Compression iRules - GZIP vs. Deflate Preference

Corsmith, you are largely correct. F5 used to prefer deflate since it is slightly more efficient to compute due to some additional checksumming required by gzip. However, future versions of BIG-IP will prefer gzip for greater compatibility.

 

 

The zlib faq explains why:

 

http://www.gzip.org/zlib/zlib_faq.html

 

 

What's the difference between the "gzip" and "deflate" HTTP 1.1 encodings?

 

"gzip" is the gzip format, and "deflate" is the zlib format. They should probably have called the second one "zlib" instead to avoid confusion with the raw deflate compressed data format. While the HTTP 1.1 RFC 2616 correctly points to the zlib specification in RFC 1950 for the "deflate" transfer encoding, there have been reports of servers and browsers that incorrectly produce or expect raw deflate data per the deflate specficiation in RFC 1951, most notably Microsoft. So even though the "deflate" transfer encoding using the zlib format would be the more efficient approach (and in fact exactly what the zlib format was designed for), using the "gzip" transfer encoding is probably more reliable due to an unfortunate choice of name on the part of the HTTP 1.1 authors.

 

 

Bottom line: use the gzip format for HTTP 1.1 encoding.