However, these organizations will certainly
want to conserve Internet bandwidth whenever possible. Web chaining allows these
organizations to deploy a hierarchical array of ISA Servers that can effectively distribute
the proxying workload among each other.
The caching web proxy functionality of ISA Server 2006 will be covered in more
detail in Chapter 14; look there for further details. However, it is useful to understand
how Web Chaining rules interact with the web proxy function. The basics of web
chaining require that you understand that a downstream server is closer to the inside
of the network where the client nodes are. Upstream servers are out on the perimeter,
closer to the Internet. As a network node makes a request to the local web proxy
server, that downstream server will evaluate its proxy and web chaining rules as
follows:
1. ISA Server will check to ensure that the request is allowed.
2. If the request is allowed, the server is set to cache content, and a valid version
of the object exists in the cache, then the server will return the content to
the requestor.
3. If the server could not fulfi ll the request, it will check the Web Chaining
rules to determine where to forward the request.
4. The next server upstream will perform the same steps to attempt to fulfi ll
the request. If no caching proxies can fulfi ll the request it will eventually be
forwarded to the Internet.
Configuring Microsoft Internet Security and Acceleration Server 2006 ??? Chapter 11 397
Cache
As we just noted, the caching web proxy functionality of ISA Server will be covered
in greater detail in Chapter 14.
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