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Network Working Group                                          M. Tuexen
Internet-Draft                        Muenster Univ. of Applied Sciences
Expires: April 20, 2006                                       R. Stewart
                                                     Cisco Systems, Inc.
                                                        October 17, 2005


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

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Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This document describes a simple method of encapsulating SCTP
   Packets.  This makes it possible to use SCTP in networks with legacy
   NAT not supporting SCTP.







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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Architecture  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Port Number Table . . . . . . . . . . . . . . . . . . . . . . . 3
   4.  Encapsulating procedures  . . . . . . . . . . . . . . . . . . . 4
   5.  Decapsulating procedures  . . . . . . . . . . . . . . . . . . . 4
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
   7.  Security Considerations . . . . . . . . . . . . . . . . . . . . 4
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 5
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 5
     9.1.  Normative References  . . . . . . . . . . . . . . . . . . . 5
     9.2.  Informative References  . . . . . . . . . . . . . . . . . . 5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 6
   Intellectual Property and Copyright Statements  . . . . . . . . . . 7




































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1.  Introduction

   This document describes a simple method of encapsulating SCTP
   Packets.  This makes it possible to use SCTP in networks with legacy
   NAT not supporting SCTP.  This described method interworks without
   any problems with the NAT mechanism described in SCTP_NAT [3].  For
   general NAT considerations regarding SCTP see SCTP_NAT_CONS [2].


2.  Architecture

   The basic architecture is shown in the following figure.

                  +----------------+   +----------------+
                  | Encapsulating/ |   | Encapsulating/ |
                +-| Decapsulating  |---| Decapsulating  |-+
                | |     Point      |   |     Point      | |
   +----------+ | +----------------+   +----------------+ | +----------+
   |          |-+                                         +-|          |
   |   SCTP   |                                             |   SCTP   |
   | Endpoint |                                             | Endpoint |
   |          |-+                                         +-|          |
   +----------+ | +----------------+   +----------------+ | +----------+
                | | Encapsulating/ |   | Encapsulating/ | |
                +-| Decapsulating  |---| Decapsulating  |-+
                  |     Point      |   |     Point      |
                  +----------------+   +----------------+

   On each path there is a pair of encapsulating/decapsulating points
   (EDPs).  When the left SCTP endpoint sends an SCTP packet to the
   right SCTP endpoint, the first EDP on the path encapsulates the SCTP
   packet and the second EDP decapsulates it.  Between the EDP a UDP
   packet is sent which can be processed by legacy NATs.  The EDPs on
   different paths do not need to be synchronized.


3.  Port Number Table

   Every EDP maintains an encapsulating table (ET) where each row
   consists of the following entries:

   1.  Source Address

   2.  Source Port

   3.  Destination Address





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   4.  Destination Port

   5.  Time Stamp

   Please note that the port numbers in the ET are used to build the UDP
   header while encapsulating.  A row SHOULD be deleted when the time
   stamp is older than T1 seconds.  The default value for T1 is 300
   seconds.


4.  Encapsulating procedures

   When an EDP has to encapsulate an SCTP packet it looks up the source
   and destination port number in the row with matching source and
   destination addresses of the ET.  If no matching row is found, the
   IANA registered value 9899 is used for the source and destination
   port as the result of the lookup procedure.  If a matching row was
   found, the time stamp of that row is set to the current time.

   The EDP inserts then an UDP header between the IP and SCTP header of
   the SCTP packet using the source port and the destination port from
   the above lookup procedure.  Furthermore the length and the checksum
   field of the UDP header have to be set accordingly.  Finally the IP
   header is updated to indicate that it now encapsulates an UDP packet.


5.  Decapsulating procedures

   When an EDT has to decapsulate an SCTP packet, it removes the UDP
   header from the packet.  The IP header is updated to indicate that it
   now encapsulates an SCTP packet.  If the source and destination port
   numbers are not both equal to 9899, the EDP performs a lookup in the
   ET to find a row with the source address of the packet being the
   destination address in the row and the destination address of the
   packet being the source address in the row.  If such a row is found,
   the port numbers are updated.  If no row is found, a new one is
   created using the addresses and the port numbers from the packet by
   exchanging the source and destination information.  In both cases the
   time stamp of the row is set to the current time.


6.  IANA Considerations

   This document does not require any actions from IANA.


7.  Security Considerations




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   This section is not complete yet.


8.  Acknowledgments

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


9.  References

9.1.  Normative References

   [1]  Stewart, R., Xie, Q., Morneault, K., Sharp, C., Schwarzbauer,
        H., Taylor, T., Rytina, I., Kalla, M., Zhang, L., and V. Paxson,
        "Stream Control Transmission Protocol", RFC 2960, October 2000.

9.2.  Informative References

   [2]  Xie, Q., "SCTP NAT Traversal Considerations",
        draft-xie-behave-sctp-nat-cons-00 (work in progress),
        April 2005.

   [3]  Stewart, R. and M. Tuexen, "Stream Control Transmission Protocol
        (SCTP) Network Address Translation",
        draft-stewart-behave-sctpnat-00 (work in progress), April 2005.

























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Authors' Addresses

   Michael Tuexen
   Muenster Univ. of Applied Sciences
   Stegerwaldstr. 39
   48565 Steinfurt
   Germany

   Email: tuexen@fh-muenster.de


   Randall R. Stewart
   Cisco Systems, Inc.
   4875 Forest Drive
   Suite 200
   Columbia, SC  29206
   USA

   Email: rrs@cisco.com
































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   Internet Society.




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