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RFC 7413 - TCP Fast Open

Publication Date: December 2014
Authors: Y. Cheng, J. Chu, S. Radhakrishnan, A. Jain
Status: Experimental
Organization: Google, Inc.

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, providing a reduction in connection latency. TFO is particularly valuable for latency-sensitive applications such as web services.

Technical Significance: TCP Fast Open can reduce HTTP request-response time by one full round-trip time (RTT), especially beneficial for short-lived connections.

Contents​

Main Sections​

Appendices​

Key Technical Points​

  • Cookie Generation: Server generates cookie using encryption based on client IP address
  • Cookie Validation: Client includes cookie in subsequent connections for validation
  • Data Carrying: After validation, data in SYN packet can be received by application layer

Performance Benefits​

  • Reduces one full RTT latency
  • Particularly suited for short connections and request-response patterns
  • Significant performance improvement for web browsing and API calls

Security Protection​

  • Prevents amplification attacks: Limits SYN data size
  • Prevents resource exhaustion: Cookie validation mechanism
  • Compatibility: Transparently coexists with traditional TCP
  • RFC 793: Transmission Control Protocol
  • RFC 6994: Shared Use of Experimental TCP Options
  • RFC 7323: TCP Extensions for High Performance

Implementation Status​

This RFC is experimental and has been implemented in several major operating systems:

  • Linux kernel (3.6+)
  • Apple iOS and macOS
  • Windows 10 (1607+)

Note: Experimental status means this mechanism is still under evaluation; implementations should carefully consider security and compatibility implications.

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