Behavior Engineering for Hindrance R. Denis-Courmont
Avoidance (if taken) VideoLAN project
Internet-Draft February 17, 2008
Intended status: Standards Track
Expires: August 20, 2008
Network Address Translation (NAT) Behavioral Requirements for DCCP
draft-denis-behave-nat-dccp-01.txt
Status of This Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
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."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on August 20, 2008.
Copyright Notice
Copyright (C) The IETF Trust (2008).
Abstract
This document defines a set of requirements for NATs that handle
DCCP.
Denis-Courmont Expires August 20, 2008 [Page 1]
Internet-Draft NAT DCCP Requirements February 2008
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Applicability statement . . . . . . . . . . . . . . . . . . . . 3
4. DCCP Connection Initiation . . . . . . . . . . . . . . . . . . 4
5. NAT Session Refresh . . . . . . . . . . . . . . . . . . . . . . 5
6. Application Level Gateways . . . . . . . . . . . . . . . . . . 5
7. Other Requirements Applicable to DCCP . . . . . . . . . . . . . 6
8. DCCP without NAT support . . . . . . . . . . . . . . . . . . . 6
9. DCCP simultaneous open . . . . . . . . . . . . . . . . . . . . 7
10. Security Considerations . . . . . . . . . . . . . . . . . . . . 7
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 7
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
13.1. Normative References . . . . . . . . . . . . . . . . . . . 7
13.2. Informative References . . . . . . . . . . . . . . . . . . 8
Denis-Courmont Expires August 20, 2008 [Page 2]
Internet-Draft NAT DCCP Requirements February 2008
1. Introduction
For historical reasons, NAT devices are not typically capable of
handling datagrams and flows for application using the Datagram
Congestion Control Protocol (DCCP)[RFC4340].
This draft discusses the technical issues involved, and proposes a
set of requirements for NAT devices to handle DCCP in a way that
enables when either or both of the DCCP endpoints are located behind
one or more NAT devices. All definitions and requirements in
[RFC4787] are inherited here. The requirements are otherwise
designed similarly to those in [I-D.ietf-behave-tcp], from which this
memo borrows its structure and much of its content.
Note however that, if both endpoints are hindered by NAT devices, the
normal model of asymmetric connection model of DCCP will not work. A
simultaneous open must be performed, as in
[I-D.fairhurst-dccp-behave-update]. Also, a separate unspecified
mechanism may be needed, such as UNSAF protocols, if an endpoint
needs to learn its own external NAT mappings.
2. Definitions
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].
This documentation uses the term "DCCP connection" to refer to
invidual DCCP flows, as uniquely identified by the the 4-tuple
(source and destination IP addresses and DCCP ports) at a given time.
This document uses the term "NAT mapping" to refer to state at the
NAT necessary for network address and port translation of DCCP
connections. This document also uses the terms "endpoint independent
mapping", "address dependent mapping", "address and port dependent
mapping", "filtering behavior", "endpoint independent filtering",
"address dependent filtering", "address and port dependent
filtering", "port assignment", "port overloading", "hairpinning", and
"external source IP address and port" as defined in [RFC4787].
3. Applicability statement
This document applies to NAT devices that want to handle DCCP
datagrams. It is not the intent of this document to deprecate the
overwhelming majority of deployed NAT devices. These NATs are simply
not expected to handle DCCP, so this memo is not applicable to them.
Expected NAT behaviors applicable to DCCP connections are very
Denis-Courmont Expires August 20, 2008 [Page 3]
Internet-Draft NAT DCCP Requirements February 2008
similar to those applicable to TCP connections (with the exception or
REQ-6 below). The following requirements are discussed and justified
extensively in [I-D.ietf-behave-tcp]. These justifications are not
reproduced here for the sake of brevity.
In addition to the usual changes to the IP header (in particular the
IP addresses), NAT devices need to mangle:
o the DCCP source port, for outgoing packets, depending on the NAT
mapping
o the DCCP destination port, for incoming packets, depending on the
NAT mapping
o the DCCP checksum, to compensate for IP address and port number
modifications.
Because changing the the source or destination IP address of a DCCP
packet will normally invalidate the DCCP checksum, it is not possible
to use DCCP through a NAT without dedicated support. Some NAT
devices are known to provide a "generic" transport protocol support,
whereby only the IP header is mangled. That scheme is not sufficient
to support DCCP in any case.
4. DCCP Connection Initiation
4.1. Address and Port Mapping Behavior
A NAT uses a mapping to translate packets for each DCCP connection.
A mapping is dynamically allocated for connections initiated from the
internal side, and potentially reused for certain subsequent
connections. NAT behavior regarding when a mapping can be reused
differs for different NATs as described in [RFC4787].
REQ-1: A NAT MUST have an "Endpoint Independent Mapping" behavior for
DCCP.
4.2. Internally Initiated Connections
FIXME/TBD: may change as DCCP simultaneous open progresses.
REQ-2: A NAT MUST support all valid sequences of DCCP packets
(defined in [RFC4340] and its updates) for connections initiated both
internally as well as externally when the connection is permitted by
the NAT.
In particular, in addition to handling the DCCP 3-way handshake mode
of connection initiation, A NAT MUST handle the DCCP simultaneous-
open mode of connection initiation (FIXME: currently work-in-progress
in the DCCP working group).
Denis-Courmont Expires August 20, 2008 [Page 4]
Internet-Draft NAT DCCP Requirements February 2008
4.3. Externally Initiated Connections
REQ-3: If application transparency is most important, it is
RECOMMENDED that a NAT have an "Endpoint independent filtering"
behavior for DCCP. If a more stringent filtering behavior is most
important, it is RECOMMENDED that a NAT have an "Address dependent
filtering" behavior.
o The filtering behavior MAY be an option configurable by the
administrator of the NAT.
o The filtering behavior for TCP MAY be independent of thefiltering
behavior for UDP.
REQ-4: A NAT MUST NOT respond to an unsolicited inbound DCCP-Request
(TBD: add stuff for DCCP simultaneous open) packet for at least 6
seconds after the packet is received. If during this interval the
NAT receives and translates an outbound DCCP packet (TBD: DCCP packet
type) for the connection the NAT MUST silently drop the original
unsolicited inbound DCCP-Request packet. Otherwise the NAT SHOULD
send an ICMP Port Unreachable error (Type 3, Code 3) for the original
DCCP-Request, unless the security policy forbids it.
5. NAT Session Refresh
The "established connection idle-timeout" for a NAT is defined as the
minimum time a DCCP connection in the established phase must remain
idle before the NAT considers the associated session a candidate for
removal. The "transitory connection idle-timeout" for a NAT is
defined as the minimum time a DCCP connection in the CLOSEREQ or
CLOSING phases must remain idle before the NAT considers the
associated session a candidate for removal. DCCP connections in the
TIMEWAIT state are not affected by the "transitory connection idle-
timeout".
REQ-5: If a NAT cannot determine whether the endpoints of a DCCP
connection are active, it MAY abandon the session if it has been idle
for some time. In such cases, the value of the "established
connection idle-timeout" MUST NOT be less than 2 hours 4 minutes.
The value of the "transitory connection idle-timeout" MUST NOT be
less than 4 minutes. The value of the NAT idle-timeouts MAY be
configurable.
NAT behavior for handling DCCP-Reset packets, or connections in
TIMEWAIT state is left unspecified.
6. Application Level Gateways
Contraty to TCP, DCCP is a loss-tolerant protocol. Therefore,
modifying the payload of DCCP packets present a significant
Denis-Courmont Expires August 20, 2008 [Page 5]
Internet-Draft NAT DCCP Requirements February 2008
additionnal challenge in maintaining sane DCCP sequence numbers, if
the size of the payload were altered. Also, there are no known DCCP-
capable Application Level Gateways (ALGs) at the time of writing this
document.
REQ-6: If a NAT includes ALGs, it MUST NOT affect DCCP.
NOTE: This is not consistent with REQ-6 of [I-D.ietf-behave-tcp].
7. Other Requirements Applicable to DCCP
A list of general and UDP specific NAT behavioral requirements are
described in [RFC4787]. A list of ICMP specific NAT behavioral
requirements are described in [I-D.ietf-behave-nat-icmp]. The
requirements listed below reiterate the requirements from these two
documents that directly affect DCCP. The following requirements do
not relax anyrequirements in [RFC4787] or [I-D.ietf-behave-nat-icmp].
7.1. Port Assignment
REQ-7: A NAT MUST NOT have a "Port assignment" behavior of "Port
overloading" for DCCP.
7.2. Hairpinning Behavior
REQ-8: A NAT MUST support "Hairpinning" for DCCP. Futhermore, A
NAT's Hairpinning behavior MUST be of type "External source IP
address and port".
7.3. ICMP Responses to DCCP Packets
REQ-9: If a NAT translates DCCP, it SHOULD translate ICMP Destination
Unreachable (Type 3) messages.
REQ-10: Receipt of any sort of ICMP message MUST NOT terminate the
NAT mapping or DCCP connection for which the ICMP was generated.
8. DCCP without NAT support
If the NAT device cannot be updated to support DCCP, DCCP datagram
could be encapsulated within an additionnal UDP transport header.
Indeed, most NAT devices are already capable of handling UDP.
There are significant disadvantages to this approach:
o Both sides of the DCCP session need must be updated to use
tunnelling, even though only one side might be hindered with a
NAT.
Denis-Courmont Expires August 20, 2008 [Page 6]
Internet-Draft NAT DCCP Requirements February 2008
o A method MUST be defined to negociate when to use tunnelling.
o The per-packet overhead is increased.
A DCCP transport-specific solution is specified by
[I-D.phelan-dccp-natencap]. Alternatively, existing IP tunneling
protocols, such as ESP-in-UDP[RFC3948] (especially with the NULL
cipher suite) or Teredo[RFC4380], could be used.
9. DCCP simultaneous open
When both parties to an intended DCCP session are located behind
either a NAT device or a stateful firewall, neither can act as the
paassive endpoint in the connection establishment.
Unfortunately, at the time of writing, the DCCP connection state
machine does not allow both peers to behave as active endpoint, as is
the case in TCP simultaneous open. It is expected that this issue
will be tackled in the DCCP working group shortly (TODO: reference
relevant I-D).
10. Security Considerations
TBD.
11. IANA Considerations
This document raises no IANA considerations.
12. Acknowledgments
The author would like to thank ... for their comments on this
document.
This memo borrows heavily from draft-ietf-behave-tcp-07, by S. Guha
(editor), K. Biswas, B. Ford, S. Sivakumar and P. Srisuresh.
13. References
13.1. Normative References
[I-D.ietf-behave-nat-icmp] Srisuresh, P., Ford, B.,
Sivakumar, S., and S. Guha, "NAT
Behavioral Requirements for ICMP
protocol",
draft-ietf-behave-nat-icmp-07
(work in progress),
February 2008.
Denis-Courmont Expires August 20, 2008 [Page 7]
Internet-Draft NAT DCCP Requirements February 2008
[RFC2119] Bradner, S., "Key words for use
in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119,
March 1997.
[RFC4340] Kohler, E., Handley, M., and S.
Floyd, "Datagram Congestion
Control Protocol (DCCP)",
RFC 4340, March 2006.
[RFC4787] Audet, F. and C. Jennings,
"Network Address Translation
(NAT) Behavioral Requirements for
Unicast UDP", BCP 127, RFC 4787,
January 2007.
13.2. Informative References
[I-D.fairhurst-dccp-behave-update] Fairhurst, G. and G. Renker, "An
Update for DCCP Connection
Establishment to Assist NAT &
Firewall Traversal", draft-
fairhurst-dccp-behave-update-01
(work in progress),
November 2007.
[I-D.ietf-behave-tcp] Guha, S., "NAT Behavioral
Requirements for TCP",
draft-ietf-behave-tcp-07 (work in
progress), April 2007.
[I-D.phelan-dccp-natencap] Phelan, T., "Datagram Congestion
Control Protocol (DCCP)
Encapsulation for NAT Traversal
(DCCP-NAT)",
draft-phelan-dccp-natencap-00
(work in progress),
February 2008.
[RFC3948] Huttunen, A., Swander, B., Volpe,
V., DiBurro, L., and M. Stenberg,
"UDP Encapsulation of IPsec ESP
Packets", RFC 3948, January 2005.
[RFC4380] Huitema, C., "Teredo: Tunneling
IPv6 over UDP through Network
Address Translations (NATs)",
RFC 4380, February 2006.
Denis-Courmont Expires August 20, 2008 [Page 8]
Internet-Draft NAT DCCP Requirements February 2008
Author's Address
Remi Denis-Courmont
VideoLAN project
EMail: rem@videolan.org
URI: http://www.videolan.org/
Denis-Courmont Expires August 20, 2008 [Page 9]
Internet-Draft NAT DCCP Requirements February 2008
Full Copyright Statement
Copyright (C) The IETF Trust (2008).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Acknowledgement
Funding for the RFC Editor function is provided by the IETF
Administrative Support Activity (IASA).
Denis-Courmont Expires August 20, 2008 [Page 10]