A] and the origin server (origin server) [Server B] [proxy server between Z], in order to obtain content from the origin server, user A sends to the proxy server Z a request and specify the target (server B), then the proxy server to server B Z transmit the contents of the request and get back to the client. Clients must be some special settings to use forward proxy.
From the above concept, we see that the text is a so-called proxy servers to replace forward proxy access side [User A] to access a target server [Server B]
This is the significance of forward proxy. And why use a proxy server to access the side instead of [User A] to access server B do? This from talking about the significance of the proxy server to use.
Forward Proxy role with the following main points:
Access the inaccessible server B
We throw in addition complex network routing plot, assuming from left to right router named R1, R2
Assuming the initial user A to B needs to access the server through R1 and R2 routers such a routing node, if the router R1 or R2 router fails, then it can not access the server B it. However, if user A to Z to replace their own proxy server to access the server B, Z not because the proxy server in the router R1 or R2 node, but through other routing node access server B, then user A can get the data server B.
Real-world example is the "over the wall" But since the VPN technology is widely used, the "over the wall" is not only using the traditional forward proxy technology, and some also use VPN technology.
Accelerated access to Server B
This argument is currently not so popular, mainly the rapid development of bandwidth traffic. Early forward proxy, many people use the forward proxy is speed.
Suppose the user A to server B, through R1 and R2 routers router, router R1 to R2 link is a low -bandwidth link. The user A to the proxy server Z, Z from the proxy server to server B are high- bandwidth links. Then obviously you can speed up access server B.
Cache Role
Cache ( Cache ) technology and agency services technology are closely linked ( not just forward proxy, reverse proxy also uses the Cache ( cache ) technology also shown above.
A caching proxy server accelerates service requests by retrieving content saved from a previous request made by the same client or even other clients. Caching proxies keep local copies of frequently requested resources, allowing large organizations to significantly reduce their upstream bandwidth usage and costs, while significantly increasing performance. Most ISPs and large businesses have a caching proxy.
Client Access License
Content of this field is still in use today more and more, for example, some companies use ISA SERVER as a forward proxy server to authorize the user has permission to access the Internet.
Firewall as a gateway to filter external network access to it. Assuming the user A and the user B are set to a proxy server, the user A to allow access to the Internet, and the user B is not allowed to access the Internet (the proxy server that no limitation on Z) so that the user A as authorized to access the server through a proxy server B, while user B because Z was not authorized proxy server, so access to the server B, the packet is discarded.
Hide Visitors Whereabouts
We can see that Server B does not know is the user access to their actual A, because the proxy server A to Z instead of the user to interact directly with the server B. If the proxy server Z full control by the user A (or incomplete control), will be used to order "chicken" Terminology title.
Forward proxy, in order to obtain content from the origin server, the client sends a request to the proxy and specify the destination (origin server), then a proxy server to forward the request and the original the content will be returned to the client. The client must set the forward proxy server, of course, the premise is to know the forward proxy server's IP address, as well as the agent's port.