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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. Additionally, you can specify a maximum size for the Metadata cache, in megabytes. All BIG-IP applications share the same Metadata cache.
BIG-IP policies cache ETag headers, which include the following: