Network Working Group B. Carpenter
Internet-Draft Univ. of Auckland
Intended status: Experimental November 7, 2007
Expires: May 10, 2008
Shimmed IPv4/IPv6 Address Network Translation Interface (SHANTI)
draft-carpenter-shanti-01
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Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
There is a pragmatic need for a packet-level translation mechanism
between IPv4 and IPv6, for scenarios where no other mode of IPv4 to
IPv6 interworking is possible. The mechanism defined here uses a
shim in both the translator and the IPv6 host to mitigate the
problems introduced by stateless translation.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Disclaimer . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Summary of operation . . . . . . . . . . . . . . . . . . . 3
1.3. Requirements notation . . . . . . . . . . . . . . . . . . 5
2. Scenario of addresses and ports . . . . . . . . . . . . . . . 5
3. General walkthroughs . . . . . . . . . . . . . . . . . . . . . 8
4. Placement of the shim . . . . . . . . . . . . . . . . . . . . 9
5. DNS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
6. ICMP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
7. Unresolved issues . . . . . . . . . . . . . . . . . . . . . . 10
8. Security Considerations . . . . . . . . . . . . . . . . . . . 13
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
11. Change log [RFC Editor: please remove this section] . . . . . 14
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
12.1. Normative References . . . . . . . . . . . . . . . . . . . 14
12.2. Informative References . . . . . . . . . . . . . . . . . . 14
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 15
Intellectual Property and Copyright Statements . . . . . . . . . . 16
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Dedication
A few days before his tragic death, itojun (Jun-ichiro Itoh Hagino)
responded to a comment that "I absolutely don't like to see ::FFFF/96
on the wire" by writing "then we'd have to deprecate SIIT at least.
still, you cannot be sure that ::ffff:0:0/96 are not on the wire."
This directly inspired the idea behind SHANTI. This proposal is
dedicated to itojun.
1. Introduction
1.1. Disclaimer
This proposal is incomplete. It is posted to seek comments on
plausibility; much more work is needed to make it implementable.
1.2. Summary of operation
There has long been a defined mechanism for stateless translation
betweeen IPv4 and IPv6 packet formats, named SIIT [RFC2765]. Its
intended use is any scenario where dual stack coexistence between
IPv4 and IPv6, possibly accompanied by dual stack application level
proxies, is insufficient. In the most stringent case, this will
occur when communication is needed between unmodified ("legacy") IPv4
hosts and IPv6-only hosts that have no IPv4 code, and no dual stack
proxy is available for the application protocol of interest. Thus
the scenario of interest is one where an IPv6-only host is modified
(with the inclusion of a shim and DNS resolver changes) to allow it
to leverage a separate device (the translator) to access IPv4-only
sections of the Internet.
The previously proposed solution for this requirement, NAT-PT
[RFC2766], has known issues and has been deprecated [RFC4966]. The
present proposal does not resolve all of those issues; a later
section will identify the issues believed to remain open. This
proposal aims to resolve those issues that can be handled if the IPv6
protocol stack communicating with a translator can obtain information
about the translation. The objectives are to ensure that
o from the IPv4 host's point of view, nothing is worse than in the
case of an IPv4-to-IPv4 translation
o from the IPv6 host's point of view, no special code is generally
required in the transport layer or above. However, information
about the translation is available in the IPv6 host's network
stack, as needed. This is the crucial difference from NAT-PT.
o IPv6 routing is not affected in any way, and there is no risk of
importing "entropy" from the IPv4 routing tables into IPv6.
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To achieve these goals, a shim is inserted in the protocol stack at
both the IPv6 host and at the translator. Its objective is to allow
the IPv6 stack at the host to be aware of the presence of the
translator, of the addresses involved in the translation, and of any
other information known by the translator that may be of value to the
IPv6 host. A shim model is chosen, as in SHIM6
[I-D.ietf-shim6-proto], so that upper layer protocols (ULPs) have no
need to be aware of anything unusual. The mechanism is known as
SHimmed Address Network Translation Interface (SHANTI, which means
"inner peace" in Sanskrit).
As in SHIM6, ULPs are presented with an upper layer identifier (ULID)
in the form of an IPv6 address which is independent of any
manipulation of addresses in the shim or translator.
Additionally, packets that flow over the IPv6 network all have quite
normal IPv6 addresses, with no topological constraints. The same
applies on the IPv4 side. This means that the translator may be
positioned anywhere that is operationally convenient (e.g., on the
IPv6 host's own site, within its ISP's network, or much closer to the
IPv4 host). The only requirement is that there exists an IPv6 path
between the IPv6 host and the translator, and an IPv4 path between
the translator and the IPv4 host.
There are two cases to consider:
1. A new flow of packets is started by an IPv6 host. In this case,
the principle of operation is that the shim in the IPv6 host
exchanges information with the shim in the translator before the
first packet of the new flow is released from the sending buffer.
The result of the information exchange is that the shim knows
what addresses and ports will be used for both IPv6 and IPv4, and
can appropriately manipulate the packets before sending them to
the translator via IPv6.
2. A new flow of packets is started by an IPv4 host. In this case,
the principle of operation is that the shim in the translator
sends the first packet to the IPv6 host with a shim header
defining what addresses and ports will be used for both IPv6 and
IPv4. The shim in the IPv6 host can appropriately manipulate the
packets before delivering them to the upper layer protocol.
In neither case is any IPv4 component aware of any difference from a
normal IPv4 packet stream.
The reader is assumed to have a general understanding of SHIM6.
Although this early draft does not assume that the SHIM6 mechanisms
defined in [I-D.ietf-shim6-proto] would be used unchanged, they form
a proof of concept for the type of communication required between two
network-layer shims.
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It should be noted that this mechanism adds complexity to an IPv6-
only host. This has to be balanced against the complexity of a dual-
stack host. In this model, no residual IPv4 code is needed in the
IPv6 host. The shim has to handle the rewriting of addresses and
port numbers, but nothing else.
1.3. Requirements notation
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].
2. Scenario of addresses and ports
Consider an IPv6-only host X and and IPv4-only host Y.
Let A(x) be an IPv6 address for X, and let a(y) be an IPv4 address
for Y. Let the port in use at X be P(x) and at Y be P(y).
We will observe later that it is irrelevant whether a(y) is
translated by an IPv4 NAT, and whether P(y) is translated by an IPv4
NAPT.
Additionally, consider a translator T between X and Y. On the IPv6
side it has address A(t) and on the IPv4 side it has address a(t).
If port translation is in effect, P(x) will become P(tx) on the IPv4
side. We will observe later that the A(t) address can be chosen from
an address pool. We cannot assume that a(t) can be chosen from a
pool, which is why port translation will be needed.
Thus A() is always an IPv6 address and a() is always an IPv4 address.
A diagram of the solution follows:
X T Y
___________ A(x) A(t) _______________ a(t) a(y) _______
| | | V6|P(x) P(y)| V6| | | V4|P(tx) P(y)| V4| |
| | S | | | | S | S | | | | |
| U | H | S | | S | H | I | S | | S | U |
| L | I | T |------------| T | I | I | T |-----------| T | L |
| P | M | A | | A | M | T | A | | A | P |
| | | C | | C | | | C | | C | |
| | X | K | | K | T | | K | | K | |
|___|___|___| |___|___|___|___| |___|___|
We will refer to the shim in X as SHIMX, and the shim in T as SHIMT.
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The address set used by the shims for X is conceptually {a(t),A(x)},
and for Y it is conceptually {a(y),A(t)}. In other words the ULP at
X sees its own ULID as a(t) and Y's ULID as a(y), both filled out to
128 bits. On the wire, the IPv6 packets between X and T use A(x) and
A(t) as the actual address pair. The IPv4 packets between T and Y
use a(t) and a(y). P(y) can be used everywhere, but we must assume
that P(x) will be used on the IPv6 side and P(tx) on the IPv4 side.
When a(t) and a(y) are filled out to 128 bits, an appropriate /96
prefix must be used. This must checksum to zero when 16-bit
transport checksums are computed. In SIIT, the ::ffff:0:0/96 IPv4-
mapped format is used to fill out addresses for IPv4 hosts. Also in
SIIT, an "IPv4-translated" address format is introduced to represent
a synthetic IPv4 address for the IPv6 host, with the ::ffff:0:0:0/96
prefix. This format, which is not in the IPv6 address architecture
[RFC4291], could be used as the ULID for X. But since the shim has
explicit knowledge of the addresses in use, is there any reason to
use this format in preference to the IPv4-mapped format? The latter
is assumed here for simplicity.
Further to this, because these addresses never appear on the IPv6
wire in SHANTI, there seems to be no reason in principle why the
deprecated ::/96 "IPv4-compatible" prefix could not be used for
further simplicity. However, this has been avoided to respect the
deprecation.
If there's an IPv4 NAT with routable address a(n) on the IPv4 path,
it won't know anything is special, and a(y) will be represented by
a(n). X, Y and T won't know that the NAT is there. X and T will not
know if Y has a private [RFC1918] address or if additional port
translation takes place.
T must have a large pool of A(t) addresses, and should have a
complete /64 to itself for maximum flexibility.
SHIMX is configured with knowledge of a default A(t) to start any new
exchange with SHIMT, and with knowledge of a(t). SHIMX will catch
all packets sent to ::ffff:0:0/96 by any ULP in X. When a ULP sends a
first packet to ::ffff:0:0:a(y)/128, we need to start a SHIM6-like
process. SHIMX will carry out a message exchange with SHIMT to
discover the relevant A(t) and P(tx) values. It can then update the
port number and recompute a transport checksum if needed, rewrite the
addresses as A(t),A(x), and send the packet on to A(t). Subsequent
packets in the same flow will not require a shim message exchange.
Note that the network stack in X will use the ULID ::ffff:0:0:a(t)/
128 as the source address for checksum purposes. Source address
selection MUST choose this when the destination address matches
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::ffff:0:0/96. This is why a(t) must be configured in SHIMX.
Checksum recomputation by SHIMX will only be needed if P(tx) != P(x).
The NAT-like code for this will require data sharing between the
transport protocols and SHIMX.
T needs to select a specific A(t) and P(tx) for each new flow, and
exchange SHIM6-like messages with X, to tell SHIMX the values of A(t)
and P(tx) . This should create enough state in both shims to know
what to do with outbound and return packets. If T has a full /64 to
work with, it can create a new A(t) for each new X or even for each
new flow if that turns out to be needed.
Note that unlike SHIM6, SHANTI must perform the shim exchange before
sending the first packet of an outbound traffic flow from X. This is
because SHIMX must learn if P(tx) is unequal to P(x). A consequence
of this is that SHIMX should buffer packets of a new outbound flow
until it has completed its shim exchange with T. For this to scale,
it is important that the translator has adequate capacity for the
number of IPv6 hosts it serves, and adequate network connectivity to
them, so as to minimize buffering requirements.
When a data packet reaches T from X, there will already be shim state
established. The shim will pass the packet on to SIIT for
translation and IPv4 transmission.
Once the shim state is established, the ULPs in both X and Y will
work as normal. Since T uses a specific A(t) for each X, and the
shim at X is aware of that A(t), all port numbers are available in
each direction on the IPv6 side. Port mapping, if required, will
only affect the IPv4 side of T. Also, SHIMX is aware that the ULP in
Y believes it is using the address pair {a(t), a(y)} and the ports
{P(tx), P(y)}. Thus, address and port dependent fix-ups can be
performed, if needed, by SHIMX. This means that TCP and UDP
checksums do not need to be fixed up by T. This has scaling
advantages compared to NAT-PT.
Additionally, with this knowledge being available in the host rather
than being hidden in the translator as in NAT-PT, it is in principle
possible for any address and port dependencies in the ULP to be fixed
up in the host itself, precluding the need for Application Level
Gateways (ALGs). Although this would introduce a layer violation, it
is in principle a more robust design than associating ALGs with a
"stateless" translator. In particular, it means that new
applications on the IPv6 host do not require new ALG code in the
translator, removing a strong dependency in deployment scenarios.
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3. General walkthroughs
Consider first an IPv6 client attempting to contact an IPv4 server
via this mechanism. The main steps that must occur are:
1. ULP in X obtains Y's IPv4-mapped address ::ffff:0:0:a(y)/128.
See DNS discussion below.
2. ULP sends unsolicited packet to that address.
3. SHIMX recognises the packet as needing attention.
4. SHIMX creates local state for a(y), P(x), and buffers the
packet. Also, it creates a packet to send to T. This is a
packet containing nothing but a shim header indicating that a
first packet is ready from A(x):P(x) to a(y):P(y).
5. SHIMT receives this shim header and checks for existing state
for {A(x):P(x),a(y):P(y)}.
6. If no such state exists, assign an A(t) value from the pool, and
create state. Includes the ports. If P(x) is already in use by
T, assign a P(tx). Otherwise, P(tx)=P(x).
7. SHIMT creates a packet to return to X. This is a packet
containing nothing but a shim header indicating the assigned
A(t) and P(tx).
8. SHIMX records this additional state, including P(tx) as the
translated port.
9. SHIMX now applies the following process to buffered and future
packets sent from ::ffff:0:0:a(t), port P(x) to ::ffff:0:0:a(y),
port P(y).
1. If P(tx) != P(x), recompute transport checksum as for
addresses DA=::ffff:0:0:a(y), SA=::ffff:0:0:a(t) and ports
DP=P(y), SP=P(tx).
2. Rewrite destination address as A(t).
3. Rewrite source address as A(x).
4. Rewrite destination port as P(tx).
5. Send packet.
10. SHIMT rewrites the addresses as DA=::ffff:0:0:a(y), SA=::ffff:0:
0:a(t), and hands the packet off to SIIT.
11. SIIT translates the packet to IPv4 and sends it on (destination
= a(y), source = a(t)).
12. When an IPv4 return packet comes into SIIT, SIIT translates the
packet to IPv6 and hands it to SHIMT.
13. The shim performs port demultiplexing on the destination port
(which will be P(tx)) to identify the A(x) involved.
14. The shim rewrites the addresses as A(x), A(t) and sends the
packet on to A(x).
15. The shim at X receives the packet, rewrites the header to
restore the original ULIDs and P(x), and sends the packet on up
the stack.
Now consider an IPv4 client attempting to contact an IPv6 server via
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T. The main steps that must occur are:
1. T must be pre-configured to admit traffic for P(x) and forward it
to A(x). This is a normal port-forwarding issue, to be solved as
for NATs or perhaps as proposed in [I-D.woodyatt-ald]. It cannot
be performed without pre-existing state. Assuming T has only one
a(t), a given P(x) can only have one IPv6 listener.
2. ULP in Y obtains an IPv4 address for T (believing it to be the
actual server X).
3. Y sends an unsolicited packet from a(y) to a(t), port P(x).
4. It is passed to SIIT in T, translated to IPv6 format, and passed
on to SHIMT.
5. SHIMT performs port demultiplexing and determines that the packet
is destined for A(x). It creates state if none exists.
6. SHIMT inserts a shim header that will tell X the translation in
effect, translates the addresses, and sends the packet from A(t)
to A(x).
7. SHIMX receives the packet, and translates the addresses to
::ffff:0:0:a(t)/128 and ::ffff:0:0:a(y)/128. This should
checksum OK. SHIMX creates state if none exists.
8. The packet is delivered to the ULP, minus the shim header.
Subsequent packets will flow as in the previous case.
Shim state will be torn down (deleted) using inactivity timers, as
for SHIM6 and typical NATs.
4. Placement of the shim
In SHIM6 the shim is logically placed below both the transport and
IPsec layers, so that their checksums do not need recalculation. In
SHANTI, the transport layer checksum does need to be recalculated by
the shim, rather in the manner that a NAT behaves. However, this
cannot be done for cryptographic checksums for obvious reasons. The
shim should perhaps be regarded as logically below transport, but a
better implementation would be for each transport layer to invoke the
shim in-line prior to executing its checksum calculation.
5. DNS
It is required that the IPv6 hosts "behind" a SHANTI translator
either have a resolver that maps A records into AAAA records expanded
with ::ffff:0:0/96, or a DNS server that actually stores such
records, or performs this transformation on the fly. On the
assumption that hosts behind a translator will need to be configured
in any case, in order to activate the shim, a mapping resolver seems
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likely to be the most robust choice, applying the fate-sharing
principle. It would also work in a network with a mixture of SHANTI
and dual-stack hosts. The former would see A records mapped as AAAA,
and the latter would see native A records.
This illustrates that SHANTI is an all-or-nothing approach. It
doesn't seem plausible to activate SHANTI on a dual stack host since
DNS entries are either mapped, or they aren't. But why would it be
needed?
"Outside" the translator, SHANTI hosts must be represented by an A
record with the address of their translator. Specifically, the
host's FQDN will have one or more AAAA records with its IPv6
address(es) and an A record with its translator's address. A dynamic
DNS-ALG is not needed.
6. ICMP
In general, ICMP translation in both directions will proceed as
defined in SIIT.
The pool of IPv4 addresses concerned (section 3.5 of [RFC2765]) will
contain only a(t), and SHIMT will have to perform port demultiplexing
in order to dispatch ICMP messages translated from IPv4 to the
correct A(x). SHIMX will have to perform address or checksum
rewriting as for other packets. (More details TBD).
7. Unresolved issues
This section comments on issues raised in [RFC4966] with regard to
whether they are mitigated or resolved by the present specification.
The relevant section headings from RFC 4966 are included for
reference.
2.1. Issues with Protocols Embedding IP Addresses
In SHANTI, these can in principle be resolved within the IPv6
host, with no dependency on an up-to-date translator. This does
require the protocol implementation in the IPv6 host to be SHANTI-
aware. Also see issue 5 below.
2.2. NAPT-PT Redirection Issues
This concerns protocols where the port number is absent or
encrypted, so port de-multiplexing is impossible. SHANTI cannot
solve this problem; it is intrinsic in sharing one IPv4 address
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among many IPv6 hosts. However, since it's an intrinsic problem
of the NAPT model, SHANTI doesn't create this problem either; IPv4
hosts already have to live with it.
2.3. NAT-PT Binding State Decay
This concerns protocols whose idle times may exceed any reasonable
tear-down timer, leading to a risk of P(tx) being reassigned while
still in use. This risk should be mitigated in SHANTI, since the
tear-down can be synchronized between SHIMX and SHIMT. It would
even be theoretically possible for SHIMX to probe the application.
2.4. Loss of Information through Incompatible Semantics
This concerns inevitable loss of information such as the IPv6 Flow
Label. SHANTI cannot solve this problem; it is intrinsic, as
observed in [RFC1671] section B1.
2.5. NAT-PT and Fragmentation
Put simply, fragments can't be port-demultiplexed without
reassembly. SHANTI cannot solve this problem; it is intrinsic in
sharing one IPv4 address among many IPv6 hosts. Only applications
that probe for the available MTU size can overcome this issue.
However, since it's an intrinsic problem of the NAPT model, SHANTI
doesn't create this problem either; IPv4 hosts already have to
live with it.
2.6. NAT-PT Interaction with SCTP and Multihoming
SCTP includes alternative addresses in its messages. This is
solved as in issue 2.1 above. SHANTI would remain a single point
of failure for SCTP.
2.7. NAT-PT as a Proxy Correspondent Node for MIPv6
The problem is that MIPv6 route optimization cannot possibly be
supported on the IPv4 network. This is intrinsic, but in SHANTI
it would be possible for SHIMX to suppress messages and headers
relating to changes of care-of addresses, including reverse
routing checks, at their source, if they are sent to the ::FFFF:0:
0/96 prefix.
2.8. NAT-PT and Multicast
SHANTI does not handle multicast translation.
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Issues 3.1 through 4.5 are partly or completely related to NAT-
PT's requirement for a DNS-ALG. SHANTI does require DNS entries
for IPv4 hosts to be presented to the ULP as AAAA records, but
this does not require a dynamic DNS-ALG to be colocated with the
SHANTI translator (see Section 5). Thus, these issues are
intrinsically mitigated by SHANTI.
3.1. Network Topology Constraints Implied by NAT-PT
Not relevant to SHANTI.
3.2. Scalability and Single Point of Failure Concerns
Compared to NAT-PT, a SHANTI translator has a simpler job since
checksum calculations are left to the IPv6 host, and DNS-ALG is
not needed. Scalability of performance is therefore less of a
concern. SHANTI remains a single point of failure, unless a load
sharing feature with failover is added. These issues are
intrinsic to any translator scenario.
3.3. Issues with Lack of Address Persistence
In the absence of DNS-ALG, this appears to be identical to issue
2.3 above.
3.4. DoS Attacks on Memory and Address/Port Pools
In the absence of DNS-ALG, this appears to be a "standard" DoS
threat to which almost any protocol is exposed. See Section 8.
4.1. Address Selection Issues when Communicating with Dual-Stack
End-Hosts
In the absence of DNS-ALG, there should be no problem in
configuring IPv6 hosts to prefer native IPv6 addresses to IPv4-
mapped addresses. Also, the resolver code (Section 5) could be
designed to always return IPv4-mapped addresses last in the
response to getaddrinfo().
4.2. Non-Global Validity of Translated RR Records
If an IPv4-mapped address known by host X in the above scenario is
passed on to any other IPv6 host equipped with SHANTI, it will
work, assuming that the IPv4 address is globally unique. If it's
a private [RFC1918] address, it may fail, but that is intrinsic to
private IPv4 addressing. Otherwise, in the absence of DNS-ALG,
this issue is not applicable to SHANTI.
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4.3. Inappropriate Translation of Responses to A Queries
In the absence of DNS-ALG, this is not applicable to SHANTI.
4.4. DNS-ALG and Multi-Addressed Nodes
In the absence of DNS-ALG, this is not applicable to SHANTI.
4.5. Limitations on Deployment of DNS Security Capabilities
In the absence of DNS-ALG, this is not applicable to SHANTI.
5. Impact on IPv6 Application Development
This is closely related to issue 2.1. As noted above, a SHANTI
host is aware of the translation in effect. SHANTI will work "out
of the box" for any application that runs through a traditional
NAT or NAPT without problems *and* has been upgraded to AF_INET6
sockets. In other cases, the shimmed IPv6 stack can make an
application aware of the both the ULIDs in use and of the
translated port number, perhaps via socket options. Although
modifying application code to take this into account may appear
complex, application developers might prefer this to today's
obscure failure modes caused by IPv4 NAPT or NAT-PT.
In conclusion, it seems that SHANTI overcomes or mitigates many of
the issues noted with NAT-PT. Those that remain appear to be
intrinsic to any translation scenario.
8. Security Considerations
As for NAT-PT, there is no obvious way to carry network layer IPsec
across a SHANTI translator. There seems to be no reason IKE
[RFC4306] cannot run in a SHANTI scenario, using its port agility
intended for NAT tolerance. But that in itself isn't very useful.
It seems likely that security solutions running above the transport
layer will be required in order to protect a SHANTI session.
The use of a shim layer in SHANTI will raise some of the security
issues considered for SHIM6 . More analysis of the potential
spoofing and denial of service threats is needed to determine whether
a cryptographic solution is needed, or if there is a straightforward
way to prevent attackers taking over a session by impersonating the
shim. It may be possible to find a simple method of arranging a
shared secret between X and T, such that an elementary hash can be
used to authenticate the shim headers.
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9. IANA Considerations
This document has not yet been exhaustively checked for possible
action by the IANA.
10. Acknowledgements
Vital comments on a very primitive version of this proposal were made
by Marcelo Bagnulo Braun and Iljitsch van Beijnum. Contributions and
comments by David Miles and others are gratefully acknowledged.
This document was produced using the xml2rfc tool [RFC2629].
11. Change log [RFC Editor: please remove this section]
draft-carpenter-shanti-01: added dedication, clarifications, bug
fixes, added RFC4966 analysis, 2007-11-08
draft-carpenter-shanti-00: original version, 2007-10-28
12. References
12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2765] Nordmark, E., "Stateless IP/ICMP Translation Algorithm
(SIIT)", RFC 2765, February 2000.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
12.2. Informative References
[I-D.ietf-shim6-proto]
Bagnulo, M. and E. Nordmark, "Shim6: Level 3 Multihoming
Shim Protocol for IPv6", draft-ietf-shim6-proto-09 (work
in progress), November 2007.
[I-D.woodyatt-ald]
Woodyatt, J., "Application Listener Discovery (ALD) for
IPv6", draft-woodyatt-ald-01 (work in progress),
June 2007.
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[RFC1671] Carpenter, B., "IPng White Paper on Transition and Other
Considerations", RFC 1671, August 1994.
[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, February 1996.
[RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
June 1999.
[RFC2766] Tsirtsis, G. and P. Srisuresh, "Network Address
Translation - Protocol Translation (NAT-PT)", RFC 2766,
February 2000.
[RFC4306] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
RFC 4306, December 2005.
[RFC4966] Aoun, C. and E. Davies, "Reasons to Move the Network
Address Translator - Protocol Translator (NAT-PT) to
Historic Status", RFC 4966, July 2007.
Author's Address
Brian Carpenter
Department of Computer Science
University of Auckland
PB 92019
Auckland, 1142
New Zealand
Email: brian.e.carpenter@gmail.com
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