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Module 4: Configuring Caching. Overview Cache Overview Configuring Cache Policy Configuring Cache Settings Configuring Scheduled Content Downloads.

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Presentation on theme: "Module 4: Configuring Caching. Overview Cache Overview Configuring Cache Policy Configuring Cache Settings Configuring Scheduled Content Downloads."— Presentation transcript:

1 Module 4: Configuring Caching

2 Overview Cache Overview Configuring Cache Policy Configuring Cache Settings Configuring Scheduled Content Downloads

3 When you deploy Microsoft® Internet Security and Acceleration (ISA) Server 2000 in Cache mode or in Integrated mode, ISA Server maintains a centralized cache of Internet objects and fulfills client requests from this cache. When ISA Server retrieves objects from its cache, only local network traffic occurs because the objects are not retrieved from the Internet. By using caching, ISA Server can help an organization reduce the bandwidth consumption of Internet connections.

4 After completing this module, you will be able to: Describe the cache process that ISA Server uses to process requests from client computers. Configure the cache policy. Configure cache settings. Configure scheduled content downloads.

5 Cache Overview Caching Functions Processing Requests for New Objects Processing Requests for Cached Objects

6 ISA Server uses several caching functions to provide users with fast and efficient access to Web objects. The Microsoft Web Proxy service supports requests from ISA Server clients for access to Web sites and File Transfer Protocol (FTP) sites. When a user requests access to a site on an external network, such as the Internet, the request goes to the ISA Server computer for processing. The process that ISA Server uses to fulfill the request depends on whether the ISA Server computer retrieves the object from the Internet or from its cache. Tip: When configuring ISA Server to perform caching of Web objects, configure the Web browsers on the client computers to use the smallest possible amount of disk space for local Web caching.

7 In this lesson you will learn about the following topics: Caching functions Processing requests for new objects Processing requests for cached objects Configuring scheduled content downloads

8 Caching Functions RAM and Disk Caching Most of Working Set in RAM Directory of Cached Objects Single Cache File Quick Recovery Efficient Cache Updates Active Caching Cache Pre-Fetching Automatic Cleanup Cache

9 ISA Server includes the following functions that optimize cache performance:

10 RAM and disk caching. Allocates random access memory (RAM) for caching popular objects and caches other objects on disk. When caching an object, ISA Server places an object into the RAM cache first and then writes objects to disk. RAM and disk caching help to improve access speed for users to popular Web sites.

11 Most of working set in RAM. Keeps most of the memory that is used for caching in RAM instead of paging it to disk to ensure faster processing.

12 Directory of cached objects. Maintains a directory of cached objects in RAM to enable fast access to cached objects.

13 Single cache file. Maintains a single cache file per disk partition to hold cached objects so that gaining access to objects does not incur additional system resources that would be needed for opening and closing multiple files.

14 Quick recovery. Quickly rebuilds the directory of cached objects on startup, even after an abnormal termination.

15 Efficient cache updates. Automatically determines which objects to keep in the RAM cache. This decision is based on the likelihood of a user requesting the same object again, which is determined by how recently and how frequently an object is accessed.

16 Active caching. Retrieves a more current version of an object automatically from the original Web site before an object becomes outdated. Active caching ensures that the objects that users gain access to most frequently are contained in the cache.

17 Cache pre-fetching. Allows administrators to define Web sites that ISA Server can cache in advance of the first user gaining access to the site.

18 Automatic cleanup. Removes objects that have not been accessed recently or frequently when the disk space that is allocated to the cache starts to fill up.

19 Processing Requests for New Objects RAM Disk Cache Directory Objects 1 Request A 4 A Cache Directory Backup Cache Entry 1 Allocate Cache Entry A Internet 3 5 Batch Update

20 When a user requests a Hypertext Transfer Protocol (HTTP) or FTP object, the Web Proxy client sends the request to the Web Proxy service that is included with ISA Server. An HTTP object is an object, such as Web pages and images, that a client retrieves from a Web server by using the HTTP protocol. An FTP object is an object, such as a program file, that a client retrieves from an FTP server by using the FTP protocol.

21 When the Web Proxy service receives the request, the following actions occur: 1. The Web Proxy client sends a Web request to the ISA Server computer. 2. The Web Proxy service checks the cache directory to determine whether the ISA Server computer holds a copy of the requested object in its cache. If the object is not in its cache, the Web Proxy service creates an entry for the object in the cache directory and allocates space for the object in the RAM cache. 3. The Web Proxy service retrieves the object from the Internet and then places a copy of the object into the RAM cache. 4. The Web Proxy service returns the object to the Web Proxy client.

22 5. Periodically, the Web Proxy service copies multiple objects from the RAM cache to the disk cache. These operations are called batch updates because ISA Server copies multiple objects when system usage is lower. 6. Periodically, ISA Server creates a backup copy of its cache directory on the hard disk. This backup copy aides in recovering cache information when restarting the Web Proxy service after an abnormal termination of the service. Note: By default, the Microsoft Firewall service forwards HTTP requests from Firewall clients and SecureNAT clients to the Web Proxy service, which then caches these requests. Forwarding the request results in improved performance for all types of clients.

23 Processing Requests for Cached Objects RAM Disk Cache Directory Objects 1 Request A A 3 Cache Directory Backup Cache Entry 1 2

24 When a user requests a cached HTTP or FTP object, the Web Proxy service retrieves the object that ISA Server caches in RAM or writes to the hard disk. Whether the Web Proxy service retrieves the object from RAM or from the hard disk, the client receives the object quickly and no Internet traffic occurs.

25 When a user requests an HTTP or FTP object that ISA Server has in its cache, the following actions occur: 1. The client sends a Web request to the ISA Server computer. 2. The Web Proxy service checks the cache directory to determine whether the ISA Server computer holds a copy of the requested object in its cache. If the object is in the cache, it can be located either in RAM or on the hard disk. 3. The Web Proxy service retrieves the object from the cache and then returns the object to the client.

26  Configuring Cache Policy Configuring HTTP Caching Configuring Expiration Policies Configuring Active Caching Configuring FTP Caching Configuring Advanced Cache Settings Configuring Actions for Inaccessible Objects

27 Depending on how you configure the cache policy, ISA Server determines whether to retrieve the Internet content from its cache or from another server. You can configure cache policies for both HTTP and FTP objects. You can configure a policy for expiration, rate of renewal, and types of content. You can also configure actions to occur when objects are not accessible to a client.

28 In this lesson you will learn about the following topics: Configuring HTTP caching Configuring expiration policies Configuring active caching Configuring FTP caching Configuring advanced cache settings Configuring actions for inaccessible objects

29 Configuring HTTP Caching Cache Configuration Properties General OKCancelApply No less than:15Minutes No more than:1Days No less than:15Minutes No more than:1Days Enable HTTP Caching Unless source specifies expiration, update source: Restore Defaults HTTPFTPActive CachingAdvanced Frequently (Expire immediately) Normally Less frequently (Reduced network traffic is important) Set Time To Live (TTL) of object in cache to: This percentage of content age20 (Time since creation of modification): Select to enable HTTP caching.

30 When you enable HTTP caching, you configure ISA Server to store HTTP objects in the cache. ISA Server keeps an object in its cache for an amount of time that is specific to the object. The time for an object to remain in the cache is called the Time-to-Live ( TTL ) period. When ISA Server places an object into its cache, it sets a TTL for the object. ISA Server returns the HTTP object that is stored in its cache to clients until the TTL has expired. ISA Server can set the TTL based on the creation date and the modification date of the object or by using the settings that you configure. Important: Many Web pages use meta-tags to set expiration dates for content. When a Web page has an expiration date, ISA Server sets the TTL of the object to match the Web page's expiration date. For more information about Web pages and caching, see Microsoft Knowledge Base Article Q at support/kb/articles/Q234/0/67.ASP and the HTTP 1.1 specification in RFC 2616, "Hypertext Transfer Protocol - HTTP/1.1," under Additional Readings on the Student Materials compact disc.

31 To enable HTTP caching: 1. In ISA Management, in the console tree, click Cache Configuration, and then in the details pane, click Configure Cache Policy. 2. In the Cache Configuration Properties dialog box, on the HTTP tab, select the Enable HTTP caching check box.

32 Configuring Expiration Policies Cache Configuration Properties General OKCancelApply No less than:15Minutes No more than:1Days Enable HTTP Caching Unless source specifies expiration, update source: Restore Defaults HTTPFTPActive CachingAdvanced Frequently (Expire immediately) Normally Less frequently (Reduced network traffic is important) Set Time To Live (TTL) of object in cache to: This percentage of content age20 (Time since creation of modification): Select to create pre- configured expiration policies. Select to create custom expiration policies.

33 When you enable HTTP caching, you can use the default expiration policy for HTTP objects for ISA Server, or you can configure a customized expiration policy. ISA Server retrieves updated copies of cached Web pages from the Internet based on the expiration policy.

34  Selecting an Expiration Policy ISA Server includes preconfigured options for expiration policies. The following preconfigured options are always overwritten by the source's expiration policy: Frequently. Objects in the cache are more current, but network performance may be degraded because the ISA Server computer retrieves objects more often from the Internet. Choose this setting when you have available bandwidth to the Internet at all times. Normally. Objects are updated somewhat frequently, but network performance is considered. This setting is the default policy, which provides the best performance in most situations. Less frequently. Objects in the cache will be less current, but network performance is not degraded. Choose this setting when the available bandwidth to the Internet is severely limited.

35 To select an expiration policy for HTTP caching: In ISA Management, in the console tree, click Cache Configuration, and then in the details pane, click Configure Cache Policy. In the Cache Configuration Properties dialog box, on the HTTP tab, select an expiration policy option, and then click OK.

36  Customizing an Expiration Policy If none of the preconfigured expiration policies meets the needs of your organization, you can use custom settings to modify an expiration policy. ISA Server sets the TTL of objects that do not contain an expiration date based on a percentage of content age, which is the time since the object was created or modified. ISA Server obtains the content age from the HTTP header of the object. Using the content age ensures that ISA Server caches objects that are infrequently updated on the Web server for a longer time than objects that are frequently updated. Decreasing the percentage of content age configures ISA Server to update cached objects more frequently but results in more network traffic. Increasing the percentage reduces network traffic but makes it more likely that users receive outdated Web pages. Configure an expiration policy that balances your organization's need for current data with the need for network performance.

37 To customize an expiration policy: 1. In ISA Management, in the console tree, click Cache Configuration, and then in the details pane, click Configure Cache Policy. 2. In the Cache Configuration Properties dialog box, on the HTTP tab, click Set Time-to-Live (TTL) of object in cache.

38 3. In the At this percentage of content age (Time since creation or modification) box, type the percentage of content age to which ISA Server will set the TTL as follows, and then click OK: In the No less than box, type the minimum time that the HTTP objects should remain in the cache, and then in the No more than box, type the maximum time that the HTTP objects should remain in the cache. In the No less than and No more than lists, select a unit of time: Seconds, Minutes, Hours, Days, or Weeks. Note: To reset the HTTP expiration policy to the default settings, in the Cache Configuration Properties dialog box, on the HTTP tab, click Restore Defaults.

39 Cache Configuration Properties General OKCancelApply Enable active Caching Active caching automatically retrieves frequently accessed files. Restore Defaults HTTPFTPActive CachingAdvanced Frequently (Client performance is more important) Normally (Client performance and reduced network traffic are equally important) Less frequently (Reduced network traffic is more important) Retrieve files: Configuring Active Caching Select to create an active caching policy.

40 With active caching enabled, ISA Server analyzes HTTP objects that are in the cache to determine which are the most frequently accessed objects. When the TTL of an object in the cache is close to expiring, ISA Server automatically updates the object, even if there is no current client request for the object. Active caching ensures that recent versions of frequently accessed objects are in the cache for the next client request. You can configure policies for active caching to ensure that users have access to popular content in a manner that balances your organization's need for current data with network performance. Important: When you configure ISA Server to connect to the Internet by using a dial-up connection, ISA Server will dial out to the Internet Service Provider (ISP) when retrieving the requested content. You should disable active caching if you need to reduce the amount of time that ISA Server is connected to the Internet.

41  Enabling Active Caching To enable active caching: 1. In ISA Management, in the console tree, click Cache Configuration, and then in the details pane, click Configure cache policy. 2. In the Cache Configuration Properties dialog box, on the Active Caching tab, select the Enable active caching check box.

42  Selecting an Active Caching Policy When you enable active caching, you must select an expiration policy for the cached objects. ISA Server has the following preconfigured options for active caching: Frequently. Objects in the cache are more current, but network performance may be degraded because ISA Server retrieves objects more often from the Internet. Normally. Objects are updated somewhat frequently, but ISA Server considers network performance. This option is the default policy. Less frequently. Objects in the cache will be less current, but network performance is not degraded.

43 To select an expiration policy for active caching: In ISA Management, in the console tree, click Cache Configuration, and then in the details pane, click Configure Cache Policy. In Cache Configuration Properties dialog box, on the Active Caching tab, select an active caching option, and then click OK. Note: To reset caching to the default settings, in Cache Configuration Properties dialog box, on the Active Caching tab, click Restore Defaults.

44 Cache Configuration Properties General OKCancel Enable FTP caching Restore Defaults HTTPFTPActive CachingAdvanced Configuring FTP Caching Specify a time for FTP objects to remain in the cache. Apply Time to Live for all objects: 1440Minutes

45 In addition to HTTP objects, you can configure ISA Server to store FTP objects in the cache. When you configure FTP caching, the cache settings apply to all of the files that users retrieve by using the FTP protocol. For FTP objects, you can choose whether to activate caching and you can configure the TTL for FTP objects. A high TTL setting increases the likelihood of users receiving outdated FTP objects. A low TTL setting decreases the likelihood of users receiving outdated FTP objects but increases Internet traffic. By default, the TTL for all FTP objects is set to one day. Important: Unlike the HTTP protocol, the FTP protocol has no provisions for specifying file expiration. Because ISA Server cannot determine the appropriate TTL for specific files, ISA Server applies the same TTL to all FTP objects.

46 To configure FTP caching: 1. In ISA Management, in the console tree, click Cache Configuration, and then in the details pane, click Configure Cache Policy. 2. In the Cache Configuration Properties dialog box, on the FTP tab, select the Enable FTP caching check box. 3. In the Time to Live for all objects box, type a time for FTP objects to remain in the cache. 4. In the Time to Live for all objects list, select a unit of time: Seconds, Minutes, Hours, Days, or Weeks, and then click OK.

47 Configuring Advanced Cache Settings Cache Configuration Properties General OKCancelApply Restore Defaults HTTPFTPActive CachingAdvanced Maximum size of URL cached in memory (bytes):12800 Do not return the expired object (return an error page) Return the expired object only if expiration was: At less that this percentage of original Time 50 to Live: But no more than (minutes):60 If Web site of expired object cannot be reached: Percentage of available memory to use for caching:50 Do not cache objects larger than:1KB Cache objects that have an unspecified last modification time Cache objects even if they do not have an HTTP status code of 200 Cache dynamic content (objects with question marks in the URL) Select to configure cache settings for specific objects.

48 You can configure how ISA Server caches specific types of HTTP objects. By limiting certain types of content, you can improve the efficiency of the caching process. For example, you can configure ISA Server to limit the size of cached objects to reserve cache space for additional smaller objects.

49 To configure content settings for caching: In ISA Management, in the console tree, click Cache Configuration, and then in the details pane, click Configure Cache Policy. In the Cache Configuration Properties dialog box, on the Advanced tab, select one or more of the following options, and then click OK. Cache Configuration Properties

50 Configuring Actions for Inaccessible Objects ISA Server ISA Server Client 301 Client requests object 1 Object is not available 2 ISA Server returns the expired object from its cache and caches error response 3 Internet

51 You can configure ISA Server to retrieve an object from its cache when the object is not accessible on the Internet, even if the TTL for the object has expired. Configure settings for returning expired objects only when viewing an expired version of an object is preferable to not viewing the object at all. You can also cache the response to requests that failed to return an object. This type of caching is referred to as negative caching. When you configure negative caching, ISA Server returns error messages to clients more quickly. Important: When you configure negative caching, ISA Server caches negative results, even if the Web site is temporarily unavailable. Until the TTL expires, clients may receive an error message from ISA Server even if the object is available again.

52  Returning Expired Objects If the cache settings permit, ISA Server can return an expired version of an object from the cache. If the expiration time exceeds the percentage of the TTL that you specify, ISA Server does not return the object. In addition, if the expiration time exceeds the maximum time that you specify, ISA Server does not return the object. For example, if you specify 30 minutes as the maximum time, and the original TTL was 100 minutes, ISA Server returns an object only if no more than 30 minutes has passed since the original TTL expired.

53 To return expired objects from the cache when a Web server is not accessible: 3. In ISA Management, in the console tree, click Cache Configuration, and then in the details pane, click Configure Cache Policy. 4. In the Cache Configuration Properties dialog box, on the Advanced tab, click Return the expired object only if expiration was, specify the TTL limits for the object as follows, and then click OK: In the At less than this percentage of original Time to Live box, specify the maximum percentage of the TTL for which ISA Server returns an object after the object's original TTL expired. In the But no more than (minutes) box, specify the maximum number of minutes for which ISA Server returns an object after the object's TTL expired.

54  Configuring Negative Caching You can configure negative caching to cache error responses to client requests. When you configure negative caching, HTTP objects with the following status codes are cached: Status code Description 203Partial information 300Redirection 301Object has moved permanently 410Object is gone

55 To configure negative caching: 1. In ISA Management, in the console tree, click Cache Configuration, and then in the details pane, click Configure Cache Policy. 2. In the Cache Configuration Properties dialog box, on the Advanced tab, select the Cache objects even if they do not have an HTTP status code of 200 check box, and then click OK. Tip: You can change the error messages that ISA Server returns to client computers by editing the Web pages in the ErrorHtmls folder, which is located under the ISA Server installation folder.

56  Configuring Cache Settings Adjusting Cache Size Adjusting Memory Allocation

57 For each ISA Server computer, you can configure the size and the location of the cache used by the Web Proxy service. It is important that you allocate an appropriate amount of cache space because objects are dropped from the cache when the cache reaches its capacity. You can also configure the percentage of total memory to use for caching. Configuring cache settings properly will improve the efficiency of ISA Server caching operations.

58 In this lesson you will learn about the following topics: Adjusting cache size Adjusting memory allocation

59 Adjusting Cache Size LONDON Properties Cache Drives LONDON OKCancelApply Set 100Maximum cache size (MB): Total disk space (MB):39064 Total maximum cache size (MB):100 Specify the size of the cache. urlcache FileEditViewFavoritesToolsHelp Back dir1File Folder9/6/2000 9:43 PM dir1100,800 KBMicrosoft ISA Server Cache File9/18/2000 9:28 PM SearchFoldersHistory Go NameSizeTypeModified Addressurlcache Select an item to view its description See also: My Documents My Network Places 2 object(s) 98.4 MB My Computer The.cdat file on the drive will be the same size as the cache. DriveTypeDisk space…Free space…Cache Size…

60 When you configure a drive to be used for caching, ISA Server creates a file with a.cdat extension in the \urlcache folder on that drive. The.cdat file is as large as the amount of space that you dedicated for caching on that drive. As ISA Server caches the objects, it places the objects into the.cdat file. If the.cdat file is too full to hold a new object, ISA Server removes older objects from the cache by using a formula that evaluates age, popularity, and size. Note: If the cache file becomes corrupted, you can recover by deleting and re?creating the \urlcache folder. To perform this procedure, stop the Web Proxy service, delete the \urlcache folder, and then restart the service. ISA Server re?creates the \urlcache folder when you restart the Web Proxy service. However, all cached content is lost, which causes slower ISA Server responses and increased network traffic to the Internet until the cache content has been rebuilt.

61 Adjusting Cache Size To configure cache size: 1. In ISA Management, in the console tree, expand Cache Configuration, and then click Drives. 2. In the details pane, right-click server (where server is the name of your ISA Server computer), and then click Properties. 3. In the Properties dialog box, click the appropriate drive. 4. In the Maximum cache size (MB) box, type the size of the drive, click Set, and then click OK. 5. If configuring ISA Server to maintain the cache on multiple drives, repeat this procedure for the remaining drives.

62 Adjusting Memory Allocation Cache Configuration Properties General OKCancelApply Restore Defaults HTTPFTPActive CachingAdvanced Maximum size of URL cached in memory (bytes):12800 Do not return the expired object (return an error page) Return the expired object only if expiration was: At less that this percentage of original Time 50 to Live: But no more than (minutes):60 If Web site of expired object cannot be reached: Percentage of available memory to use for caching:50 Do not cache objects larger than:1KB Cache objects that have an unspecified last modification time Cache objects even if they do not have an HTTP status code of 200 Cache dynamic content (objects with question marks in the URL) Type a number between 1 and 100 to specify the maximum percentage of memory.

63 To run ISA Server cache operations most efficiently, it is important that you allocate the correct amount of memory to ISA Server caching. Configure ISA Server to use a large percentage of free memory, such as 80 percent to 90 percent, when the only task that the server performs is Web caching. Configure a lower percentage when you run other applications on the server, particularly if they are memory-intensive applications.

64 To configure the percentage of free memory to use for caching: 1. In ISA Management, in the console tree, click Cache Configuration, and then click Properties. 2. In the Cache Configuration Properties dialog box, on the Advanced tab, in the Percentage of free memory to use for caching box, type a number between 1 and 100, and then click OK.

65 Name the Job Select the Date and Time Select the Frequency Enter the URL Specify Job Parameters Configuring Scheduled Content Downloads StartStart FinishFinish

66 Scheduled content downloads enables you to download content from the Internet directly to the cache according to a predefined schedule. Scheduled content downloads enable you to update the cache with HTTP objects that users request on a regular basis. For example, users may frequently request a price list from the Web site of a business partner. You can configure a scheduled content download so that the ISA Server computer retrieves the price list each night. By using a scheduled content download, the most recent version of the price list will be in the cache each morning. You can also use scheduled content downloads to ensure that Web content is always available to users even when they are unable to connect to the Internet.

67 In addition, you can schedule content downloads of frequently accessed Web pages during periods when there is more available bandwidth, such as during non- business hours. When configured properly, scheduled content downloads can save network bandwidth and improve the overall cache performance. Tip: To determine the Web sites for which it is recommended that you create scheduled download jobs, review the ISA Server reports for the most frequently accessed Web sites. You can create scheduled download jobs so that ISA Server will retrieve content from these Web sites when there is the most available bandwidth.

68 To configure scheduled content downloads: 1. In ISA Management, in the console tree, expand Cache Configuration, right-click Scheduled Content Download Jobs, point to New, and then click Job. 2. In the New Scheduled Content Download Job Wizard, type a name for the job, and then click Next. 3. On the Start Time page, select the date and the time to download the content, and then click Next. 4. On the Frequency page, select how often to download the content, and then click Next.

69 5. On the Content page, type the URL of the content that you want to download, select one or both of the following options for content settings, and then click Next: Content only for URL domain (not sites to which it links). Select this option to prevent downloading linked content from other Web sites. Cache dynamic content. Select this option to cache Web content that is likely to change frequently.

70 6. On the Links and Download Objects page, select the following job parameters, and then click Next: TTL. Specify to override an existing or undefined TTL with a new TTL. Links depth. Specify a maximum link depth to limit the depth of the links or to specify no limit. Specifying no limit on maximum depth may cause excessive Internet network traffic. A links depth that is set too low may result in additional Internet network traffic when users click on the links on the cached Web pages. Maximum number of cached objects. Specify a maximum number of cached objects between 1 and to manage the size of a scheduled content download.

71 7. On the Completing the New Scheduled Content Download Job Wizard page, review your choices, and then click Finish.

72 Lab A: Configuring Caching

73 Review Cache Overview Configuring Cache Policy Configuring Cache Settings Configuring Scheduled Content Downloads


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