Network Working Group                                          M. Tuexen
Internet-Draft                          Muenster Univ. of Appl. Sciences
Intended status: Standards Track                              R. Stewart
Expires: April 23, August 11, 2014                                  Adara Networks
                                                                R. Jesup
                                                WorldGate Communications
                                                               S. Loreto
                                                        October 20, 2013
                                                        February 7, 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.

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 April 23, August 11, 2014.

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Table of Contents

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

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 or IPv6.  This document specifies how SCTP is used on
   top of the Datagram Transport Layer Security (DTLS) protocol. protocol defined
   in [RFC6347].  This encapsulation is used for example within the
   RTCWeb protocol suite (see [I-D.ietf-rtcweb-overview] for an
   overview) for transporting non-media data between browsers.  The
   architecture of this stack is described in

1.2.  Terminology

   This document uses the following terms:

   Association:  An SCTP association.

   Stream:  A unidirectional stream of an 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.

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 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.  DTLS Considerations

   The DTLS implementation MUST be based on [RFC6347].

   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 bit set.

   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.

5.  SCTP Considerations

5.1.  Base Protocol

   SCTP as specified in [RFC4960] is used.  However, the following
   restrictions are necessary to reflect that the lower layer is the
   connection oriented
   connection-oriented protocol DTLS instead of the connection less
   protocol IPv4 and IPv6:

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

   o  All associations MUST be single-homed.

   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.

5.2.  Padding Extension

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

5.3.  Dynamic Address Reconfiguration Extension

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

5.4.  SCTP Authentication Extension

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

5.5.  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.

5.6.  Stream Reset Extension

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

5.7.  Interleaving of Large User Message 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 can be used
   with DTLS encapsulation.

6.  IANA Considerations

   This document requires no actions from IANA.

7.  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.

8.  Acknowledgments

   The authors wish to thank Gorry Fairhurst for his invaluable

9.  References

9.1.  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.

9.2.  Informative References

   [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.

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

              Jesup, R., Loreto, S., and M. Tuexen, "RTCWeb Data
              Channels", draft-ietf-rtcweb-data-channel-05 draft-ietf-rtcweb-data-channel-06 (work in
              progress), July October 2013.


              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), July
              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