Chapter 10 - Deploying the Squid Web Proxy Cache Server

Abstract

Proxy cache servers are implemented at the application layer and process specific Internet protocols, such as Hypertext Transfer Protocol (HTTP) and File Transfer Protocol (FTP). Rules are set up on the proxy server to determine how a workstation request should be processed. One of the main tasks of a proxy server is to cache Web pages and FTP files for proxy clients. These types of proxy servers are called proxy cache servers. Caching increases the performance of the network by decreasing the amount of data transferred from outside of a local network. To implement proxy caching, each workstation on the network is configured as a proxy client for a specific service. For example, a Web proxy client would configure his or her browser to acknowledge the proxy server. When the client makes a Web browser request to download a certain Web page, the client's browser makes the request to the proxy server. The proxy server has a cache of recently visited Web pages. This cache contains Web pages that workstations throughout the network have recently downloaded. The proxy server checks its cache to see if the Web page exists. If the page exists in the cache, then the cached page is sent to the client. If the page does not exist in the cache, the proxy server downloads the client's Web page from the specific Web site, enters it into the cache, and sends the page to the workstation. To ensure that the Web pages in the proxy cache are not out of date, proxy cache data expires after a preset time. In the Squid program, this setting is called the object refresh time. The refresh time ensures that old data is not transferred to the proxy clients.