HTTP: The Definitive Guide

Overview of Redirection Protocols

The goal of redirection is to send HTTP messages to available web servers as quickly as possible. The direction that an HTTP message takes on its way through the Internet is affected by the HTTP applications and routing devices it passes from, through, and toward. For example:

• The browser application that creates the client’s message could be configured to send it to a proxy server.

• DNS resolvers choose the IP address that is used for addressing the message. This IP address can be different for different clients in different geographical locations.

• As the message passes through networks, it is divided into addressed packets; switches and routers examine the TCP/IP addressing on the packets and make decisions about routing the packets on that basis.

• Web servers can bounce requests back to different web servers with HTTP redirects.

Browser configuration, DNS, TCP/IP routing, and HTTP all provide mechanisms for redirecting messages. Notice that some methods, such as browser configuration, make sense only for redirecting traffic to proxies, while others, such as DNS redirection, can be used to send traffic to any server.

Table 20-1 summarizes the redirection methods used to redirect messages to servers, each of which is discussed later in this chapter.

Table 20-1. General redirection methods

Mechanism	How it works	Basis for rerouting	Limitations
HTTP redirection	Initial HTTP request goes to a first web server that chooses a “best” web server to ...