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Versions: 00 01 02 03 04                                                
Network Working Group                                           G. Daley
Internet-Draft                                          NetStar Networks
Intended status: Standards Track                             E. Nordmark
Expires: April 29, 2010                                 Sun Microsystems
                                                                N. Moore
                                                        October 26, 2009


 Tentative Options for Link-Layer Addresses in IPv6 Neighbour Discovery
                    draft-ietf-dna-tentative-04.txt

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
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   This Internet-Draft will expire on April 29, 2010.

Copyright Notice

   Copyright (c) 2009 IETF Trust and the persons identified as the
   document authors.  All rights reserved.



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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents in effect on the date of
   publication of this document (http://trustee.ietf.org/license-info).
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.

Abstract

   The proposed IPv6 Duplicate Address Detection (DAD) Optimization
   "Optimistic DAD" defines a set of recoverable procedures which allow
   a node to make use of an address before DAD completes.  Essentially,
   Optimistic DAD forbids usage of certain Neighbour Discovery options
   which could pollute active neighbour cache entries, while an address
   is tentative.

   This document defines a new option and procedures to replace cache
   polluting options, in a way which is useful to tentative nodes.
   These procedures are designed to be to backward compatible with
   existing devices which support IPv6 Neighbour Discovery.
































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Table of Contents

   1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     2.1.  Tentative Option format  . . . . . . . . . . . . . . . . .  5
     2.2.  Tentative Option semantics . . . . . . . . . . . . . . . .  5
   3.  Sending solicitations containing Tentative Options . . . . . .  6
     3.1.  Sending Neighbour Solicitations with Tentative Options . .  6
     3.2.  Sending Router Solicitations with Tentative Options  . . .  6
   4.  Receiving Tentative Options  . . . . . . . . . . . . . . . . .  6
     4.1.  Handling Tentative Options . . . . . . . . . . . . . . . .  7
     4.2.  Receiving Neighbour Solicitations containing Tentative
           Options  . . . . . . . . . . . . . . . . . . . . . . . . .  7
     4.3.  Receiving a Router Solicitation containing a Tentative
           Option . . . . . . . . . . . . . . . . . . . . . . . . . .  8
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  8
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   7.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 10
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 10
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 10
   Appendix A.  Constraints imposed by IPv6 Neighbour Discovery . . . 11
     A.1.  Constraints on Neighbour Solicitations . . . . . . . . . . 11
     A.2.  Constraints on Router Solicitations  . . . . . . . . . . . 11
   Appendix B.  Interactions with legacy nodes  . . . . . . . . . . . 11
     B.1.  Legacy Neighbour Solicitation processing . . . . . . . . . 12
     B.2.  Legacy Router Solicitation processing  . . . . . . . . . . 12
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13























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1.  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 in
     RFC 2119
   [RFC2119]

     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
     RFC 2119


2.  Introduction

   Source Link-Layer Address Options (SLLAOs) are sent in Neighbour
   discovery messages in order to notify neighbours of a mapping between
   a specific IPv6 Network layer address and a link-layer (or MAC)
   address.  Upon reception of a Neighbour Discovery message containing
   such an option, nodes update their neighbour cache entries with the
   IP to link-layer address mapping in accordance with procedures
   defined in IPv6 Neighbour Discovery [RFC4861].

   Optimistic DAD [RFC4429] prevents usage of these options in Router
   and Neighbour Solicitation messages from a tentative address (while
   Duplicate Address Detection is occurring).  This is because receiving
   a Neighbour Solicitation (NS) or Router Solicitation (RS) containing
   an SLLAO would otherwise overwrite an existing cache entry, even if
   the cache entry contained the legitimate address owner, and the
   solicitor was a duplicate address.

   Neighbour Advertisement (NA) messages don't have such an issue, since
   the Advertisement message contains a flag which explicitly disallows
   overriding of existing cache entries, by the target link-layer
   address option carried within.

   The effect of preventing SLLAOs for tentative addresses is that
   communications with these addresses are sub-optimal for the tentative
   period.  Sending solicitations without these options causes an
   additional round-trip for Neighbour Discovery if the advertiser does
   not have an existing neighbour cache entry for the solicitor.  In
   some cases, multicast advertisements will be scheduled, where
   Neighbour Discovery is not possible on the advertiser.

   This document proposes Tentative Options which designed to replace
   the existing Source Link-Layer Address Options available in IPv6



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   Neighbour Discovery, when a device is performing Optimistic DAD.

   Operations in this document are safe with respect to existing nodes
   that implement IPv6 Neighbor Discovery [RFC4861] and Stateless
   Address Autoconfiguration [RFC4862].  Expected behaviours of legacy
   devices are summarized in Appendix B.

2.1.  Tentative Option format


     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 5 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |     Type      |    Length     |    Link-Layer Address ...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Fields:
     Type   TBD    (Requires IANA Allocation)

     Length         The length of the option (including the type and
                    length fields) in units of 8 octets.

     Link-Layer Address
                    The variable length link-layer address.

     Description
                    The Tentative option contains the link-layer
                    address of the sender of the packet.  It is used
                    in the Neighbour Solicitation and Router
                    Solicitation packets.

2.2.  Tentative Option semantics

   The Tentative Option (TO) functions in the same role as the Source
   Link-Layer Address option defined for [RFC4861], but it MUST NOT
   override an existing neighbour cache entry.

   The differing neighbour cache entry MUST NOT be affected by the
   reception of the Tentative Option.  This ensures that tentative
   addresses are unable to modify legitimate neighbour cache entries.

   In the case where an entry is unable to be added to the neighbour
   cache, a node MAY send responses direct to the link-layer address
   specified in the TO.

   For these messages, no Neighbour Cache entry may be created, although
   response messages may be directed to a particular unicast address.




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   These procedures are discussed further in Section 4.3.


3.  Sending solicitations containing Tentative Options

   Tentative Options may be sent in Router and Neighbour Solicitations,
   as described below.

   In a case where it is safe to send a Source Link-Layer Address
   Option, a host SHOULD NOT send a TO, since the message may be
   misinterpreted by legacy nodes.  Importantly, a node MUST NOT send a
   Tentative Option in the same message where a Source Link-Layer
   Address Option is sent.

   Particularly, Tentative Options are permitted to be sent when
   addressing state precludes sending the SLLAO, but a neighbour cache
   entry will be created on a peer node [RFC4429].

3.1.  Sending Neighbour Solicitations with Tentative Options

   Neighbour Solicitations sent to unicast addresses MAY contain a
   Tentative Option.

   Since delivery of a packet to a unicast destination requires prior
   knowledge of the destination's hardware address, unicast Neighbour
   Solicitation packets may only be sent to destinations for which a
   neighbour cache entry already exists.

   For example, if checking bidirectional reachability to a router, it
   may be possible to send a Neighbour Solicitation with Tentative
   Option to the router's advertised address.

   As discussed in [RFC4861], the peer device may not have a cache entry
   even if the soliciting host does, in which case reception of the
   Tentative Option may create a neighbour cache entry, without the need
   for Neighbour Discovering the original solicitor.

3.2.  Sending Router Solicitations with Tentative Options

   Any Router Solicitation from a Preferred, Deprecated or Optimistic
   address MAY be sent with a Tentative Option [RFC4429].


4.  Receiving Tentative Options

   Receiving a Tentative Option allows nodes to unicast responses to
   solicitations without performing Neighbour Discovery.




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   It does this by allowing the solicitation to create STALE neighbour
   cache entries if one doesn't exist, but only update an entry if the
   link-layer address in the option matches the entry.

4.1.  Handling Tentative Options

   Use of Tentative Options is only defined for Neighbour and Router
   Solicitation messages.

   In any other received message, the presence of the option is silently
   ignored, that is, the packet is processed as if the option was not
   present.

   It is REQUIRED that the same validation algorithms for Neighbour and
   Router Solicitations received with TO as in the IPv6 Neighbour
   Discovery specification [RFC4861], are used.

   In the case that a solicitation containing a Tentative Option is
   received, The only processing differences occur in checking and
   updating the neighbour cache entry.  Particularly, there is no reason
   to believe that the host will remain tentative after receiving a
   responding advertisement.

   As defined in Section 2.1, Tentative Options do not overwrite
   existing neighbour cache entries where the link-layer addresses of
   the option and entry differ.

   If a solicitation from a unicast source address is received where no
   difference exists between the TO and an existing neighbour cache
   entry, the option MUST be treated as if it were an SLLAO after
   message validation, and processed accordingly.

   In the case that a cache entry is unable to be created or updated due
   to existence of a conflicting neighbour cache entry, it MUST NOT
   update the neighbour cache entry.

4.2.  Receiving Neighbour Solicitations containing Tentative Options

   The Tentative Option is only allowed in Neighbour Solicitations with
   specified source addresses for which SLLAO is not required.

   A Neighbour Solicitation message received with a TO and an
   unspecified source address MUST be silently discarded.

   Upon reception of a Tentative Option in a Neighbour Solicitation for
   which the receiver has the Target Address configured, a node checks
   to see if there is a neighbour cache entry with conflicting link-
   layer address.



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   If no such entry exists, the neighbour cache of the receiver SHOULD
   be updated, as if the Tentative Option was a SLLAO.

   Sending of the solicited Neighbour Advertisement then proceeds
   normally, as defined in section 7.2.4 of [RFC4861].

   If there is a conflicting neighbour cache entry, the node processes
   the solicitation as defined in Section 7.2.4 of [RFC4861], except
   that the Neighbour Cache entry MUST NOT be modified.

4.3.  Receiving a Router Solicitation containing a Tentative Option

   In IPv6 Neighbour Discovery [RFC4861], responses to Router
   Solicitations are either sent to the all-nodes multicast address, or
   may be sent to the solicitation's source address if it is a unicast
   address.

   Including a Tentative Option in the solicitation allows a router to
   choose to send a packet directly to the link-layer address even in
   situations where this would not normally be possible.

   For Router Solicitations with unicast source addresses, neighbour
   caches SHOULD be updated with the link-layer address from a Tentative
   Option if there is no differing neighbour cache entry.  In this case,
   Router Advertisement continues as in Section 6.2.6 of [RFC4861].

   For received solicitations with a differing link-layer address to
   that stored in the neighbour cache, the node processes the
   solicitation as defined in Section 6.2.6 of [RFC4861], except that
   the Neighbour Cache entry MUST NOT be modified.


5.  IANA Considerations

   IANA action of options for IPv6 Neighbor Discovery require RFC
   Approval [RFC2780].

   This document asks the IANA to allocate the Tentative Option for
   link-layer addressing (Section Section 2.1) from the IPv6 Neighbour
   Discovery options for IPv6.


6.  Security Considerations

   The use of the Tentative Option in Neighbour and Router Solicitation
   messages acts in a similar manner to SLLAO, updating neighbour cache
   entries, in a way which affects the transmission of subsequent
   packets.



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   An attacker may cause messages may be sent to another node by an
   advertising node (a reflector), without creating any ongoing state on
   the reflector.

   This is attack requires one solicitation for each advertisement and
   the advertisement has to go to a unicast MAC destination.  That said,
   the size of the advertisement may be significantly larger than the
   solicitation, or the attacker and reflector may be on a medium with
   greater available bandwidth than the victim.

   For link-layers where it isn't possible to spoof the link-layer
   source address this allows a slightly increased risk of reflection
   attacks from nodes which are on-link.

   Additionally, since a SEND host must always advertise using SEND
   options and signatures, a non-SEND attacker may cause excess
   computation on both a victim node and a router by causing SEND
   advertisement messages to be transmitted to a particular MAC address
   and the lall-nodes multicast.  SEND specifies guidelines to hosts
   receiving unsolicited advertisements in order to mitigate such
   attacks [RFC3971].

   While this is the same effect as experienced when accepting SLLAO
   from non-SEND nodes, the lack of created neighbour cache entries on
   the advertiser may make such attacks more difficult to trace.

   Modification of Neighbour Discovery messages on the network is
   possible, unless SEND is used.  [RFC3971] provides a protocol
   specification in which soliciting nodes sign ND messages with a
   private key and use addresses generated from this key.

   Even if SEND is used, the lifetime of a neighbour cache entry may be
   extended by continually replaying a solicitation message to a
   particular router or hosts.  Since this may be achieved for any
   Neighbour or Router Solicitation message, corresponding
   advertisements to the original transmitters of these solicitation
   messages may occur.

   SEND defines use of Timestamp values to protect a device from attack
   through replay of previously sent messages.  Although this applies to
   Neighbour and Router Solicitation messages, granularity of the
   timestamp allows the messages to be used for up to five minutes
   [RFC3971].

   All Router and Neighbour Solicitations using SEND contain a Nonce
   option, containing a random identifier octet string.  Since SEND
   messages are digitally signed, and may not be easily modified, replay
   attacks will contain the same Nonce option, as was used in the



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   original solicitation.

   While the Nonce Option included in a transmission to another node may
   not vary within one short solicitation period (the host may itself
   replay solicitations in the case of packet loss), the presence of the
   timestamp option ensures that for later solicitations, a different
   Timestamp and Nonce will be used.

   Therefore, a receiver seeing a solicitation with the same Timestamp
   and Nonce (and signature) for more than either of
   MAX_RTR_SOLICITATIONS (for Router Solicitations), MAX_UNICAST_SOLICIT
   or MAX_MULTICAST_SOLICIT (for Neighbour Solicitations), SHOULD ignore
   further solicitations with this (Nonce,Timestamp,Source) triple,
   ensuring that no modification is made to neighbour cache entries.
   This applies to any solicitation packet capable of carrying a SEND
   payload, whether they use a Tentative Option or SLLAO.

   Stations noticing such an attack SHOULD notify their administrator of
   the attempt at Denial-of-service.


7.  Acknowledgments

   Erik Nordmark coined a proposal for Tentative version of the SLLAO
   during a conversation with JinHyeock Choi and Greg Daley.


8.  References

8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              September 2007.

   [RFC4429]  Moore, N., "Optimistic Duplicate Address Detection for
              IPv6", RFC RFC4429, April 2006.

   [RFC3971]  Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
              Neighbor Discovery (SEND)", RFC 3971, March 2005.

8.2.  Informative References

   [RFC2780]  Bradner, S. and V. Paxson, "IANA Allocation Guidelines For
              Values In the Internet Protocol and Related Headers",



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              BCP 37, RFC 2780, March 2000.

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862, September 2007.


Appendix A.  Constraints imposed by IPv6 Neighbour Discovery

   Hosts which send and receive Tentative Options may be interacting
   with legacy nodes which support IPv6 Neighbour Discovery procedures,
   but do not understand the new option.

   For these nodes, the presence of the option is silently ignored, that
   is, the packet is processed as if the option was not present.
   Therefore all messages sent with Tentative Options MUST be compliant
   with the existing requirements for options and addressing specified
   in the IPv6 Neighbour Discovery RFC [RFC4861].

A.1.  Constraints on Neighbour Solicitations

   As described in Section 7.2.2 of [RFC4861], packets sent to solicited
   nodes' multicast addresses MUST contain Source Link-Layer Address
   options.

      Neighbour solicitations to multicast addresses MUST NOT contain
      Tentative Options

   Neighbour Solicitations to unicast addresses SHOULD include a link-
   layer address (if the sender has one has one) as a Source Link-Layer
   Address option.

      Unicast neighbour solicitations without Source Link-Layer Address
      Options MAY contain Tentative Options, if the solicitor has a
      Link-Layer address.

A.2.  Constraints on Router Solicitations

   As described in Section 6.3.7 of [RFC4861], Router Solicitations
   SHOULD contain Source Link-Layer Address Options.

      Router Solicitations without Source Link-Layer Address options MAY
      contain a Tentative Option.


Appendix B.  Interactions with legacy nodes

   Devices which do not implement Tentative Options will act as if no
   option was placed within the Neighbour Discovery message.  The



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   following sections summarize how legacy hosts will interact with
   messages containing Tentative Options.

B.1.  Legacy Neighbour Solicitation processing

   A node can include the Tentative Option in a unicast NS (and no SLLAO
   option) when the transmitter's address is either preferred, tentative
   or optimistic.

      An RFC 2461 host receiving such a packet will "see" a packet
      without an SLLAO option, which is allowed in RFC4861.

      If the recipient host has an existing neighbour cache entry for
      the transmitter, it can then send a Neighbour Advertisement.

      Where no neighbour cache entry exists, the recipient will send a
      multicast NS (containing its own SLLAO) in order for the original
      transmitter to respond with an NA.  Upon reception of the original
      transmitter's NA, an NA is sent back to the origin.

   The Tentative Option MUST NOT be included in an NS message which has
   no source address.

      An RFC 2461 host sees an NS without a source address as a
      Duplicate Address Detection message.

      Reception of duplicate address detection messages may cause side-
      effects on other hosts, which may cause them to treat addresses as
      invalid.

B.2.  Legacy Router Solicitation processing

   A node can include the Tentative Option in an RS with a unicast
   source address (and no SLLAO option) when the transmitter's address
   is either tentative or optimistic.

      An RFC 2461 router receiving such a packet will "see" a packet
      without an SLLAO option, which is allowed in RFC4861.

      If the router has an existing neighbour cache entry for this host,
      it may send a Unicast RA in response, but may send a multicast in
      preference.

      If no neighbour cache entry exists, some routers will not be able
      to provide a unicast response.  These routers will schedule a
      multicast response.





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      Other routers may attempt to perform neighbour discovery (by
      sending a multicast NS), and unicast a response when a neighbour
      cache entry has been created.


Authors' Addresses

   Greg Daley
   NetStar Australia Pty Ltd
   Lvl 9/636 St Kilda Rd
   Melbourne, Victoria  3004
   Australia

   Phone: +61 401 772 770
   Email: gdaley@netstarnetworks.com


   Erik Nordmark
   Sun Microsystems, Inc.
   17 Network Circle
   Mountain View, CA
   USA

   Phone: +1 650 786 2921
   Email: erik.nordmark@sun.com


   Nick "Sharkey" Moore

   Email: sharkey@zoic.org





















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