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 2014Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
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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 ...........................11
4.2.2. TCP Fast Open ......................................12
5. Security Considerations ........................................14
5.1. Resource Exhaustion Attack by SYN Flood with Valid
Cookies ...................................................14
5.1.1. Attacks from behind Shared Public IPs (NATs) .......15
5.2. Amplified Reflection Attack to Random Host ................16
6. TFO Applicability ..............................................17
6.1. Duplicate Data in SYNs ....................................17
6.2. Potential Performance Improvement .........................17
6.3. Example: Web Clients and Servers ..........................18
6.3.1. HTTP Request Replay ................................18
6.3.2. HTTP over TLS (HTTPS) ..............................18
6.3.3. Comparison with HTTP Persistent Connections ........18
6.3.4. Load Balancers and Server Farms ....................19
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