Reply #40: Damn. The more I'm learning, the less I like this

[Duer 157099]

And again, not because it's DU doing it, but because of who *else* is using this.

Here's some more info, and another good link:

http://www.oreilly.com/catalog/webcaching/chapter/ch05.html

As we discussed in Chapter 4, "Configuring Cache Clients", one of the most difficult problems you might face in deploying a web caching service is getting users to use your cache. In some cases, the problem is mostly political; users might resist caching because of privacy concerns or fears they will receive stale information. But even if users are convinced to use the cache -- or have no choice -- administrative hurdles may still be a problem. Changing the configuration of thousands of installed clients is a daunting task. For ISPs, the issue is slightly different -- they have little or no control over their customers' browser configurations. An ISP can provide preconfigured browsers to their customers, but that doesn't necessarily ensure that customers will continue to use the caching proxy.

Because of problems such as these, interception caching has become very popular recently. The fundamental idea behind interception caching (or proxying) is to bring traffic to your cache without configuring clients. This is different from a technique such as WPAD (see "Web Proxy Auto-Discovery"), whereby clients automatically locate a nearby proxy cache. Rather, your clients initiate TCP connections directly to origin servers, and a router or switch on your network recognizes HTTP traffic and redirects it to your cache. Web caches require only minor modifications to process requests received in this manner.

As wonderful as this may sound, a number of issues surround interception caching. Interception caching breaks the rules of the Internet Protocol. Routers and switches are supposed to deliver IP packets to their intended destination. Diverting web traffic to a cache is similar to a postal service that opens your mail and reads it before deciding where to send it or whether it needs to be sent at all.<1> The phrase connection hijacking is often used to describe interception caching, as a reminder that it violates the Internet Protocol standards. Interception also leads to problems with HTTP. Clients may not send certain headers, such as &Cachectrl;, when they are unaware of the caching proxy.