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Network Working Group                                           J. Arkko
Internet-Draft                                                  Ericsson
Expires: September 1, 2003                                 March 3, 2003


                        Effects of ICMPv6 on IKE
                 draft-arkko-icmpv6-ike-effects-02.txt

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on September 1, 2003.

Copyright Notice

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

Abstract

   The ICMPv6 protocol provides many functions which in IPv4 were either
   non-existent or provided by lower layers.  IPv6 architecture also
   makes it possible to secure all IP packets using IPsec, even ICMPv6
   messages.  IPsec architecture has a Security Policy Database that
   specifies which traffic is protected, and how.  It turns out that the
   specification of policies in the presence of ICMPv6 traffic is hard,
   particularly with ICMPv6 packets related to Neighbor Discovery.
   Sound looking policies may easily lead to loops: The establishment of
   security requires Neighbor Discovery messages which can not be sent
   since security has not been established yet.  The purpose of this
   draft is to inform system administrators and IPsec implementors in
   which manner they can handle the ICMPv6 messages.  Common



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   understanding of the way that these messages are handled is also
   necessary for interoperability, in case vendors hardcode such rules
   in to products.

Table of Contents

   1.   Introduction . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.   Terminology  . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.   Neighbor Discovery and ICMPv6 Tasks  . . . . . . . . . . . .   5
         3.1  Path MTU Discovery . . . . . . . . . . . . . . . . . . . 5
         3.2  Error Notification . . . . . . . . . . . . . . . . . . . 5
         3.3  Informational Notifications  . . . . . . . . . . . . . . 5
         3.4  Router and Prefix Discovery  . . . . . . . . . . . . . . 5
         3.5  Address Autoconfiguration  . . . . . . . . . . . . . . . 6
         3.6  Duplicate Address Detection  . . . . . . . . . . . . . . 6
         3.7  Address Resolution . . . . . . . . . . . . . . . . . . . 6
         3.8  Neighbor Reachability Detection  . . . . . . . . . . . . 6
         3.9  Redirect . . . . . . . . . . . . . . . . . . . . . . . . 7
         3.10 Router Renumbering . . . . . . . . . . . . . . . . . . . 7
   4.   Factors Affecting the Policy Rules . . . . . . . . . . . . .   8
         4.1  Nature of the Addresses  . . . . . . . . . . . . . . . . 8
         4.2  Network Topology . . . . . . . . . . . . . . . . . . . . 8
         4.3  Role in Estaliblishing Communications  . . . . . . . . . 9
         4.4  Protecting the Infrastructure versus Communications  . .10
   5.   Analysis of the ICMPv6 Messages  . . . . . . . . . . . . . .  11
         5.1  Destination Unreachable  . . . . . . . . . . . . . . . .11
         5.2  Packet Too Big . . . . . . . . . . . . . . . . . . . . .11
         5.3  Time Exceeded  . . . . . . . . . . . . . . . . . . . . .11
         5.4  Parameter Problem  . . . . . . . . . . . . . . . . . . .11
         5.5  Echo Request . . . . . . . . . . . . . . . . . . . . . .11
         5.6  Echo Reply . . . . . . . . . . . . . . . . . . . . . . .12
         5.7  Redirect . . . . . . . . . . . . . . . . . . . . . . . .12
         5.8  Router Solicitation  . . . . . . . . . . . . . . . . . .12
         5.9  Router Advertisement . . . . . . . . . . . . . . . . . .12
         5.10 Neighbour Solicitation . . . . . . . . . . . . . . . . .12
         5.11 Neighbour Advertisement  . . . . . . . . . . . . . . . .12
         5.12 Router Renumbering . . . . . . . . . . . . . . . . . . .13
   6.   Summary  . . . . . . . . . . . . . . . . . . . . . . . . . .  14
   7.   Further Work . . . . . . . . . . . . . . . . . . . . . . . .  16
        Normative References . . . . . . . . . . . . . . . . . . . .  17
        Informative References . . . . . . . . . . . . . . . . . . .  18
        Author's Address . . . . . . . . . . . . . . . . . . . . . .  18
   A.   Acknowledgements . . . . . . . . . . . . . . . . . . . . . .  19
        Intellectual Property and Copyright Statements . . . . . . .  20







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1. Introduction

   The ICMPv6 [8] and IPv6 Neighbor Discovery [6] protocols provide many
   functions which in IPv4 were either non-existent or provided by lower
   layers.  For instance, IPv6 implements address resolution using an IP
   packet, ICMPv6 Neighbour Solicitation message.  In contrast, IPv4
   uses an ARP message at a lower layer.

   IPv6 architecture makes it possible to secure all IP packets using
   IPsec [4], even ICMPv6 and Neighbor Discovery messages and even to
   multicast addresses.  IPsec architecture has a Security Policy
   Database that specifies which traffic is protected, and how.  It
   turns out that the specification of policies in the presence of
   Neighbor Discovery traffic is not easy.  For instance, a simple
   policy of protecting all traffic between two hosts on the same
   network would trap even address resolution messages, leading to a
   situation where IKE ca not establish a Security Association since in
   order to send the IKE UDP packets one would have had to send the
   Neighbour Solicitation Message, which would have required an SA.

   The purpose of this draft is to inform system administrators and
   IPsec implementors in which manner they can handle the Neighbor
   Discovery messages.  System administrators do not want to study the
   IPv6 specifications in order to understand how they shall configure
   their routers.  IPsec implementors want to understand what kind of
   policies they can offer with respect to the Neighbor Discovery
   messages.

   Common understanding of the way that these messages are handled is
   also very much necessary for interoperability, as some vendors may be
   hardcoding some of the low-level policy operations in their products.
   If the rules between two vendors' products are incompatible for a
   particular message we may end with the sender sending cleartext and
   the receiver requiring IPsec, causing the packet to be dropped and
   possibly all connectivity between the two nodes lost.

   This document does not imply any changes to the ICMPv6, Neighbor
   Discovery, IPsec, or IKE specifications.  It is merely provided for
   configuration guidance.












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2. Terminology

   The keywords "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].














































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3. Neighbor Discovery and ICMPv6 Tasks

   In IPv6, ICMP has several tasks, and many of these tasks are
   overloaded on a few central message types such as the Neighbour
   Discovery message.  In this chapter we explain the tasks and their
   effects in order to understand better how the messages should be
   treated.

3.1 Path MTU Discovery

   Path MTUs are dynamically determined by IPv6 in order to optimize the
   size of the packets sent to a particular destination [1].

   The ICMPv6 Packet Too Big messages [8] are used as a part of the Path
   MTU Discovery procedure.

3.2 Error Notification

   ICMPv6 handles basic error situations of the IP layer, such as
   finding out that a particular destination is not available.

   The Destination Unreachable, Packet Too Big, Parameter Problem, and
   Time Exceeded messages are a part of the error handling procedure
   [8].  Note that the Packet Too Big message also plays a role in the
   Path MTU Discovery procedure.

3.3 Informational Notifications

   For debugging and network analysis purposes, ICMPv6 includes
   informational messages [8].  These message are necessary also in
   IPsec contexts and over IPsec tunnels due to the complex nature of
   some tunnel setups.

   The Echo Request and Echo Reply messages are used solely for this
   purpose.

3.4 Router and Prefix Discovery

   Router and prefix discovery is a part of the Neighbour Discovery
   protocol [6], which in turn is a part of the ICMPv6.  The main
   purpose of the router discovery is to find neighboring routers that
   are willing to forward packets on the behalf of hosts.  Prefix
   discovery involves determining which destinations are local for an
   attached link.  This information is used both by the address
   autoconfiguration process, and routing.  Typically, address
   autoconfiguration and other tasks can not proceed at all until the
   router discovery process has run.




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   The Router Solicitation and Router Advertisement messages are used
   for this and only this purpose.

3.5 Address Autoconfiguration

   Address autoconfiguration is another part of the Neighbour Discovery
   protocol [6].  It's purpose is to automatically assign addresses to
   interfaces.  It comes in two variants, stateless and statefull.  In
   this document we consider only the stateless autoconfiguration
   aspects.  Obviously, no higher layer traffic can be sent until all
   participating nodes have addresses.  This includes also IKE UDP
   traffic.

   The Neighbour Solicitation and Advertisement messages are used for
   this purpose, among other things.  Furthermore, Router and Prefix
   Discovery and Duplicate Address Detection have an effect to the
   Address Autoconfiguration tasks.

3.6 Duplicate Address Detection

   As a part of the stateless address autoconfiguration procedure, nodes
   check for duplicate addresses prior to assigning an address to an
   interface [7].  This procedure uses the same messages as the
   Neighbour Discovery protocol.  Since the rules outlined in RFC 2462
   [7] forbid the use of an address for both sending and receiving
   packets until it has been found unique, no higher layer traffic is
   possible until this procedure has completed.

   The Neighbour Solicitation and Advertisement messages are used also
   for this purpose.

3.7 Address Resolution

   In address resolution, nodes determine the link-layer address of a
   local destination given only the destination's IP address [6].
   Again, no higher level traffic can proceed until the sender knows the
   hardware address of the destination or the next hop router.

   The Neighbour Solicitation and Advertisement messages are used also
   for this purpose.

3.8 Neighbor Reachability Detection

   Hosts monitor the reachability of local destinations and routers in
   the Neighbour Unreachability procedure, which is a part of the
   Neighbour Discovery protocol [6].  No higher level traffic can
   proceed if this procedure flushes out neighbour cache entries after
   (perhaps incorrectly) determining that the peer is not reachable.



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   The Neighbour Solicitation and Advertisement messages are used also
   for this purpose.

3.9 Redirect

   In the Redirect procedure, a router informs a host of a better
   first-hop node to reach a particular destination [6].  It is a part
   of the Neighbour Discovery protocol.  As routers forward packets
   regardless of them being sent first to the wrong place,
   communications can still be established without the ability to
   process Redirect messages.

   The Redirect message is used solely for the Redirect procedure.

3.10 Router Renumbering

   This procedure [9] allows address prefixes on routers to be
   configured and reconfigured in the similar manner as Neighbor
   Discovery and Address Autoconfiguration works for hosts.  Incorrect
   processing or blocking of messages related to this procedure may
   render a node's address sets invalid, thereby preventing further
   communications.

   The Router Renumbering message is used solely for the Router
   Renumbering procedure.


























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4. Factors Affecting the Policy Rules

4.1 Nature of the Addresses

   Neighbor Discovery messages are sent using various kinds of source
   and destination address types.  The nature of the destination address
   is of relevance here, as the destination address is used to find the
   right security association.  The destination address can be either a
   well known multicast address, a computed multicast address, such as
   the solicited-node multicast address, or a unicast address.  Many
   Neighbor Discovery messages use multicast addresses in most cases.
   Some messages can also be sent to unicast addresses in certain
   situations.  For instance, the Neighbor Solicitation messages are
   usually sent to multicast addresses, but the Neighbor Advertisement
   messages are also sent to unicast addresses when sent as a response
   to a node that has an address.

   ICMPv6 messages are sent using various kinds of source and
   destination address types.  The source address is usually a unicast
   address, but during address autoconfiguration message exchanges, the
   unspecified address :: is also used as a source address [7].  The
   destination address can be either a well known multicast address, a
   generated multicast address such as the solicited-node multicast
   address, or a unicast address.  While many ICMPv6 messages use
   multicast addresses most of the time, some also use unicast addresses
   sometimes.  For instance, the Neighbour Solicitation messages are
   usually sent to multicast addresses, but the Neighbour Advertisement
   messages are also sent to unicast addresses when sent as a response
   to a node that has an address.

   IPsec [4] can be used for the protection of both unicast and
   multicast traffic.  However, in order to automatically negotiate
   mutually acceptable security associations and to refresh keys, IKE
   [5] needs to be used.  IKE is only capable of negotiating SAs for
   unicast communications.

   Obviously, policies MUST be configured so that multicast traffic does
   not require dynamic SAs.  However, while this is a necessary
   condition it is not sufficient to make sure that that IKE works.  The
   policies MUST also exclude unicast traffic which is contains ICMPv6
   messages required before UDP can work between the two nodes.

4.2 Network Topology

   ICMP traffic has different implications for hosts and security
   gateways.  In general, security gateways SHOULD carry all ICMP
   traffic related to the protected traffic in the same tunnel as the
   traffic itself.  For instance, when an ICMPv6 Packet Too Big message



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   is generated on the unprotected segment of a packet's path, that
   message should relayed through the tunnel to ensure that the sender
   recognizes the MTU problem.

   Between hosts similar rules apply.  However, messages related to the
   establishment of communication between the hosts - such as for
   address resolution - MUST NOT be passed through the tunnel at least
   when the tunnel does not exist yet and IKE would be needed to
   establish it.

   Note that the distinctions in network topology are more due to the
   actual network architecture than the selected IPsec mode, be it
   tunnel or transport.

   ICMPv6 messages can be classified according to whether they are meant
   for end-to-end communications or communications within a link.  There
   are also messages that we classify as 'any-to-end', which can be sent
   from any point within a path back to the source, typically to
   announce an error in processing the original packet.  For instance,
   the address resolution messages are solely for local communications
   [6], whereas the Destination Unreachable messages are any-to-end in
   nature.  End-to-end and any-to-end messages MUST always be passed
   through tunnels.  Local messages may be passed through IPsec process
   under certain conditions.

4.3 Role in Estaliblishing Communications

   ICMPv6 messages can also be classified according to their role for
   establishing communications between two nodes.  For the purposes of
   this discussion, the relevant issue is whether or not the messages
   must be passed through before IKE can use UDP packets to negotiate
   SAs.  For instance, address autoconfiguration, duplicate address
   detection, and address resolution obviously MUST be completed before
   UDP packets can be passed.

   Neighbour reachability detection is also capable of disrupting IKE
   communications.  The reference [6] states the following:

      In some cases (e.g., UDP-based protocols and routers
      forwarding packets to hosts) such reachability information
      may not be readily available from upper-layer protocols.
      When no hints are available and a node is sending packets
      to a neighbor, the node actively probes the neighbor using
      unicast Neighbor Solicitation messages to verify that the
      forward path is still working.

   This means that unless the IKE implementation explicitly handles
   forward progress notifications towards the IPv6 stack, the stack can



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   not know about the reachability towards the other host.  Since the
   hosts may be using tunnel mode and other address in the inner packets
   than the regular addresses on the hosts, the stack can not learn of
   forward progress through regular IPsec AH or ESP packets.

   Therefore, neighbour reachability MUST also be allowed to work
   independent of IKE SA establishment.

   As IKE messages may contain certificates, it is quite possible that
   an MTU limit may be exceeded somewhere within the network.  If this
   is possible in a given network, the policies MUST allow ICMP Packet
   Too Big messages to be received.  Note that these messages may well
   be received either in the clear, on manually configured SAs, or on
   dynamic SAs.  If the router generating the Packet Too Big message
   does not yet have an SA with the original host, it can initiate IKE
   negotiations to create one.  In case that this new negotiation fails
   due to reaching another MTU limit, other routers may be involved
   along the way.  But ultimately the process reaches the closest router
   to which the MTU is known and will not cause any ICMP error messages.

4.4 Protecting the Infrastructure versus Communications

   IPsec can be used to protect the end-to-end communications or the
   underlying control messages (such as ICMPv6).  It can even be used to
   protect both.  Since many of the control messages are sent to
   multicast addresses, if IPsec is used then manual SA configuration
   MUST be performed instead of IKE-based SA negotiation.

   As we have talked about some messages in some situations having to be
   independent of IKE, it does not necessarily imply that they have to
   passed through in the clear.  Instead, systems MAY use manually
   configured IPsec SAs to protect e.g.  all ICMPv6 communications
   within one network.  (Note that setting these manual SAs up requires
   some care as discussed in [13].)

   A plausible security policy configuration could therefore be one
   where all ICMPv6 messages within the local network must be protected
   by manual SAs, and all other communications must be protected by
   IKE-negotiated SAs.












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5. Analysis of the ICMPv6 Messages

5.1 Destination Unreachable

   This message is always sent between unicast addresses [8].  It is an
   end-to-end message  Destination Unreachable is never a relevant
   message for establishing dynamic SAs, unless advanced failover
   schemes rely on the knowledge to quickly determine unreachable IKE
   peers.

5.2 Packet Too Big

   This message is also always sent between unicast addresses [8] even
   if might be sent as a response to a multicast message.  It is an
   end-to-end message.

   Packet Too Big has, however, a role in establishing communications.
   End-to-end communications, that is.  In order to pass through long
   IKE packets, Packet Too Big responses from the network MUST be
   considered.  Therefore, it MUST be possible for policies to be
   configured so that such messages can be received.  Note that as
   dicussed previously, the Packet Too Big messages themselves can be
   protected in various ways.

5.3 Time Exceeded

   This message is also always sent between unicast addresses [8] and is
   an end-to-end message.  Like Packet Too Big, it too has a role in
   establishing end-to-end communications under certain special
   situations.

5.4 Parameter Problem

   This message is similar to Packet Too Big in the sense that it uses
   only unicast messages even if it could be sent as a response to a
   multicast packet.  It's role is also end-to-end.  While in theory its
   role in establishing communications is similar to Packet Too Big and
   Time Exceeded, in practise it is hard to see the kind of IKE and IPv6
   stack version problem that could result in this message being sent.

5.5 Echo Request

   Echo Request uses unicast addresses as source addresses, but may be
   sent to any legal IPv6 address, even multicast and anycast addresses
   [8].  Echo Requests run end-to-end but never have a role in
   establishing communications.





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5.6 Echo Reply

   Echo Reply is similar to Echo Request in other respects, but uses
   only unicast addresses.

5.7 Redirect

   The Redirect message is always sent between unicast addresses [6].
   It is only used for local purposes, not for end-to-end
   communications.  It is not strictly necessary in order to establish
   communications.  Nevertheless, it can be viewed as a logical add-on
   to the Neighbour Discovery messages such as Router Advertisement, and
   as such SHOULD be treated in a similar manner.

5.8 Router Solicitation

   This message uses either the unspecified address or an unicast
   address as a source address.  The destination address is typically a
   multicast address.  This message is always used only local.  Since
   address autoconfiguration and routing depend on the ability of the
   routers and address prefixes to be found, this message is required
   before any communications can be established.  Therefore, this
   message MUST be allowed to work independent of IKE SA establishment.

5.9 Router Advertisement

   This message has always a unicast source address, but the destination
   address can be either a unicast or a multicast address.  Like the
   solicitation message, the advertisement is also link local only and
   required for establishing any communications.  Therefore, this
   message MUST be allowed to work independent of IKE SA establishment.

5.10 Neighbour Solicitation

   The source address of this message is either a unicast address or (if
   Duplicate Address Detection is in progress) the unspecified address
   [6, 8].  The destination is either a multicast address, unicast
   address, or an anycast address.  Neighbour Solicitation and
   Advertisement messages are used for multiple purposes: address
   autoconfiguration, duplicate address detection, and reachability
   detection.  In all these roles they act only locally on the link, and
   getting them through is required before any communications can be
   established.  Therefore, this message MUST be allowed to work
   independent of IKE SA establishment.

5.11 Neighbour Advertisement

   The source address of this message is a unicast address, and the



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   destination is either a unicast or a multicast address.  Like the
   solication message, this message is link local only and is required
   before any communications can be established.  Therefore, this
   message MUST be allowed to work independent of IKE SA establishment.

5.12 Router Renumbering

   These messages are sent from a unicast address to either a multicast
   or a unicast address.  The message are not solely link local, they
   are used for end-to-end purposes such as having a central management
   station renumber all routers in a corporate network.  As a result of
   the RR procedure, automatically configured addresses and prefixes may
   be changed.  However, it is expected that a transition period exists
   where both addresses are still acceptable, making it possible to
   still proceed with IKE negotiations to create SAs for the RR
   procedure.  We can therefore assume that the procedure MAY use manual
   or dynamic SAs as desired by the system administrators.


































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6. Summary

   Based on the above, the ICMPv6 messages can be classified as follows:

   +-------------------+------------+-----------------+
   | MESSAGE           | ROLE       | USE IKE?        |
   +-------------------+------------+-----------------+
   | Dest Unreachable  | Any-to-End | MAY(1,2)        |
   +-------------------+------------+-----------------+
   | Packet Too Big    | Any-to-End | MAY(1,3)        |
   +-------------------+------------+-----------------+
   | Time Exceeded     | Any-to-End | MAY(1,3)        |
   +-------------------+------------+-----------------+
   | Parameter Problem | End-to-End | MAY(4)          |
   +-------------------+------------+-----------------+
   | Echo Request      | End-to-End | MAY(4)          |
   +-------------------+------------+-----------------+
   | Echo Reply        | End-to-End | MAY(4)          |
   +-------------------+------------+-----------------+
   | Redirect          | Link Local | SHOULD NOT(5)   |
   +-------------------+------------+-----------------+
   | Router Solicit    | Link Local | MUST NOT(6)     |
   +-------------------+------------+-----------------+
   | Router Advert     | Link Local | MUST NOT(6)     |
   +-------------------+------------+-----------------+
   | Neighbour Solicit | Link Local | MUST NOT(6)     |
   +-------------------+------------+-----------------+
   | Neighbour Advert  | Link Local | MUST NOT(6)     |
   +-------------------+------------+-----------------+
   | Router Renumbering| End-to-End | MAY(4)          |
   +-------------------+------------+-----------------+

   Explanations:

   (1) These error messages have an end-to-end nature but may be
      generated by intermediate routers as well.

   (2) This MAY have to be considered by implementations that wish to
      base failover decisions on the Unreachable message.

   (3) These messages have an impact on the success of IKE messages e.g.
      when certificates are passed in IKE packets.  It MUST be possible
      for policies to be configured so that these messages can be
      received while the IKE negotiations are still ongoing.  Different
      security policy configurations MUST be supported, including
      trusting cleartext messages or protecting the messages from
      intermediate nodes using other, new dynamic SA negotiations.




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   (4) These messages MAY be treated using regular IPsec and/or IKE
      processing.

   (5) This message SHOULD NOT use IKE in order to make their treatment
      equal with the rest of the link local messages, but in theory
      Redirect MAY be handled differently, e.g.  using dynamic SAs.

   (6) These messages MUST NOT use dynamic SAs.

   These policy rules may be expressed in various ways on a particular
   host or a router.  It is necessary to use the ICMPv6 type in making
   the policy decisions.  As [9] states, "This is consistent with,
   although not mentioned by, the Security Architecture specification".
   Only the following requirement for all implementations is stated
   here.  Products that provide hardcoded security policies for ICMPv6
   messages SHOULD enable user specified policies to be expressed at a
   higher priority level so that a possibility is still retained for
   modifying the rules due to e.g.  interoperability problems.

































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7. Further Work

   This draft discusses the use of IPsec on ICMPv6 messages on a
   principle level.  It does not take a stand on how the policies are
   expressed, for instance whether IPsec products need to have hardcoded
   rules for handling these messages, or whether the Security Policy
   Databases should be general enough to make it possible to express the
   policies in them even for the ICMPv6 messages.

   This draft does not address stateful address autoconfiguration
   aspects of IPv6.

   This draft does not address the use of dynamic security associations
   in the context of multicast traffic.  Now that the multicast key
   management working group has been founded in the IETF, a question
   eventually arises whether or not the results of that work can be used
   to protect the infrastructure multicast messages.


































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Normative References

   [1]   McCann, J., Deering, S. and J. Mogul, "Path MTU Discovery for
         IP version 6", RFC 1981, August 1996.

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

   [3]   Hinden, R. and S. Deering, "IP Version 6 Addressing
         Architecture", RFC 2373, July 1998.

   [4]   Kent, S. and R. Atkinson, "Security Architecture for the
         Internet Protocol", RFC 2401, November 1998.

   [5]   Harkins, D. and D. Carrel, "The Internet Key Exchange (IKE)",
         RFC 2409, November 1998.

   [6]   Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery
         for IP Version 6 (IPv6)", RFC 2461, December 1998.

   [7]   Thomson, S. and T. Narten, "IPv6 Stateless Address
         Autoconfiguration", RFC 2462, December 1998.

   [8]   Conta, A. and S. Deering, "Internet Control Message Protocol
         (ICMPv6) for the Internet Protocol Version 6 (IPv6)
         Specification", RFC 2463, December 1998.

   [9]   Crawford, M., "Router Renumbering for IPv6", RFC 2894, August
         2000.

   [10]  Narten, T. and R. Draves, "Privacy Extensions for Stateless
         Address Autoconfiguration in IPv6", RFC 3041, January 2001.



















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Informative References

   [11]  Arkko, J., Kempf, J., Sommerfeld, B. and B. Zill, "SEcure
         Neighbor Discovery (SEND) Protocol",
         draft-ietf-send-ipsec-00.txt (work in progress), February 2003.

   [12]  Nikander, P., "IPv6 Neighbor Discovery trust models and
         threats", draft-ietf-send-psreq-00 (work in progress), October
         2002.

   [13]  Arkko, J., "Manual SA Configuration for IPv6 Link Local
         Messages", draft-arkko-manual-icmpv6-sas-01 (work in progress),
         June 2002.

   [14]  Nikander, P., "Denial-of-Service, Address Ownership, and Early
         Authentication in the IPv6 World", Proceedings of the Cambridge
         Security Protocols Workshop, April 2001.


Author's Address

   Jari Arkko
   Ericsson
   Jorvas  02420
   Finland

   EMail: jari.arkko@ericsson.com
























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Appendix A. Acknowledgements

   The author would like to thank Pekka Nikander, Markku Rossi, Tero
   Kivinen, Michael Richardson, Erik Nordmark, and James Kempf for
   interesting discussions in this problem space.














































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