Cache Overview

ISA Server implements a cache of frequently-requested objects to improve network performance. You can configure the cache to ensure that it contains the data that is most frequently used by the organization or accessed by your Internet clients.

ISA Server can be used to allow communication between your local network and the Internet. Communication may be internal clients accessing servers on the Internet—in this case, ISA Server implements forward caching. Communication may be external clients accessing internal, publishing servers—for this case, ISA Server features reverse caching. Both scenarios can benefit from the ability of ISA Server to cache information, making it more quickly available to users.

ISA Server caching features include:

• Distributed caching. When you set up an array of ISA Server computers, you benefit from distributed content caching. ISA Server uses the Cache Array Routing Protocol (CARP) to enable multiple ISA Server computers to be arrayed as a single logical cache.
• Hierarchical caching. ISA Server further extends distributed caching by allowing you to set up a hierarchy of caches, chaining together arrays of ISA Server computers, so that clients can access objects from the cache geographically nearest them.
• Scheduled caching. Use the scheduled cache content download service to configure when the ISA Server should fetch commonly-requested content from the Internet to its cache.
• Reverse caching. ISA Server can cache content of publishing Web servers, thereby improving their performance and accessibility. All ISA Server caching features are applicable for the content on published servers.

For more information about the ISA Server cache, see About the ISA Server Cache.

Forward caching

ISA Server can be deployed as a forward caching server that provides internal clients with access to the Internet. ISA Server maintains a centralized cache of frequently requested Internet objects that can be accessed by any web-browser client. Objects served from the disk cache require significantly less processing than objects served from the Internet. This improves client browser performance, decreases user response time, and reduces bandwidth consumption on your Internet connection.

Reverse caching

ISA Server can be deployed in front of an organization's Web server that is hosting a commercial Web business or providing access to business partners. With incoming Web requests, ISA Server can impersonate a Web server to the outside world, fulfilling client requests for Web content from its cache. ISA Server forwards requests to the Web server only when the requests cannot be served from its cache.