118 Intel NetStructure Cache Appliance Administrator’s Guide
✔The min-fresh field, sent by clients, is an acceptable freshness tolerance.
The client wants the object to be at least this fresh. If a cached document does
not remain fresh at least this long in the future, it is revalidated.
✔The max-stale field, sent by clients, permits the appliance to serve stale
documents provided they are not too old. Some browsers might be willing to
take stale documents in exchange for improved performance, especially
during periods of poor Internet availability.
The appliance applies Cache-Control servability criteria after HTTP freshness
criteria. For example, a document might be considered fresh, but if its age is
greater than its max-age, it is not served.
Configuring HTTP freshness options
You can configure the following freshness guidelines for the Intel NetStructure
Cache Appliance:
✔How often to revalidate (when to consider objects stale). See Configuring
HTTP revalidation below.
✔Whether to cache documents without freshness information. See Configuring
HTTP cachability below.
✔Whether to use an upper boundary to determine if the Last-Modified / Date
freshness limit is too long.
✔What absolute freshness lifetime to use when estimating the freshness of
documents without Expires or Last-Modified headers.
See Freshness‚ on page 36 for instructions.

Configuring HTTP revalidation

The following HTTP revalidation options are available:
✔Always revalidate (everything is considered stale).
✔Never revalidate (everything is considered fresh).
✔Revalidate all objects without Expires headers. Evaluate the freshness of
objects with Expires headers by first checking the Expires header, and
then checking Cache-Control headers.