Internet DRAFT - draft-denis-behave-v4v6exthdr
draft-denis-behave-v4v6exthdr
Behavior Engineering for Hindrance R. Denis-Courmont
Avoidance Nokia
Internet-Draft March 09, 2009
Intended status: Experimental
Expires: September 10, 2009
IPv6 destination header option for IPv4 translator mapping notification
draft-denis-behave-v4v6exthdr-01
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Abstract
This memo defines a new IPv6 Destination header option to convey the
transport mapping information from an IPv4-IPv4 protocol translator
to the IPv6 end of a protocol-translated packet flow.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. IPv4-IPv6 Translation . . . . . . . . . . . . . . . . . . . . 5
3.1. Inserting the flow mapping option . . . . . . . . . . . . 5
3.1.1. Usage with connection-oriented protocols . . . . . . . 5
3.1.2. Usage with other protocols . . . . . . . . . . . . . . 6
3.2. Receiving the flow mapping option . . . . . . . . . . . . 6
4. Option format . . . . . . . . . . . . . . . . . . . . . . . . 7
5. UNSAF Considerations . . . . . . . . . . . . . . . . . . . . . 8
5.1. Exit strategy . . . . . . . . . . . . . . . . . . . . . . 8
5.2. Interactions with legacy NATs . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
8. API Considerations . . . . . . . . . . . . . . . . . . . . . . 11
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
9.1. Normative References . . . . . . . . . . . . . . . . . . . 12
9.2. Informative References . . . . . . . . . . . . . . . . . . 12
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 13
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1. Introduction
To overcome the shortage of IPv4 addresses within the Internet,
Network Address and Port Translators (NATs) have been widely
deployed, such that multiple IPv4 nodes can share a single IPv4
address. However, that method is known to break certain application
protocols, which need to know their own assigned external IP address
and/or port number (i.e. the transport address). New solutions are
now under consideration which would extend NAT mechanisms such that
IPv6 nodes could access the IPv4 Internet.
This memo proposes an in-band method for such a IPv6-IPv4 NAT to
notify affected IPv6 applications of the IPv4 transport address
associated with any of their active communication flows. A new
option for the IPv6 Destination extension header, the Translated Flow
Mapping option is hereby defined to carry this information.
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2. Definitions
TBD.
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].
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3. IPv4-IPv6 Translation
An IPv4-IPv6 NAT performs two separate functions:
o It receives IPv4 packets on its IPv4 interface, translates them to
IPv6. To that end, for each IPv4 packet, it crafts a new IPv6
header to replace the IPv4 header, may modify the inner transport
protocol header. Then, it sends the resulting translated IPv6
packets through its IPv6 interface.
o Reciprocally, it translates IPv6 packets into IPv4 packets.
The details of IPv4-IPv6 translation are beyond the scope of this
document, please refer to [whatever IETF ends up specifying for this]
instead.
3.1. Inserting the flow mapping option
When a translator receives an IPv4 packet, following certain
conditions, it inserts an IPv6 Destination extension header
containing a Translated Flow Mapping option (as defined in the next
section).
As a general rule, this option MUST NOT be inserted, if the resulting
packet would exceed the known MTU to the IPv6 destination, or 1280
bytes if there is no known MTU.
3.1.1. Usage with connection-oriented protocols
For connection-oriented transport protocols, this option SHOULD be
inserted is part of the protocol handshake, and SHOULD NOT be
inserted otherwise.
3.1.1.1. Datagram Congestion Control Protocol (DCCP)
This option SHOULD be inserted within DCCP Sync, DCCP Sync/Ack and
DCCP Listen packets. See [RFC4340] and [I-D.ietf-dccp-simul-open].
3.1.1.2. Stream Control Transmission Protocol (SCTP)
TBD.
3.1.1.3. Transmission Control Protocol (TCP)
This option SHOULD be inserted within TCP SYN and TCP SYN/ACK
packets. See [RFC0793].
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3.1.2. Usage with other protocols
So long as a translated packet is small enough (with regards to the
MTU rule above), and uses a non-connection-oriented (including UDP
and UDP-Lite) or unknown transport protocol, the translator MAY
insert the option. If it is known that the packet is one of the
first 10 (FIXME: is this OK?) packets translated in the same
direction for the corresponding mapping, then the translator SHOULD
insert the option.
3.2. Receiving the flow mapping option
Processing of the flow mapping option is optional. In fact, an IPv6
implementation that does not support the flow mapping option MUST
ignore it, according to [RFC2460] (this is not a new requirement for
IPv6 implementation).
The content of the flow mapping option is merely informational.
Hence, there are no particular requirements as regards its
processing. An IPv6 stack that implements the flow mapping option
MAY store and or forward the flow mapping informations, as it sees
fit. For instance, it might forward the informations to the
application (see below for an example API) if it requests them.
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4. Option format
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Option Length | Mapped Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mapped IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Translated Flow Mapping option
The Translated Flow Mapping option format is defined as follow:
Option Type: XXX (TBD: IANA)
Option Length: 10 (10 bytes worth of data)
Mapped Port: If the type of the first header that is not an IPv6
extension header is DCCP, SCTP, TCP, UDP or UDP-Lite, the
transport protocol mapped port number. This is the destination
port number found in the original IPv4 packet that was translated
into the IPv6 packet containing this option. Otherwise, this must
be set to zero by sender, and ignored by receivers.
Mapped IPv4 Address: Destination IPv4 address, as found in the
origin IPv4 packet before translation.
Remote IPv4 Address: Source IPv4 address, as found in the origin
IPv4 packet before translation.
The Translated Flow Mapping option requires a 4n alignment (as
defined per [RFC2460] section 4.2). In particular, if it is the only
non-padding option in an IPv6 extension header, it will be preceded
by two bytes of padding. That is normally achieved through a single
PadN option with a zero-length payload.
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5. UNSAF Considerations
The Translated Flow Mapping option can be inserted by translators and
received by IPv6 nodes.
5.1. Exit strategy
It is expected that any applicable translation mechanism will define
its own UNSAF Considerations, at least as regards the translators.
Those should be referred to when it comes to inserting the Flow
Mapping option. In particular, such a specification shall narrow
down the scope of the translation scheme, define an exit strategy and
longer term solutions (e.g. complete translation-free native IPv6
networking). See [RFC3424] for further references.
However, a dedicated exit strategy is required for the IPv6 nodes
that would be capable of parsing the Translated Flow Mapping option.
When applicable translator deployments are being phased out, parsing
the option becomes increasingly irrelevant, as the option will be
absent from any received packets. At that point, IPv6
implementations can stop recognizing and parsing the option. They
can instead return an error to any IPv6 application that would still
try to use of the Flow Mapping option. IPv6 applications MUST be
prepared to deal with IPv6 implementations that do not support this
specification.
5.2. Interactions with legacy NATs
Legacy NATs do not support this option. This situation can normally
be detected by the absence of the Translated Flow Mapping option.
Problems may occur if a translator that implements this specification
is located behind a legacy NAT. In this case, the Translated Flow
Mapping option may contain incorrect informations. This can most
often be detected by verifying that the embedded IPv4 address is a
globally unique one rather than a private one (as defined by
[RFC1918] and [RFC3927]).
However, any application using this extension SHOULD be prepared to
fail gracefully if incorrect informations are received. Indeed, a
legacy NAT could internally use public address space. Or the (non-
legacy) translator could be deployed in a closed network using
private IPv4 addresses, even in the absence of legacy NATs.
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6. Security Considerations
By maliciously inserting or altering a Translated Flow Mapping option
to an IPv6 packet, an attacker could cause manipulate IP and
transport addressing informations to be received.
This may specifically allow an IPv6 attacker to refer the victim
recipient node to an arbitrary IPv4 third party. As usual, IP nodes
should not make assumptions to lightly as regard the IP address
information they get. This problem is very similar to that of an
IPv6 node handling a source-spoofed IPv6 packet, and the same
precautions applies. In particular, proper transport or application-
layer congestion control mechanisms need to be used, to prevent a
distributed denial-of-service attack. Also, in security-sensitive
cases, adequate security protocols are needed, such as TLS or IPsec.
The Translated Flow Mapping option can also cause a victim recipient
to assume an incorrect arbitrary IPv4 self-referral address. TBD: Do
we need to fix this? How?
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7. IANA Considerations
The Translated Flow Mapping option requires an IPv6 Option number.
IPv6 Option Number [RFC2460]:
HEX act chg rest
--- --- --- -----
XX 00 0 XXXXX Translated Flow Mapping
The first two bits indicate that the IPv6 node may skip over this
option and continue processing the header if it doesn't recognize the
option type, and the third bit indicates that the Option Data may not
change en-route.
This document should be listed as the reference document.
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8. API Considerations
This section is non-normative. It defines a potential API to
retrieve the flow mapping information as an extension to the Advanced
IPv6 socket API [RFC3542].
The flow mapping informations shall be passed to applications using a
structure defined in <netinet/in.h>, and containing at least the
following fields:
struct in6_ipv4flowmapping {
struct uint16_t i4fm6_mapped_port;
struct in_addr i4fm6_mapped_addr;
struct in_addr i4fm6_remote_addr;
};
Flow mapping structure
For datagram (type SOCK_DGRAM) and raw (type SOCK_RAW) sockets, a
socket option can configure receiving the flow information as
ancilliary data on a per-packet basis, using recvmsg. This socket
option shall be set to 0 (off) by default. Setting it to 1 (on)
shall enabled flow mapping infos reception. Setting it to -1
(default) shall disable it. When enabled, an ancilliary data with
level IPPROTO_IPV6, type IPV6_IPV4FLOWMAPPING shall be returned to
the application, if a Flow Mapping option was found in the received
packet.
int on = 1;
setsockopt(fd, IPPROTO_IPV6, IPV6_RECVIPV4FLOWMAPPING,
&yes, sizeof(yes));
Per-packet socket option
For a connected socket, a read-only socket option may be used to
fetch the flow mapping information if known (i.e. if at least one
packet with a Flow Mapping Option was received). If unknown, the
returned structure shall contain all zeroes.
struct in6_ipv4flowmapping val;
getsockopt(fd, IPPROTO_IPV6, IPV6_IPV4FLOWMAPPING,
&val, sizeof(val));
Connected socket option
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9. References
9.1. Normative References
[I-D.ietf-dccp-simul-open]
Fairhurst, G., "DCCP Simultaneous-Open Technique to
Facilitate NAT/Middlebox Traversal",
draft-ietf-dccp-simul-open-07 (work in progress),
February 2009.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, September 1981.
[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, February 1996.
[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.
[RFC3424] Daigle, L. and IAB, "IAB Considerations for UNilateral
Self-Address Fixing (UNSAF) Across Network Address
Translation", RFC 3424, November 2002.
[RFC3927] Cheshire, S., Aboba, B., and E. Guttman, "Dynamic
Configuration of IPv4 Link-Local Addresses", RFC 3927,
May 2005.
[RFC4340] Kohler, E., Handley, M., and S. Floyd, "Datagram
Congestion Control Protocol (DCCP)", RFC 4340, March 2006.
9.2. Informative References
[RFC3542] Stevens, W., Thomas, M., Nordmark, E., and T. Jinmei,
"Advanced Sockets Application Program Interface (API) for
IPv6", RFC 3542, May 2003.
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Author's Address
Remi Denis-Courmont
Nokia Corporation
P.O. Box 407
NOKIA GROUP 00045
FI
Phone: +358 50 487 6315
Email: remi.denis-courmont@nokia.com
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