We've discussed techniques to redirect traffic to general servers and specialized techniques to vector traffic to proxies and gateways. This final section will explain some of the more sophisticated redirection techniques used for caching proxy servers. These techniques are more complex than the previously discussed protocols because they try to be reliable, high-performance, and content-aware—dispatching requests to locations likely to have particular pieces of content.
Cisco Systems developed the Web Cache Coordination Protocol (WCCP) to enable routers to redirect web traffic to proxy caches. WCCP governs communication between routers and caches so that routers can verify caches (make sure they are up and running), load balance among caches, and send specific types of traffic to specific caches. WCCP Version 2 (WCCP2) is an open protocol. We'll discuss WCCP2 here.
Here's a brief overview of how WCCP redirection works for HTTP (WCCP redirects other protocols similarly):
Start with a network containing WCCP-enabled routers and caches that can communicate with one another.
A set of routers and their target caches form a WCCP service group. The configuration of the service group specifies what traffic is sent where, how traffic is sent, and how load should be balanced among the caches in the service group.
If the service group is configured to redirect HTTP traffic, routers in the service group send HTTP requests ...