Caching with ISA Server

Microsoft ISA Server is a firewall system that also provides sophisticated caching capabilities for speeding up access to Web content. ISA Server acts as a secure intermediary between an internal network and the external Internet. Its caching capabilities provide accelerated access to information on both sides of the firewall. Specifically, ISA Server provides two broad types of caching:

• Forward caching: This is for internal clients that are accessing information on the Internet. ISA Server maintains a local cache of frequently cached pages, which reduces the access time significantly for internal clients . In addition, the system administrator can schedule ISA Server to scan the Internet for specific content so that it will already be available in the cache the first time that it is accessed.

• Reverse caching: This is for external clients that are accessing information on internal, published servers. ISA Server impersonates the internal servers for external clients and fulfills requests directly from its cache. ISA Server will redirect the request directly to the internal server only if the external client's request cannot be fulfilled from the cache.

ISA Server stores cached content locally both on disk and in memory. This mechanism will obviously consume resources on the server, so ISA Server provides two complementary caching mechanisms for reducing this burden :

• Distributed caching: ISA Server will cache content across an array of servers, but it will organize the content as a single logical cache. Essentially , ISA Server is distributing the caching burden across multiple servers. It accomplishes this using the Cache Array Routing Protocol (CARP).

• Hierarchical caching: ISA Server extends the distributed caching mechanism by administering multiple server arrays (essentially a supergroup of multiple groups of servers). ISA Server will route client requests to the most available server array.

The performance improvements with ISA Server can be dramatic. Internal clients will experience reduced response times for retrieving Internet content. In addition, bandwidth usage on the Internet connection will be reduced, which will result in a potentially faster Internet connection for all clients.

Microsoft recommends that the ideal deployment scenario for .NET Web applications is to use nondistributed deployment with ISA Server. This means you should install your application in a Web farm (in other words, on multiple servers) and use ISA Server for load balancing and caching services. It is not ideal to manually distribute components across multiple servers and have them communicate using .NET remoting.

Note

You can read more about ISA Server at http://msdn.microsoft.com/library/default.asp?url=/library/en-us/isa/isaabout_0sdz.asp . You can read more about non-distributed deployment with ISA Server at http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dwamish7/html/vtconNon-DistributedDeploymentWithISAServer.asp .

This concludes our discussion of caching in ASP.NET.