Details:

  1. Enter in the browser address bar
  2. Browsers look at caches (expires and cache-control) to determine whether a resource has expired

The Expires header specifies a date/time after which the HTTP response is considered outdated. An invalid date, such as 0, indicates that the resource has expired

Cache-control, a generic header field, implements the caching mechanism by specifying instructions. The cache instructions are one-way and represent instructions set in the request, which are not necessarily included in the response. If the resource is not cached, send a new request b. If the resource is cached, check whether it is fresh enough. If it is fresh enough, provide it to the client. 3. The browser parses the URL and obtains the port, path, protocol, and host. The browser assembles an HTTP request packet. 5. The browser obtains the host IP address.