Network Working Group M. Tuexen
Internet-Draft Muenster Univ. of Appl. Sciences
Intended status: Standards Track R. Stewart
Expires: January 12, 2012 Adara Networks
July 11, 2011
UDP Encapsulation of SCTP Packets
draft-tuexen-sctp-udp-encaps-07.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.
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the Trust Legal Provisions and are provided without warranty as
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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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