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Versions: 00 01 02 03 04 RFC 6951

Network Working Group                                          M. Tuexen
Internet-Draft                          Muenster Univ. of Appl. Sciences
Intended status: Standards Track                              R. Stewart
Expires: January 26, 2012                                 Adara Networks
                                                           July 25, 2011


                   UDP Encapsulation of SCTP Packets
                draft-ietf-tsvwg-sctp-udp-encaps-00.txt

Abstract

   This document describes a simple method of encapsulating SCTP Packets
   into UDP packets and its limitations.  This allows the usage of SCTP
   in networks with legacy NAT not supporting SCTP.  It can also be used
   to implement SCTP on hosts without directly accessing the IP-layer,
   for example implementing it as part of the application without
   requiring special privileges.

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
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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on January 26, 2012.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   publication of this document.  Please review these documents
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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of



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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
     3.1.  Portable SCTP Implementations . . . . . . . . . . . . . . . 3
     3.2.  Legacy NAT traversal  . . . . . . . . . . . . . . . . . . . 4
   4.  SCTP over UDP . . . . . . . . . . . . . . . . . . . . . . . . . 4
     4.1.  Architectural Considerations  . . . . . . . . . . . . . . . 4
     4.2.  Packet Format . . . . . . . . . . . . . . . . . . . . . . . 4
     4.3.  Encapsulation Procedure . . . . . . . . . . . . . . . . . . 5
     4.4.  Decapsulation Procedure . . . . . . . . . . . . . . . . . . 5
     4.5.  ICMP considerations . . . . . . . . . . . . . . . . . . . . 6
     4.6.  Path MTU considerations . . . . . . . . . . . . . . . . . . 6
     4.7.  Handling of Embedded IP-addresses . . . . . . . . . . . . . 6
     4.8.  ECN considerations  . . . . . . . . . . . . . . . . . . . . 6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 7
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 7
     8.2.  Informative References  . . . . . . . . . . . . . . . . . . 7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 8
























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1.  Introduction

   This document describes a simple method of encapsulating SCTP packets
   into UDP packets.  SCTP is defined in [RFC4960].  There are two main
   reasons for this:

   o  Allow SCTP traffic to pass legacy NATs, which do not provide
      native SCTP support as specified in [I-D.ietf-behave-sctpnat] and
      [I-D.ietf-tsvwg-natsupp].

   o  Allow SCTP to be implemented on hosts which do not provide direct
      access to the IP-layer.  In particular, applications can use their
      own SCTP implementation if the operating system does not provide
      one.


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.  Use Cases

   This section discusses two important use cases for encapsulating SCTP
   into UDP.

3.1.  Portable SCTP Implementations

   Some operating systems support SCTP natively.  For other operating
   systems implementations are available, but require special privileges
   to install and/or use them.  In some cases no kernel implementation
   might be available at all.  When proving an SCTP implementation as
   part of a user process, most operating systems require special
   privileges to access the IP layer directly.

   Using UDP encapsulation makes it possible to provide an SCTP
   implementation as part of a user process which does not require any
   special privileges.

   A crucial point for implementing SCTP in userland is controlling the
   source address of outgoing packets.  This is not an issue when using
   all available addresses.  However, this is not the case when also
   using the address management required for NAT traversal described in
   Section 4.7.





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3.2.  Legacy NAT traversal

   Using UDP encapsulation allows an SCTP communication traversing
   legacy NATs not supporting SCTP as described in
   [I-D.ietf-behave-sctpnat] and [I-D.ietf-tsvwg-natsupp].  It is
   important to realize that for single homed associations it is only
   necessary that no IP addresses are listen in the INIT- and INIT-ACK
   chunks.  Dynamic address reconfiguration to change the single address
   has to make use of wildcard addresses as described in [RFC5061].

   For multi-homed SCTP association the address management as described
   in Section 4.7 MUST be performed.


4.  SCTP over UDP

4.1.  Architectural Considerations

   An SCTP implementation supporting UDP encapsulation MUST store a UDP
   encapsulation port per destination address for each SCTP association.

4.2.  Packet Format

   To encapsulate an SCTP packet, a UDP header header as defined in
   [RFC0768] is inserted between the IP header and the SCTP common
   header.

   Figure 1 shows the packet format of an encapsulated SCTP packet when
   IPv4 is used.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         IPv4 Header                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         UDP Header                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      SCTP Common Header                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        SCTP Chunk #1                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           ...                                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        SCTP Chunk #n                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                 Figure 1




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   The packet format for an encapsulated SCTP packet when using IPv6 is
   shown in Figure 2.  Please note the the number m of IPv6 extension
   headers can be 0.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      IPv6 Base Header                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    IPv6 Extension Header #1                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           ...                                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    IPv6 Extension Header #m                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         UDP Header                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      SCTP Common Header                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        SCTP Chunk #1                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           ...                                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        SCTP Chunk #n                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                 Figure 2

   The UDP checksum MUST NOT be zero.

4.3.  Encapsulation Procedure

   When inserting the UDP header, the source port is 9899, the
   destination port is the one stored for the destination address the
   packet is sent to or 9899 if not destination address is stored.

   The length of the UDP packet is the length of the SCTP packet plus
   the size of the UDP header.

   The checksum MUST be computed.

4.4.  Decapsulation Procedure

   When an encapsulated packet is received, the UDP header is removed.
   Then a lookup is performed to find the association the received SCTP
   packet belongs to.  The UDP source port is stored as the
   encapsulation port of the SCTP destination address the received SCTP
   packet is sent from.



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4.5.  ICMP considerations

   When receiving ICMP or ICMPv6 response packet, there might not be
   enough bytes in the payload to identify the SCTP association which
   the SCTP packet triggering the ICMP or ICMPv6 packet belongs to.  If
   a received ICMP or ICMPv6 packet can to be related to a specific SCTP
   association, it MUST be discarded silently.

4.6.  Path MTU considerations

   If an SCTP endpoint starts to encapsulate the packets of a path, it
   MUST decrease the path MTU of that path by the size of an UDP header.
   If it stops encapsulating them, the path MTU MUST be increased by the
   size of an UDP header.

   When performing path MTU discovery as described in [RFC4820] it MUST
   take into account that it cannot rely on the feedback provided by
   ICMP or ICMPv6 due to the limitation laid out in Section 4.5.

4.7.  Handling of Embedded IP-addresses

   When using UDP encapsulation is used for legacy NAT traversal, IP
   address that might be translated MUST NOT be put into any SCTP
   packet.

   This means that an SCTP association is setup singled homed and the
   protocol extension [RFC5061] is used to add multiple address.  Only
   wildcard addresses are put into the SCTP packet.

   When addresses are changed during the lifetime of the association
   [RFC5061] MUST be used with wildcard addresses only.

4.8.  ECN considerations

   TBD


5.  IANA Considerations

   This document does not require any actions from IANA.


6.  Security Considerations

   Encapsulating SCTP into UDP does not add any additional security
   considerations to the ones given in [RFC4960] and [RFC5061].





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7.  Acknowledgments

   The authors wish to thank Irene Ruengeler for her invaluable
   comments.


8.  References

8.1.  Normative References

   [RFC0768]  Postel, J., "User Datagram Protocol", STD 6, RFC 768,
              August 1980.

   [RFC0791]  Postel, J., "Internet Protocol", STD 5, RFC 791,
              September 1981.

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

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

   [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.

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

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

8.2.  Informative References

   [I-D.ietf-behave-sctpnat]
              Stewart, R., Tuexen, M., and I. Ruengeler, "Stream Control
              Transmission Protocol (SCTP) Network Address Translation",
              draft-ietf-behave-sctpnat-05 (work in progress),
              June 2011.



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   [I-D.ietf-tsvwg-natsupp]
              Stewart, R., Tuexen, M., and I. Ruengeler, "Stream Control
              Transmission Protocol (SCTP) Network Address Translation
              Support", draft-ietf-tsvwg-natsupp-01 (work in progress),
              June 2011.


Authors' Addresses

   Michael Tuexen
   Muenster University of Applied Sciences
   Stegerwaldstr. 39
   48565 Steinfurt
   DE

   Email: tuexen@fh-muenster.de


   Randall R. Stewart
   Adara Networks
   Chapin, SC  29036
   USA

   Email: randall@lakerest.net



























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