Interception caching begins at the IP (network) layer, where all sorts of IP packets are routed between nodes. Here, a router or switch recognizes HTTP packets and diverts them to a cache instead of forwarding them to their original destination. There are a number of ways to accomplish the interception:
An inline cache is a device that combines both web caching and routing (or bridging) into a single piece of equipment. Inline caches usually have two or more network interfaces. Products from Cacheflow and Network Appliance can operate in this fashion, as can Unix boxes running Squid.
Switching is normally a layer two (datalink layer) activity. A layer four switch, however, can make forwarding decisions based on upper layer characteristics, such as IP addresses and TCP port numbers. In addition to HTTP redirection, layer four switches are also often used for server load balancing.
WCCP is an encapsulation protocol developed by Cisco Systems that requires implementation in both a router (or maybe even a switch) and the web cache. Cisco has implemented two versions of WCCP in their router products; both are openly documented as Internet Drafts. Even so, use of the protocol in a product may require licensing from Cisco.
Policy routing refers to a router’s ability to make forwarding decisions based on more than the destination address. We can use this to divert packets based on destination ...