HTTP does not walk the Web alone. The data in an HTTP message is governed by many protocols on its journey. HTTP cares only about the endpoints of the journey-the sender and the receiver-but in a world with mirrored servers, web proxies, and caches, the destination of an HTTP message is not necessarily straightforward.

This chapter is about redirection technologies-network tools, techniques, and protocols that determine the final destination of an HTTP message. Redirection technologies usually determine whether the message ends up at a proxy, a cache, or a particular web server in a server farm. Redirection technologies may send your messages to places a client didn't explicitly request.

In this chapter, we'll take a look at the following redirection techniques, how they work, and what their load-balancing capabilities are (if any):

·         HTTP redirection

·         DNS redirection

·         Anycast routing

·         Policy routing

·         IP MAC forwarding

·         IP address forwarding

·         The Web Cache Coordination Protocol (WCCP)

·         The Intercache Communication Protocol (ICP)

·         The Hyper Text Caching Protocol (HTCP)

·         The Network Element Control Protocol (NECP)

·         The Cache Array Routing Protocol (CARP)

·         The Web Proxy Autodiscovery Protocol (WPAD)

 

Hypertext Transfer Protocol (HTTP)