Network Support for TCP Fast Open

Notes: Biggest issue was firewalls incorrectly dropping TCP packets with these options. Broken code in firewalls in the systems that they investigated. So middleboxes are making improvements difficult. APprox 20 percent of sites had issues with middlebox-induced failures.

TCP Fast Open (TFO) is a novel extension to TCP that allows to shortcut TCP's
handshake, by sending data on the SYN-segment and allowing the server to reply
before the handshake finished. The benefits are a much better user-experience
as the data reaches the client much faster. We at Apple have deployed TCP Fast
Open for a particular service, sending 100000 requests per second at peak times.
While TFO provides a huge benefit significantly improving the user-experience, we
also observed some major issues. Many middleboxes and firewalls in the operator
networks interfere with TCP Fast Open. In some cases, we have observed that
middleboxes are blacklisting clients that use TFO.