HTTP protocol

The underlying protocol that carries web application traffic between the web server and the client is known as the Hypertext Transport Protocol (HTTP). HTTP/1.1, the most common implementation of the protocol, is defined in RFCs 7230-7237, which replaced the older version defined in RFC 2616. The latest version, known as HTTP/2, was published in May 2015, and it is defined in RFC 7540. The first release, HTTP/1.0, is now considered obsolete and is not recommended.

As the internet evolved, new features were added to the subsequent releases of the HTTP protocol. In HTTP/1.1, features such as persistent connections, OPTIONS method, and several other improvements in the way HTTP supports caching were added.

HTTP is a client-server protocol, wherein the client (web browser) makes a request to the server and in return the server responds to the request. The response by the server is mostly in the form of HTML-formatted pages. By default, HTTP protocol uses port 80, but the web server and the client can be configured to use a different port.

HTTP is a cleartext protocol, which means that all of the information between the client and server travels unencrypted, and it can be seen and understood by any intermediary in the communication chain. To tackle this deficiency in HTTP's design, a new implementation was released that establishes an encrypted communication channel with the Secure Sockets Layer (SSL) protocol and then sends HTTP packets through it. This was called HTTPS or HTTP over SSL. In recent years, SSL has been increasingly replaced by a newer protocol called Transport Layer Security (TLS), currently in version 1.2.