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Versions: 00 01 02 03 04                                                
Network Working Group                                           J. Bound
Internet-Draft                                           Hewlett Packard
Expires: April 20, 2006                                       L. Toutain
                                                       GET/ENST Bretagne
                                                             JL. Richier
                                                        October 17, 2005

          Dual Stack IPv6 Dominant Transition Mechanism (DSTM)

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   The list of current Internet-Drafts can be accessed at

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   This Internet-Draft will expire on April 20, 2006.

Copyright Notice

   Copyright (C) The Internet Society (2005).


   In an IPv6 dominant environment, some applications will still require
   IPv4 addresses to interoperate.  Dual stack may be configured on
   these hosts, but this will imply the configuration of network
   equipments (such as routers) to proceed IPv4 packets.  The Dual Stack
   IPv6 Dominant Transition Mechanism (DSTM) is based on the use of

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   IPv4-over-IPv6 tunnels to carry IPv4 traffic within an IPv6 network
   and provides a method to allocate a temporary IPv4 address to Dual IP
   Layer IPv6/IPv4 capable nodes.  DSTM is also a way to avoid the use
   of Network Address Translation for early adopter IPv6 deployment to
   communicate with IPv4 legacy nodes and applications.

Table of Contents

   1.   Introduction . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.   Specification of Requirements  . . . . . . . . . . . . . . .   3
   3.   Terminology  . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.   DSTM Problem Statement and Assumptions . . . . . . . . . . .   4
   5.   DSTM Deployment Example  . . . . . . . . . . . . . . . . . .   6
   6.   DSTM Client  . . . . . . . . . . . . . . . . . . . . . . . .   8
     6.1  DSTM Server Access Module  . . . . . . . . . . . . . . . .   8
     6.2  DSTM Dynamic Tunnel Interface (DTI)  . . . . . . . . . . .   8
   7.   DSTM Server  . . . . . . . . . . . . . . . . . . . . . . . .   8
     7.1  DSTM Client Access Module  . . . . . . . . . . . . . . . .   8
     7.2  DSTM Address Pool Access Module  . . . . . . . . . . . . .   8
     7.3  DSTM Routing Information Access Module . . . . . . . . . .   9
   8.   Tunnel End Point (TEP) . . . . . . . . . . . . . . . . . . .   9
   9.   Using TSP protocol between a DSTM client and Server  . . . .   9
   10.  Applicability Statement  . . . . . . . . . . . . . . . . . .  10
   11.  Security Considerations  . . . . . . . . . . . . . . . . . .  11
   12.  Acknowledgement  . . . . . . . . . . . . . . . . . . . . . .  11
   13.  References . . . . . . . . . . . . . . . . . . . . . . . . .  12
     13.1   Normative References . . . . . . . . . . . . . . . . . .  12
     13.2   Informative References . . . . . . . . . . . . . . . . .  12
        Authors' Addresses . . . . . . . . . . . . . . . . . . . . .  13
        Intellectual Property and Copyright Statements . . . . . . .  14

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1.  Introduction

   In an IPv6 dominant environment, some applications will still require
   IPv4 addresses to interoperate.  Dual stack may be configured, with a
   permanent IPv4 address, on these hosts, but this will imply the
   configuration of network equipments (such as routers) to proceed IPv4
   packets.  The Dual Stack IPv6 Dominant Transition Mechanism (DSTM) is
   used to transition dual stack network to an overlay network where
   IPv4 packets are sent over IPv6.  DSTM is based on the use of IPv4-
   over-IPv6 tunnels to carry IPv4 traffic within an IPv6 network and
   provides a method to allocate a temporary IPv4 address to Dual IP
   Layer IPv6/IPv4 capable nodes.  DSTM is also a way to avoid the use
   of Network Address Translation for early adopter IPv6 deployment to
   communicate with IPv4 legacy nodes and applications.

   The DSTM architecture is composed of a DSTM address server, and DSTM
   capable nodes.  The DSTM server is responsible for IPv4 address
   allocation to client nodes and MAY >LT : MUST ? < also provide tunnel
   end points (TEP) to the DSTM nodes.  The DSTM server MUST guarantee
   the uniqueness of the IPv4 address for a period of time.  The DSTM
   nodes will use TEPs to tunnel IPv4 packets within IPv6 to a DSTM
   Border router.  The DSTM border router then decapsulates the IPv6
   packets and transmits the IPv4 packets to the destination IPv4 node.
   The DSTM server controls also the creation/suppression of tunnel on
   the TEP.

   This document describes DSTM basic behavior.  DSTM is targeted to
   help the interoperation of IPv6 newly deployed networks with existing
   IPv4 networks, where the user wants to begin IPv6 adoption with an
   IPv6 dominant network plan, or later in the transition of IPv6, when
   IPv6 dominant networks will be more prevalent.  In that case DSTM is
   used to avoid blocking situation where transition is delayed due to a
   lack of IPv6 porting for some applications.  DSTM can also be used as
   an access mechanism in case an host is located on a IPv6 network.  In
   that case the DSTM client may contact a remote DSTM server to get a
   temporary IPv4 address to access to remote resources.

2.  Specification of Requirements

   In this document, several words are used to signify the requirements
   of the specification.  These words are often capitalized.  The key
   "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document
   are to be interpreted as described in [RFC2119].

3.  Terminology

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   DSTM Domain:
      The network areas on an Intranet where dual IPv6/IPv4 nodes use
      DSTM to assure IPv4 communication.  An IPv4 address allocation
      server may be deployed inside the domain to manage an IPv4 address
      pool.  IPv4 routing access may not be maintained within a DSTM

   DSTM Client:
      A Dual IP Layer IPv4/IPv6 Capable Node that has implemented the
      DSTM client software in this specification.

   DSTM Server:
      A Dual IP Layer IPv4/IPv6 Capable Node that has implemented the
      DSTM server software in this specification.

      A Dual IP Layer IPv4/IPv6 Capable Node ensuring encapsulation/
      decapsulation of tunneled packets.  TEP tunnel creation/deletion
      is controlled by the DSTM server.

   IPv6 Dominant Network:
      A network that is using IPv6 as the dominant network transport for
      network operations.

4.  DSTM Problem Statement and Assumptions

   Since the IPv4 globally routable address space available is becoming
   a scarce resource, it is assumed that users will deploy IPv6 to
   reduce the need and reliability on IPv4 within a portion of their
   networks.  Some users will require an aggressive transition to IPv6
   and will begin the deployment of IPv6 reducing immediately the
   reliance on IPv4 wherever possible.  Under this premise, supporting
   native IPv4 and native IPv6 simultaneously largely increases the
   complexity and cost of network administration (e.g. address plan,
   routing infrastructure).  It is proposed, in this case, to define the
   network strategy plan to support IPv6 only use as soon as possible.
   Reliance on IPv4 infrastructure points like name service and address
   allocation for Dual IPv6/IPv4 capable nodes will move to an IPv6

   Using DSTM, DHCPv4 [RFC2131] may be used to assign IPv4 addresses to
   a DSTM nodes, since IPv4 routing is not maintained within an IPv6
   dominant network implementation, to support DHCPv4 some IPv4 network
   connecvity would be required.  Using DHCPv6 [RFC3315] reduces the
   reliance on IPv4 infrastructure for the transition to IPv6 with DSTM.
   But, DHCPv6 and DHCPv4 are not the only mechanisms that can be
   supported to allocate IPv4 addresses to a DSTM client.

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   DSTM is a transition mechanism that uses existing protocols.  DSTM
   does not specify a protocol.  However, DSTM defines client, server,
   and border router behavior and the properties of the temporary
   addresses allocation mechanisms.

   The core assumption within DSTM is that it is completely transparent
   to applications, which can continue to work with IPv4 addresses.  It
   is also transparent to the network, which carries only IPv6 packets.
   DSTM assumes the user, has deployed IPv6 to support end-2-end
   applications and security, without translation.

   DSTM implementation would also support the use of IPv6 dominant
   networks as specified in IPv6 Enterprise Scecnarios and Analysis
   [RFC4057] [ENTANA]

   The DSTM architecture base assumptions are as follows:
   1.  The DSTM domain is within an Intranet not on the Internet.
   2.  Dual IPv6/IPv4 nodes do not maintain IPv4 addresses except on a
       temporary basis, to communicate with IPv4 Applications.
   3.  The temporary IPv4 address allocation is done by the DSTM server,
       different protocols such as DHCPv6 or other mechanism can be used
       to assign the IPv4 address.  DHCPv6 is the recommended default
   4.  DSTM will keep IPv4 routing tables to a minimum and use IPv6
       routing, which will reduce the network management required for
       IPv4 during transition within a DSTM Dominant IPv6 Network.
   5.  Once IPv6 nodes have obtained IPv4 addresses Dynamic Tunneling is
       used to encapsulate the IPv4 packet within IPv6 and then forward
       that packet to an IPv6 TEP DSTM border router, where the packet
       will be decapsulated and forwarded using IPv4.  The IPv4
       allocation mechanism, from the DSTM server, can provide the TEP
       IPv6 address to the DSTM client, in addition to manual
   6.  Existing IPv4 applications or nodes do not have to be modified.

   Implementation defined software will have to exist to support DSTM:
   1.  DSTM server implementation is required to maintain configuration
       information about TEPs for encapsulating IPv4 packets between
       IPv6 nodes that can forward IPv4 packets to an IPv4 routing
       destination, and to maintain a pool of IPv4 addresses.
   2.  DSTM client implementation is required to support the dynamic
       tunneling mechanisms in this specification to encapsulate IPv4
       packets within IPv6, and be able to communicate with the DSTM
       server to obtain IPv4 addresses and TEPs.
   3.  DSTM border router implementation is required to support the
       decapsulation of IPv6 packets from DSTM clients and forward them
       to the IPv4 destination, and cache the IPv6 address and the
       source IPv4 address used by the DSTM client.

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   |                                                |       IPv4
   |  Intranet                                      |
   |          DSTM Domain Intranet                  | Internet or
   |                                                | Intranet
   |                  _____________________         |
   |                 |                     |        |
   |                 |   DSTM Server       |        | Applications
   |                 |_____________________|        | Domain
   |                               ^                |
   |                               |                |
   |     __________________        |                |
   |    |                  |       |                |
   |    | IPv6/IPv4 Node   |       |               ----------------
   |    |------------------|       |              | DSTM Border    |
   |    |  DSTM client     |       |              | Router         |
   |    |                  |<-------              |                |
   |    |------------------|                      | Address mapping|
   |    |    DTI/Route     | /------------------\ |----------------|
   |    |                  |     IPv4 in IPv6     | IPv6/IPv4 node |
   |     ------------------  \------------------/  ----------------
   |                                               |

                        Figure 1: DSTM Architecture

5.  DSTM Deployment Example

   In the example below, the following notation will be used:
   X  will designate a dual IPv6/IPv4 node, X6 will be the IPv6 address
      of this node and X4 the IPv4 address
   Y  will designate a DSTM border router at the boundary between an
      IPv6 DSTM domain and an IPv4-only domain.
   Z  will designate an IPv4-only node and Z4 its address.
   ==>  means an IPv6 packet
   -->  means an IPv4 packet
   ++>  means a tunneled IPv4 packet is encapsulated in an IPv6 packet
   ..>  means a DNS query or response.  The path taken by this packet
      does not matter in the examples
   "a"  means the DNS name of a node
   This example describes the case where an application running on a
   dual IPv6/IPv4 node (X6) wants to establish a session with an IPv4
   application (Z4).

   The IPv4 routing table of node X is configured to send IPv4 packets

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   to the nodes Dynamic Tunnel Interface (DTI) interface.

   Server        DNS
   X6        Y6/Y4         Z4
   |           |           |
   |. . . . . . .>   Z     |    - IPv4 application asks the DNS for
   |           |           |      the A RR for "Z". (IPv6 application
   |           |           |      asks the DNS for the AAAA RR for "Z".)
   |           |           |
   |<. . . . . . .   Z4    |    - the answer is Z4 (or IPv4-mapped
   |           |           |      IPv6 address ::FFFF:Z4).
   |           |           |
   |           |           |    - The IPv4 application sends its first
   |           |           |      IPv4 packet which arrives to the DTI
   |           |           |      interface. (The IPv6 application
   |           |           |      can do this through an IPv4-mapped
   |           |           |      address).
   |           |           |
   |           |           |    - X6 needs an IPv4 address (first use).
   |====>      |           |    - X6 queries the DSTM server for an
   |           |           |      IPv4 address.
   |<====      |           |    - The DSTM server locates the client
   |           |           |      and provides a temporary IPv4
   |           |           |      global address and the IPv6 TEP
   |           |           |      address.
   |++++++++++>|           |    - The DTI sends the IPv6 packet to the
   |           |           |      TEP.
   |           |---------->|    - Y sends the packet to the
   |           |           |      destination Z4.
   |           |           |    - Y caches the association .
   |           |<----------|    - Z4 answers.
   |           |           |
   |<++++++++++|           |    - Y uses the mapping between X4 and X6
   |           |           |      to tunnel the packet to the
   |           |           |      destination.

                         Figure 2: DSTM exchanges

   When Z responds the packet returns back through Y. Y having cached
   the association between the IPv4 and the IPv6 address of X, is able
   to send the packet encapsulating the IPv4 packet within IPv6 back to

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6.  DSTM Client

   A DSTM client requires the implementation of a DSTM Server Access
   Module and a Dynamic Tunnel Interface.

6.1  DSTM Server Access Module

   A DSTM Server Access Module connects to the DSTM Server to obtain an
   IPv4 address and TEP.  TSB/TSP [TSP] is mandatory.  The client may
   implement other addresses allocation protocols such as DHCPv6
   [RFC3315] but in case of failure MUST use TSP.

   The DSTM client may also receive an expiration life time for that
   IPv4 address, which when expired the DSTM client cannot continue to
   used that IPv4 address.

   The DSTM client must not perform any Dynamic updates to the DNS
   [RFC2136] for any IPv4 address returned to the DSTM Server Access

   The TEP can also be manually configured on the DSTM client.

6.2  DSTM Dynamic Tunnel Interface (DTI)

   The DSTM client implementation after obtaining an IPv4 address and
   TEP configures its DTI to send an IPv4 packet to the IPv6 TEP of a
   DSTM border router, and receive IPv4 packets from an IPv6 TEP for an
   IPv4 application on a DSTM client.

7.  DSTM Server

   A DSTM server implementation requires the implementation of a DSTM
   Client Access Module, Address Pool Access Module, and Routing
   Information Access Module.

7.1  DSTM Client Access Module

   The DSTM Client Access Module is required to accept requests from
   DSTM clients for an IPv4 address and TEPs, and then return an IPv4
   address and TEPs to the DSTM client.  DSTM mandates the use of a TSP
   as the default behavior.

7.2  DSTM Address Pool Access Module

   The DSTM Address Pool Module is required to maintain a pool of IPv4
   addresses for DSTM clients and maintain the lifetimes for those
   addresses.  The lifetime for those IPv4 addresses can be provided to
   the DSTM client with the IPv4 address and TEPs.

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7.3  DSTM Routing Information Access Module

   The DSTM Routing Information Access Module is required to learn or
   manually configure the TEPs within the DSTM domain to provide TEPs to
   the DSTM clients.

8.  Tunnel End Point (TEP)

   The DSTM border router or TEP is required to be able to receive IPv6
   packets from DSTM clients and then decapsulate the inner IPv4 packets
   and send to the IPv4 destination address in the IPv4 packets.  The
   DSTM border router is required to maintain the IPv6 address of the
   DSTM clients that send IPv6 packets with IPv4 encapsulated, so IPv4
   packets sent to the DSTM clients can be tunneled back to the DSTM
   client.  DSTM Border router is configured by the DSTM Server.

   TEP role can be played by any router without any modification.  For
   instance CLI commands can be sent by the DSTM Server to setup and
   destroy dynamically tunnels.

9.  Using TSP protocol between a DSTM client and Server

   When using TSB/TSP, the DSTM Client contacts the server using the TCP
   mode of TSP, addressing the known IPv6 server address.  The TCP
   server port should be the TSP assigned service port.

   The message are formatted as described in [TSP].  The connection
   should be secured using SASL as described in [RFC2222].

   The client sends a tunnel request of type v4v6 (cf. Figure 3).  The
   message contains the  DSTM Client IPv6 global address (the one which
   will be the tunnel extremity).

           <tunnel action="create" type="v4v6">
                 <address type="ipv6"> GLOBAL_IPV6_ADDR </address>

            Figure 3: Request sent by the client to the server

   When the DTSM client wants to extend the lease, it sends the same

   When the DTSM address is not needed anymore, the client should
   release the address by sending a similar message, but with action set

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   to "delete".

   If the DSTM server accepts the client create request, it sends a
   response (cf. Figure 4).

           <tunnel action="info" type="v4v6" lifetime="LIFE">
              <address type="ipv4" length="32"> TEPV4ADDR </address>
              <address type="ipv6"> TEPV6ADDR </address>
             <address type="ipv4" length="32"> ASSIGNEDV4ADDR </address>

                Figure 4:  Response of the DSTM the server

      - ASSIGNEDV4ADDR is the IPv4 address for the DSTM client.
      - LIFE is the duration of the lease (or of the extension of the
      lease), in minutes.
      - TEPV6ADDR is the IPv6 address of the TEP.  The DSTM client and
      the TEP should create a point to point IPv4 on IPv6 tunnel between
      - TEPV4ADDR is an IPv4 address of the TEP.  If the client uses a
      pseudo IPv4 interface for the IPv4 on IPv6 tunnel, TEPV4ADDR may
      be used as the remote IPv4 address for the point to point
      interface (in the case unnumbered interface are not possible).
      Also TEPV4ADDR can be used by the DSTM client as the default IPv4
      Both TEPV4ADDR and ASSIGNEDV4ADDR are host addresses, with a
      prefix length of 32.
   When receiving this response, the client should accept it by sending
   the message (cf. Figure 5):

          <tunnel action="accept"></tunnel>

                Figure 5: acknowledgement from DSTM client

10.  Applicability Statement

   DSTM is applicable for use from within a DSTM Domain in which hosts
   need to communicate with IPv4-only hosts or through IPv4-only
   applications on a user Intranet or over the Internet.

   The motivation of DSTM is to allow dual IP layer nodes to communicate

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   using global IPv4 addresses across an Intranet or Internet, where
   global addresses are required.  However, the mechanisms used in DSTM
   can also be deployed using private IPv4 addresses to permit the
   Intranet use of DSTM where users require temporary access to IPv4
   services within their Intranet.

   In DSTM, a mechanism is needed to perform the address allocation
   process.  This can be decoupled in two functions: the management of
   the IPv4 address pool and the communication protocol between server
   and clients.  A number of mechanisms, like DHCPv6, can perform these

   The exact capacities of the DTI required by DSTM is implementation
   defined.  Optionally, it is allowed that DSTM nodes configure
   manually (in a static manner) the tunnel to the TEP; but the
   recommendation is not to do this.  The dynamic configuration of DTI
   as a result of the address allocation process is the right way to
   execute DSTM on an IPv6 Network.

   DSTM also assumes that all packets returning from an IPv4 node to a
   DSTM node are routed through the originating DSTM TEP who maintains
   the association of the DSTM client's IPv4/IPv6 addresses.  At this
   time it is beyond the scope of this proposal to permit IPv4 packets
   destined to a DSTM node to be forwarded through a non-originating

11.  Security Considerations

   The DSTM mechanism can use all of the defined security specifications
   for each functional part of its operation.  For DNS, the DNS Security
   Extensions/Update can be used.  Concerning address allocation, when
   connections are initiated by the DSTM nodes, the risk of Denial of
   Service attacks (DOS) based on address pool exaustion is limited
   since DSTM is configured in an Intranet environement.  In this
   scenario, If DHCPv6 is deployed, the DHCPv6 Authentication Message
   can be used too.  Also, since the TEPs are inside an Intranet, they
   can not be used as an open relay.  Finally, for IPv4 communications
   on DSTM nodes, once the node has an IPv4 address, IPsec can be used
   since DSTM does not break secure end-to-end communications at any
   point.  Also TSP can be used with the Transport Layer Security
   protocol over a VPN.

12.  Acknowledgement

   The authors want to thank the members of the DSTM IPv6 forun design
   team.  A special thank to David Binet, Tim Chown, Francis Dupont,
   Florent Parent, Jaehwoon Lee and Myung-Ki Shin for their help and c

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13.  References

13.1  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",
              RFC 2131, March 1997.

   [RFC2136]  Vixie, P., Rekhter, Y., and J. Bound, "Dynamic Updates in
              the Domain Name System (DNS UPDATE)", RFC 2136,
              April 1997.

   [RFC2222]  Myers, J., "Simple Authentication and Security Layer
              (SASL)", RFC 2222, October 1997.

   [RFC3053]  Durand, A., Fasano, P., Guardini, I., and D. Lento, "IPv6
              Tunnel Broker", RFC 3053, January 2001.

   [RFC3315]  Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
              and M. Carney, "Dynamic Host Configuration Protocol for
              IPv6 (DHCPv6)", RFC 3315, July 2003.

13.2  Informative References

   [ENTANA]   Bound, J., Pouffary, Y., Klynsma, S., Chown, T., and D.
              Green, "IPv6 Enterprise Network Analysis",
              draft-ietf-v6ops-ent-analysis-03.txt (work in progress),
              July 2005.

   [RFC4057]  Bound, J., "IPv6 Enterprise Network Scenarios", RFC 4057,
              June 2005.

   [TSP]      Blanchet, M. and F. Parent, "Tunnel Setup Protocol",
              draft-blanchet-v6ops-tunnelbroker-tsp-03.txt (work in
              progress), Mars 2006.

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Authors' Addresses

   Jim Bound
   Hewlett Packard
   110 Spit Brook Road
   CS 17607
   Nashua, NH 03062-2698

   Email: Jim.Bound@hp.com

   Laurent Toutain
   GET/ENST Bretagne
   2 rue de la Chataigneraie
   CS 17607
   35576 Cesson-Sevigne Cedex

   Fax:   +33 2 99 12 70 30
   Email: Laurent.Toutain@enst-bretagne.fr

   Jean-Luc Richier
   BP 72
   38 402 Saint Martin d'Heres cedex

   Fax:   +33 4 76 82 72 87
   Email: Jean-Luc.Richier@imag.fr

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Intellectual Property Statement

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Disclaimer of Validity

   This document and the information contained herein are provided on an

Copyright Statement

   Copyright (C) The Internet Society (2005).  This document is subject
   to the rights, licenses and restrictions contained in BCP 78, and
   except as set forth therein, the authors retain all their rights.


   Funding for the RFC Editor function is currently provided by the
   Internet Society.

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