Understanding Apple's Back to My Mac (BTMM) Service
RFC 6281

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Internet Engineering Task Force (IETF)                       S. Cheshire
Request for Comments: 6281                                    Apple Inc.
Category: Informational                                           Z. Zhu
ISSN: 2070-1721                                                     UCLA
                                                             R. Wakikawa
                                                              Toyota ITC
                                                                L. Zhang
                                                                    UCLA
                                                               June 2011

          Understanding Apple's Back to My Mac (BTMM) Service

Abstract

   This document describes the implementation of Apple Inc.'s Back to My
   Mac (BTMM) service.  BTMM provides network connectivity between
   devices so that a user can perform file sharing and screen sharing
   among multiple computers at home, at work, or on the road.  The
   implementation of BTMM addresses the issues of single sign-on
   authentication, secure data communication, service discovery, and
   end-to-end connectivity in the face of Network Address Translators
   (NATs) and mobility of devices.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   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/rfc6281.

Cheshire, et al.              Informational                     [Page 1]
RFC 6281                          BTMM                         June 2011

Copyright Notice

   Copyright (c) 2011 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.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
   2.  An Overview of Back to My Mac  . . . . . . . . . . . . . . . .  3
   3.  Encoding Host Information in DNS Resource Records  . . . . . .  5
   4.  NAT Traversal  . . . . . . . . . . . . . . . . . . . . . . . .  6
     4.1.  Introduction to NAT-PMP  . . . . . . . . . . . . . . . . .  6
     4.2.  Requesting/Removing a Port Mapping . . . . . . . . . . . .  7
     4.3.  Obtaining NAT Box's Public IP Address  . . . . . . . . . .  7
     4.4.  Unsupported Scenarios  . . . . . . . . . . . . . . . . . .  8
   5.  Handling IP Address or Port Changes  . . . . . . . . . . . . .  8
     5.1.  Updating Local Interfaces and Tunnels  . . . . . . . . . .  8
     5.2.  Dynamically Updating Reachability Information  . . . . . .  8
     5.3.  Getting Up-to-Date DNS Resource Records without Polling  .  9
   6.  IPv6 ULA as Host ID  . . . . . . . . . . . . . . . . . . . . . 11
     6.1.  The Need for a Host Identifier . . . . . . . . . . . . . . 11
     6.2.  What to Use as Host Identifiers  . . . . . . . . . . . . . 11
     6.3.  IPv6 ULA Configuration . . . . . . . . . . . . . . . . . . 11
   7.  Securing Communication . . . . . . . . . . . . . . . . . . . . 12
     7.1.  Authentication for Connecting to Remote Host . . . . . . . 12
     7.2.  Authentication for DNS Exchanges . . . . . . . . . . . . . 12
     7.3.  IPsec for Secure End-to-End Data Communication . . . . . . 13
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 14
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     9.1.  Normative Reference  . . . . . . . . . . . . . . . . . . . 14
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 15

Cheshire, et al.              Informational                     [Page 2]
RFC 6281                          BTMM                         June 2011

1.  Introduction

   Apple Inc.'s Back to My Mac (BTMM) service was first shipped with MAC
   OS X 10.5 release in October 2007; since then, it has been widely
   used.  BTMM provides an integrated solution to host mobility support,
   NAT traversal, and secure end-to-end data delivery through a