A TCP Authentication Option Extension for NAT Traversal
RFC 6978

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Independent Submission                                          J. Touch
Request for Comments: 6978                                       USC/ISI
Category: Experimental                                         July 2013
ISSN: 2070-1721

        A TCP Authentication Option Extension for NAT Traversal

Abstract

   This document describes an extension to the TCP Authentication Option
   (TCP-AO) to support its use over connections that pass through
   Network Address Translators and/or Network Address and Port
   Translators (NATs/NAPTs).  This extension changes the data used to
   compute traffic keys, but it does not alter TCP-AO's packet
   processing or key generation algorithms.

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 is a contribution to the RFC Series, independently
   of any other RFC stream.  The RFC Editor has chosen to publish this
   document at its discretion and makes no statement about its value for
   implementation or deployment.  Documents approved for publication by
   the RFC Editor are not 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/rfc6978.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.

Touch                         Experimental                      [Page 1]
RFC 6978                  TCP-AO NAT Extension                 July 2013

Table of Contents

   1. Introduction ....................................................2
   2. Conventions Used in This Document ...............................2
   3. Background ......................................................3
   4. Extension to Allow NAT Traversal ................................3
   5. Intended Use ....................................................4
   6. Security Considerations .........................................5
   7. References ......................................................5
      7.1. Normative References .......................................5
      7.2. Informative References .....................................5
   8. Acknowledgments .................................................6

1.  Introduction

   This document describes an extension to the TCP Authentication Option
   (TCP-AO) [RFC5925] called TCP-AO-NAT to support its use in the
   presence of Network Address Translators and/or Network Address and
   Port Translators (NATs/NAPTs) [RFC2663].  These devices translate the
   source address and/or the source port number of a TCP connection.
   TCP-AO without TCP-AO-NAT extensions would be sensitive to these
   modifications and would discard authenticated segments.

   At least one potential application of TCP-AO-NAT is to support the
   experimental multipath TCP protocol [RFC6824], which uses multiple IP
   addresses to support a single TCP transfer.

   This document assumes detailed familiarity with TCP-AO [RFC5925].  As
   a preview, this document focuses on how TCP-AO generates traffic
   keys, and it does not otherwise alter the TCP-AO mechanism or that of
   its key generation [RFC5926].

2.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].
   When used in lower case, these words have their conventional meaning
   and do not convey the interpretations in RFC 2119.

Touch                         Experimental                      [Page 2]
RFC 6978                  TCP-AO NAT Extension                 July 2013

3.  Background

   TCP-AO generates traffic keys that are specific to a socket pair
   [RFC5925].  The following information is used to create a
   connection's traffic keys.  (Note that 'local' and 'remote' are
   interpreted as in TCP-AO [RFC5925].)

   o  IP local address

   o  IP remote address

   o  TCP local port

   o  TCP remote port

   o  TCP local Initial Sequence Number (ISN)

   o  TCP remote Initial Sequence Number (ISN)

   Of these fields, the remote ISN is not known for SYN segments and is
   excluded from the traffic key used to authenticate them.  Otherwise,
   all fields are used in the traffic keys of all other segments.

   NATs and NAPTs (both referred to herein as "NATs", even if port