Ignore
Select the following options to ignore some web caching features.
• If-modified-since
By default, if the time specified by the if-modified-since (IMS) header in the client's conditional request is greater than the last modified time of the object in the cache, it is a strong indication that the copy in the cache is stale. If so, HTTP does a conditional GET to the Overlay Caching Scheme (OCS), based on the last modified time of the cached object.
Enable ignoring if-modified-since to override this behavior.
• HTTP 1.1 conditionals
HTTP 1.1 provides additional controls to the client over the behavior of caches toward stale objects. Depending on various cache-control headers, the FortiGate unit can be forced to consult the OCS before serving the object from the cache. For more information about the behavior of cache-control header values, see
RFC 2616.
Enable ignoring HTTP 1.1 Conditionals to override this behavior.
• Pragma-no-cache
Typically, if a client sends an HTTP GET request with a pragma no-cache (PNC) or cache-control no-cache header, a cache must consult the OCS before serving the content. This means that the FortiGate unit always re-fetches the entire object from the OCS, even if the cached copy of the object is fresh.
• Because of this behavior, PNC requests can degrade performance and increase server-side bandwidth utilization. However, if you enable ignoring Pragma-no-cache, then the PNC header from the client request is ignored. The FortiGate unit treats the request as if the PNC header is not present.
• IE Reload
Some versions of Internet Explorer issue Accept / header instead of Pragma no-cache header when you select Refresh. When an Accept header has only the / value, the FortiGate unit treats it as a PNC header if it is a type-N object.
Enable ignoring IE reload to cause the FortiGate unit to ignore the PNC interpretation of the Accept / header.