Network Support for TCP Fast Open

Latency is the dominant factor for the user-experience of the Internet users. TCP, the most widely used transport protocol involves a handshake before any data can …

Latency is the dominant factor for the user-experience of the Internet users. TCP, the most widely used transport protocol involves a handshake before any data can be sent over the connection. As round-trip-times between client and server are often in the order of hundreds of milliseconds, TCP’s handshake introduces a significant delay until data can be sent. 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. In this talk we give a detailed explanation of the behavior and benefits of TCP Fast Open. We continue by providing examples of how firewalls interfere with TFO according to our experience with its deployment. Our talk finishes with a call to network operators and firewall vendors to take TFO into account in the configuration of their equipment, so as TFO can operate efficiently and provide the latency benefit to the end-users.