Responses from origin web servers include entity tags (ETags), which are arbitrary strings attached to a document that specify some characteristic of the document, such as a version, serial number, or checksum of content. A changed document includes a different ETag, enabling a client's GET request to use an If-None-Match conditional header to acquire a new copy of the document. Because not all web applications generate ETags consistently, the BIG-IP device creates its own ETag for each cached document that is based on a signature, or checksum, of the document's content. The BIG-IP device stores content signatures in the Metadata cache for other optimizations, including Intelligent Browser Referencing.

BIG-IP applications provide options to always or never send metadata. All BIG-IP applications share the same Metadata cache.

BIG-IP policies cache ETag headers, which include the following:

• Request URL
• Content signature of the response body
• Application name for the matching request
• Metadata, including the expiration time, read time, and update time for content

For the General Options list, this table describes the Advanced settings and strings for Metadata Cache Options.