BEHAVE                                                      G. Camarillo
Internet-Draft                                                   O. Novo
Intended status: Standards Track                                Ericsson
Expires: June 20, 2010                                 S. Perreault, Ed.
                                                                Viagenie
                                                       December 17, 2009


      Traversal Using Relays around NAT (TURN) Extension for IPv6
                     draft-ietf-behave-turn-ipv6-08

Abstract

   This document adds IPv6 support to Traversal Using Relays around NAT
   (TURN).  IPv6 support in TURN includes IPv4-to-IPv6, IPv6-to-IPv6,
   and IPv6-to-IPv4 relaying.  This document defines the REQUESTED-
   ADDRESS-FAMILY attribute for TURN.  The REQUESTED-ADDRESS-FAMILY
   attribute allows a client to explicitly request the address type the
   TURN server will allocate (e.g., an IPv4-only node may request the
   TURN server to allocate an IPv6 address).

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
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   This Internet-Draft will expire on June 20, 2010.

Copyright Notice

   Copyright (c) 2009 IETF Trust and the persons identified as the
   document authors.  All rights reserved.



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   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 BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Overview of Operation  . . . . . . . . . . . . . . . . . . . .  3
   4.  Creating an Allocation . . . . . . . . . . . . . . . . . . . .  4
     4.1.  Sending an Allocate Request  . . . . . . . . . . . . . . .  4
       4.1.1.  The REQUESTED-ADDRESS-FAMILY Attribute . . . . . . . .  4
     4.2.  Receiving an Allocate Request  . . . . . . . . . . . . . .  5
       4.2.1.  Unsupported Address Family . . . . . . . . . . . . . .  6
     4.3.  Receiving an Allocate Error Response . . . . . . . . . . .  6
   5.  Refreshing an Allocation . . . . . . . . . . . . . . . . . . .  6
     5.1.  Sending a Refresh Request  . . . . . . . . . . . . . . . .  6
     5.2.  Receiving a Refresh Request  . . . . . . . . . . . . . . .  6
   6.  CreatePermission . . . . . . . . . . . . . . . . . . . . . . .  6
     6.1.  Sending a CreatePermission Request . . . . . . . . . . . .  6
     6.2.  Receiving a CreatePermission request . . . . . . . . . . .  7
       6.2.1.  Peer Address Family Mismatch . . . . . . . . . . . . .  7
   7.  Channels . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
     7.1.  Sending a ChannelBind Request  . . . . . . . . . . . . . .  7
     7.2.  Receiving a ChannelBind Request  . . . . . . . . . . . . .  7
   8.  Packet Translations  . . . . . . . . . . . . . . . . . . . . .  7
     8.1.  IPv4-to-IPv6 Translations  . . . . . . . . . . . . . . . .  8
     8.2.  IPv6-to-IPv6 Translations  . . . . . . . . . . . . . . . .  9
     8.3.  IPv6-to-IPv4 Translations  . . . . . . . . . . . . . . . . 10
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
     10.1. New STUN Attribute Registry  . . . . . . . . . . . . . . . 12
     10.2. New STUN Response Code Registry  . . . . . . . . . . . . . 12
   11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
   12. Normative References . . . . . . . . . . . . . . . . . . . . . 12
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12








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1.  Introduction

   Traversal Using Relays around NAT (TURN) [I-D.ietf-behave-turn] is a
   protocol that allows for an element behind a NAT to receive incoming
   data over UDP or TCP.  It is most useful for elements behind
   symmetric NATs that wish to be on the receiving end of a connection
   to a single peer.

   The base specification of TURN [I-D.ietf-behave-turn] only defines
   IPv4-to-IPv4 relaying.  This document adds IPv6 support to TURN,
   which includes IPv4-to-IPv6, IPv6-to-IPv6, and IPv6-to-IPv4 relaying.
   This document defines the REQUESTED-ADDRESS-FAMILY attribute, which
   is an extension to TURN that allows a client to explicitly request
   the address type the TURN server will allocate (e.g., an IPv4-only
   node may request the TURN server to allocate an IPv6 address).  This
   document also defines and registers new error response codes.


2.  Terminology

   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 [RFC2119].


3.  Overview of Operation

   When a user wishes a TURN server to allocate an address of a specific
   type, it sends an Allocate Request to the TURN server with a
   REQUESTED-ADDRESS-FAMILY attribute.  TURN can run over UDP and TCP,
   as it allows for a client to request address/port pairs for receiving
   both UDP and TCP.

   Assuming the request is authenticated, the TURN server allocates a
   transport address of the type indicated in the REQUESTED-ADDRESS-
   FAMILY attribute.  This address is called the allocated transport
   address.

   The TURN server returns the allocated address in the response to the
   Allocate Request.  This response contains a XOR-RELAYED-ADDRESS
   attribute indicating the IP address and port that the server
   allocated for the client.

   TURN servers allocate a single relayed-transport-address per
   allocation request.  Therefore, Allocate Requests cannot carry more
   than one REQUESTED-ADDRESS-FAMILY attribute.  Consequently, a client
   that wishes to allocate more than one address at a TURN server (e.g.,
   an IPv4 and an IPv6 address) needs to perform several allocation



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   requests (one allocation request per address).

   A TURN server that supports a set of address families is assumed to
   be able to relay packets between them.  If a server does not support
   the address family requested by a client, the server returns a 440
   (Address Family not Supported) error response.


4.  Creating an Allocation

   The behavior specified here affects the processing defined in Section
   6 of [I-D.ietf-behave-turn].

4.1.  Sending an Allocate Request

   A client that wishes to obtain a transport address of a specific
   address type includes a REQUESTED-ADDRESS-FAMILY attribute, which is
   defined in Section 4.1.1, in the Allocate Request that it sends to
   the TURN server.  Clients MUST NOT include more than one REQUESTED-
   ADDRESS-FAMILY attribute in an Allocate Request.  The mechanisms to
   formulate an Allocate Request are described in Section 6.1 of
   [I-D.ietf-behave-turn].

   Clients MUST NOT include a REQUESTED-ADDRESS-FAMILY attribute in an
   Allocate request that contains a RESERVATION-TOKEN attribute.

4.1.1.  The REQUESTED-ADDRESS-FAMILY Attribute

   The REQUESTED-ADDRESS-FAMILY attribute is used by clients to request
   the allocation of a specific address type from a server.  The
   following is the format of the REQUESTED-ADDRESS-FAMILY attribute.
   Note that TURN attributes are TLV (Type-Length-Value) encoded, with a
   16 bit type, a 16 bit length, and a variable-length value.



     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |         Type                  |            Length             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |     Family    |            Reserved                           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


          Figure 1: Format of REQUESTED-ADDRESS-FAMILY Attribute

   Type: the type of the REQUESTED-ADDRESS-FAMILY attribute is 0x0017.



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    As specified in [RFC5389], attributes with values between 0x0000 and
   0x7FFF are comprehension-required, which means that the client or
   server cannot successfully process the message unless it understands
   the attribute.

   Length: this 16-bit field contains the length of the attribute in
   bytes.  The length of this attribute is 4 bytes.

   Family: there are two values defined for this field and specified in
   [RFC5389]: 0x01 for IPv4 addresses and 0x02 for IPv6 addresses.

   Reserved: at this point, the 24 bits in the reserved field MUST be
   set to zero by the client and MUST be ignored by the server.

   The REQUEST-ADDRESS-TYPE attribute MAY only be present in Allocate
   Requests.

4.2.  Receiving an Allocate Request

   Assuming the request is authenticated and has not been tampered with,
   the TURN server processes the Allocate request.  If it contains both
   a RESERVATION-TOKEN and a REQUESTED-ADDRESS-FAMILY, the server
   replies with a 400 (Bad Request) Allocate Error Response.  Following
   the rules in [RFC5389], if the server does not understand the
   REQUESTED-ADDRESS-FAMILY attribute, it generates an Allocate Error
   Response, which includes an ERROR-CODE attribute with response code
   420 (Unknown Attribute).  This response will contain an UNKNOWN-
   ATTRIBUTE attribute listing the unknown REQUESTED-ADDRESS-FAMILY
   attribute.

   If the server can successfully process the request, it allocates a
   transport address to the TURN client, called the allocated transport
   address, and returns it in the response to the Allocate Request.

   As specified in [I-D.ietf-behave-turn], the Allocate Response
   contains the same transaction ID contained in the Allocate Request
   and the XOR-RELAYED-ADDRESS attribute that sets it to the allocated
   transport address.

   The XOR-RELAYED-ADDRESS attribute indicates the allocated IP address
   and port.  It is encoded in the same way as the XOR-MAPPED-ADDRESS
   [RFC5389].

   If the REQUESTED-ADDRESS-FAMILY attribute is absent, the server MUST
   allocate an IPv4 transport address to the TURN client.  If allocation
   of IPv4 addresses is disabled by local policy, the server returns a a
   440 (Address Family not Supported) Allocate Error Response.




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   If the server does not support the address family requested by the
   client, it MUST generate an Allocate Error Response, and it MUST
   include an ERROR-CODE attribute with the 440 (Address Family not
   Supported) response code, which is defined in Section 4.2.1.

4.2.1.  Unsupported Address Family

   This document defines the following new error response code:

   440 (Address Family not Supported):  The server did not support the
      address family requested by the client.

4.3.  Receiving an Allocate Error Response

   If the client receives an Allocate error response with the 440
   (Unsupported Address Family) error code, the client SHOULD NOT retry
   its request.


5.  Refreshing an Allocation

   The behavior specified here affects the processing defined in Section
   7 of [I-D.ietf-behave-turn].

5.1.  Sending a Refresh Request

   To perform a binding refresh, the client generates a Refresh Request
   as described in Section 7.1 of [I-D.ietf-behave-turn].  The client
   MUST NOT include any REQUESTED-ADDRESS-FAMILY attribute in its
   Refresh Request.

5.2.  Receiving a Refresh Request

   If a server receives a Refresh Request with a REQUESTED-ADDRESS-
   FAMILY attribute, and the attribute's value doesn't match the address
   family of the allocation, the server MUST reply with a 443 (Peer
   Address Family Mismatch) Refresh Error Response.


6.  CreatePermission

   The behavior specified here affects the processing defined in Section
   9 of [I-D.ietf-behave-turn].

6.1.  Sending a CreatePermission Request

   The client MUST only include XOR-PEER-ADDRESS attributes with
   addresses of the same address family as the relayed transport address



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   for the allocation.

6.2.  Receiving a CreatePermission request

   If an XOR-PEER-ADDRESS attribute contains an address of an address
   family different than the relayed transport address for the
   allocation, the server MUST generate an error response with the 443
   (Peer Address Family Mismatch) response code, which is defined in
   Section 6.2.1.

6.2.1.  Peer Address Family Mismatch

   This document defines the following new error response code:

   443 (Peer Address Family Mismatch):  A peer address was of a
      different address family than the relayed transport address of the
      allocation.


7.  Channels

   The behavior specified here affects the processing defined in Section
   11 of [I-D.ietf-behave-turn].

7.1.  Sending a ChannelBind Request

   The client MUST only include a XOR-PEER-ADDRESS attribute with an
   address of the same address family as the relayed transport address
   for the allocation.

7.2.  Receiving a ChannelBind Request

   If the XOR-PEER-ADDRESS attribute contains an address of an address
   family different than the relayed transport address for the
   allocation, the server MUST generate an error response with the 443
   (Peer Address Family Mismatch) response code, which is defined in
   Section 6.2.1.


8.  Packet Translations

   The TURN specification [I-D.ietf-behave-turn] describes how TURN
   relays should relay traffic consisting of IPv4 packets (i.e., IPv4-
   to-IPv4 translations).  The relay translates the IP addresses and
   port numbers of the packets based on the allocation's state data.
   How to translate other header fields is also specified in
   [I-D.ietf-behave-turn].  This document addresses IPv4-to-IPv6, IPv6-
   to-IPv4, and IPv6-to-IPv6 translations.



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   TURN relays performing any translation MUST translate the IP
   addresses and port numbers of the packets based on the allocation's
   state information as specified in [I-D.ietf-behave-turn].  The
   following sections specify how to translate other header fields.

   As discussed in Section 2.6 of [I-D.ietf-behave-turn], translations
   in TURN are designed so that a TURN server can be implemented as an
   application that runs in userland under commonly available operating
   systems and that does not require special privileges.  The
   translations specified in the following sections follow this
   principle.

   The descriptions below have two parts: a preferred behavior and an
   alternate behavior.  The server SHOULD implement the preferred
   behavior.  However, if that is not possible for a particular field,
   then the server SHOULD implement the alternative behavior.

      Note that the use of the behaviors specified in the following
      sections is at the "should" level.  Having its use at the "should"
      level instead of at the "must" level makes it possible to use
      different translation algorithms that may be developed in the
      future.

8.1.  IPv4-to-IPv6 Translations

   Flow Label


      Preferred behavior: The relay sets the Flow label to 0.  The relay
      can choose to set the Flow label to a different value if it
      supports [RFC3697].

      Alternative behavior: the relay sets the Flow label to the default
      value for outgoing packets.

   Hop Limit


      Preferred behavior: as specified in Section 2 of
      [I-D.ietf-behave-v6v4-xlate].

      Alternative behavior: the relay sets the Hop Limit to the default
      value for outgoing packets.

   Fragmentation






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      Preferred behavior: as specified in Section 2 of
      [I-D.ietf-behave-v6v4-xlate].

      Alternative behavior: the relay assembles incoming fragments.  The
      relay follows its default behavior to send outgoing packets.

      For both preferred and alternative behavior, the DONT-FRAGMENT
      attribute MUST be ignored by the server.

   Extension Headers


      Preferred behavior: the relay sends outgoing packet without any
      IPv6 extension headers, with the exception of the Fragmentation
      header as described above.

      Alternative behavior: same as preferred.

8.2.  IPv6-to-IPv6 Translations

   Flow Label

   The relay should consider that it is handling two different IPv6
   flows.  Therefore, the Flow label [RFC3697] SHOULD NOT be copied as
   part of the translation.

      Preferred behavior: The relay sets the Flow label to 0.  The relay
      can choose to set the Flow label to a different value if it
      supports [RFC3697].

      Alternative behavior: the relay sets the Flow label to the default
      value for outgoing packets.

   Hop Limit


      Preferred behavior: the relay acts as a regular router with
      respect to decrementing the Hop Limit and generating an ICMPv6
      error if it reaches zero.

      Alternative behavior: the relay sets the Hop Limit to the default
      value for outgoing packets.

   Fragmentation






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      Preferred behavior: If the incoming packet did not include a
      Fragment header and the outgoing packet size does not exceed the
      outgoing link's MTU, the relay sends the outgoing packet without a
      Fragment header.

      If the incoming packet did not include a Fragment header and the
      outgoing packet size exceeds the outgoing link's MTU, the relay
      drops the outgoing packet and send an ICMP message of type 2 code
      0 ("Packet too big") to the sender of the incoming packet.  If the
      packet is being sent to the peer, the relay reduces the MTU
      reported in the ICMP message by 48 bytes to allow room for the
      overhead of a Data indication.

      If the incoming packet included a Fragment header and the outgoing
      packet size (with a Fragment header included) does not exceed the
      outgoing link's MTU, the relay sends the outgoing packet with a
      Fragment header.  The relay sets the fields of the Fragment header
      as appropriate for a packet originating from the server.

      If the incoming packet included a Fragment header and the outgoing
      packet size exceeds the outgoing link's MTU, the relay MUST
      fragment the outgoing packet into fragments of no more than 1280
      bytes.  The relay sets the fields of the Fragment header as
      appropriate for a packet originating from the server.

      Alternative behavior: the relay assembles incoming fragments.  The
      relay follows its default behavior to send outgoing packets.

      For both preferred and alternative behavior, the DONT-FRAGMENT
      attribute MUST be ignored by the server.

   Extension Headers


      Preferred behavior: the relay sends outgoing packet without any
      IPv6 extension headers, with the exception of the Fragmentation
      header as described above.

      Alternative behavior: same as preferred.

8.3.  IPv6-to-IPv4 Translations

   Type of Service and Precedence







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      Preferred behavior: as specified in Section 3 of
      [I-D.ietf-behave-v6v4-xlate].

      Alternative behavior: the relay sets the Type of Service and
      Precedence to the default value for outgoing packets.

   Time to Live


      Preferred behavior: as specified in Section 3 of
      [I-D.ietf-behave-v6v4-xlate].

      Alternative behavior: the relay sets the Time to Live to the
      default value for outgoing packets.

   Fragmentation


      Preferred behavior: as specified in Section 3 of
      [I-D.ietf-behave-v6v4-xlate].  Additionally, when the outgoing
      packet's size exceeds the outgoing link's MTU, the relay needs to
      generate an ICMP error (ICMPv6 Packet Too Big) reporting the MTU
      size.  If the packet is being sent to the peer, the relay SHOULD
      reduce the MTU reported in the ICMP message by 48 bytes to allow
      room for the overhead of a Data indication.

      Alternative behavior: the relay assembles incoming fragments.  The
      relay follows its default behavior to send outgoing packets.

      For both preferred and alternative behavior, the DONT-FRAGMENT
      attribute MUST be ignored by the server.


9.  Security Considerations

   The attribute and error response code defined in this document do not
   have any special security considerations beyond those for other
   attributes and Error response codes.  All the security considerations
   applicable to STUN [RFC5389] and TURN are applicable to this document
   as well.


10.  IANA Considerations

   The IANA is requested to register the following values under the STUN
   Attributes registry and under the STUN Response Code Registry.





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10.1.  New STUN Attribute Registry


     0x0017: REQUESTED-ADDRESS-FAMILY

10.2.  New STUN Response Code Registry


     440  Address Family not Supported
     443  Peer Address Family Mismatch


11.  Acknowledgements

   The authors would like to thank Alfred E. Heggestad, Dan Wing, Marc
   Petit-Huguenin, Philip Matthews, and Remi Denis-Courmont for their
   feedback on this document.


12.  Normative References

   [I-D.ietf-behave-turn]
              Rosenberg, J., Mahy, R., and P. Matthews, "Traversal Using
              Relays around NAT (TURN): Relay Extensions to Session
              Traversal Utilities for NAT (STUN)",
              draft-ietf-behave-turn-16 (work in progress), July 2009.

   [I-D.ietf-behave-v6v4-xlate]
              Li, X., Bao, C., and F. Baker, "IP/ICMP Translation
              Algorithm", draft-ietf-behave-v6v4-xlate-05 (work in
              progress), December 2009.

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

   [RFC3697]  Rajahalme, J., Conta, A., Carpenter, B., and S. Deering,
              "IPv6 Flow Label Specification", RFC 3697, March 2004.

   [RFC5389]  Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
              "Session Traversal Utilities for NAT (STUN)", RFC 5389,
              October 2008.










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Authors' Addresses

   Gonzalo Camarillo
   Ericsson
   Hirsalantie 11
   Jorvas  02420
   Finland

   Email: Gonzalo.Camarillo@ericsson.com


   Oscar Novo
   Ericsson
   Hirsalantie 11
   Jorvas  02420
   Finland

   Email: Oscar.Novo@ericsson.com


   Simon Perreault (editor)
   Viagenie
   2600 boul. Laurier, suite 625
   Quebec, QC  G1V 4W1
   Canada

   Phone: +1 418 656 9254
   Email: simon.perreault@viagenie.ca
   URI:   http://www.viagenie.ca






















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