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Before describing how to cross the domain, let's get a sense of the concept: URL. The following is excerpted from Wikipedia.
Uniform Resource Locator (or Unified Resource Locator / location address ,URL address , etc., English:uniform/universal Resource Locator, Often abbreviated as a URL), sometimes referred to as the Web address ( URL ).
The standard format for Uniform Resource Locators is as follows:
Protocol type://server address (need to add port number if necessary)/path/file name
There are many types of protocols, such as: HTTP and HTTPS are the most commonly used for browsing Web pages, and there are ed2k and thunder,qq chat Tencent for downloading resources. Of course there are many other types of agreements, which are not listed here.
The Uniform Resource Locator for Hypertext Transfer Protocol (HTTP) will include five basic elements of information from the Internet in a simple address:
Most Web browsers do not require users to enter the "http://" section of the Web page, because most Web content is Hypertext Transfer Protocol files. Similarly, "A" is a common port number for Hypertext Transfer Protocol files, so it is not generally necessary to specify. In general, users simply type part of the Uniform Resource Locator (zh.wikipedia.org/wiki/special:%e9%9a%8f%e6%9c%ba%e9%a1%b5%e9%9d%a2).
Because the Hypertext Transfer Protocol allows the server to redirect the browser to another Web page address, many servers allow users to omit parts of the web address, such as www. Technically, the omitted page address is actually a different web address, and the browser itself cannot determine whether the new address is available, and the server must complete the redirected task.
Here is the server part of the URL, some of the information is also known as the domain name.
Take zh.wikipedia.org as an example ,org is the top-level domain name,wikipedia.org is a domain name,zh.wikipedia.org is a level two domain name. Of course, there is also information about Wikipedia as a first-class domain name, zh is called a two-level domain name, such as Wikipedia is so called, no matter what kind of argument, the key is to know that the domain name has such a division method. And so on, there are three level domain name, four level domain name and so on.