CHAPTER 5
CONFIGURING INTERNET ACCELERATION
THROUGH THE ISA SERVER CACHE
In its function as a cache server, ISA Server improves network performance by maintaining a
cache of frequently requested Web objects. Creating a cache policy entails configuring routing
rules, cache configuration properties, and optionally, access policy and publishing rules.
ISA Server includes an HTTP redirector filter, which allows both firewall and SecureNAT clients
to benefit from the caching features. When the HTTP redirector is enabled, Web requests from
Firewall and SecureNAT clients can both be cached. Usually only cache HTTP, disable FTP.
· Forward = Outgoing
· Reverse = Ingoing
Routing Rules
The most basic aspect of creating a cache policy is to configure routing rules that specify when ISA
Server should cache content and when ISA Server should retrieve content from the cache. Routing
rules can be configured in ISA Management through the Network Configuration node.
Cache goes to the largest available space on the NTFS partition.
Rule Order
Routing rules are ordered, with the default routing rule processes last. For each new connection,
the ISA Server computer processes the routing rules in order from first to last. If the request
matches the conditions specified by the rule, the request is routed, redirected, and cached
accordingly.
F5 forces a “refresh” for users, forces it to go on the Internet to get
new
information.
Cache Filtering
By applying different routing rules to different destinations, you can configure ISA Server to
cache content only from the destinations you choose. This effectively lets you filter which
content will be cached.
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Additional Cache Policy
The site and content rules limit which sites and Multipurpose Internet Mail Extensions (MIME)
content can be accessed by specific Internet users and client computers.
Web publishing rules map requests from Internet clients to the appropriate Web server on the
corporate network. Web publishing rules affect reverse caching behavior by determining
which client address sets can access the cache and which servers can upload data to the
cache.
Lesson Summary:
Routing rules do one of the following:
version of the requested object from the cache;
requested object (valid or not) from the cache; or
the request.
Routing rules are ordered, and the default routing rule is processed last.
Because these properties of the default routing rule cannot be changed, you must create
new routing rules if you want to configure a customized cache policy.
Lesson 2:
Configuring Cache Properties in ISA Server
Cache properties are settings that can be configured for cache size, cache location, RAM
caching, TTL parameters, active caching, negative caching, cache object restrictions, and
caching behavior.
Configuring Cache Drives
By default, Setup searches for the largest NTFS partition and sets a default cache size of
100MB if there are at least 150MB available. When configuring the cache drives, you
must allocate at least one drive and 5MB for caching. However, it is recommended that
you allocate at least 100MB and add .0.5MB for each Web Proxy client, rounded up to
the nearest full megabyte. Cache
must be on NTFS. To optimize cache, put
it in
separate memory space.
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WARNING: Do not modify or delete the cache content files.
Configuring How ISA Server Caches Objects
Through routing rules allow you to specify which content should be cached according to
destination and according to content type (dynamic versus static), the Cache Configuration
Properties dialog box allows you to specify with more precision which objects should be
cached, and when.
Configuring Which Content to Cache
You can configure whether ISA Server should cache the following types of HTTP objects:
NOTE: To limit maximum size of URLs cached in memory, in the Maximum Size of the
URL Cached in Memory (Bytes) text box, type the maximum number of bytes that can
be cached. In RAM.
RAM Caching
ISA Server caches objects to RAM and to the disk. Objects cached to memory can be
retrieved faster than objects cached to the disk. By default, objects smaller than 12,800
bytes are stored in RAM and on the disk. By default, all larger objects are cached only
to the disk.
Response Headers
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Configuring Expiration Policy
For HTTP and FTP objects, you can choose whether or not to activate caching, and you
can configure the expiration policy. You can also configure whether to return expired
objects, under specific circumstances.
HTTP Object Caching
ISA Server can keep and use expired objects in the cache from a specified amount of time
if the source Internet site for an object becomes unavailable.
Depending on your particular organization’s needs, you can specify one of the following
expiration policies for HTTP objects, as shown:
Frequently. This means that objects in the cache will be more current, although there
may be a degradation in network performance because objects are retrieved more
regularly from the Internet.
Less Frequently. This means that objects in the cache will be less current,
but network performance will not suffer.
Normally. This balanced approach is the default. Objects are updated somewhat
frequently, but network performance is not ignored.
Custom Settings. You can set TTL to zero or to a specified percentage of the
content’s age. The higher the percentage, the less frequently the cache is updated.
NOTE: To reset FTP caching policy to the default settings, click Restore Default.
Configuring Active Caching
When popular objects in the cache are about to expire, ISA Server automatically refreshes
the content in the cache.
You can configure the active caching policy. Select one of the following:
Frequently. In this case, frequently requested objects are downloaded to the cache regularly,
as they are about to expire.
Normally. This balanced approach is the default. Objects are updated somewhat frequently,
but network performance is not ignored.
Less Frequently. Some frequently requested objects will be down-loaded to the cache.
Although there is less likelihood that the object will be fresh in the cache, network
performance may be improved, since active caching is at a minimum.
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Configuring Negative Caching
When ISA Server cannot retrieve an object from a specific Web server, the response may
be cached. This is referred to as negative caching.
When you configure negative caching, you specify that HTTP objects with the following status
code should be cached: 203, 300, 301, and 410.
Lesson Summary:
node and in the properties dialog box of each server in the Drives folder in ISA Management.
configure HTTP caching, set expiration policies, determine when to return cached
objects, restrict the size of objects to be cached, configure the % of available RAM to
be used for caching, enable active caching, and configure negative caching.
Lesson 3:
Scheduling Cache Content Downloads
Web content downloads from the Internet directly to the ISA Server cache.
NOTE: If you click Always Override Object’s TTL, the TTL is determined either by the TTL
specified here or by the TTL specified in cache configuration properties.
WARNING: If the Web server from which the object is being downloaded requires client
authentication, the scheduled content download job will fail.
Lesson Summary:
that may soon be requested by Web Proxy clients.
create a download job, you can configure a download for a single URL, multiple URLs,
or an entire Web Site.