Internet Draft RJ Atkinson
draft-irtf-rrg-ilnp-noncev6-00.txt Consultant
Expires: 09 JUL 2012 S Bhatti
Category: Experimental U. St Andrews
9 January 2012
IPv6 Nonce Destination Option for ILNPv6
draft-irtf-rrg-ilnp-noncev6-00.txt
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Internet-Drafts are working documents of the Internet
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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
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The list of Internet-Draft Shadow Directories can be accessed at
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This document is not on the IETF standards-track and does not
specify any level of standard. This document merely provides
information for the Internet community.
This document is part of the ILNP document set, which has had
extensive review within the IRTF Routing Research Group. ILNP is
one of the recommendations made by the RG Chairs. Separately,
various refereed research papers on ILNP have also been published
during this decade. So the ideas contained herein have had much
broader review than the IRTF Routing RG. The views in this
document were considered controversial by the Routing RG, but the
RG reached a consensus that the document still should be
published. The Routing RG has had remarkably little consensus on
anything, so virtually all Routing RG outputs are considered
controversial.
Abstract
The Identifier-Locator Network Protocol (ILNP) is an
experimental, evolutionary enhancement to IP. ILNP has multiple
instantiations. This document describes an experimental Nonce
Destination Option used only with ILNP for IPv6 (ILNPv6). This
document is a product of the IRTF Routing RG.
Table of Contents
1. Introduction ...............................................2
2. Syntax......................................................3
3. Transport Protocol Effects..................................5
4. Location Changes............................................5
5. Implementation Considerations...............................6
6. Backwards Compatibility.....................................6
7. Security Considerations ....................................8
8. IANA Considerations ........................................9
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9. References .................................................9
1. Introduction
This document describes a new option for the IPv6 Destination
Options header that is used with the Identifier Locator Network
Protocol for IPv6 (ILNPv6). ILNPv6 is an experimental protocol
that is backwards compatible with, and incrementally upgradable
from, IPv6. This option is ONLY used in ILNPv6 sessions and is
never used with classic IPv6 sessions.
The Nonce option for the IPv6 Destination Options Header that is
described in this document provides two functions. First, it
provides protection against off-path attacks for packets when an
Identifier/Locator split is in use. Second, it provides a signal
during initial IP session creation that the Identifier/ Locator
Split operating mode is proposed for use with this session. This
last function is particularly important for ensuring that the new
Identifier/Locator Split operating mode is both incrementally
deployable and backwards compatible with IPv6. Consequently,
this option must not be used except by a node operating in the
I/L Split (ILNP) mode.
Further, each Nonce value is unidirectional. Since packets often
travel asymmetric paths between two correspondents, having
separate Nonces for each direction limits the number of on-path
nodes that can easily learn a session's nonce. So a typical TCP
session will have 2 different nonce values in use: one nonce is
used from Local Node to the Correspondent Node and a different
nonce is used from the Correspondent Node to the Local Node.
1.1 ILNP Document Roadmap
The Identifier-Locator Network Protocol (ILNP), is described in
the ILNP Architecture [ILNP-ARCH] document, which should be read
first. ILNP can have multiple instantiations. [ILNP-ENG]
discusses engineering and implementation aspects common to all
ILNP instantiations. [ILNP-DNS] defines new Domain Name System
(DNS) resource records for ILNP. [ILNP-ICMPv6] defines a new
ICMPv6 Locator Update message for use with ILNPv6. Other
documents describe ILNP for IPv4 (ILNPv4).
1.2 Terminology
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
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in RFC 2119. [RFC 2119]
2. Syntax
The Nonce Option is carried within an IPv6 Destination Option
Header. Section 4 of [RFC 2460] provides much more information
on the various options and optional headers used with IPv6.
More than one option might be inside the IPv6 Destination Option
Header, however at most 1 Nonce Option exists in a given IPv6
packet.
A system that receives a packet containing more than one Nonce
option SHOULD discard the packet as "Authentication Failed"
(instead of passing the packet up to the appropriate
transport-layer protocol or to ICMP) and SHOULD log the event,
including the Source Locator, Source Identifier, Destination
Locator, Destination Identifier, upper-layer protocol (e.g. OSPF,
TCP, UDP) if any, and transport-layer port numbers (if any),
as a security fault in accordance with local logging policies.
As of this writing, IPv6 Destination Option Headers, and the
options carried by such headers, are extremely uncommon in the
deployed Internet. So, it is expected that this Nonce Option
commonly would be the only IPv6 Destination Option present in
a given IPv6 packet.
In the diagram below, we show not only the Nonce Option, but also
the IPv6 Destination Option Header that carries the Nonce Option.
------------------------------------------------------------
| Next Header | Hdr Ext Len | Option Type | Option Length|
+-------------+---------------+-------------+--------------+
/ Nonce Value /
+-------------+---------------+-------------+--------------+
Next Header: 8-bit selector. Identifies the type of header
immediately following the Destination Options
header. Uses the same values as the IPv4
Protocol field [RFC 1700 et seq.].
Hdr Ext Len: 8-bit unsigned integer. Length of the
Destination Options header in 8-octet units,
not including the first 8 octets.
Option Type: This contains the value XXX, which is used
to indicate the start of the Nonce Option.
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Option Length: This indicates the length in 8-bit octets of
the Nonce Value field of the Nonce Option.
This value must be selected so that the
enveloping IPv6 Destination Option complies
with the IPv6 header alignment rules. Common
values are 4 (when the Nonce Value is
32-bits), and 12 (when the Nonce value is
96-bits).
Nonce Value: An unpredictable cryptographically random value
used to prevent off-path attacks on an ILNP
session. [RFC 4086] This field has variable
length, with the length indicated by the
Option Length field preceding it. Note that
the overall IPv6 IPv6 Destination Option must
comply with IPv6 header alignment rules.
Implementations must support sending and
receiving 32-bit and 96-bit Nonce values.
3. Transport Protocol Effects
When the initial packet(s) of an IPv6 session contain this Nonce
Destination Option, then ILNPv6 is in use for that communications
session.
When a communications session is using ILNPv6, then the
transport-layer pseudo-header calculations MUST zero the
high-order 64-bits ("Locator" or "Routing Prefix") of each IPv6
address. This has the effect that the transport-layer is no
longer aware of the topological network location of either node
in the session.
The preceding rule applies not only to unicast sessions, but also
to multicast or anycast sessions that use ILNPv6.
4. Location Changes
When a node has an unexpected change in its Locator set that
causes all previously valid Locators to become invalid, the node
MUST send an ICMP Locator Update message (containing the Nonce
Option with the appropriate nonce value) to each of its
correspondents.
In the deployed Internet, packets sometimes arrive at a
destination out of order. A receiving node MUST drop a packet
arriving from a correspondent if the Source Locator of the
received packet is not in the receiving node's ILNP Correspondent
Cache's Set of Correspondent Locator(s) UNLESS that packet
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contains a Nonce Option with the appropriate nonce value for that
Source Identifier and Destination Identifier pair. This is done
to reduce the risk of session hijacking or session interference
attacks.
Hence, the node that unexpectedly had all previously valid
Locators become invalid MUST include the Nonce Option with the
appropriate nonce value in all packets (data or otherwise) to all
correspondents for at least 3 round-trip times for each
correspondent. (NB: An implementation need not actually
calculate RTT values; it could just use a fixed timer with a time
long enough to cover the longest RTT path, such as 1 minute.)
This 'gratuitous authentication' ensures that the correspondent
can authenticate any received packet, even if the ICMP Locator
Update control message arrives and is processed AFTER some other
packet using the new Source Locator(s). If a session is using IP
Security, then, of course, IP Security SHOULD continue to be
used. Because IP Security for ILNP [ILNP-ENG] binds only to the
Identifiers, and not to the Locators in the packet, changes in
Locator value have no impact on IP Security for ILNP sessions.
As mobility and multi-homing are functionally equivalent,
this section applies equally to either situation, and also
to any other situation in which a node's set of Locators
might change over time.
5. Implementation Considerations
Implementers may use any internal implementation they wish,
PROVIDED that the externally visible behaviour is the same as
this implementation approach.
5.1 ILNP Correspondent Cache
As described in [ILNP-ENG], ILNP nodes maintain an ILNP
Correspondent Cache (ILCC) that contains several variables for
each correspondent. The ILNP Nonce value is an important part of
that cache.
5.2 Mode Indicator
To support ILNP, and to retain needed incremental deployability
and backwards compatibility, the network layer needs a (logical)
mode bit in the Transport Control Block (or equivalent for one's
implementation) to track which IP sessions are using traditional
IP and which IP sessions are using ILNP.
If a given transport-layer session is using ILNP, then an entry
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corresponding to that session also will exist in the ILNP
Correspondent Cache. Multiple transport-layer sessions between a
given pair of nodes MAY share a single entry in the Correspondent
Cache if they are similar except for details above the
network-layer.
5.3 IP Security
Whether or not ILNP is in use, the IPsec subsystem MUST maintain
an IPsec Security Association Database (SAD) and also MUST
maintain information about which IPsec Selectors apply to traffic
received by or sent from the local node. [RFC 4301] By combining
the information in the IPsec SAD, of what IPsec Selectors apply,
and information in the ILNP Correspondent Cache, an
implementation has sufficient knowledge to apply IPsec properly
to both received and transmitted packets.
6. Backwards Compatibility
If a node supports ILNP and the node wishes to be able to receive
incoming new ILNP sessions, then that node's fully-qualified
domain name SHOULD have one or more ID records and also one or
more Locator (i.e. L64 or LP) records associated with it in the
DNS.
When a host ("initiator") initiates a new IP session with a
correspondent ("responder"), it normally will perform a DNS
lookup to determine the address(es) of the responder. A host
that has been enhanced to support the Identifier/ Locator Split
operating mode SHOULD look for Identifier ("ID") and Locator
("L64") records in any received DNS replies. DNS servers that
support ID and Locator (i.e., L64 or LP) records SHOULD include
them (when they exist) as additional data in all DNS replies to
DNS queries for DNS A or AAAA records associated with a
specified DNS Fully-Qualified Domain Name (FQDN).
If the initiator supports ILNP, and from DNS data learns that the
responder also supports ILNP, then the initiator SHOULD attempt
to use ILNP for new sessions with that responder. In such cases,
the initiator MUST generate an unpredictable nonce value, MUST
store that value in the local correspondent cache, and MUST
include the ILNP Nonce Destination Option in its initial
packet(s) to the responder. The IETF has provided advice on
generating cryptographically random numbers, such as this nonce
value. [RFC 4086]
If the responder supports ILNP and receives initial packet(s)
containing the ILNP Nonce Destination Option, the responder will
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thereby learn that the initiator supports ILNP and the responder
also will use ILNP for this new IP session.
If the responder supports ILNP and receives initial IP packet(s)
NOT containing the Nonce Destination Option, the responder will
thereby learn that the initiator does NOT support ILNP and the
responder will use classic IPv6 for this new IP session.
If the responder does not support ILNP and receives initial
packet(s) containing the ILNP Nonce Destination Option, the
responder MUST drop the packet and MUST send an ICMP "Parameter
Problem" error message back to the initiator. [RFC 4443]
If the initiator EITHER does not receive a response from the
responder in a timely manner (e.g. within the applicable TCP
timeout for a TCP session) and also does not receive an ICMP
Unreachable error message for that packet, OR if the initiator
receives an ICMP Parameter Problem error message for that packet,
then the initiator infers that the responder is not able to
support ILNP. In this case, the initiator should try again to
create the new IP session, but this time use classic IPv6 and
hence MUST NOT include the ILNP Nonce Destination Option.
7. Security Considerations
The ILNPv6 Nonce Destination Option is used ONLY for ILNPv6
sessions, because this option is part of the backwards-
compatibility and incremental-deployment approach for the
Identifier-Locator Network Protocol (ILNP). This option
MUST NOT be used with classic IPv6 sessions.
The ILNPv6 Nonce Destination Option only seeks to provide
protection against off-path attacks on an IP session. Ordinary
IPv6 is vulnerable to on-path attacks unless IP Security is in
use. [CA-1995-01] [RFC 4301] This option exists to provide
non-cryptographic protection for ILNP sessions, protection
equivalent to the security of IP sessions that do NOT use IPsec.
When ILNPv6 is in use for a communications session, the ILNP
Nonce Destination Option MUST be included in any ICMP control
messages (e.g. ICMP Unreachable, ICMP Locator Update) sent by
participants in that ILNPv6 session, even if IP Security also is
in use for that session. Note that certain ICMP messages, for
example a "Path Too Big" message, might be generated by transit
devices that are not aware of the ILNP Nonce in use for that
session and hence are not able to include the ILNP Nonce.
Again, this also is true of classic IPv6 in the same operational
situations, so this does not create a new security issue.
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For ILNPv6 sessions, any ICMP control messages received from a
participant in that ILNPv6 session that lack a Nonce Destination
Option MUST be discarded as forgeries. This security event
SHOULD be logged in accordance with local security logging
policies, including details of the received packet (i.e. Source
Locator, Source Identifier, Destination Locator, Destination
Identifier, upper-layer protocol (e.g. TCP, UDP, OSPF) if any,
transport-layer port numbers if any, and the date and time the
packet was received).
For ILNPv6 sessions, ICMP control messages received from a
participant in that ILNPv6 session that have a Nonce Destination
Option, but do NOT have the correct nonce value inside the Nonce
Destination Option, MUST be discarded as forgeries. This
security event SHOULD be logged as described above.
Of course, longer nonce values provide greater resistance to
random guessing of the nonce value. However, ILNPv6 sessions
operating in higher risk environments SHOULD also use the
cryptographic authentication provided by IP Security for ILNP
[ILNP-ENG] [RFC 4301]. Use of IP Security for ILNP for an ILNPv6
session does not eliminate the need for the ILNPv6 Nonce Option
to be included as described here or as described in
[ILNP-ICMPv6].
As a performance optimisation, it is suggested that when both the
Nonce Option and IP Security are present in a packet and the
Nonce Option has not been encrypted, that the Nonce Option value
be checked for validity before beginning IP Security processing.
This minimises the ability of an off-path attacker to force the
receipient to perform expensive cryptographic computations on
received control packets.
For environments with data at differing Sensitivity Levels
operating over common infrastructure (e.g. when the IPv6 CALIPSO
is deployed), it is recommended that the Nonce Option be
encrypted by using ESP Transport-Mode or ESP Tunnel-Mode in order
to reduce the covert channel bandwidth potential created by the
Nonce Option, and to prevent a node at one sensitivity level from
attacking a session at a different sensitivity level [RFC 5570].
Further, multi-level secure systems SHOULD use different nonce
values for sessions with different Sensitivity Levels [RFC 5570].
In all cases, the Nonce Value MUST be unpredictable and
cryptographically random. [RFC 4086] provides concrete advice
on how to generate a suitable nonce value.
As this is an option within the IPv6 Destination Option Header,
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rather than an option within the IPv6 Hop-by-Hop Option Header,
the presence of this option in an IPv6 packet ought not disturb
routers along the path an IP packet containing this option
happens to travel. Further, many deployed modern IP routers
(both IPv4 and IPv6) have been explicitly configured to ignore
all IP options, even including the "Router Alert" option, when
forwarding packets not addressed to the router itself. Reports
indicate this has been done to preclude use of IP options as a
(Distributed) Denial-of-Service (D)DOS attack vector on backbone
routers.
8. IANA Considerations
IANA is requested to assign a new IPv6 Destination Option Type value
(replacing XXX, in Section 2 above).
The Nonce Option MUST NOT change in transit and MUST be included
in IP Authentication Header calculations.
Further, if an end system receives a packet containing this
option, but does not recognise the option, the end system MUST
drop the received packet. In that case, if and only if the
Destination Address was NOT an IPv6 multicast address the
receiving end system MUST send an ICMP Parameter Problem, Code 2,
message to the packet's Source Address, pointing to the
unrecognised Option Type.
9. References
9.1. Normative References
[ILNP-ARCH] R. Atkinson and S. Bhatti, "ILNP Architecture",
draft-irtf-rrg-ilnp-arch, January 2012.
[ILNP-ENG] R. Atkinson and S. Bhatti, "ILNP Engineering
and Implementation Considerations",
draft-irtf-rrg-ilnp-eng, January 2012.
[ILNP-DNS] R. Atkinson and S. Bhatti, "DNS Resource Records
for ILNP", draft-irtf-rrg-ilnp-dns, January 2012.
[ILNP-ICMPv6] R. Atkinson & S. Bhatti, "ICMP Locator Update
message for ILNPv6", draft-irtf-rrg-ilnp-icmpv6,
January 2012.
[RFC 2119] Bradner, S., "Key words for use in RFCs to
Indicate Requirement Levels", BCP 14, RFC 2119,
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March 1997.
[RFC 2460] S. Deering & R. Hinden, "Internet Protocol
Version 6 Specification", RFC 2460,
December 1998.
[RFC 4301] S. Kent & K. Seo, "Security Architecture for
the Internet Protocol", RFC 4301, December 2005.
[RFC 4443] A. Conta, S. Deering, M. Gupta, Ed.,
"Internet Control Message Protocol (ICMPv6)
for IPv6 Specification", RFC 4443, March 2006.
9.2. Informative References
[8+8] M. O'Dell, "8+8 - An Alternate Addressing
Architecture for IPv6", Internet-Draft,
October 1996.
[GSE] M. O'Dell, "GSE - An Alternate Addressing
Architecture for IPv6", Internet-Draft,
February 1997.
[CA-1995-01] US CERT, "CERT Advisory 1995-01", Pittsburgh,
PA, USA, 1995.
[RFC 4086] D. Eastlake 3rd, J. Schiller, & S. Crocker,
"Randomness Requirements for Security",
RFC 4086, June 2005.
[RFC 5570] M. StJohns, R. Atkinson, and G. Thomas, "Common
Architecture Label IPv6 Security Option (CALIPSO)",
RFC-5570, July 2009.
ACKNOWLEDGEMENTS
Steve Blake, Noel Chiappa, Steve Hailes, Joel Halpern, Mark
Handley, Volker Hilt, Tony Li, and Yakov Rehkter (in alphabetical
order) provided review and feedback on earlier versions of ILNP
documents. Steve Blake provided an especially thorough review of
the entire ILNP document set, which led to significant
improvements in this document.
Authors' Addresses:
RJ Atkinson
Consultant
San Jose, CA
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95125 USA
rja.lists@gmail.com
S Bhatti
School of Computer Science
University of St Andrews
North Haugh, St Andrews
Fife, Scotland, UK
KY16 9SX
Expires: 09 JUL 2012
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