Implementing ISA ServerCaching

Caching Overview

• ISA Server supports caching as a way to improve the speed of retrieving information from the Internet.

• From the internal user’s point of view, caching improves Internet access performance.

• From the network administrator’s point of view, caching provides the added benefit of reducing the use of network bandwidth

• ISA Server extends the benefits of caching by enabling scheduled content download jobs in which ISA Server downloads Internet content to the cache before any user requests the object

What Is Caching

• Caching stores Web content on the ISA Server computer in memory or on the server’s hard disk.

• When a user requests Web information that is in the cache, ISA Server provides the information from the cache, enabling a quicker response to the client.

• ISA Server can be configured to enable the caching of Hypertext Transfer Protocol (HTTP) and File Transfer Protocol (FTP) objects.

benefits

• Improved performance

• Reduced bandwidth usage

How Caching Works

1. The Web proxy client sends a request for content located on an Internet Web server. The Web request is intercepted by ISA Server and forwarded to the Web proxy filter.

• 2. ISA Server checks whether the requested content is contained in its cache. If the content is not in the cache, or if the content has expired (that is, the header information in the content indicates that it should no longer be served from a cache),ISA Server forwards the request to the Web server on the Internet.

3. The Web server on the Internet returns the information requested.

4. The ISA Server Web proxy filter places the Web content in its in-memory cache. ISA Server uses an in-memory cache to store the most frequently requested content.

5. After placing the Web content in the in-memory cache, ISA Server Web caching server returns the content to the requesting user

6. After a time, the ISA Server Web proxy filter will copy the contents of the in-memory cache to the disk-based cache. If the content is not frequently accessed, the in-memory cache will flush the content and the only copy of the content on ISA server will reside in the disk-based cache.

Caching Scenarios

• ISA Server supports both forward and reverse caching

• Forward caching occurs when a user on the corporate network makes a request for Web content located on an Internet Web server.

• The user initiates an HTTP, Hypertext Transfer Protocol Secure (HTTPS), or FTP request to an Internet Web server and the request is intercepted by ISA Server. ISA Server retrieves the content from the Internet Web server, stores that content in its cache, and returns the content to the user.

• Reverse caching occurs when users on the Internet request Web content located on a server on the corporate network that is accessible through a Web publishing rule.

• When an Internet user requests content from the internal server, ISA Server forwards the request to the Web server. The Web server sends the requested content to ISA Server, which then returns the content to the Internet user who made the request.

• In this scenario, ISA Server will cache a copy of the requested information so that the next request for the same information can be provided from the ISA Server cache rather than again accessing the internal Web server

What Are Content Download Jobs?

• ISA Server extends caching performance by enabling content download jobs.

• By monitoring and analyzing Internet access, you can determine which Web content is most likely to be requested by internal clients.

• You can then create a content download job to download the Web content to the ISA Server cache before any client requests the object.

• Content download jobs allow you to schedule content for download at a specific time or at recurring times.

Benefits of Using Content Download Jobs

• The main reasons for using content download jobs are to improve Internet access performance and decrease the use of bandwidth to the Internet.

How Content Download Jobs Work

1. Create a content download job that specifies Web content to be retrieved from the Internet and when content retrieval occurs.

2. At the scheduled time, ISA Server uses a background process to retrieve the content from the Web server. The content is stored in the ISA Server cache based on the settings specified by the content download job.

3. A user on the internal network sends a request for the Web content to the ISA Server computer. The Firewall service passes the request to the Web proxy filter.

4. The ISA Server Web proxy filter determines that the content is in the Web cache, so ISA Server retrieves the content from the cache.

5. Content retrieved from cache is returned to the requesting user

How Caching Is Implemented in ISA Server

• RAM and disk caching:ISA Server allocates RAM for caching popular objects and caches other objects on disk.

• When caching an object, ISA Server first places an object into the RAM cache and then writes objects to disk.

• By default, ISA Server uses 10 percent of the RAM on the server to cache Web content

• Maintaining the RAM cache in physical memory:

• Directory of cached object

• Single cache file

• Quick recovery

• Efficient cache updates

• Automatic cleanup

What Is Web Chaining and Caching

• Some organizations include multiple locations with computers running ISA Server deployed in each location.

• In this scenario, you can combine caching with Web proxy chaining to optimize caching performance.

• Web proxy chaining is useful when your organization has multiple branch-office locations but all Internet requests are routed through one location at the head office.

• Implement :install ISA Server in each office and then configure ISA Server at the branch offices to route all Internet requests to the ISA Server computer at the head office.

benefits of using Web chaining

• If all the servers running ISA Server in the branch offices are configured to forward their requests to the head-office ISA Server, the head-office ISA Server will develop a large cache that contains many requested items

branch-office/main-office scenario

branch-office/main-office scenario

1. The client sends a request for Web content to the Web caching server at the branch office. If the Web caching server at the branch office contains a valid version of the Web content in its cache, it will return the content to the requesting user.

2. If the content requested by the branch-office user is not contained in the branchoffice server’s cache, the request is forwarded to an upstream Web caching server in the Web proxy chain.

3. If the upstream Web caching server has a valid copy of the requested content in cache, the content is returned to the branch-office Web caching server. The branch-office Web caching server places the content in its own Web cache and then returns the content to the branch-office user who requested the content.

4. If the upstream Web caching server at the main office does not contain the requested content in its cache, it will forward the request to the Web server on the Internet. The Internet Web server returns the requested content to the main-office Web caching server. The Web caching server at the main office places the content in cache.

5. The main office returns the content to the branch-office Web caching server. The branch-office Web caching server places the content in its cache.

6. The branch-office Web caching server returns the content from its cache to the requesting user.

Configuring Caching

• How to Enable Caching and Configure Cache Drives

How to Configure Cache Settings

What Are Cache Rules

• Why Use Cache Rules• EX: users in your organization may frequently

access a Web site, so you may want to configure the cache so that all content from that Web site is cached on the computer running ISA Server.

• If the Web site contains critical information that changes frequently, you may need to implement the opposite solution, that is, configure the Web site to never be cached.

Managing Cache Rules

• Modifying settings

• Managing rule order

• Disabling or deleting cache rules

• Export and import cache rules

Configuring Content Download Jobs

• How to Configure Content Download Jobs