From Dr. Tom Shinder's Configuring ISA Server 2004
Web Proxy Chaining as a Form of Network Routing
Web Proxy Chaining is a method you can use to forward Web Proxy connections from one ISA firewall to another ISA firewall. Web Proxy chains consist of upstream and downstream ISA firewalls. The upstream ISA firewalls are those closer to the Internet connection, and the downstream ISA firewalls are those further away from the Internet connection. Downstream ISA firewalls forward Web Proxy requests to upstream ISA firewalls. The first ISA firewall in the Web Proxy chain is the one closest to the Internet and the one responsible for obtaining the Internet content.
Web Proxy Chaining is useful in a number of scenarios.
Branch office ISA firewalls can be chained to upstream ISA firewalls at the corporate office.
Departmental ISA firewalls, which protect department-specific networks within the organization can be chained to upstream ISA firewalls located on a network services segment or upstream ISA firewalls that are directly connected to the Internet.
ISPs or large corporate customers can chain downstream ISA firewall Web caching arrays with upstream ISA firewall or ISA firewall Web caching array.
The advantage of using Web Proxy chaining is that you can reduce the overall bandwidth utilization on both the Internet link and all links between the downstream and upstream ISA firewalls in the Web Proxy chain. Figure 4.59 shows an example of a Web Proxy chain and the flow of information through the chain.
Figure 4.59: WebProxyChaining.vsd
A client on a protected Network behind an ISA...
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