Proxy servers have three major purposes:
1. Filtering and Firewalling
2. Sharing of connection
3. Caching
These features of proxy servers are particularly important to the corporate and other large networks. They work at the application layer which is the seventh layer in the OSI model. They are not as easy to implement and use as the common firewalls. The functionality of the proxy server for each of the protocol like HTTP, SOCKS must be downloaded individually. Nevertheless proxy servers improve performance and security. Firewalls by themselves cannot do that. Proxy servers also have a greater filtering capacity when compared to the ordinary routers. Using proxy servers to cache can improve the network in three ways; network bandwidth is conserved hence improving the scalability, response time is reduced, and it increases the accessibility to web pages even if the source is offline.
There are also some disadvantages of caching using a proxy server. First of them is the bottleneck that may form because of the multitudes of client requests. Also there is proxy hierarchy whereby each request goes through levels in hierarchy when the request is missed in the first level. Refreshed pages are not well cached using proxy servers. There is also measurement uncertainty that is introduced by the proxy servers into the Internet.
Other than HTTP proxy servers work well with:
1 SHTTP – Secure Hyper Text Transfer Protocol
2 FTP – File Transfer Protocol
3 SOCKS – It is a protocol of firewall security.
4 WAIS – Wide Area Indexing Service
If a browser has to be manually specified, host identifier and port number must be defined. Host identifier is either the IP address or the network name of the host. The TCP/IP port is the port number that the server uses to act on the client requests. Special configuration files are now being used to automatically configure the proxy servers.
Some of the common types of proxy servers are web, intercepting, transparent, open, reverse, and split proxy servers. Web proxies filter web content that is offensive. Intercepting proxies are used in large organizations to ease administration and ensure that network use policies are abided by. Transparent proxy is similar to web proxy but is used only for emails. Open proxies accept connections from all IP addresses. Reverse proxies are installed along with web servers. Split proxies are two proxy servers that are installed in two computers.
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