Intel 1520 User Manual

Appendix A Caching Solutions and Performance

✔ Evaluate freshness as follows:

Use the 

Expires

 header test, if applicable, otherwise go to step 2. If the 

object is stale, revalidate. If it is fresh, check the 

Cache-Control

 headers.

Use the 

Last-Modified

 / 

Date

 header test, if applicable, otherwise go to 

step 3. If the object is fresh according to the 

Last-Modified

 / 

Date

 test, 

check the 

Cache-Control

 headers for any freshness restrictions. 

Use the absolute freshness limit specified in the Freshness section of the 
Configure: Cache page. Revalidate if the age is past the freshness limit.

The following HTTP cachability options are available:

✔ Cache only documents that have 

Expires

 headers 

✔ Cache only documents that have 

Expires

 or 

Last-Modified

 headers

✔ Do not restrict caching

Caching HTTP alternates

Some Web servers answer requests for the same URL by serving a variety of 
objects. The content of these objects can vary widely, according to whether a 
server delivers content for different languages, targets different browsers with 
different presentation styles, or delivers variable content at different times of the 
day. Different versions of the same object are termed alternates. 

Header information identifies alternates. You can configure the Intel NetStructure 
Cache Appliance to cache all alternates according to a particular header. For 
example, if you tell the appliance to vary on the 

User-Agent

 header, the 

appliance caches all the different user-agent versions of documents it encounters. 
To configure caching of alternates, see Variable content‚ on page 38.

To cache or not to cache?

Depending on the type of object, you can direct the Intel NetStructure Cache 
Appliance to cache or not cache an object:

You can limit article caching to specific news groups. See Blocking particular 
groups‚ on page 140. 

You can configure never-cache rules for specific types of FTP documents by 
using the command-line interface. See Configuring caching rules‚ on page 79.

The appliance responds to caching directives from clients and origin servers, as 
well as configured options in the Manager UI and the command-line interface.