Transparent proxy caching eliminates one of the big drawbacks of the proxy server approach: the requirement to configure web browsers. Transparent caches work by intercepting HTTP requests (TCP traffic destined to port 80) and redirecting them to web cache servers or cache clusters. This style of caching establishes a point at which different kinds of administrative control are possible, for example, deciding how to load balance requests across multiple caches.
The filtering of HTTP requests from all outbound Internet traffic adds additional latency. For example, caches deployed in conjunction with Layer 4 (L4) switches rely on the fact that these switches intercept all traffic which is directed at port 80 and send all other traffic directly to the WAN router.
There are two ways to deploy transparent proxy caching: at the switch level and at the router level. Router-based transparent proxy caching uses policy-based routing to direct requests to the appropriate cache(s). For example, requests from certain clients can be associated with a particular cache.
In switch-based transparent proxy caching, the switch acts as a dedicated load balancer. Switches are generally less expensive than routers. Switch-based transparency is also often viewed as more attractive than router-based transparency because there is not the additional overhead that policy-based routing incurs.
The use of L4 switches for transparent caching is an example of how related network components play a role in the effectiveness of a web caching solution. For transparent caching, these switches provide a form of local load balancing.