Internet Draft R. Atkinson
draft-rja-ilnp-nonce-00.txt Extreme Networks
Expires: 10 December 2008 10 June 2008
Category: Experimental
Nonce Destination Option
draft-rja-ilnp-nonce-00.txt
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Abstract
This document describes an experimental Nonce Destination
Option that could be used as part of an Identifier Locator
Network Protocol (ILNP) that is based upon IPv6.
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Table of Contents
1. Introduction ...............................................2
2. Syntax......................................................3
3. Transport Protocol Effects..................................4
4. Backwards Compatibility.....................................4
5. Security Considerations ....................................5
6. IANA Considerations ........................................5
7. References .................................................6
1. Introduction
At present, the IRTF Routing Research Group is studying
different approaches to evolving the Internet Architecture.
Several different classes of evolution are being considered.
One class is often called "Map and Encapsulate", where
traffic would be mapped and then tunnelled through the
inter-domain core of the Internet. Another class being
considered is sometimes known as "Identifier/Locator
Split".[GSE][8+8] This document relates to a proposal that
is in the latter class of evoluationary approaches. This
particular approach, the Identifier Locator Network Protocol
(ILNP), described in this document and in related
Internet-Drafts, is a possible evolutionary direction for
IPv6.[ILNP-Intro] [ILNP-DNS][ILNP-ICMP][RFC-2460]
The Nonce Destination Option 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 classical IPv6.
Before reading this draft, readers should read the related
Internet-Draft titled "ILNP Concept of Operations", as that
document will help the reader understand the overall context
for this option.
2. Syntax
The Nonce Option is an IPv6 Destination Option.
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In the diagram below, we show not only the Nonce Option,
but also the 2-byte header for the IPv6 Destination Option.
More than one option type might be inside the IPv6
Destination Option, however at most 1 Nonce Option exists
in a given IPv6 packet..
However, it is expected that normally the Nonce Option would
be the only type of IPv6 Destination Option present in a
given packet.
------------------------------------------------------------
| 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 0x1e, which is
used (for now) to indicate the start of
the Nonce Option.
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: This contains an unpredictable
cryptographically random value used to
prevent off-path attacks on an ILNP
session. The value should be created in
accordance with RFC-4086. [RFC-4086] The
length of this field is variable,
indicated by the Nonce Length field
preceding it. However, the overall IPv6
Destination Option must comply with IPv6
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header alignment rules. Common lengths
are 32-bits or 96-bits.
3. Transport Protocol Effects
When the initial packet(s) of an IPv6 session contain this
Nonce Destination Option, the Identifier/Locator Split
operating mode is in use for that IP session.
When an IPv6 session is in the Identifier/Locator Split
operating mode, the transport-layer pseudo-header
calculations 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 cognizant 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 when the
Identifier/Locator Split operating mode is in use.
4. Implementation Considerations
Implementers may use any internal implementation they wish,
provided that the external appearance is the same as this
implementation approach.
To support the Identifier/Locator Split operating mode,
and retain the incremental deployability and backwards
compatibility needed, the network layer needs a mode bit
in the Transport Control Block (or equivalent) to track
which IP sessions are using the classic IPv6 mode, and
which IP sessions are using the Identifier/Locator Split
mode.
Further, when in the Identifier/Locator Split mode, nodes
will need to retain a per-session/per-flow cache containing
several variables for that flow. Conceptually, and
architecturally, this cache is at the top of the
network-layer since it contains network-layer information
(e.g. Locators) that ought not be made visible to the
transport-layer.
This per-session/per-flow cache contains at least:
- Source Identifier(s) in use
- Source Locator(s) in use
- Destination Identifier(s) in use
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- Destination Locator(s) in use
- Session Nonce value in use
- Transport Layer source port and destination port
5. Backwards Compatibility
If a node has been enhanced to support the Identifier/
Locator Split operating mode, that node's fully-qualified
domain name will normally have one or more I records and one
or more L 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 normally will look for
Identifier ("I") and Locator ("L") records in any received
DNS replies. DNS servers that support I and L records
should include them (when they exist) as additional data in
all DNS replies to queries for DNS AAAA records.
If the initiator supports the I/L Split mode and from DNS
data learns that the responder also supports the I/L Split
mode, then the initiator will generate an unpredictable
nonce value, store that value in a local session cache, and
will include the Nonce Destination Option in its initial
packet(s) to the responder. [RFC-4086]
If the responder supports the I/L Split mode and receives
initial packet(s) containing the Nonce Destination Option,
the responder will thereby know that the initiator supports
the I/L Split mode and the responder will also operate in
I/L Split mode for this new IP session.
If the responder supports the I/L Split mode and receives
initial packet(s) NOT containing the Nonce Destination
Option, the responder will thereby know that the initiator
does NOT support the I/L Split mode and the responder will
operate in classic IPv6 mode for this new IP session.
If the responder does not support the I/L Split mode and
receives initial packet(s) containing the Nonce Destination
Option, the responder will drop the packet and send an ICMP
Parameter Problem error message back to the initiator.
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
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Unreachable error message for that packet, OR if the
initiator receives an ICMP Parameter Problem error message
for that packet, then the initiator knows that the responder
is not able to support the I/L Split Operating mode. In
this case, the initiator should try again to create the new
IP session but this time using classic IPv6 mode and hence
OMITTING the Nonce Destination Option.
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6. Security Considerations
The Nonce Destination Option is used ONLY for IP sessions
in the Identifier/Locator Split mode, because this option
is part of the backwards-compatibility and incremental-
deployment approach for the Identifier/Locator Network
Protocol (ILNP).
The 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 the IP
Authentication Header or IP Encapsulating Security Payload
are in use. This option exists to provide equivalent
protection for non-IPsec traffic when the Identifier/Locator
Split mode is in use for an IP session.
When the Identifier/Locator split mode is in use for an
existing IP session, the Nonce Destination Option must be
included in any ICMP control messages (e.g. ICMP
Unreachable, ICMP Locator Update) sent with regard to that
IPv6 session, even if IP Security is also in use for that
session.
When in the I/L Split operating mode for an existing IPv6
session, any ICMP control messages received without a Nonce
Destination Option must be discarded as forgeries. This
security event should be logged.
When in the I/L Split operating mode for an existing IPv6
session, ICMP control messages received without a correct
nonce value inside the Nonce Destination Option must be
discarded as forgeries. This security event should be
logged.
For ID/Locator Split mode sessions operating in higher risk
environments, the use of the cryptographic authentication
provided by IP Authentication Header is recommended. Note
that the Nonce Option must be present -- even if the IP
Authentication Header is in use for a given session. As an
implementation optimisation, it is suggested that when both
the Nonce Option and IP Security are present in a packet,
that the Nonce Option value be checked for validity before
beginning IP Security processing.
For environments with data at differing sensitivity levels
operating over common infrastructure, it is recommended that
the Nonce Option be protected using ESP Transport-Mode or
ESP Tunnel-Mode in order to reduce the covert channel
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bandwidth potential created by the Nonce Option.
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.[RFC-4086]
7. IANA Considerations
A new option number will need to be assigned by IANA to the
Nonce Option described in this note.
Temporarily, for early experimentation, the value 0x1e is
used to mark the Nonce Option.
8. References
8.1. Normative References
[RFC-2119] Bradner, S., "Key words for use in RFCs to
Indicate Requirement Levels", BCP 14, RFC 2119,
March 1997.
[RFC-2460] S. Deering & R. Hinden, "Internet Protocol
Version 6 Specification", RFC-2460,
December 1998.
8.2. 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.
[ILNP-Intro] Atkinson, R, "Identifier/Locator Concept of
Operations", draft-rja-ilnp-intro-01.txt,
June 2008.
[ILNP-DNS] Atkinson, R, "DNS Resource Records for
Identifier/Locator Use",
draft-rja-ilnp-dns-00.txt, June 2008.
[ILNP-ICMP] Atkinson, R, "ICMP Locator Update message"
draft-rja-ilnp-icmp-00.txt, June 2008.
[RFC-4086] D. Eastlake 3rd, J. Schiller, & S. Crocker,
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"Randomness Requirements for Security",
RFC-4086, June 2005.
(Additional references to be added later.)
Author's Address
R. Atkinson
Extreme Networks
3585 Monroe Street
Santa Clara, CA
95051 USA
+1 (408)579-2800
rja@extremenetworks.com
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