Internet Engineering Task Force (IETF)                          Y. Cheng
Request for Comments: 7413                                        J. Chu
Category: Experimental                                  S. Radhakrishnan
ISSN: 2070-1721                                                  A. Jain
                                                                  Google
                                                           December 2014


                             
TCP Fast Open

Abstract

   This document describes an experimental TCP mechanism called TCP Fast
   Open (TFO).  TFO allows data to be carried in the SYN and SYN-ACK
   packets and consumed by the receiving end during the initial
   connection handshake, and saves up to one full round-trip time (RTT)
   compared to the standard TCP, which requires a three-way handshake
   (3WHS) to complete before data can be exchanged.  However, TFO
   deviates from the standard TCP semantics, since the data in the SYN
   could be replayed to an application in some rare circumstances.
   Applications should not use TFO unless they can tolerate this issue,
   as detailed in the Applicability section.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for examination, experimental implementation, and
   evaluation.

   This document defines an Experimental Protocol for the Internet
   community.  This document is a product of the Internet Engineering
   Task Force (IETF).  It represents the consensus of the IETF
   community.  It has received public review and has been approved for
   publication by the Internet Engineering Steering Group (IESG).  Not
   all documents approved by the IESG are a candidate for any level of
   Internet Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7413.











Cheng, et al.                 Experimental                      [Page 1]

RFC 7413                      TCP Fast Open                December 2014


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   described in the Simplified BSD License.

Table of Contents

   1. Introduction ....................................................3
      1.1. Terminology ................................................4
   2. Data in SYN .....................................................4
      2.1. Relaxing TCP Semantics on Duplicated SYNs ..................4
      2.2. SYNs with Spoofed IP Addresses .............................5
   3. Protocol Overview ...............................................5
   4. Protocol Details ................................................7
      4.1. Fast Open Cookie ...........................................7
           4.1.1. Fast Open Option ....................................8
           4.1.2. Server Cookie Handling ..............................8
           4.1.3. Client Cookie Handling ..............................9
                  4.1.3.1. Client Caching Negative Responses .........10
      4.2. Fast Open Protocol ........................................11
           4.2.1. Fast Open Cookie Request ...........................