Network Working Group M. Tuexen Internet-Draft Muenster Univ. of Appl. Sciences Intended status: Standards Track R. Stewart Expires: July 19, 2015 Netflix, Inc. R. Jesup WorldGate Communications S. Loreto Ericsson January 15, 2015 DTLS Encapsulation of SCTP Packets draft-ietf-tsvwg-sctp-dtls-encaps-08.txt Abstract 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 the encapsulation method described in this document, SCTP is unaware of the protocols being used below DTLS; hence explicit IP addresses cannot be used in the SCTP control chunks. As a consequence, the SCTP associations carried over DTLS can only be single homed. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on July 19, 2015. Copyright Notice Copyright (c) 2015 IETF Trust and the persons identified as the document authors. All rights reserved. Tuexen, et al. Expires July 19, 2015 [Page 1] Internet-Draft SCTP over DTLS January 2015 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. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Encapsulation and Decapsulation Procedure . . . . . . . . . . 3 4. General Considerations . . . . . . . . . . . . . . . . . . . 3 5. DTLS Considerations . . . . . . . . . . . . . . . . . . . . . 3 6. SCTP Considerations . . . . . . . . . . . . . . . . . . . . . 4 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 8. Security Considerations . . . . . . . . . . . . . . . . . . . 6 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 Appendix A. NOTE to the RFC-Editor . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 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 [RFC2460]. This document specifies how SCTP is used on top of the Datagram Transport Layer Security (DTLS) protocol. DTLS 1.0 is defined in [RFC4347] and the present latest version, DTLS 1.2, is defined in [RFC6347]. This encapsulation is used for example within the WebRTC protocol suite (see [I-D.ietf-rtcweb-overview] for an overview) for transporting non-SRTP data between browsers. The architecture of this stack is described in [I-D.ietf-rtcweb-data-channel]. +----------+ | SCTP | +----------+ | DTLS | +----------+ | ICE/UDP | +----------+ Figure 1: Basic stack diagram Tuexen, et al. Expires July 19, 2015 [Page 2] Internet-Draft SCTP over DTLS January 2015 This encapsulation of SCTP over DTLS over or UDP or ICE/UDP (see [RFC5245]) can provide a NAT traversal solution together with confidentiality, source authentication, and integrity protected transfers. Please note that the procedures defined in [RFC6951] for dealing with the UDP port numbers do not apply here. When using the encapsulation defined in this document, SCTP is unaware about the protocols used below DTLS. 2. Conventions 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. Encapsulation and Decapsulation Procedure When an SCTP packet is provided to the DTLS layer, the complete SCTP packet, consisting of the SCTP common header and a number of SCTP chunks, is 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 is passed 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. The path MTU discovery is performed by SCTP when SCTP over DTLS is used for data channels (see Section 5 of [I-D.ietf-rtcweb-data-channel]). 5. DTLS Considerations The DTLS implementation MUST support DTLS 1.0 [RFC4347] and SHOULD support the most recently published version of DTLS, which is DTLS 1.2 [RFC6347] as of December 2014. In the absence of a revision to this document, the latter requirement applies to all future versions of DTLS when they are published as RFCs. This document will only be revised if a revision to DTLS or SCTP makes a revision to the encapsulation necessary. Tuexen, et al. Expires July 19, 2015 [Page 3] Internet-Draft SCTP over DTLS January 2015 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. 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 SHOULD allow the DTLS user to enforce that the corresponding IPv4 packet is sent with the 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. It is RECOMMENDED that the safe value does not exceed 1200 bytes. Please note that [RFC1122] only requires end hosts to be able to reassemble fragmented IP packets up to 576 bytes in length. The DTLS implementation SHOULD allow the DTLS user to set the Differentiated services code point (DSCP) used for IP packets being sent (see [RFC2474]). 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 (see [RFC3168]). The implementation of DTLS and its lower layer have to provide this support. If this is not possible, for example due to implementation restrictions, ECN can't be used by SCTP. 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 [RFC4960] with the following restrictions, which are required to reflect that the lower layer is DTLS instead of IPv4 and IPv6 and that SCTP does not deal with the IP addresses or the transport protocol used below DTLS: Tuexen, et al. Expires July 19, 2015 [Page 4] Internet-Draft SCTP over DTLS January 2015 o A DTLS connection MUST be established before an SCTP association can be set up. o Multiple SCTP associations MAY be multiplexed over a single DTLS connection. The SCTP port numbers are used for multiplexing and demultiplexing the SCTP associations carried over a single DTLS connection. o All SCTP associations are single-homed, because DTLS does not expose any address management to its upper layer. Therefore it is RECOMMENDED to set the SCTP parameter path.max.retrans to association.max.retrans. 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. o If the SCTP layer is notified about a path change by its lower layers, SCTP SHOULD retest the Path MTU and reset the congestion state to the initial state. The window-based congestion control method specified in [RFC4960], resets the congestion window and slow start threshold to their initial values. 6.2. Padding Extension When the SCTP layer performs path MTU discovery as specified in [RFC4821], the padding extension defined in [RFC4820] MUST be supported and used for probe packets (HEARTBEAT chunks bundled with PADDING chunks [RFC4820]). 6.3. Dynamic Address Reconfiguration Extension If the dynamic address reconfiguration extension defined in [RFC5061] is used, ASCONF chunks MUST use wildcard addresses only. 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. Tuexen, et al. Expires July 19, 2015 [Page 5] Internet-Draft SCTP over DTLS January 2015 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, for example the ones defined in [I-D.ietf-tsvwg-sctp-prpolicies]. 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 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 [RFC4347] and for SCTP in [RFC4960], [RFC3758], and [RFC6525]. The combination of SCTP and DTLS introduces no new security considerations. SCTP should not process the IP addresses used for the underlying communication since DTLS provides no guarantees about them. It should be noted that the inability to process ICMP or ICMPv6 messages does not add any security issue. When SCTP is carried over a connection-less lower layer like IPv4, IPv6, or UDP, processing of these messages is required to protect other 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 David Black, Spencer Dawkins, Francis Dupont, Gorry Fairhurst, Christer Holmberg, Eric Rescorla, Tom Taylor, Joe Touch and Magnus Westerlund for their invaluable comments. Tuexen, et al. Expires July 19, 2015 [Page 6] Internet-Draft SCTP over DTLS January 2015 10. References 10.1. Normative References [RFC1122] Braden, R., "Requirements for Internet Hosts - Communication Layers", STD 3, RFC 1122, October 1989. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC4347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer Security", RFC 4347, April 2006. [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 1981. [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998. [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, "Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers", RFC 2474, December 1998. [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition of Explicit Congestion Notification (ECN) to IP", RFC 3168, September 2001. Tuexen, et al. Expires July 19, 2015 [Page 7] Internet-Draft SCTP over DTLS January 2015 [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 2007. [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment (ICE): A Protocol for Network Address Translator (NAT) Traversal for Offer/Answer Protocols", RFC 5245, April 2010. [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. [I-D.ietf-rtcweb-overview] Alvestrand, H., "Overview: Real Time Protocols for Browser-based Applications", draft-ietf-rtcweb-overview-13 (work in progress), November 2014. [I-D.ietf-rtcweb-data-channel] Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data Channels", draft-ietf-rtcweb-data-channel-13 (work in progress), January 2015. [I-D.ietf-tsvwg-sctp-prpolicies] Tuexen, M., Seggelmann, R., Stewart, R., and S. Loreto, "Additional Policies for the Partial Reliability Extension of the Stream Control Transmission Protocol", draft-ietf- tsvwg-sctp-prpolicies-06 (work in progress), December 2014. [I-D.ietf-tsvwg-sctp-ndata] Stewart, R., Tuexen, M., Loreto, S., and R. Seggelmann, "Stream Schedulers and a New Data Chunk for the Stream Control Transmission Protocol", draft-ietf-tsvwg-sctp- ndata-02 (work in progress), January 2015. Tuexen, et al. Expires July 19, 2015 [Page 8] Internet-Draft SCTP over DTLS January 2015 Appendix A. NOTE to the RFC-Editor Although the references to [I-D.ietf-tsvwg-sctp-prpolicies] and [I-D.ietf-tsvwg-sctp-ndata] are informative, put this document in REF-HOLD until these two references have been approved and update these references to the corresponding RFCs. Authors' Addresses Michael Tuexen Muenster University of Applied Sciences Stegerwaldstrasse 39 48565 Steinfurt DE Email: tuexen@fh-muenster.de Randall R. Stewart Netflix, Inc. Chapin, SC 29036 US Email: randall@lakerest.net Randell Jesup WorldGate Communications 3800 Horizon Blvd, Suite #103 Trevose, PA 19053-4947 US Phone: +1-215-354-5166 Email: randell_ietf@jesup.org Salvatore Loreto Ericsson Hirsalantie 11 Jorvas 02420 FI Email: Salvatore.Loreto@ericsson.com Tuexen, et al. Expires July 19, 2015 [Page 9]