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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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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Internet-Draft UDP Encapsulation of SCTP Packets October 2005
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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Internet-Draft UDP Encapsulation of SCTP Packets October 2005
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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Internet-Draft UDP Encapsulation of SCTP Packets October 2005
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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