TCP Fast Open

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In computer networking, TCP Fast Open (TFO) is an extension to speed up the opening of successive Transmission Control Protocol (TCP) connections between two endpoints. It works by using a TFO cookie (a TCP option), which is a cryptographic cookie stored on the client and set upon the initial connection with the server. When the client later reconnects, it sends the initial SYN packet along with the TFO cookie data to authenticate itself. If successful, the server may start sending data to the client even before the reception of the final ACK packet of the three-way handshake, skipping that way a round-trip delay and lowering the latency in the start of data transmission.

The cookie is generated by applying a block cipher keyed on a key held secret by the server to the client's IP address, generating an authentication tag that is difficult for third parties to spoof, even if they can forge a source IP address or make two-way connections to the same server from other IP addresses. Although it uses cryptographic techniques to generate the cookie, TFO is not intended to provide more security than the three-way handshake it replaces, and does not give any form of cryptographic protection to the resulting TCP connection, or provide identity assurance about either endpoint. It also is not intended to be resistant to man-in-the-middle attacks.

The TFO proposal was originally presented in 2011 and was, as of February 2017, an IETF Internet Draft. The specification was published as RFC 7413 in December 2014. TCP Fast Open shares the goal of bypassing the three-way handshake of TCP with an earlier proposal from 1994, called T/TCP (RFC 1644). In contrast to TCP Fast Open, T/TCP paid no attention to security, opening a path for vulnerabilities and failing to gain traction.

TFO implementations include the following:

• IPv4 support for TFO was merged into the Linux kernel mainline in kernel versions 3.6 (support for clients) and 3.7 (support for servers), and was turned on by default in kernel version 3.13. TFO support for IPv6 servers was merged in kernel version 3.16.
• FreeBSD from versions 10.3 and 11.0 (only server support. Not in default config, need to rebuild kernel).
• Mozilla Firefox from version 58.
• Google Chrome and Chromium browsers have support for TFO on Linux, including Chrome OS and Android.
• Exim mail transfer agent (MTA) from version 4.88.
• Unbound DNS Resolver from version 1.5.10
• BIND Domain Name System (DNS) from version 9.11.0.
• Apple's iOS 9 and OS X 10.11 both support TCP Fast Open, but it is not enabled for individual connections by default.
• Microsoft Edge supports TCP Fast Open since Windows 10 Preview build 14352.
• PowerDNS Recursor supports TCP Fast Open from version 4.1.

Video TCP Fast Open

See also

• SPDY
• SYN cookies
• TCP Cookie Transactions

Maps TCP Fast Open

References

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External links

• RFC 7413 specification

Source of article : Wikipedia