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A proxy auto-config (PAC) file defines how web browsers and other user agents can automatically choose the appropriate proxy server (access method) for fetching a given URL. A PAC file contains a JavaScript function “ FindProxyForURL(url, host)”. This function returns a string with one or more access method specifications. These specifications cause the user agent to use a particular proxy server or to connect directly.Multiple specifications provide a fall-back when a proxy fails to respond. The browser fetches this PAC file before requesting other URLs. The URL of the PAC file is either configured manually or determined automatically by the Web Proxy Autodiscovery Protocol. == Context == Modern web browsers implement several levels of automation; users can choose the level that is appropriate to their needs. The following methods are commonly implemented: * Automatic proxy selection: Specify a host-name and a port number to be used for all URLs. Most browsers allow you to specify a list of domains (such as localhost) that will bypass this proxy.* Proxy auto-configuration (PAC): Specify the URL for a PAC file with a JavaScript function that determines the appropriate proxy for each URL. This method is more suitable for laptop users who need several different proxy configurations, or complex corporate setups with many different proxies. * Web Proxy Autodiscovery Protocol (WPAD): Let the browser guess the location of the PAC file through DHCP and DNS lookups. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Proxy auto-config」の詳細全文を読む スポンサード リンク
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