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Internet Draft                                           R. Atkinson
draft-rja-ilnp-nonce-01.txt                         Extreme Networks
Expires:  10 June 2009                              10 December 2008
Category: Experimental

                        Nonce Destination Option
                      draft-rja-ilnp-nonce-01.txt


Status of this Memo

 Distribution of this memo is unlimited.

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  This document is a contribution to the IRTF Routing
  Research Group.  It is neither a contribution to the IETF,
  nor to any IETF Working Group, nor to any IETF Area.


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. Location Changes............................................4
   5. Implementation Considerations...............................5
   6. Backwards Compatibility.....................................6
   7. Security Considerations ....................................8
   8. IANA Considerations ........................................9
   9. References .................................................9


1. Introduction

   At present, the IRTF Routing Research Group is studying several
   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.

   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.

   Before reading this draft, readers should read the related



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   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.

   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 might be inside the IPv6 Destination Option,
   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).

   As of this writing, IPv6 Destination Options are extremely
   uncommon in the deployed Internet.  So, it is expected that
   most commonly Nonce Option would be the only IPv6 Destination
   Option present in a given IPv6 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),



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                      and 12 (when the Nonce value is 96-bits).

   Nonce Value:       This is an unpredictable cryptographically
                      random value used to prevent off-path
                      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, 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.  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 will drop a packet arriving from a
   correspondent if the Source Locator of the received packet is not
   in the receiving node's ILNP Correspondents Cache's Correspondent
   Locator Set UNLESS that packet 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



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   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 in this case.  Because IP Security for ILNP
   binds only to the Identifiers, and not to the Locators in the packet,
   changes in Locator value have no impact on IP Security sessions.

   As mobility and multi-homing are functionally equivalent,
   this section applies equally to either situation.

5.  Implementation Considerations

   Implementers may use any internal implementation they wish,
   provided that the external appearance is the same as this
   implementation approach.

5.1 Mode Indicator

   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 for one's implementation) to track which IP sessions are
   using the classic IPv6 mode, and which IP sessions are using the
   Identifier/Locator Split mode.

   If a given transport-layer session is in the I/L Split Mode, then an
   entry corresponding to that session will exist in the Correspondent
   Cache.  Note that multiple transport-layer sessions between a given
   pair of nodes normally share a single entry in the Correspondent
   Cache.

5.2 Correspondent Cache

   Further, when in the Identifier/Locator Split mode, nodes will need to
   retain a Correspondent cache containing several variables for each
   correspondent.  This cache is per-correspondent, rather than per-flow
   or per-session so that if there are multiple sessions with a single
   correspondent, Locator changes for all sessions with that
   correspondent are handled with a single Locator Update message.
   Conceptually, and architecturally, this Correspondents 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.



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   The Correspondent Cache contains, for each correspondent, at least:
        - Local Identifier(s) in use
        - Local Locator(s) in use
        - Correspondent's Identifier(s) in use
        - Correspondent's Locator(s) in use
        - Session Nonce value used Local Node to Correspondent
           - Session Nonce value used Correspondent to Local Node
        - Information about whether IPsec is being used with
          this correspondent.

5.3 IP Security

   Note that (whether or not the I/L-Split Mode is in use) the IPsec
   subsystem is required to maintain an IPsec Security Association
   Database (SAD) and also 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 the Correspondent Cache, an implementation
   has sufficient knowledge to apply IPsec properly to both received
   and transmitted packets.

6.  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



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   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
   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 IPv6 sessions using
   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.

   Of course, longer nonce values provide greater resistance to random
   guessing of the nonce value.  However, ID/Locator Split mode sessions
   operating in higher risk environments should use the cryptographic
   authentication provided by IP Authentication Header.  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
   is encrypted by using ESP Transport-Mode or ESP Tunnel-Mode in order
   to reduce the covert channel bandwidth potential created by the
   Nonce Option.

   In all cases, the Nonce Value must be unpredictable and



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   cryptographically random.  RFC-4086 provides concrete advice
   on how to generate a suitable nonce value.[RFC-4086]

   This option could be designed to optionally carry a 64-bit unsigned
   Identifier for the sender as well, if that were considered important.

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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