Microsoft Internet Security and Acceleration (ISA) Server 2000 has received a lot of attention during its beta development and recent release into the marketplace—and rightly so. ISA Server is a powerful product that is easy to use, yet highly versatile and scalable. In networking environments, the need to provide clients with Internet access while protecting the private network from security threats from the Internet has been a growing problem during the past decade. In today's e-commerce environment, connectivity with the Internet is often seen as essential for many businesses. But that connectivity often comes with a price and its own set of problems.
ISA Server is Microsoft's first server product that combines smart-caching features for Internet acceleration with multilayered IP firewall protection. Using this product, Windows 2000 networks can leverage the power of the Internet while protecting the network from potential intruders and threats. If you're considering deploying Microsoft ISA Server in your environment, you need to study its features and usage. For now, however, let's begin with an overview of ISA Server.
ISA Server is a combination product that provides acceleration and security. The acceleration feature of ISA Server simply means that ISA Server uses advanced caching of Internet objects, URLs, pages, and so on in order to speed client access to the Internet. The ISA Server resides between the private network and the Internet so that clients never directly access the Internet, but all traffic flows through the ISA Server. Using caching, ISA Server can store Internet objects on its local hard drive and return those objects directly from the cache.
Let's consider an example. Let's say that Client A wants to access the http://www.isanexample.com Web site. The client's browser makes this request to the ISA Server. ISA Server checks its cache, and if a valid version of the Web page resides in the cache, ISA Server provides Client A with that cached data. To the user on Client A, it appears as if the information has quickly returned from the Internet. http://www.isanexample.com is not found in the cache, ISA Server retrieves it from the Internet, caches it, and returns it to the client. When the next request for http://www.isanexample.com is made, it can be served directly from the cache. This caching process speeds client browsing because popular Web pages can be serviced from the cache instead of having to retrieve them from the Internet each time they are needed. Likewise, caching reduces traffic on the Internet link as well.
ISA Server includes a number of caching features that you can manage as an ISA Server administrator. You can choose to use Active Caching, in which ISA server actively reaches popular Web objects before they expire so that items are always current in the cache. You can also manage time-to-live values for HTTP and FTP content so that you have control over the way caching functions in your network. If your environment provides a Web server to the Internet, ISA Server can work with that Web server and provide reverse caching to Internet clients, which speeds access and reduces the burden on the Web server. Finally, ISA Server also supports hierarchical caching features, in which multiple ISA Servers or ISA server arrays can be "chained together" in a number of different ways. As you can see, ISA Server provides many caching features that provide service to all kinds of network implementation scenarios.