Network Working Group                                          M. Tuexen
Internet-Draft                          Muenster Univ. of Appl. Sciences
Intended status: Standards Track                              R. Stewart
Expires: August 11, November 14, 2014                                Adara Networks
                                                                R. Jesup
                                                WorldGate Communications
                                                               S. Loreto
                                                        February 7,
                                                            May 13, 2014

                   DTLS Encapsulation of SCTP Packets


   The Stream Control Transmission Protocol (SCTP) is a transport
   protocol originally defined to run on top of the network protocols
   IPv4 or IPv6.  This document specifies how SCTP can be used on top of
   the Datagram Transport Layer Security (DTLS) protocol.  Using
   encapsulation method described in this document, SCTP is agnostic
   about the protocols being used below DTLS, explicit IP addresses can
   not be used in the SCTP control chunks.  As a consequence, the SCTP
   associations are single homed.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on August 11, November 14, 2014.

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Table of Contents

   1.  Introduction  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . .   3   2
   3.  Encapsulation and Decapsulation Procedure . . . . . . . . . .   3
   4.  General Considerations  . . . . . . . . . . . . . . . . . . .   3
   5.  DTLS Considerations . . . . . . . . . . . . . . . . . . . . .   3
   6.  SCTP Considerations . . . . . . . . . . . . . . . . . . . . .   3
   6.   4
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   5
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   5   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6   7

1.  Introduction

1.1.  Overview

   The Stream Control Transmission Protocol (SCTP) as defined in
   [RFC4960] is a transport protocol running on top of the network
   protocols IPv4 [RFC0791] or IPv6. IPv6 [RFC2460].  This document specifies
   how SCTP is used on top of the Datagram Transport Layer Security
   (DTLS) protocol defined in [RFC6347].  This encapsulation is used for
   example within the
   RTCWeb WebRTC protocol suite (see
   [I-D.ietf-rtcweb-overview] for an overview) for transporting non-media
   non-(S)RTP data between browsers.  The architecture of this stack is
   described in [I-D.ietf-rtcweb-data-channel].

1.2.  Terminology

   This document uses

   Please note that the following terms:

   Association:  An SCTP association.

   Stream:  A unidirectional stream of an procedures defined in [RFC6951] for dealing with
   the UDP port numbers do not apply here.  When using the encapsulation
   defined in this document, SCTP association.  It is
      uniquely identified by a stream identifier.

1.3.  Abbreviations

   DTLS:  Datagram Transport Layer Security.

   MTU:  Maximum Transmission Unit.

   PPID:  Payload Protocol Identifier.

   SCTP:  Stream Control Transmission Protocol.

   TCP:  Transmission Control Protocol.

   TLS:  Transport Layer Security. agnostic about the protocols used
   below DTLS.

2.  Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

3.  Encapsulation and Decapsulation Procedure

   When an SCTP packet is sent down provided to the DTLS layer, the complete SCTP
   packet, consisting of the SCTP common header and a number of SCTP
   chunks, MUST be handled as the payload of the application layer
   protocol of DTLS.  When the DTLS layer has processed a DTLS record
   containing a message of the application layer protocol, the payload
   MUST be given up to the SCTP layer.  The SCTP layer expects an SCTP
   common header followed by a number of SCTP chunks.

4.  General Considerations

   An implementation of SCTP over DTLS MUST implement and use a path
   maximum transmission unit (MTU) discovery method that functions
   without ICMP to provide SCTP/DTLS with an MTU estimate.  An
   implementation of "Packetization Layer Path MTU Discovery" [RFC4821]
   either in SCTP or DTLS is RECOMMENDED.

5.  DTLS Considerations

   The DTLS implementation MUST be based on DTLS 1.2 [RFC6347].  The
   support of future versions of DTLS is RECOMMENDED if defined.

   If path MTU discovery is performed by the DTLS layer, the method
   described in [RFC4821] MUST be used.  For probe packets, the
   extension defined in [RFC6520] MUST be used.

   If path MTU discovery is performed by the SCTP layer and IPv4 is used
   as the network layer protocol, the DTLS implementation MUST allow the
   DTLS user to enforce that the corresponding IPv4 packet is sent with
   the DF Don't Fragment (DF) bit set.  If controlling the DF bit is not
   possible, for example due to implementation restrictions, a safe
   value for the path MTU has to be used by the SCTP stack.

   The DTLS implementation SHOULD allow the DTLS user to set the
   Differentiated services code point (DSCP) used for IP packets being
   sent.  This requires the DTLS implementation to pass the value
   through and the lower layer to allow setting this value.  If the
   lower layer does not support setting the DSCP, then the DTLS user
   will end up with the default value used by protocol stack.  Please
   note that only a single DSCP value can be used for all packets
   belonging to the same SCTP association.

   Using explicit congestion notifications (ECN) in SCTP requires the
   DTLS layer to pass the ECN bits through and its lower layer to expose
   access to them for sent and received packets.  If this is not
   possible, for example due to implementation restrictions, ECN can't
   be used by SCTP.

   SCTP performs segmentation and reassembly based on the path MTU.
   Therefore the DTLS layer MUST NOT use any compression algorithm.

   The DTLS MUST support sending messages larger than the current path
   MTU.  This might result in sending IP level fragmented messages.


6.  SCTP Considerations


   This section describes the usage of the base protocol and the
   applicability of various SCTP extensions.

6.1.  Base Protocol

   This document uses SCTP as specified in [RFC4960] is used.  However, with the following
   restrictions restrictions,
   which are necessary required to reflect that the lower layer is the
   connection-oriented protocol DTLS instead of the connection less
   IPv4 and IPv6: IPv6 and that SCTP doesn't deal with the IP addresses or the
   transport protocol used below DTLS:

   o  A DTLS connection MUST be established before an SCTP association
      can be set up.

   o  All SCTP associations MUST be are single-homed.  Therefore it is
      RECOMMENDED to set the SCTP parameter path.max.retrans to

   o  The INIT and INIT-ACK chunk MUST NOT contain any IPv4 Address or
      IPv6 Address parameters.  The INIT chunk MUST NOT contain the
      Supported Address Types parameter.

   o  The implementation MUST NOT rely on processing ICMP or ICMPv6
      packets.  This applies in particular to path MTU discovery when
      performed by SCTP.


6.2.  Padding Extension

   The padding extension defined in [RFC4820] MUST be supported and used
   for probe packets when performing path MTU discovery as specified in


6.3.  Dynamic Address Reconfiguration Extension

   If the dynamic address reconfiguration extension defined in [RFC5061]
   is used, only wildcard addresses MUST be used in ASCONF chunks.


6.4.  SCTP Authentication Extension

   The SCTP authentication extension defined in [RFC4895] can be used
   with DTLS encapsulation, but does not provide any additional benefit.


6.5.  Partial Reliability Extension

   Partial reliability as defined in [RFC3758] can be used in
   combination with DTLS encapsulation.  It is also possible to use
   additional PR-SCTP policies.


6.6.  Stream Reset Extension

   The SCTP stream reset extension defined in [RFC6525] can be used with
   DTLS encapsulation.  It is used to reset SCTP streams and add SCTP
   streams during the lifetime of the SCTP association.


6.7.  Interleaving of Large User Messages

   SCTP as defined in [RFC4960] does not support the interleaving of
   large user messages that need to be fragmented and reassembled by the
   SCTP layer.  The protocol extension defined in
   [I-D.ietf-tsvwg-sctp-ndata] overcomes this limitation can and can be used
   with DTLS encapsulation.


7.  IANA Considerations

   This document requires no actions from IANA.


8.  Security Considerations

   Security considerations for DTLS are specified in [RFC6347] and for
   SCTP in [RFC4960], [RFC3758], and [RFC6525].  The combination of SCTP
   and DTLS introduces no new security considerations.


   It should be noted that the inability to process ICMP or ICMPv6
   messages does not add any security issue.  The processing of these
   messages for SCTP carried over a connection-less lower layer like IP,
   IPv6 or UDP is required to protect nodes not supporting SCTP.  Since
   DTLS provides a connection-oriented lower layer, this kind of
   protection is not necessary.

9.  Acknowledgments

   The authors wish to thank Gorry Fairhurst Fairhurst, Joe Touch and Magnus
   Westerlund for his their invaluable comments.


10.  References


10.1.  Normative References

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

   [RFC4820]  Tuexen, M., Stewart, R., and P. Lei, "Padding Chunk and
              Parameter for the Stream Control Transmission Protocol
              (SCTP)", RFC 4820, March 2007.

   [RFC4821]  Mathis, M. and J. Heffner, "Packetization Layer Path MTU
              Discovery", RFC 4821, March 2007.

   [RFC4960]  Stewart, R., "Stream Control Transmission Protocol", RFC
              4960, September 2007.

   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, January 2012.

   [RFC6520]  Seggelmann, R., Tuexen, M., and M. Williams, "Transport
              Layer Security (TLS) and Datagram Transport Layer Security
              (DTLS) Heartbeat Extension", RFC 6520, February 2012.


10.2.  Informative References

   [RFC0791]  Postel, J., "Internet Protocol", STD 5, RFC 791, September

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, December 1998.

   [RFC3758]  Stewart, R., Ramalho, M., Xie, Q., Tuexen, M., and P.
              Conrad, "Stream Control Transmission Protocol (SCTP)
              Partial Reliability Extension", RFC 3758, May 2004.

   [RFC4895]  Tuexen, M., Stewart, R., Lei, P., and E. Rescorla,
              "Authenticated Chunks for the Stream Control Transmission
              Protocol (SCTP)", RFC 4895, August 2007.

   [RFC5061]  Stewart, R., Xie, Q., Tuexen, M., Maruyama, S., and M.
              Kozuka, "Stream Control Transmission Protocol (SCTP)
              Dynamic Address Reconfiguration", RFC 5061, September

   [RFC6525]  Stewart, R., Tuexen, M., and P. Lei, "Stream Control
              Transmission Protocol (SCTP) Stream Reconfiguration", RFC
              6525, February 2012.

   [RFC6951]  Tuexen, M. and R. Stewart, "UDP Encapsulation of Stream
              Control Transmission Protocol (SCTP) Packets for End-Host
              to End-Host Communication", RFC 6951, May 2013.

              Alvestrand, H., "Overview: Real Time Protocols for Brower-
              based Applications", draft-ietf-rtcweb-overview-08 draft-ietf-rtcweb-overview-09 (work
              in progress), September 2013. February 2014.

              Jesup, R., Loreto, S., and M. Tuexen, "RTCWeb "WebRTC Data
              Channels", draft-ietf-rtcweb-data-channel-06 draft-ietf-rtcweb-data-channel-08 (work in
              progress), October 2013. April 2014.

              Stewart, R., Tuexen, M., Loreto, S., and R. Seggelmann, "A
              New Data Chunk for Stream Control Transmission Protocol",
              draft-ietf-tsvwg-sctp-ndata-00 (work in progress),
              February 2014.

Authors' Addresses

   Michael Tuexen
   Muenster University of Applied Sciences
   Stegerwaldstrasse 39
   48565 Steinfurt


   Randall R. Stewart
   Adara Networks
   Chapin, SC  29036


   Randell Jesup
   WorldGate Communications
   3800 Horizon Blvd, Suite #103
   Trevose, PA  19053-4947

   Phone: +1-215-354-5166
   Salvatore Loreto
   Hirsalantie 11
   Jorvas  02420