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Versions: 00 01 draft-arkko-send-ndopt

Network Working Group                                           J. Arkko
Internet-Draft                                                  Ericsson
Expires: December 4, 2003                                       J. Kempf
                                          DoCoMo Communications Labs USA
                                                           B. Sommerfeld
                                                        Sun Microsystems
                                                                 B. Zill
                                                               Microsoft
                                                             P. Nikander
                                                                Ericsson
                                                            June 5, 2003


                    SEcure Neighbor Discovery (SEND)
                      draft-ietf-send-ipsec-01.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
   Task Force (IETF), its areas, and its working groups.  Note that
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   Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
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   The list of current Internet-Drafts can be accessed at http://
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   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on December 4, 2003.

Copyright Notice

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

Abstract

   IPv6 nodes use the Neighbor Discovery (ND) protocol to discover other
   nodes on the link, to determine each other's link-layer addresses, to
   find routers and to maintain reachability information about the paths
   to active neighbors.  If not secured, ND protocol is vulnerable to



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   various attacks.  This document specifies an extension to IPsec for
   securing ND.  Contrary to the original ND specifications that also
   called for use of IPsec, this extension does not require the creation
   of a large number of manually configured security associations.

Table of Contents

   1.     Introduction . . . . . . . . . . . . . . . . . . . . . . .   4
   2.     Terms  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.     Neighbor and Router Discovery Overview . . . . . . . . . .   7
   4.     Secure Neighbor Discovery Overview . . . . . . . . . . . .  10
   5.     Modifications to Neighbor Discovery  . . . . . . . . . . .  12
          5.1    Unspecified Source Address . . . . . . . . . . . . . 12
          5.2    Secure-Solicited-Node Multicast Address  . . . . . . 12
          5.3    Nonce Option . . . . . . . . . . . . . . . . . . . . 13
          5.4    Proxy Neighbor Discovery . . . . . . . . . . . . . . 14
   6.     Authorization Delegation Discovery . . . . . . . . . . . .  15
          6.1    Delegation Chain Solicitation Message Format . . . . 15
          6.2    Delegation Chain Advertisement Message Format  . . . 17
          6.3    Trusted Root Option  . . . . . . . . . . . . . . . . 19
          6.4    Certificate Option . . . . . . . . . . . . . . . . . 20
          6.5    Router Authorization Certificate Format  . . . . . . 21
                 6.5.1  Field Values . . . . . . . . . . . . . . . . .22
          6.6    Processing Rules for Routers . . . . . . . . . . . . 23
          6.7    Processing Rules for Hosts . . . . . . . . . . . . . 24
   7.     IPsec Extensions . . . . . . . . . . . . . . . . . . . . .  27
          7.1    The AH_RSA_Sig Transform . . . . . . . . . . . . . . 27
                 7.1.1  Reserved SPI Number  . . . . . . . . . . . . .27
                 7.1.2  Authentication Data Format . . . . . . . . . .27
                 7.1.3  AH_RSA_Sig Security Associations . . . . . . .29
                 7.1.4  Replay Protection  . . . . . . . . . . . . . .30
                 7.1.5  Processing Rules for Senders . . . . . . . . .31
                 7.1.6  Processing Rules for Receivers . . . . . . . .32
          7.2    Other IPsec Extensions . . . . . . . . . . . . . . . 33
                 7.2.1  Destination Agnostic Security Associations . .33
                 7.2.2  ICMP Type Specific Selectors . . . . . . . . .33
   8.     Securing Neighbor Discovery with SEND  . . . . . . . . . .  34
          8.1    Neighbor Solicitation Messages . . . . . . . . . . . 34
                 8.1.1  Sending Secure Neighbor Solicitations  . . . .34
                 8.1.2  Receiving Secure Neighbor Solicitations  . . .34
          8.2    Neighbor Advertisement Messages  . . . . . . . . . . 35
                 8.2.1  Sending Secure Neighbor Advertisements . . . .35
                 8.2.2  Receiving Secure Neighbor Advertisements . . .35
          8.3    Other Requirements . . . . . . . . . . . . . . . . . 36
          8.4    Configuration  . . . . . . . . . . . . . . . . . . . 36
   9.     Securing Router Discovery with SEND  . . . . . . . . . . .  39
          9.1    Router Solicitation Messages . . . . . . . . . . . . 39
                 9.1.1  Sending Secure Router Solicitations  . . . . .39



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                 9.1.2  Receiving Secure Router Solicitations  . . . .39
          9.2    Router Advertisement Messages  . . . . . . . . . . . 39
                 9.2.1  Sending Secure Router Advertisements . . . . .40
                 9.2.2  Receiving Secure Router Advertisements . . . .40
          9.3    Redirect Messages  . . . . . . . . . . . . . . . . . 40
                 9.3.1  Sending Redirects  . . . . . . . . . . . . . .40
                 9.3.2  Receiving Redirects  . . . . . . . . . . . . .41
          9.4    Other Requirements . . . . . . . . . . . . . . . . . 41
          9.5    Configuration  . . . . . . . . . . . . . . . . . . . 42
   10.    Co-Existence of SEND and ND  . . . . . . . . . . . . . . .  44
          10.1   Behavior Rules . . . . . . . . . . . . . . . . . . . 44
          10.2   Configuration  . . . . . . . . . . . . . . . . . . . 46
   11.    Performance Considerations . . . . . . . . . . . . . . . .  49
   12.    Implementation Considerations  . . . . . . . . . . . . . .  50
   13.    Security Considerations  . . . . . . . . . . . . . . . . .  51
          13.1   Threats to the Local Link Not Covered by SEND  . . . 51
          13.2   How SEND Counters Threats to Neighbor Discovery  . . 51
                 13.2.1 Neighbor Solicitation/Advertisement Spoofing .51
                 13.2.2 Neighbor Unreachability Detection Failure  . .53
                 13.2.3 Duplicate Address Detection DoS Attack . . . .53
                 13.2.4 Router Solicitation and Advertisement Attacks 53
                 13.2.5 Replay Attacks . . . . . . . . . . . . . . . .53
                 13.2.6 Neighbor Discovery DoS Attack  . . . . . . . .54
          13.3   Attacks against SEND Itself  . . . . . . . . . . . . 54
   14.    IANA Considerations  . . . . . . . . . . . . . . . . . . .  56
          Normative References . . . . . . . . . . . . . . . . . . .  57
          Informative References . . . . . . . . . . . . . . . . . .  59
          Authors' Addresses . . . . . . . . . . . . . . . . . . . .  60
   A.     Contributors . . . . . . . . . . . . . . . . . . . . . . .  62
   B.     Acknowledgements . . . . . . . . . . . . . . . . . . . . .  63
   C.     IPR Considerations . . . . . . . . . . . . . . . . . . . .  64
          Intellectual Property and Copyright Statements . . . . . .  65



















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1. Introduction

   IPv6 defines the Neighbor Discovery (ND) protocol in RFC 2461 [6].
   Nodes on the same link use the ND protocol to discover each other's
   presence, to determine each other's link-layer addresses, to find
   routers and to maintain reachability information about the paths to
   active neighbors.  The ND protocol is used both by hosts and routers.
   Its functions include Router Discovery (RD), Address Auto-
   configuration, Address Resolution, Neighbor Unreachability Detection
   (NUD), Duplicate Address Detection (DAD), and Redirection.

   RFC 2461 called for the use of IPsec for protecting the ND messages.
   However, it turns out that in this particular application IPsec can
   only be used with a manual configuration of security associations due
   to chicken-and-egg problems in using IKE [23, 21] before ND is
   operational.  Furthermore, the number of such manually configured
   security associations needed for protecting ND is impractically large
   [24].  Finally, RFC 2461 did not specify detailed instructions for
   using IPsec to secure ND.

   Section 4 describes our overall approach to securing ND.  This
   approach involves the use of IPsec AH [3] to secure all
   advertisements relating to Neighbor and Router Discovery.  A new
   transform for AH allows public keys to be used.  Routers are
   certified by a trusted root, and a zero-configuration mechanism for
   showing address ownership.  The formats, procedures, and
   cryptographic mechanisms for this zero-configuration mechanism are
   described in a related specification [27].

   Section 6 describes the mechanism for distributing certificate chains
   to establish authorization delegation chain to a common trusted root.
   Section 7 describes the necessary modifications to IPsec.  Section 8
   and Section 9 show how to apply these components to securing Neighbor
   and Router Discovery.  A few small changes are required in the
   Neighbor Discovery protocol and these are discussed in Section 5.

   Finally, Section 10 discusses the co-existence of secure and
   non-secure Neighbor Discovery on the same link, Section 11 discusses
   performance considerations, Section 12 discusses the implementation
   considerations related to the IPsec extensions, and Section 13
   discusses security considerations for SEND.










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2. Terms

   Authorization Certificate (AC)

      The signer of an authorization certificate has authorized the
      entity designated in the certificate for a specific task or
      service.

   Authorization Delegation Discovery (ADD)

      This is a process through which SEND nodes can acquire a
      certificate chain from a peer node to a trusted root.

   Cryptographically Generated Addresses (CGAs)

      A technique [27, 30] where the address of the node is
      cryptographically generated from the public key of the node and
      some other parameters using a one-way hash function.

   Duplicate Address Detection (DAD)

      This mechanism defined in RFC 2462 [7] assures that two IPv6 nodes
      on the same link are not using the same addresses.

   Internet Control Message Protocol version 6 (ICMPv6)

      The IPv6 control signaling protocol.  Neighbor Discovery is a part
      of ICMPv6.

   Neighbor Discovery (ND)

      The IPv6 Neighbor Discovery protocol [6].

   Neighbor Unreachability Detection (NUD)

      This mechanism defined in RFC 2461 [6] is used for tracking the
      reachability of neighbors.

   Nonce

      Nonces are random numbers generated by a node.  In SEND, they are
      used to ensure that a particular advertisement is linked to the
      solicitation that triggered it.

   Security association

      A security association is a simplex "connection" that affords
      security services to the traffic carried by it.  Security services



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      are afforded to a security association by the use of AH, or ESP,
      but not both.  A security association is uniquely identified by a
      triple consisting of a Security Parameter Index (SPI), an IP
      Destination Address, and a security protocol (AH or ESP)
      identifier [2].

   Security association database

      A nominal database containing parameters that are associated with
      each (active) security association.  For inbound and outbound
      IPsec processing, these databases are separate.

   Security Parameters Index (SPI)

      An arbitrary 32-bit value.  Together with the destination IP
      address and security protocol (ESP or AH) identifier, the SPI
      uniquely identifies the Security Association.  Values from 1 to
      255 are reserved.

   Special SPI

      A Security Parameters Index from the reserved range 1 to 255.

   Security policy

      The security policy determines the security services afforded to
      an IPsec protected packet and the treatment of the packet in the
      network.

   Security policy database

      A nominal database containing a list of policy entries.  Each
      policy entry is keyed by one or more selectors that define the set
      of IP traffic encompassed by this policy entry.  Separate entries
      for inbound and outbound traffic is required  [2].
















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3. Neighbor and Router Discovery Overview

   IPv6 Neighbor and Router Discovery have several functions.  Many of
   these functions are overloaded on a few central message types such as
   the ICMPv6 Neighbor Discovery message.  In this section we explain
   some of these tasks and their effects in order to understand better
   how the messages should be treated.  Where this section and the
   original Neighbor Discovery RFCs are in conflict, the original RFCs
   take precedence.

   In IPv6, many of the tasks traditionally done at lower layers such as
   ARP have been moved to the IP layer.  As a consequence, unified
   mechanisms can be applied across link layers, security mechanisms or
   other extensions can be adopted more easily, and a clear separation
   of the roles between the IP and link layer can be achieved.

   The main functions of IPv6 Neighbor Discovery are as follows:

   o  Neighbor Unreachability Detection (NUD) is used for tracking the
      reachability of neighbors, both hosts and routers.  NUD is defined
      in Section 7.3 of RFC 2461 [6].  NUD is security-sensitive,
      because no higher level traffic can proceed if this procedure
      flushes out neighbor cache entries after (perhaps incorrectly)
      determining that the peer is not reachable.

   o  Duplicate Address Detection (DAD) is used for preventing address
      collisions [7].  A node that intends to assign a new address to
      one of its interfaces runs first the DAD procedure to verify that
      other nodes are not using the same address.  Since the outlined
      rules forbid the use of an address until it has been found unique,
      no higher layer traffic is possible until this procedure has
      completed.  Thus, preventing attacks against DAD can help ensure
      the availability of communications for the node in question.

   o  Address Resolution is similar to IPv4 ARP [20].  The Address
      Resolution function resolves a node's IPv6 address to the
      corresponding link-layer address for nodes on the link.  Address
      Resolution is defined in Section 7.2 of RFC 2461 [6] and it is
      used for hosts and routers alike.  Again, no higher level traffic
      can proceed until the sender knows the hardware address of the
      destination node or the next hop router.  Note that like its
      predecessor in ARP, IPv6 Neighbor Discovery does not check the
      source link layer address against the information learned through
      Address Resolution.  This allows for an easier addition of network
      elements such as bridges and proxies, and eases the stack
      implementation requirements as less information needs to be passed
      from layer to layer.




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   o  Address Autoconfiguration is used for automatically assigning
      addresses to a host [7].  This allows hosts to operate without
      configuration related to IP connectivity.  The Address
      Autoconfiguration mechanism is stateless, where the hosts use
      prefix information delivered to them during Router Discovery to
      create addresses, and then test these addresses for uniqueness
      using the DAD procedure.  A stateful mechanism, DHCPv6 [25],
      provides additional Autoconfiguration features.  Router and Prefix
      Discovery and Duplicate Address Detection have an effect to the
      Address Autoconfiguration tasks.

   o  The Redirect function is used for automatically redirecting hosts
      to an alternate router.  Redirect is specified in Section 8 of RFC
      2461 [6].  It is similar to the ICMPv4 Redirect message [19].

   o  The Router Discovery function allows IPv6 hosts to discover the
      local routers on an attached link.  Router Discovery is described
      in Section 6 of RFC 2461 [6].  The main purpose of Router
      Discovery is to find neighboring routers that are willing to
      forward packets on behalf of hosts.  Prefix discovery involves
      determining which destinations are directly on a link; this
      information is necessary in order to know whether a packet should
      be sent to a router or to the destination node directly.
      Typically, address autoconfiguration and other tasks can not
      proceed until suitable routers and prefixes have been found.

   The Neighbor Discovery messages follow the ICMPv6 message format and
   ICMPv6 types from 133 to 137.  The IPv6 Next Header value for ICMPv6
   is 58.  The actual Neighbor Discovery message includes an ND message
   header consisting of ICMPv6 header and ND message-specific data, and
   zero or more ND options:

                         <------------ND Message----------------->
     *-------------------------------------------------------------*
     | IPv6 Header      | ICMPv6   | ND message- | ND Message      |
     | Next Header = 58 | Header   | specific    | Options         |
     | (ICMPv6)         |          | data        |                 |
     *-------------------------------------------------------------*
                         <--ND Message header--->

   The ND message options are formatted in the Type-Length-Value format.

   All IPv6 ND protocol functions are realized using the following
   messages:







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            ICMPv6 Type      Message
            ------------------------------------
            133              Router Solicitation (RS)
            134              Router Advertisement (RA)
            135              Neighbor Solicitation (NS)
            136              Neighbor Advertisement (NA)
            137              Redirect

   The functions of the ND protocol are realized using these messages as
   follows:

   o  Router Discovery uses the RS and RA messages.

   o  Duplicate Address Detection uses the NS and NA messages.

   o  Address Autoconfiguration uses the NS, NA, RS, and RA messages.

   o  Address Resolution uses the NS and NA messages.

   o  Neighbor Unreachability Detection uses the NS and NA messages.

   o  Redirect uses the Redirect message.

   The destination addresses used in these messages are as follows:

   o  Neighbor Solicitation: The destination address is either the
      solicited-node multicast address, unicast address, or an anycast
      address.

   o  Neighbor Advertisement: The destination address is either a
      unicast address or the All Nodes multicast address [1].

   o  Router Solicitation: The destination address is typically the All
      Routers multicast address [1].

   o  Router Advertisement: The destination address can be either a
      unicast or the All Nodes multicast address [1].  Like the
      solicitation message, the advertisement is also local to the link
      only.

   o  Redirect: This message is always sent from the router's link-local
      address to the source address of the packet that triggered the
      Redirect.  Hosts verify that the IP source address of the Redirect
      is the same as the current first-hop router for the specified ICMP
      Destination Address.  Rules in [1] dictate that unspecified,
      anycast, or multicast addresses may not be used as source
      addresses.  Therefore, the destination address will always be a
      unicast address.



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4. Secure Neighbor Discovery Overview

   IPsec AH is used in to protect Neighbor and Router Discovery
   messages.  This specification introduces the use of a new transform
   for IPsec AH, extensions to the current IPsec selectors, an
   authorization delegation discovery process, and an address ownership
   proof mechanism.

   The components of the solution specified in this document are as
   follows:

   o  Trusted roots are expected to certify the authority of routers.  A
      host and a router must have at least one common trusted root
      before the host can adopt the router as its default router.
      Optionally, an authorization certificate can specify the prefixes
      for which the router is allowed to act as a router.  Delegation
      Chain Solicitation and Advertisement messages are used to discover
      a certificate chain to the trusted root without requiring the
      actual Router Discovery messages to carry lengthy certificate
      chains.

   o  Cryptographically Generated Addresses are used to assure that the
      sender of a Neighbor or Router Advertisement is the owner of an
      the claimed address.  A public-private key pair needs to be
      generated by all nodes before they can claim an address.

   o  IPsec AH is used to protect all messages relating to Neighbor and
      Router discovery.

   o  IPsec security policy database and security association database
      are configured to require the protection as indicated above.  Note
      that such configuration may take place manually or the operating
      system may perform it automatically upon enabling Secure Neighbor
      Discovery.

      This specification introduces extensions to the required selectors
      used in security policy database entries.  This is necessary in
      order to enable the protection of specific ICMP message types,
      while leaving other messages unprotected.

   o  A new transform for IPsec AH allows public keys to be used on a
      security association directly without the involvement of a key
      management protocol.  Symmetric session keys are not used, public
      key signatures are used instead.  The trust to the public key is
      established either with the authorization delegation process or
      the address ownership proof mechanism, depending on configuration
      and the type of the message protected.




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      The new transform uses also a fixed, standardized SPI (Security
      Parameters Index) number.  This is necessary again in order to
      avoid the involvement of a key management protocol.

      Given that Neighbor and Router Discovery messages are in some
      cases sent to multicast addresses, the new transform uses
      timestamps as a replay protection mechanism instead of sequence
      numbers.  To provide additional replay protection for the cases
      where required clock accuracy is not available, nonces are used in
      the Neighbor Discovery protocol.









































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5. Modifications to Neighbor Discovery

   Support for the SEND protocol can be added to a Neighbor Discovery
   implementation by providing the new Neighbor Discovery protocol
   mechanisms described in Section 6, the IPsec mechanisms described in
   Section 7, and using them together as specified in Section 9 and
   Section 8.  However, the following aspects of the Neighbor Discovery
   protocol change with SEND:

   o  The use of the unspecified address as a source address is
      discouraged.

   o  The solicited-node multicast address is replaced with the
      securely-solicited-node multicast address.

   o  The Nonce option is required in all Neighbor Discovery
      solicitations, and for all solicited advertisements.

   o  Proxy Neighbor Discovery is not supported in this specification
      (it will be specified in a future document).


5.1 Unspecified Source Address

   In SEND, the unspecified address is not used as the source address in
   Neighbor Solicitation, Neighbor Advertisement, Router Advertisement,
   or Redirect messages.  A Neighbor Solicitation sent as a part of
   Duplicate Address Detection uses the tentative address for which the
   Duplicate Address Detection is being run.

   The use of the unspecified address is avoided in Router
   Solicitations, if possible.  RFC 2461 requires that Router
   Solicitations sent from the unspecified address do not cause a
   modification in the Neighbor Cache.

5.2 Secure-Solicited-Node Multicast Address

   SEND defines the securely-solicited-node multicast addresses.  These
   addresses are of the form:

       FF02:0:0:0:0:1:FEXX:XXXX

   Like the solicited-node multicast address, this multicast address is
   computed as a function of a node's unicast and anycast addresses.
   The securely-solicited-node multicast address is formed by taking the
   low-order 24 bits of the address (unicast or anycast) and appending
   those bits to the prefix FF02:0:0:0:0:1:FE00::/104 resulting in a
   multicast address in the range FF02:0:0:0:0:1:FE00:0000 to



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   FF02:0:0:0:0:1:FEFF:FFFF.

   As discussed in Section 8.1, SEND uses the securely-solicited-node
   multicast address instead of the solicited-node multicast address
   when sending secured Neighbor Solicitations.  However, in order to
   allow for co-existence of secure and insecure Neighbor Discovery on
   the same link, SEND nodes will also send Duplicate Address Detection
   probes to the solicited-node multicast address (see Section 10).  The
   use of two different addresses is necessary in order to distinguish
   between these messages in the security policy database.

5.3 Nonce Option

   The purpose of the Nonce option is to ensure that an advertisement is
   a fresh response to a solicitation sent earlier by this same node.
   The format of the Nonce option is as described in the following:

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

   Where the fields are as follows:

   Type

      TBD <To be assigned by IANA> for Nonce.

   Length

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

   Nonce

      This field contains a random number selected by the sender of the
      solicitation message.  The length of the number MUST be at least 6
      bytes.







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5.4 Proxy Neighbor Discovery

   The Target Address in Neighbor Advertisement is required to be equal
   to the source address of the packet, except in the case of proxy
   Neighbor Discovery.  Proxy Neighbor Discovery is discussed in another
   specification.













































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6. Authorization Delegation Discovery

   Several protocols, including IPv6 Neighbor Discovery, allow a node to
   automatically configure itself based on information it learns shortly
   after connecting to a new link.  It is particularly easy for "rogue"
   routers to be configured, and it is particularly difficult for a
   network node to distinguish between valid and invalid sources of
   information when the node needs this information before communicating
   off-link.

   Since the newly-connected node likely can not communicate off-link,
   it can not be responsible for searching information to help validate
   the router; however, given a chain of appropriately signed
   certificates, it can check someone else's search results and conclude
   that a particular message comes from an authorized source.
   Similarly, the router, which is already connected to the network, can
   if necessary communicate off-link and construct the certificate
   chain.

   The Secure Neighbor Discovery protocol introduces two new ICMPv6
   messages that are used between hosts and routers to allow the client
   to learn the certificate chain with the assistance of the router.
   Where hosts have certificates from a trusted root, these messages MAY
   also optionally be used between hosts to acquire the peer's
   certificate chain.

   The Delegation Chain Solicitation message is sent by hosts when they
   wish to request the certificate chain between a router and the one of
   the hosts' trusted roots.  The Delegation Chain Advertisement message
   is sent as an answer to this message, or periodically to the All
   Nodes multicast address.  These messages are separate from the rest
   of the Neighbor Discovery in order to reduce the effect of the
   potentially voluminous certificate chain information to other
   messages.

   The Authorization Delegation Discovery process does not exclude other
   forms of discovering the certificate chains.  For instance, during
   fast movements mobile nodes may learn information - including the
   certificate chains - of the next router from the previous router.

6.1 Delegation Chain Solicitation Message Format

   Hosts send Delegation Chain Solicitations in order to prompt routers
   to generate Delegation Chain Advertisements quickly.







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      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Type      |     Code      |          Checksum             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          Identifier           |          Reserved             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Options ...
     +-+-+-+-+-+-+-+-+-+-+-+-

   IP Fields:

      Source Address

         An IP address assigned to the sending interface, or the
         unspecified address if no address is assigned to the sending
         interface.

      Destination Address

         Typically the all-routers multicast address, the
         securely-solicited-node multicast address (see Section 5.2, or
         the address of the hosts' default router.

      Hop Limit

         255

   ICMP Fields:

      Type

         TBD <To be assigned by IANA> for Delegation Chain Solicitation.

      Code

         0

      Checksum

         The ICMP checksum [8]..

      Identifier

         This 16 bit unsigned integer field acts as an identifier to
         help match advertisements to solicitations.  The Identifier
         field MUST NOT be zero.




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      Reserved

         This field is unused.  It MUST be initialized to zero by the
         sender and MUST be ignored by the receiver.

   Valid Options:

      Trusted Root

         One or more trusted roots that the client is willing to accept.

      Future versions of this protocol may define new option types.
      Receivers MUST silently ignore any options they do not recognize
      and continue processing the message.


6.2 Delegation Chain Advertisement Message Format

   Routers send out Delegation Chain Advertisement messages
   periodically, or in response to a Delegation Chain Solicitation.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Type      |     Code      |          Checksum             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          Identifier           |          Component            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                            Reserved                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Options ...
     +-+-+-+-+-+-+-+-+-+-+-+-

   IP Fields:

      Source Address

         MUST be a unicast address assigned to the interface from which
         this message is sent.

      Destination Address

         Either the securely-solicited-node multicast address of the
         receiver or the all-nodes multicast address.

      Hop Limit

         255



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   ICMP Fields:

      Type

         TBD <To be assigned by IANA> for Delegation Chain
         Advertisement.

      Code

         0

      Checksum

         The ICMP checksum [8]..

      Identifier

         This 16 bit unsigned integer field acts as an identifier to
         help match advertisements to solicitations.  The Identifier
         field MUST be zero for unsolicited advertisements and MUST NOT
         be zero for solicited advertisements.

      Component

         This is a 16 bit unsigned integer field used for informing the
         receiver which certificate is being sent, and how many are
         still left to be sent in the whole chain.  A single
         advertisement MUST be broken into separately sent components if
         there is more than one Certificate option, in order to avoid
         excessive fragmentation at the IP layer.  Unlike the
         fragmentation at the IP layer, individual components of an
         advertisement may be stored and taken in use before all the
         components have arrived; this makes them slightly more reliable
         and less prone to Denial-of-Service attacks.  The first message
         in a N-component advertisement has the Component field set to
         N-1, the second set to N-2, and so on.  Zero indicates that
         there are no more components coming in this advertisement.

      Reserved

         This field is unused.  It MUST be initialized to zero by the
         sender and MUST be ignored by the receiver.

   Valid Options:

      Certificate

         One certificate is provided in Certificate option, to establish



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         a (part of) certificate chain to a trusted root.

      Trusted Root

         Zero or more Trusted Root options may be included to help
         receivers decide which advertisements are useful for them.  If
         present, these options MUST appear in the first component of a
         multi-component advertisement.

      Future versions of this protocol may define new option types.
      Receivers MUST silently ignore any options they do not recognize
      and continue processing the message.


6.3 Trusted Root Option

   The format of the Trusted Root option is as described in the
   following:

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

   Where the fields are as follows:

   Type

      TBD <To be assigned by IANA> for Trusted Root.

   Length

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

   Name Type

      The type of the name included in the Name field.  This
      specification defines only one legal value for this field:

               1        FQDN







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   Name Length

      The length of the Name field, in bytes.  Octets beyond this length
      but within the length specified by the Length field are padding
      and MUST be set to zero by senders and ignored by receivers.

   Name

      When the Name Type field is set to 1, the Name field contains the
      Fully Qualified Domain Name of the trusted root, for example
      "trustroot.operator.com".


6.4 Certificate Option

   The format of the certificate option is as described in the
   following:

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Type      |    Length     |  Cert Type    |  Pad Length   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Certificate ...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Where the fields are as follows:

   Type

      TBD <To be assigned by IANA> for Certificate.

   Length

      The length of the option (including the Type, Length, Cert Type,
      Pad Length, and Certificate fields) in units of 8 octets.

   Cert Type

      The type of the certificate included in the Name field.  This
      specification defines only one legal value for this field:

               1        X.509 Certificate

   Pad Length

      The amount of padding beyond the end of the Certificate field but
      within the length specified by the Length field.  Padding MUST be



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      set to zero by senders and ignored by receivers.

   Certificate

      When the Cert Type field is set to 1, the Certificate field
      contains an X.509 certificate [16].


6.5 Router Authorization Certificate Format

   The certificate chain of a router terminates in a router
   authorization certificate that authorizes a specific IPv6 node as a
   router.  Because authorization chains are not common practice in the
   Internet at the time this specification is being written, the chain
   MUST consist of standard Public Key Certificates (PKC, in the sense
   of [11]) for identity from the trusted root shared with the host to
   the router.  This allows the host to anchor trust for the router's
   public key in the trusted root.  The last item in the chain is an
   Authorization Certificate (AC, in the sense of [12]) authorizing the
   router's right to route.  Stronger certification is necessary here
   than for CGAs because the right to route must be granted by an
   authorizing agency.  Future versions of this specification may
   include provision for full authorization certificate chains, should
   they become common practice.

   SEND nodes MUST support the RFC 3281 X.509 attribute certificate
   format [12] as the default format for router authorization
   certificates, and MAY support other formats.  Router authorization
   certificates MUST be signed by the network operator or other trusted
   third party whose PKC is above the router's PKC in the delegation
   chain.  Routers MAY advertise multiple ACs if the trust delegation
   obtains from different trust roots, and the authorized prefixes in
   those certificates MAY be disjoint.  A router SHOULD only advertise
   one AC corresponding to one trust root and all interfaces and
   prefixes covered by that trust root MUST be in the AC.

   In the attribute certificate, the GeneralName type MUST be either a
   dNSName or iPAddress for the router, unless otherwise specified by
   RFC 3281.  If the GeneralName attribute is a dNSName, it MUST be
   resolvable to a global unicast address assigned to the router.  If
   the GeneralName attribute is an iPAddress, it MUST be a global
   unicast address assigned to the router.  For purposes of facilitating
   renumbering, a dNSName SHOULD be used.  However, hosts MUST NOT use a
   dNSName or iPAddress for validating the certificate.  The router's
   public key hash, stored in the
   acinfo.holder.objectDigestInfo.objectDigest field of the certificate
   provides the definitive validation.  As explained in Section 9.2, the
   addresses from the certificate can be matched against the global



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   addresses claimed in the Router Advertisement.

6.5.1 Field Values

   acinfo.holder.entityName

      This field MAY contain one or several entityNames, of type dNSName
      or iPAddress, referring to global address(es) belonging to the
      router.

   acinfo.objectDigestInfo.digestedObjectType

      This field MUST be present and of type (1), publicKey.

   acinfo.holder.digestAlgorithm

      This field MUST indicate id-sha1 as indicated in RFC 3279 [10].

   acinfo.objectDigestInfo.objectDigest

      This field MUST be a SHA-1 digest over either a PKCS#1 [17] (RSA)
      or an RFC 3279 Section 2.3.2 representation [10] (DSA)
      representation of the router's public key.  If this digest does
      not match the digest of the router's public key from its PKC, a
      node MUST discard the certificate.

   acinfo.issuer.v2form.issuerName

      The field MUST contain the distinguished name from the PKC used to
      sign the router AC.

   acinfo.attrCertValidityPeriod

      A node MUST NOT accept a certificate if the validity period has
      ended or has not yet started.

   acinfo.attributes

      This field MUST contain a list of prefixes that the router is
      authorized to route, or the  unspecified  prefix  if  the  router
      is  allowed  to  route  any prefix.  The field has the following
      type:

         name: AuthorizedSubnetPrefix
          OID: {id-rcert}
       Syntax: iPAddress
       values: Multiple allowed
               Multiple prefix values are allowed.



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      The details of the above syntax are specified in Section 2.2.3.8
      of [14].

      If the router is authorized only to route specific prefixes, the
      ipAddress values consist of IPv6 addresses in standard RFC 3513
      [13] prefix format.  One iPAddress value appears for each prefix
      routed by the router.  If the router is authorized to route any
      prefix, a single ipAddress value appears with the value of the
      unspecified address.


6.6  Processing Rules for Routers

   Routers SHOULD possess a key pair and certificate from at least one
   certificate authority.

   A router MUST silently discard any received Delegation Chain
   Solicitation messages that do not satisfy all of the following
   validity checks:

   o  The IP Hop Limit field has a value of 255, i.e., the packet could
      not possibly have been forwarded by a router.

   o  If the message includes an IP Authentication Header, the message
      authenticates correctly.

   o  ICMP Checksum is valid.

   o  ICMP Code is 0.

   o  ICMP length (derived from the IP length) is 8 or more octets.

   o  Identifier field is non-zero.

   o  All included options have a length that is greater than zero.

   The contents of the Reserved field, and of any unrecognized options,
   MUST be ignored.  Future, backward-compatible changes to the protocol
   may specify the contents of the Reserved field or add new options;
   backward-incompatible changes may use different Code values.  The
   contents of any defined options that are not specified to be used
   with Router Solicitation messages MUST be ignored and the packet
   processed in the normal manner.  The only defined option that may
   appear is the Trusted Root option.  A solicitation that passes the
   validity checks is called a "valid solicitation".

   Routers MAY send unsolicited Delegation Chain Advertisements for



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   their trusted root.  When such advertisements are sent, their timing
   MUST follow the rules given for Router Advertisements in RFC 2461
   [6].  The only defined option that may appear is the Certificate
   option.  At least one such option MUST be present.  Router SHOULD
   also include at least one Trusted Root option to indicate the trusted
   root on which the Certificate is based.

   In addition to sending periodic, unsolicited advertisements, a router
   sends advertisements in response to valid solicitations received on
   an advertising interface.  A router MUST send the response to the
   all-nodes multicast address, if the source address in the
   solicitation was the unspecified address.  If the source address was
   a unicast address, the router MUST send the response to the
   securely-solicited-node multicast address corresponding to the source
   address.

   In a solicited advertisement, the router SHOULD include suitable
   Certificate options so that a delegation chain to the solicited root
   can be established.  The root is identified by the FQDN from the
   Trusted Root option being equal to an FQDN in the AltSubjectName
   field of the root's certificate.  The router SHOULD include the
   Trusted Root option(s) in the advertisement for which the delegation
   chain was found.

   If the router is unable to find a chain to the requested root, it
   SHOULD send an advertisement without any certificates.  In this case
   the router SHOULD include the Trusted Root options which were
   solicited.

   Rate limitation of Delegation Chain Advertisements is performed as
   specified for Router Advertisements in RFC 2461 [6].

6.7  Processing Rules for Hosts

   Hosts SHOULD possess the certificate of at least one certificate
   authority, and MAY possess their own key pair and certificate from
   this authority.

   A host MUST silently discard any received Delegation Chain
   Advertisement messages that do not satisfy all of the following
   validity checks:

   o  IP Source Address is a unicast address.  Note that routers may use
      multiple addresses, so this address not sufficient for the unique
      identification of routers.

   o  IP Destination Address is either the all-nodes multicast address
      or the securely-solicited-node multicast address corresponding to



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      one of the unicast addresses assigned to the host.

   o  The IP Hop Limit field has a value of 255, i.e., the packet could
      not possibly have been forwarded by a router.

   o  If the message includes an IP Authentication Header, the message
      authenticates correctly.

   o  ICMP Checksum is valid.

   o  ICMP Code is 0.

   o  ICMP length (derived from the IP length) is 16 or more octets.

   o  All included options have a length that is greater than zero.

   The contents of the Reserved field, and of any unrecognized options,
   MUST be ignored.  Future, backward-compatible changes to the protocol
   may specify the contents of the Reserved field or add new options;
   backward-incompatible changes may use different Code values.  The
   contents of any defined options that are not specified to be used
   with Delegation Chain Advertisement messages MUST be ignored and the
   packet processed in the normal manner.  The only defined option that
   may appear is the Certificate option.  An advertisement that passes
   the validity checks is called a "valid advertisement".

   Hosts SHOULD store all certificates retrieved in Delegation Chain
   Advertisements for use in subsequent verification of Neighbor
   Discovery messages.  Note that it may be useful to cache this
   information and implied verification results for use over multiple
   attachments to the network.  In order to use an advertisement for the
   verification of a specific Neighbor Discovery message, the host
   matches the key hash in acinfo.Holder.objectDigestInfo to the public
   key carried in the IPsec AH Authentication Data field.

   When an interface becomes enabled, a host may be unwilling to wait
   for the next unsolicited Delegation Chain Advertisement.  To obtain
   such advertisements quickly, a host SHOULD transmit up to
   MAX_RTR_SOLICITATIONS Delegation Chain Solicitation messages each
   separated by at least RTR_SOLICITATION_INTERVAL seconds.  Delegation
   Chain Solicitations SHOULD be sent after any of the following events:

   o  The interface is initialized at system startup time.

   o  The interface is reinitialized after a temporary interface failure
      or after being temporarily disabled by system management.

   o  The system changes from being a router to being a host, by having



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      its IP forwarding capability turned off by system management.

   o  The host attaches to a link for the first time.

   o  A movement has been indicated by lower layers or has been inferred
      from changed information in a Router Advertisement.

   o  The host re-attaches to a link after being detached for some time.

   o  A Router Advertisement has been received with a public key that is
      not stored in the hosts' cache of certificates, or there is no
      authorization delegation chain to the host's trusted root.

   Delegation Chain Solicitations MUST NOT be sent if the host has a
   currently valid certificate chain for the router to a trusted root,
   including the Attribute Certificate for the desired router (or host).

   A host MUST send Delegation Chain Solicitations either to the
   All-Routers multicast address, if it has not selected a default
   router yet, or to the default router's IP address if it has already
   been selected.

   If two hosts communicate with the solicitations and advertisements,
   the solicitations MUST be sent to the securely-solicited-node
   multicast address of the receiver.  The advertisements MUST be sent
   as specified above for routers.

   Delegation Chain Solicitations SHOULD be rate limited and timed
   similarly with Router Solicitations, as specified in RFC 2461 [6].

   When processing a possible advertisement sent as a response to a
   solicitation, the host MAY prefer to process first those
   advertisements with the same Identifier field value as in the
   solicitation.  This makes Denial-of-Service attacks against the
   mechanism harder (see Section 13.3).
















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7. IPsec Extensions

   In order to use IPsec in securing Neighbor and Router Discovery some
   extensions have been specified in this document.  These include a new
   transform suitable for the use of public keys and/or CGAs, a
   timestamp mechanism suitable for replay protection in a multicast
   environment, and some extensions to security association and security
   policy databases.

   These changes are related to the proposed new transform and the
   reserved SPI number, and do not represent a fundamental change to the
   IPsec architecture.  Some of the changes, such as the treatment of
   destination addresses, are also being proposed as a part of the
   revision of the IPsec standards.

7.1 The AH_RSA_Sig Transform

   The AH_RSA_Sig transform specifies how AH can be used without a
   symmetric key.  This transform introduces the use of a new reserved
   SPI number and a new format for the Authentication Data field in AH.

   AH_RSA_Sig MUST NOT be negotiated in IKE.  For consistency it has an
   IPsec DOI [4] Transform ID TBD <To Be Assigned by IANA>, however.

7.1.1 Reserved SPI Number

   The AH_RSA_Sig MUST be only be used with the reserved SPI number TBD
   <To Be Assigned by IANA>.

7.1.2 Authentication Data Format

   The format of the Authentication Data field in AH depends on the
   chosen transform.  For the AH_RSA_Sig transform, the format is as
   follows:

















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     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     +                          Timestamp                            +
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     .                                                               .
     .                        Key Information                        .
     .                                                               .
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     .                                                               .
     .              Digital Signature (remaining bytes)              .
     .                                                               .
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The meaning of the fields is described below:

   Timestamp

      This 64 bit unsigned integer field contains a timestamp used for
      replay protection (the Sequence Number field in AH is not used for
      AH_RSA_Sig).  The use of this field is discussed in Section 7.1.4.

   Key Information

      This variable length field contains the public key of the sender.
      It also may contain some other additional information which is
      necessary when CGA is used.

      The contents of the Key Information field are represented as ASN.1
      DER-encoded data item of the following type:

        SendKeyInformation ::= SEQUENCE {
          cgaParameters  CGAParameters OPTIONAL,
          signerInfo     SubjectPublicKeyInfo OPTIONAL }

        CGAParameters ::= SEQUENCE {
          publicKey      SubjectPublicKeyInfo,
          auxParameters  CGAAuxParameters OPTIONAL }

      (The normative definition of the type CGAParameters is in in
      [27]).

      At least one or both fields in SendKeyInformation MUST be present.
      The packet MUST be silently discarded if both are missing.  The



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      verification of the CGA is based on the contents of the
      cgaParameters field.  The verification of the Digital Signature
      field is based on the contents of the signerInfo field if it is
      present.  Otherwise, the verification is based on the publicKey
      field in the cgaParameters field.

      This specification requires that if both cgaParameters and
      signerInfo fields are present, then the public keys in them MUST
      be the same, and packets received with two different keys MUST be
      silently discarded.  Note that a future extension may provide a
      mechanism which allows the owner of an address and the signer to
      be different parties.

      The length of the Key Information field is determined by the ASN.1
      encoding.

   Digital Signature

      This variable length field contains the signature made using the
      sender's private key, over the the whole packet as defined by the
      usual AH rules [3].  The signature is made using the RSA algorithm
      and MUST be encoded as private key encryption in PKCS #1 format
      [17].

      The length of this field is determined by the PKCS #1 encoding.


7.1.3 AH_RSA_Sig Security Associations

   Incoming security associations that specify the use of AH_RSA_Sig
   transform MUST record the following additional configuration
   information:

   CGA flag

      A flag that indicates whether or not the CGA property must be
      verified.

   router authority

      Whether or not router authority must be verified as described in
      Section 6.5.

   root

      The public key of the trusted root, if authorization delegation is
      in use.




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   minbits

      The minimum acceptable key length for peer public keys (and any
      intermediaries between the trusted root and the peer).  The
      default SHOULD be 768 bits.  Implementations MAY also set an upper
      limit in order to limit the amount of computation they need to
      perform when verifying packets that use these security
      associations.

   minSec

      The minimum acceptable Sec value, if CGA verification is required
      (see Section 2 in [27].

   Outgoing security associations MUST also record the following
   additional information:

   keypair

      A public-private key pair.  If authorization delegation is in use,
      there must exist a delegation chain from a trusted root to this
      key pair.

   CGA flag

      A flag that indicates whether or not the CGA is used.

   CGA parameters

      Optionally any information required to construct CGAs, including
      the used Sec value and nonce, and the CGA itself.


7.1.4 Replay Protection

   For AH_RSA_Sig, the Sequence Number field in AH MUST be set to zero
   by the sender and ignored by receivers.

   If anti-replay has been enabled in the security association, senders
   MUST set the Timestamp field to the current time.  The format is 64
   bits, and the contents are the number of milliseconds since January
   1, 1970 00:00 UTC.

   If anti-replay has been enabled, receivers MUST be configured with an
   allowed Delta value and maintain a cache of messages received within
   this time period from each specific source address.  Receivers MUST
   then check the Timestamp field as follows:




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   o  A packet with a Timestamp field value beyond the current time plus
      or minus the allowed Delta value MUST be silently discarded.

      Recommended default value for the allowed Delta is 3,600 seconds.

   o  A packet accepted according to the above rule MUST be checked for
      uniqueness within the cache of received messages from the given
      source address.  A packet that has already been seen from the same
      source with the same Timestamp field value MUST be silently
      discard.

   o  A packet that passes both of the above tests MUST be registered in
      the cache for the given source address.

   o  If the cache becomes full, the receiver SHOULD temporarily reduce
      the Delta value for that source address so that all messages
      within that value can still be stored.

   Note that timestamps are not necessary for replay protection in
   solicited advertisements, but must be included in the messages.

7.1.5 Processing Rules for Senders

   A node sending a packet using the AH_RSA_Sig transform MUST construct
   the packet as follows:

   o  The Next Header, Payload Len, and Reserved fields are set as
      described in RFC 2402.

   o  The Security Parameters Index is set to the value specified in
      Section 7.1.1.

   o  The Sequence Number field is set to 0.

   o  The Timestamp field is set as described in Section 7.1.4.

   o  The Key Information field in the Authentication Data field is set
      to the SendKeyInformation structure according to the rules in
      Section 7.1.2 and [27].  The used public key is the one stored in
      the security association.

   o  The packet, in the form defined for AH's coverage, is signed using
      the private key in the security association, and the resulting
      PCKS #1 signature is put to the Digital Signature field.  One of
      the keys from the Key Information field is used for this purpose,
      as described in Section 7.1.2.

   o  Additionally, if the use of CGA has been specified for the



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      security association, the source address of the packet MUST be
      constructed as specified in [27].


7.1.6 Processing Rules for Receivers

   A packet received on a security association employing AH_RSA_Sig
   transform MUST be checked as follows:

   o  Next Header and Payload Len fields are valid as specified in RFC
      2402.

   o  The SPI field is equal to the value defined in Section 7.1.1.

   o  The Timestamp field is verified as described in Section 7.1.4.

   o  The Key Information and Digital Signature fields have correct
      encoding, and do not exceed the length of the Authentication Data
      field.

   o  If the use of CGA has been specified in the security association,
      we additionally require the receiving node to verify the source
      address of the packet using the algorithm described in Section 5
      of [27].  The inputs for the algorithm are the contents of the
      CGAParameters structure from the Key Information field, the source
      address of the packet, and the minimum acceptable Sec value from
      the security association.  If the CGA verification is successful,
      the recipient proceeds with the cryptographically more time
      consuming check of the AH signature.

      Note that a receiver which does not support CGA or has not
      specified its use in its security associations can still verify
      packets using trusted roots, even if CGA had been used on a
      packet.  The CGA property of the address is simply left untested.

   o  The Digital Signature verification shows that it has been
      calculated as specified in the previous sections.

   o  If the use of a trusted root has been configured for the security
      association, a valid authorization delegation chain is known
      between the receiver's trusted root and the sender's public key.

      Note that the receiver may verify just the CGA property of a
      packet, even if the sender has used a trusted root as well.

   Packets that do not pass all the above tests MUST be silently
   discarded.




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7.2 Other IPsec Extensions

7.2.1 Destination Agnostic Security Associations

   In order to allow the same security association to be used when the
   the node sends packets to different peers using the same addresses,
   an extension must be provided to the RFC 2401 rules on how security
   associations are identified.  This change is particularly important,
   for instance, when routers use the same keys and security association
   to send Router Advertisements for up to number of prefixes x 2^64
   hosts on an interface.

   This extension is mandatory for all nodes that support the AH_RSA_Sig
   transform.  Security associations that use the SPI value specified in
   Section 7.1.1 MUST be identified solely by the SPI and protocol
   numbers, not by the destination IP address.

   Note that this extension can be supported without implementation
   modifications where the proposed revisions of the IPsec standards are
   in use [26].

7.2.2 ICMP Type Specific Selectors

   In order to allow finer granularity of protection for various ICMPv6
   messages, it is necessary to extend the security policy database and
   security association selectors with the capability to distinguish
   between different messages.

   All nodes that support the AH_RSA_Sig transform MUST be capable of
   using ICMP and ICMPv6 Type field as a selector.

   Note that this can be achieved in an implementation by using the port
   number field to contain the ICMP type if the protocol field is ICMP.


















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8. Securing Neighbor Discovery with SEND

   This section describes how to use IPsec and the mechanisms from [27],
   Section 6, Section 7 in order to provide security for Neighbor
   Discovery.

8.1 Neighbor Solicitation Messages

   All Neighbor Solicitation messages are protected with AH_RSA_Sig.

8.1.1 Sending Secure Neighbor Solicitations

   Secure Neighbor Solicitation messages are sent as described in RFC
   2461 and 2462, with the additional requirements listed in the
   following.

   All Neighbor Solicitation messages sent MUST be protected with IPsec,
   using the AH_RSA_Sig transform.  The security associations used for
   this MUST be configured with the sender's key pair, optionally
   setting the CGA flag and including additional CGA parameter
   information.

   The source address of the message MUST NOT be the unspecified
   address.  A Neighbor Solicitation sent as a part of Duplicate Address
   Detection MUST use as a source address the tentative address for
   which the Duplicate Address Detection is being run.

   In SEND, Neighbor Solicitations MUST be sent either to the target
   address or to the securely-solicited-node multicast address
   corresponding to the target address.  When an interface is
   initialized, a node MUST join securely-solicited-node multicast
   address corresponding to each of the IP addresses assigned to the
   interface.  The set of addresses assigned to an interface may change
   over time.  New addresses might be added and old addresses might be
   removed [7].  In such cases the node MUST join and leave the
   securely-solicited-node multicast address corresponding to the new
   and old addresses, respectively.  Note that multiple unicast
   addresses may map into the same solicited-node multicast address; a
   node MUST NOT leave the securely-solicited-node multicast group until
   all assigned addresses corresponding to that multicast address have
   been removed.

   The Nonce option MUST be included in all messages.

8.1.2 Receiving Secure Neighbor Solicitations

   Received Neighbor Solicitation messages are processed as described in
   RFC 2461 and 2462, with the additional SEND-related requirements



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   listed in the following.

   Neighbor Solicitation messages received without an IPsec AH header
   and the AH_RSA_Sig transform MUST be silently discarded.  The
   security associations used for this MUST be configured with the
   expected authorization mechanism (CGA or trusted root), the minimum
   allowable key size, and optionally with the information related to
   the trusted root and the acceptable minSec value.

   If source address of the Neighbor Solicitation message is the
   unspecified address, the message MUST be silently discarded.

   Neighbor Solicitations received without the Nonce option MUST be
   silently discarded.

8.2 Neighbor Advertisement Messages

   All Neighbor Advertisement messages are protected with AH_RSA_Sig.

8.2.1 Sending Secure Neighbor Advertisements

   Secure Neighbor Advertisement messages are sent as described in RFC
   2461 and 2462, with the additional requirements listed in the
   following.

   All Neighbor Advertisement messages sent MUST be protected with
   IPsec, using the AH_RSA_Sig transform.  The security associations
   used for this MUST be configured with the sender's key pair,
   optionally setting the CGA flag and including additional CGA
   parameter information.

   Neighbor Advertisements sent in response to a Neighbor Solicitation
   MUST contain a copy of the Nonce option included in the solicitation.

   The source address of the message MUST NOT be the unspecified
   address.

8.2.2 Receiving Secure Neighbor Advertisements

   Received Neighbor Advertisement messages are processed as described
   in RFC 2461 and 2462, with the additional SEND-related requirements
   listed in the following.

   Neighbor Advertisement messages received without an IPsec AH header
   and the AH_RSA_Sig transform MUST be silently discarded.  The
   security associations used for this MUST be configured with the
   expected authorization mechanism (CGA or trusted root), the minimum
   allowable key size, and optionally with the information related to



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   the trusted root and the acceptable minSec value.

   Received Neighbor Advertisements sent to a unicast destination
   address without a Nonce option MUST be silently discarded.

   If source address of the Neighbor Advertisement message is the
   unspecified address, the message MUST be silently discarded.

8.3 Other Requirements

   Upon receiving a message for which the receiver has no certificate
   chain to a trusted root, the receiver MAY use Authorization
   Delegation Discovery to learn the certificate chain of the peer.

   Hosts that use stateless address autoconfiguration MUST generate a
   new CGA as specified in Section 4 of [27] for each new
   autoconfiguration run.

   It is outside the scope of this specification to describe the use of
   trusted root authorization between hosts with dynamically changing
   addresses.  Such dynamically changing addresses may be the result of
   stateful or stateless address autoconfiguration or through the use of
   RFC 3041 [9].  If the CGA method is not used, hosts would be required
   to exchange certificate chains that terminate in a certificate
   authorizing a host to use an IP address having a particular interface
   identifier.  This specification does not specify the format of such
   certificates, since there are currently a few cases where such
   certificates are required by the link layer and it is up to the link
   layer to provide certification for the interface identifier.  This
   may be the subject of a future specification.  It is also outside the
   scope of this specification to describe how stateful address
   autoconfiguration works with the CGA method.

8.4 Configuration

   This section shows example security policy and security associations
   database entries for the protection of Neighbor Solicitation and
   Advertisement messages.  The following table summarizes the inbound
   security policy data base along with the inbound security
   associations:











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   Policy entries:

    +------------------------------------------------------------------+
    |    Proto: Type   |    Source    |    Destination   |  Treatment  |
    +------------------------------------------------------------------+
    |    ICMPv6: NS    |       *      |       own        |  SA = NS_In |
    +------------------------------------------------------------------+
    |    ICMPv6: NS    |       *      |  sec-sol-node MC |  SA = NS_In |
    +------------------------------------------------------------------+
    |    ICMPv6: NA    |       *      |       own        |  SA = NA_In |
    +------------------------------------------------------------------+
    |    ICMPv6: NA    |       *      |   all-nodes MC   |  SA = NA_In |
    +------------------------------------------------------------------+

   Security associations:

    +------------------------------------------------------------------+
    |    Name    |  Direction  |     SPI     | Proto |    Transform    |
    +------------------------------------------------------------------+
    |    NS_In   |   Inbound   | To be       |   AH  |    AH_RSA_Sig   |
    |            |             | assigned    |       |CGA flag = yes/no|
    |            |             | by IANA     |       | root = ... (opt)|
    +------------------------------------------------------------------+
    |    NA_In   |   Inbound   | To be       |   AH  |    AH_RSA_Sig   |
    |            |             | assigned    |       |CGA flag = yes/no|
    |            |             | by IANA     |       | root = ... (opt)|
    +------------------------------------------------------------------+


   The following table summarizes outbound security policy database:





















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   Policy entries:

    +------------------------------------------------------------------+
    |    Proto: Type   |    Source    |    Destination   |  Treatment  |
    +------------------------------------------------------------------+
    |    ICMPv6: NS    |      own     |         *        | SA = NS_Out |
    +------------------------------------------------------------------+
    |    ICMPv6: NA    |      own     |         *        | SA = NA_Out |
    +------------------------------------------------------------------+

   Security associations:

    +------------------------------------------------------------------+
    |    Name    |  Direction  |     SPI     | Proto |    Transform    |
    +------------------------------------------------------------------+
    |    NS_Out  |  Outbound   | To be       |   AH  |    AH_RSA_Sig   |
    |            |             | assigned    |       | key pair = ...  |
    |            |             | by IANA     |       | CGA = yes/no    |
    |            |             |             |       | CGA params = ...|
    |            |             |             |       | root = ... (opt)|
    +------------------------------------------------------------------+
    |    NA_Out  |  Outbound   | To be       |   AH  |    AH_RSA_Sig   |
    |            |             | assigned    |       | key pair = ...  |
    |            |             | by IANA     |       | CGA = yes/no    |
    |            |             |             |       | CGA params = ...|
    |            |             |             |       | root = ... (opt)|
    +------------------------------------------------------------------+
























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9. Securing Router Discovery with SEND

   This section describes how to use IPsec and the mechanisms from [27],
   Section 6, Section 7 in order to provide security for Router
   Discovery.

9.1 Router Solicitation Messages

   All Router Solicitation messages are protected with AH_RSA_Sig.

9.1.1 Sending Secure Router Solicitations

   Secure Router Solicitation messages are sent as described in RFC
   2461, with the additional requirements listed in the following.

   All Router Solicitation messages sent MUST be protected with IPsec,
   using the AH_RSA_Sig transform.  The security associations used for
   this MUST be configured with the sender's key pair, optionally
   setting the CGA flag and including additional CGA parameter
   information.

   Hosts SHOULD avoid the use of the unspecified address as the source
   address in a Router Solicitation message, if other addresses are
   available.

   The Nonce option MUST be included in all messages.

9.1.2 Receiving Secure Router Solicitations

   Received Router Solicitation messages are processed as described in
   RFC 2461, with the additional SEND-related requirements listed in the
   following.

   Router Solicitation messages received without an IPsec AH header and
   the AH_RSA_Sig transform MUST be silently discarded.  The security
   associations used for this MUST be configured with the expected
   authorization mechanism (CGA or trusted root), the minimum allowable
   key size, and optionally with the information related to the trusted
   root and the acceptable minSec value.

   Router Solicitations received without the Nonce option MUST be
   silently discarded.

9.2 Router Advertisement Messages

   All Router Advertisement messages are protected with AH_RSA_Sig.





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9.2.1 Sending Secure Router Advertisements

   Secure Router Advertisement messages are sent as described in RFC
   2461, with the additional requirements listed in the following.

   All Router Advertisement messages sent MUST be protected with IPsec,
   using the AH_RSA_Sig transform.  The security associations used for
   this MUST be configured with the sender's key pair, optionally
   setting the CGA flag and including additional CGA parameter
   information.

   Router Advertisements sent in response to a Router Solicitation MUST
   contain a copy of the Nonce option included in the solicitation.

   The source address of the message MUST NOT be the unspecified
   address.

9.2.2 Receiving Secure Router Advertisements

   Received Router Advertisement messages are processed as described in
   RFC 2461, with the additional SEND-related requirements listed in the
   following.

   Router Advertisement messages received without an IPsec AH header and
   the AH_RSA_Sig transform MUST be silently discarded.  The security
   associations used for this MUST be configured with the expected
   authorization mechanism (CGA or trusted root), the minimum allowable
   key size, and optionally with the information related to the trusted
   root and the acceptable minSec value.

   Received Router Advertisements sent to a unicast destination address
   without a Nonce option MUST be silently discarded.

   If source address of the Router Advertisement message is the
   unspecified address, the message MUST be silently discarded.

9.3 Redirect Messages

   All Redirect messages are protected with AH_RSA_Sig.

9.3.1 Sending Redirects

   Secure Redirect messages are sent as described in RFC 2461, with the
   additional requirements listed in the following.

   All Redirect messages sent MUST be protected with IPsec, using the
   AH_RSA_Sig transform.  The security associations used for this MUST
   be configured with the sender's key pair, optionally setting the CGA



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   flag and including additional CGA parameter information.

   The source address of the Redirect message MUST NOT be the
   unspecified address.

9.3.2 Receiving Redirects

   Received Redirect messages are processed as described in RFC 2461,
   with the additional SEND-related requirements listed in the
   following.

   Redirect messages received without an IPsec AH header and the
   AH_RSA_Sig transform MUST be silently discarded.  The security
   associations used for this MUST be configured with the expected
   authorization mechanism (CGA or trusted root), the minimum allowable
   key size, and optionally with the information related to the trusted
   root and the acceptable minSec value.

   If only CGA-based security associations are used, hosts MUST follow
   the rules defined below when receiving Redirect messages:

   1.  The Redirect message MUST be protected as discussed above.

   2.  The receiver MUST verify that the Redirect message comes from an
       IP address to which the host may have earlier sent the packet
       that the Redirect message now partially returns.  That is, the
       source address of the Redirect message must be the default router
       for traffic sent to the destination of the returned packet.  If
       this is not the case, the message MUST be silently discarded.

       This step prevents a bogus router from sending a Redirect message
       when the host is not using the bogus router as a default router.

   If source address of the Redirect message is the unspecified address,
   the message MUST be silently discarded.

9.4 Other Requirements

   The certificate for a router MAY specify the global IP address(es) of
   the router.  If so, only these addresses can appear in advertisements
   where the Router Address (R) bit [15] is set.  All hosts MUST have
   the certificate of a trusted root.

   Hosts SHOULD use Authorization Delegation Discovery to learn the
   certificate chain of their default router or peer host, as explained
   in Section 6.  The receipt of a protected Router Advertisement
   message for which no router Authorization Certificate and certificate
   chain is available triggers Authorization Delegation Discovery.



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9.5 Configuration

   This section shows example security policy and security associations
   database entries for the protection of Redirect, Router Solicitation
   and Advertisement messages.  The following table summarizes the
   inbound security policy data base along with the inbound security
   associations:


   Policy entries:

    +------------------------------------------------------------------+
    |    Proto: Type   |    Source    |    Destination   |  Treatment  |
    +------------------------------------------------------------------+
    |    ICMPv6: RS    |       *      |       own        |  SA = RS_In |
    +------------------------------------------------------------------+
    |    ICMPv6: RS    |       *      |  all-routers MC  |  SA = RS_In |
    +------------------------------------------------------------------+
    |    ICMPv6: RA    |       *      |       own        |  SA = RA_In |
    +------------------------------------------------------------------+
    |    ICMPv6: RA    |       *      |   all-nodes MC   |  SA = RA_In |
    +------------------------------------------------------------------+
    | ICMPv6: REDIRECT |       *      |       own        |  SA = RE_In |
    +------------------------------------------------------------------+

   Security associations:

    +------------------------------------------------------------------+
    |    Name    |  Direction  |     SPI     | Proto |    Transform    |
    +------------------------------------------------------------------+
    |    RS_In   |   Inbound   | To be       |   AH  |    AH_RSA_Sig   |
    |            |             | assigned    |       |CGA flag = yes/no|
    |            |             | by IANA     |       | root = ... (opt)|
    +------------------------------------------------------------------+
    |    RA_In   |   Inbound   | To be       |   AH  |    AH_RSA_Sig   |
    |            |             | assigned    |       |CGA flag = yes/no|
    |            |             | by IANA     |       | root = ... (opt)|
    +------------------------------------------------------------------+
    |    RE_In   |   Inbound   | To be       |   AH  |    AH_RSA_Sig   |
    |            |             | assigned    |       |CGA flag = yes/no|
    |            |             | by IANA     |       | root = ... (opt)|
    +------------------------------------------------------------------+


   The following table summarizes outbound security policy database.
   The Router Advertisement and Redirect entries are only present in
   routers.




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   Policy entries:

    +------------------------------------------------------------------+
    |    Proto: Type   |    Source    |    Destination   |  Treatment  |
    +------------------------------------------------------------------+
    |    ICMPv6: RS    |      own     |         *        | SA = RS_Out |
    +------------------------------------------------------------------+
    |    ICMPv6: RA    |      own     |         *        | SA = RA_Out |
    +------------------------------------------------------------------+
    | ICMPv6: REDIRECT |      own     |         *        | SA = RE_Out |
    +------------------------------------------------------------------+

   Security associations:

    +------------------------------------------------------------------+
    |    Name    |  Direction  |     SPI     | Proto |    Transform    |
    +------------------------------------------------------------------+
    |    RS_Out  |  Outbound   | To be       |   AH  |    AH_RSA_Sig   |
    |            |             | assigned    |       | key pair = ...  |
    |            |             | by IANA     |       | CGA = yes/no    |
    |            |             |             |       | CGA params = ...|
    |            |             |             |       | root = ... (opt)|
    +------------------------------------------------------------------+
    |    RA_Out  |  Outbound   | To be       |   AH  |    AH_RSA_Sig   |
    |            |             | assigned    |       | key pair = ...  |
    |            |             | by IANA     |       | CGA = yes/no    |
    |            |             |             |       | CGA params = ...|
    |            |             |             |       | root = ... (opt)|
    +------------------------------------------------------------------+
    |    RE_Out  |  Outbound   | To be       |   AH  |    AH_RSA_Sig   |
    |            |             | assigned    |       | key pair = ...  |
    |            |             | by IANA     |       | CGA = yes/no    |
    |            |             |             |       | CGA params = ...|
    |            |             |             |       | root = ... (opt)|
    +------------------------------------------------------------------+
















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10. Co-Existence of SEND and ND

   During the transition to secure links or as a policy consideration,
   network operators may want to run a particular link with a mixture of
   secure and insecure nodes.  In such a case, the link is required to
   operate as two separate logical links, and packets between a secure
   and insecure node always go through the router.

   Routers configured for SEND advertise two sets of globally routable
   prefixes: one set for SEND nodes and one set for nodes that implement
   insecure Neighbor Discovery.  The insecure nodes will ignore the
   advertisements sent using SEND, as the original Neighbor Discovery
   specifications require silently discarding packets if they contain an
   AH header that they can not verify.

10.1 Behavior Rules

   The following considerations apply to all nodes:

   o  Nodes configured for SEND MUST listen to the solicited-node
      multicast address in addition to the securely-solicited-node
      multicast address.  The messages received on the solicited-node
      multicast address are unprotected, but the SEND node MUST respond
      to them as follows.

      Upon seeing a Neighbor Solicitation for an address which is
      currently assigned to its own interface, the SEND node sends as a
      response a Neighbor Solicitation with the following contents:

      *  Source address is the unspecified address.

      *  Destination address is the solicited-node multicast address of
         the target address.

      *  Target address is copied from the original Neighbor
         Solicitation.

      *  No AH header is included.

      *  The Nonce option is included in the Neighbor Solicitation.


      As a result of seeing this Neighbor Solicitation, the sender of
      the original Neighbor Solicitation concludes that it is attempting
      to use an address which another node is also attempting to use.
      This prevents the non-SEND node from using an address already in
      use by a SEND node.




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      On some interface types, multicast messages can loop back to the
      sending node.  In order to prevent the SEND node from responding
      to itself, the above solicitations MUST NOT be sent when the
      original Neighbor Solicitation included the Nonce option.

      Note that while SEND nodes attempt to ensure that non-SEND nodes
      use addresses not assigned to the SEND nodes, the reverse is not
      true: SEND nodes do not avoid the use of an address which is
      already claimed to be in use by a non-SEND node.  This is
      necessary in order to prevent a denial-of-service attack on secure
      Duplicate Address Detection.

   o  Similarly, when performing Duplicate Address Detection, nodes
      configured for SEND MUST send the Neighbor Solicitations both to
      the securely-solicited-node multicast address with protection, and
      to the solicited-node multicast address without protection.

   The following considerations apply to hosts:

   o  Hosts configured for SEND MUST use SEND for all of their
      addresses, including link local addresses.

   o  Hosts configured for SEND MUST validate all Router Advertisements
      with the protocol described in Section 8.  Note that this includes
      discarding advertisements received without a valid IPsec AH
      header, thus making insecure prefixes invisible to them.

   o  Hosts configured for SEND MUST secure and validate all Neighbor
      Advertisements with the protocol described in Section 8.  Note
      that this includes discarding advertisements received without a
      valid IPsec AH header.

   The following considerations apply to routers:

   o  Routers MUST send two sets of Router Advertisements.  The
      advertisements containing the secure prefixes MUST be secured with
      the protocol described in Section 9.  The advertisements
      containing the insecure prefixes MUST be sent without AH header.

   o  Routers MUST assign different addresses for their secure and
      insecure communications, including their link-local addresses.
      Secure Router and Neighbor Advertisements MUST use a source
      address that satisfies the security properties outlined in Section
      9.  Unless this address is link-local, it MUST belong to one of
      the advertised secure prefixes.  Similarly, source addresses for
      insecure advertisements MUST belong to one of the advertised
      insecure prefixes, unless the address is link-local.




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   o  Routers MUST refrain from sending Redirects to a SEND-secured node
      with the Destination Address field set to an address for an
      insecure node.  Similarly, routers MUST refrain from sending
      Redirects to a insecure node with the Destination Address field
      set to an address for a SEND-secured node

   The above rules require secure nodes to ignore all insecure Neighbor
   and Router Discovery messages, and all insecure nodes to ignore all
   SEND-secured messages.  This implies that the secure and insecure
   nodes will not be able to discover each other, or even realize that
   the other prefixes are on-link.  Thus, these hosts will request the
   router to route packets destined to a host in the other group.  The
   rules regarding Redirect messages above have been provided to ensure
   that the router performs its routing task and does not instruct the
   hosts to communicate directly.

   One effect of this is that secure hosts can not communicate with
   insecure hosts using link-local addresses, and vice versa.

   The security policy or security association database entries are
   needed for insecure nodes as far as Neighbor Discovery is concerned.
   SEND-secured nodes have the usual entries required by SEND.

10.2 Configuration

   This section presents the security policy and security association
   data base configuration required for the co-existence of SEND and
   non-SEND hosts.  The following table summarizes the inbound
   configuration on a SEND node:


   Policy entries:

    +------------------------------------------------------------------+
    |    Proto: Type   |    Source    |    Destination   |  Treatment  |
    +------------------------------------------------------------------+
    |    ICMPv6: NS    |       *      |       own        |  SA = NS_In |
    +------------------------------------------------------------------+
    |    ICMPv6: NS    |  unspecified | solicited-node MC|     pass    |
    +------------------------------------------------------------------+
    |    ICMPv6: NS    |       *      |  sec.sol-node MC |  SA = NS_In |
    +------------------------------------------------------------------+
    |    ICMPv6: NA    |       *      |       own        |  SA = NA_In |
    +------------------------------------------------------------------+
    |    ICMPv6: NA    |       *      |   all-nodes MC   |  SA = NA_In |
    +------------------------------------------------------------------+
    |    ICMPv6: RS    |       *      |       own        |  SA = RS_In |
    +------------------------------------------------------------------+



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    |    ICMPv6: RS    |       *      |  all-routers MC  |  SA = RS_In |
    +------------------------------------------------------------------+
    |    ICMPv6: RA    |       *      |       own        |  SA = RA_In |
    +------------------------------------------------------------------+
    |    ICMPv6: RA    |       *      |   all-nodes MC   |  SA = RA_In |
    +------------------------------------------------------------------+
    | ICMPv6: REDIRECT |       *      |       own        |  SA = RE_In |
    +------------------------------------------------------------------+

   Security associations:

    +------------------------------------------------------------------+
    |    Name    |  Direction  |     SPI     | Proto |    Transform    |
    +------------------------------------------------------------------+
    |    NS_In   |   Inbound   | To be       |   AH  |    AH_RSA_Sig   |
    |            |             | assigned    |       |CGA flag = yes/no|
    |            |             | by IANA     |       | root = ... (opt)|
    +------------------------------------------------------------------+
    |    NA_In   |   Inbound   | To be       |   AH  |    AH_RSA_Sig   |
    |            |             | assigned    |       |CGA flag = yes/no|
    |            |             | by IANA     |       | root = ... (opt)|
    +------------------------------------------------------------------+
    |    RS_In   |   Inbound   | To be       |   AH  |    AH_RSA_Sig   |
    |            |             | assigned    |       |CGA flag = yes/no|
    |            |             | by IANA     |       | root = ... (opt)|
    +------------------------------------------------------------------+
    |    RA_In   |   Inbound   | To be       |   AH  |    AH_RSA_Sig   |
    |            |             | assigned    |       |CGA flag = yes/no|
    |            |             | by IANA     |       | root = ... (opt)|
    +------------------------------------------------------------------+
    |    RE_In   |   Inbound   | To be       |   AH  |    AH_RSA_Sig   |
    |            |             | assigned    |       |CGA flag = yes/no|
    |            |             | by IANA     |       | root = ... (opt)|
    +------------------------------------------------------------------+


   The second table summarizes the outbound configuration:


   Policy entries:

    +------------------------------------------------------------------+
    |    Proto: Type   |    Source    |    Destination   |  Treatment  |
    +------------------------------------------------------------------+
    |    ICMPv6: NS    |  unspecified | solicited-node MC|     pass    |
    +------------------------------------------------------------------+
    |    ICMPv6: NS    |      own     |         *        | SA = NS_Out |
    +------------------------------------------------------------------+



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    |    ICMPv6: NA    |      own     |         *        | SA = NA_Out |
    +------------------------------------------------------------------+
    |    ICMPv6: RS    |      own     |         *        | SA = RS_Out |
    +------------------------------------------------------------------+
    |    ICMPv6: RA    |      own     |         *        | SA = RA_Out |
    +------------------------------------------------------------------+
    | ICMPv6: REDIRECT |      own     |         *        | SA = RE_Out |
    +------------------------------------------------------------------+

   Security associations:

    +------------------------------------------------------------------+
    |    Name    |  Direction  |     SPI     | Proto |    Transform    |
    +------------------------------------------------------------------+
    |    NS_Out  |  Outbound   | To be       |   AH  |    AH_RSA_Sig   |
    |            |             | assigned    |       | key pair = ...  |
    |            |             | by IANA     |       | CGA = yes/no    |
    |            |             |             |       | CGA params = ...|
    |            |             |             |       | root = ... (opt)|
    +------------------------------------------------------------------+
    |    NA_Out  |  Outbound   | To be       |   AH  |    AH_RSA_Sig   |
    |            |             | assigned    |       | key pair = ...  |
    |            |             | by IANA     |       | CGA = yes/no    |
    |            |             |             |       | CGA params = ...|
    |            |             |             |       | root = ... (opt)|
    +------------------------------------------------------------------+
    |    RS_Out  |  Outbound   | To be       |   AH  |    AH_RSA_Sig   |
    |            |             | assigned    |       | key pair = ...  |
    |            |             | by IANA     |       | CGA = yes/no    |
    |            |             |             |       | CGA params = ...|
    |            |             |             |       | root = ... (opt)|
    +------------------------------------------------------------------+
    |    RA_Out  |  Outbound   | To be       |   AH  |    AH_RSA_Sig   |
    |            |             | assigned    |       | key pair = ...  |
    |            |             | by IANA     |       | CGA = yes/no    |
    |            |             |             |       | CGA params = ...|
    |            |             |             |       | root = ... (opt)|
    +------------------------------------------------------------------+
    |    RE_Out  |  Outbound   | To be       |   AH  |    AH_RSA_Sig   |
    |            |             | assigned    |       | key pair = ...  |
    |            |             | by IANA     |       | CGA = yes/no    |
    |            |             |             |       | CGA params = ...|
    |            |             |             |       | root = ... (opt)|
    +------------------------------------------------------------------+







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11. Performance Considerations

   The computations related to AH_RSA_Sig transform are substantially
   more expensive than those with traditional symmetric transforms.
   While computational power is increasing, it appears still impractical
   to use asymmetric transforms for a significant number of packets.

   In the application for which AH_RSA_Sig has been designed, however,
   hosts typically have the need to perform only a few operations as
   they enter a link, and a few operations as they find a new on-link
   peer with which to communicate.

   Routers are required to perform a larger number of operations,
   particularly when the frequency of router advertisements is high due
   to mobility requirements.  Still, the number of operations on a
   router is on the order of a few dozen operations per second, some of
   which can be precomputed as discussed below.  A large number of
   router solicitations may cause higher demand for performing
   asymmetric operations, although RFC 2461 limits the rate at which
   responses to solicitations can be sent.

   Signatures related to the use of the AH_RSA_Sig transform MAY be
   precomputed for Multicast Neighbor and Router Advertisements.
   Typically, solicited advertisements are sent to the unicast address
   from which the solicitation was sent.  Given that the IPv6 header is
   covered by the AH integrity protection, it is typically not possible
   to precompute solicited advertisements.
























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12. Implementation Considerations

   In addition to the IPsec extensions discussed in this specification,
   it becomes necessary for the IPsec AH implementation and the Neighbor
   Discovery implementation to exchange some information.  Because IPsec
   security associations are typically set up either manually or using
   IKE, keys are shared and traditional IPsec does not have to deal with
   certificates.  SEND uses public key cryptography, however, and
   therefore the keys included in the AH header must be certified,
   except in the case where simple proof of IP address ownership using
   CGAs is being determined.  This requires an API between the
   AH_RSA_Sig transform processing code and the host's certificate
   store, so that the received keys can be checked.  Furthermore, if the
   necessary certificate chain is not in the certificate store, a
   Delegation Chain Solicitation message must be triggered to fetch the
   chain.  This may require an additional API, although, depending on
   how the certificate store is implemented, the API may or may not
   involve the code for the AH_RSA_Sig transform.

   Both the extensions and the API are required for all types of IPsec
   implementations, including Bump-in-the-Stack (BITS) implementations.






























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13. Security Considerations

13.1 Threats to the Local Link Not Covered by SEND

   SEND does not compensate for an insecure link layer.  In particular,
   there is no cryptographic binding in SEND between the link layer
   frame address and the IPv6 address.  On an insecure link layer that
   allows nodes to spoof the link layer address of other nodes, an
   attacker could disrupt IP service by sending out a Neighbor
   Advertisement having the source address on the link layer frame of a
   victim, a valid CGA with valid AH signature corresponding to itself,
   and a Target Link-layer Address extension corresponding to the
   victim.  The attacker could then proceed to cause a traffic stream to
   bombard the victim in a DoS attack.  To protect against such attacks,
   link layer security MUST be used.  An example of such for 802 type
   networks is port-based access control [34].

   Prior to participating in Neighbor Discovery and Duplicate Address
   Detection, nodes must subscribe to the All Nodes Multicast Group and
   Solicited Node Multicast Group for the address that they are claiming
   RFC 2461 [6].  Subscribing to a multicast group requires that the
   nodes use MLD [22].  MLD contains no provision for security.  An
   attacker could send an MLD Done message to unsubscribe a victim from
   the Solicited Node Multicast address.  However, the victim should be
   able to detect such an attack because the router sends a
   Multicast-Address-Specific Query to determine whether any listeners
   are still on the address, at which point the victim can respond to
   avoid being dropped from the group.  This technique will work if the
   router on the link has not been compromised.  Other attacks using MLD
   are possible, but they primarily lead to extraneous (but not
   overwhelming) traffic.

13.2 How SEND Counters Threats to Neighbor Discovery

   The SEND protocol is designed to counter the threats to IPv6 Neighbor
   Discovery outlined in [28].  The following subsections contain a
   regression of the SEND protocol against the threats, to illustrate
   what aspects of the protocol counter each threat.

13.2.1 Neighbor Solicitation/Advertisement Spoofing

   This threat is defined in Section 4.1.1 of [28].  The threat is that
   a spoofed Neighbor Solicitation or Neighbor Advertisement causes a
   false entry in a node's Neighbor Cache.  There are two cases:

   1.  Entries made as a side effect of a Neighbor Solicitation or
       Router Solicitation.  There are two cases:




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       1.  A router receiving a Router Solicitation with a firm IPv6
           source address and a Target Link-Layer Address extension
           inserts an entry for the IPv6 address into its Neighbor
           Cache.

       2.  A node doing Duplicate Address Detection (DAD) that receives
           a Neighbor Solicitation for the same address regards the
           situation as a collision and ceases to solicit for the
           address.

   2.  Entries made as a result of a Neighbor Advertisement sent as a
       response to a Neighbor Solicitation for purposes of on-link
       address resolution.


13.2.1.1 Solicitations with Effect

   SEND counters the threat of solicitations with effect in the
   following ways:

   1.  As discussed in Section 5, SEND nodes preferably send Router
       Solicitations with a firm IPv6 address and AH header, which the
       router can verify, so the Neighbor Cache binding is correct.  If
       a SEND node must send a Router Solicitation with the unspecified
       address, the router will not update its Neighbor Cache, as per
       RFC 2461.

   2.  When SEND nodes are performing DAD, they use the tentative
       address as the source address on the Neighbor Solicitation
       packet, and include an IPv6 AH header.  This allows the receiving
       SEND node to verify the solicitation.

   See Section 13.2.5, below, for discussion about replay protection and
   timestamps.

13.2.1.2 Address Resolution

   SEND counters attacks on address resolution by requiring that the
   responding node include an AH header with a signature on the packet,
   and that the node's interface identifier either be a CGA or that the
   node be able to produce a certificate authorizing that node to use
   the interface identifier.

   The Neighbor Solicitation and Advertisement pairs implement a
   challenge-response protocol, as explained in Section 8 and discussed
   in Section 13.2.5 below.





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13.2.2 Neighbor Unreachability Detection Failure

   This attack is described in Section 4.1.2 of [28].  SEND counters
   this attack by requiring a node responding to Neighbor Solicitations
   sent as NUD probes to include an AH header and proof of authorization
   to use the interface identifier in the address being probed.  If
   these prerequisites are not met, the node performing NUD discards the
   responses.

13.2.3 Duplicate Address Detection DoS Attack

   This attack is described in Section 4.1.3 of [28].  SEND counters
   this attack by requiring the Neighbor Advertisements sent as
   responses to DAD to include an AH header and proof of authorization
   to use the interface identifier in the address being tested.  If
   these prerequisites are not met, the node performing DAD discards the
   responses.

   When a SEND node is used on a link that also connects to non-SEND
   nodes, the SEND node defends its addresses by sending unprotected
   Neighbor Solicitations with an unspecified address, as explained in
   Section 10.   However, the SEND node ignores any unprotected Neighbor
   Solicitations or Advertisements that may be send by the non-SEND
   nodes.   This protects the SEND node from DAD DoS attacks by non-SEND
   nodes or attackers simulating to non-SEND nodes, at the cost of a
   potential address collision between a SEND node and non-SEND node.
   The probability and effects of such an address collision are
   discussed in [27].

13.2.4 Router Solicitation and Advertisement Attacks

   These attacks are described in Sections 4.2.1, 4.2.4, 4.2.5, 4.2.6,
   and 4.2.7 of [28].  SEND counters these attacks by requiring Router
   Advertisements to contain an AH header, and that the signature in the
   header be calculated using the public key of a host that can prove
   its authorization to route the subnet prefixes contained in any
   Prefix Information Options.  The router proves it authorization by
   showing an attribute certificate containing the specific prefix or
   the indication that the router is allowed to route any prefix.  A
   Router Advertisement without these protections is dropped as part of
   the IPsec processing.

   SEND does not protect against brute force attacks on the router, such
   as DoS attacks, or compromise of the router, as described in Sections
   4.4.2 and 4.4.3 of [28].

13.2.5 Replay Attacks




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   This attack is described in Section 4.3.1 of [28].  SEND protects
   against attacks in Router Solicitation/Router Advertisement and
   Neighbor Solicitation/Neighbor Advertisement transactions by
   including a Nonce option in the solicitation and requiring the
   advertisement to include a matching option.  Together with the
   signatures this forms a challenge-response protocol.  SEND protects
   against attacks from unsolicited messages such as Neighbor
   Advertisements, Router Advertisements, and Redirects by including a
   timestamp into the AH header.  A window of vulnerability for replay
   attacks exists until the timestamp expires.

   When timestamps are used, SEND nodes are protected against replay
   attacks as long as they cache the state created by the message
   containing the timestamp.  The cached state allows the node to
   protect itself against replayed messages.  However, once the node
   flushes the state for whatever reason, an attacker can re-create the
   state by replaying an old message while the timestamp is still valid.
   Since most SEND nodes are likely to use fairly coarse grained
   timestamps, as explained in Section 7.1.4, this may affect some
   nodes.

13.2.6 Neighbor Discovery DoS Attack

   This attack is described in Section 4.3.2 of [28].  In this attack,
   the attacker bombards the router with packets for fictitious
   addresses on the link, causing the router to busy itself with
   performing Neighbor Solicitations for addresses that do not exist.
   SEND does not address this threat because it can be addressed by
   techniques such as rate limiting Neighbor Solicitations, restricting
   the amount of state reserved for unresolved solicitations, and clever
   cache management.  These are all techniques involved in implementing
   Neighbor Discovery on the router.

13.3 Attacks against SEND Itself

   The CGAs have a 59-bit hash value.  The security of the CGA mechanism
   has been discussed in [27].

   Some Denial-of-Service attacks against ND and SEND itself remain.
   For instance, an attacker may try to produce a very high number of
   packets that a victim host or router has to verify using asymmetric
   methods.  While safeguards are required to prevent an excessive use
   of resources, this can still render SEND non-operational.

   Security associations based on the use of asymmetric cryptography can
   be vulnerable to Denial-of-Service attacks, particularly when the
   attacker can guess the SPIs and destination addresses used in the
   security associations.  In SEND this is easy, as both the SPIs and



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   the addresses (such as all nodes multicast address) are standardized.
   Due to the use of multicast, one packet sent by the attacker will be
   processed by multiple receivers.

   When CGA protection is used, SEND deals with these attacks using the
   verification process described in Section 7.1.6.  In this process a
   simple hash verification of the CGA property of the address is
   performed first before performing the more expensive signature
   verification.

   When trusted roots and certificates are used for address validation
   in SEND, the defenses are not quite as effective.  Implementations
   SHOULD track the resources devoted to the processing of packets
   received with the AH_RSA_Sig transform, and start selectively
   dropping packets if too many resources are spent.  Implementations
   MAY also drop first packets that are not protected with CGA.

   The Authorization Delegation Discovery process may also be vulnerable
   to Denial-of-Service attacks.  An attack may target a router by
   request a large number of delegation chains to be discovered for
   different roots.  Routers SHOULD defend against such attacks by
   caching discovered information (including negative responses) and by
   limiting the number of different discovery processes they engage in.

   Attackers may also target hosts by sending a large number of
   unnecessary certificate chains, forcing hosts to spend useless memory
   and verification resources for them.  Hosts defend against such
   attacks by limiting the amount of resources devoted to the
   certificate chains and their verification.  Hosts SHOULD also
   prioritize advertisements sent as a response to their requests above
   multicast advertisements.




















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14. IANA Considerations

   This document defines two new ICMP message types, used in
   Authorization Delegation Discovery.  These messages must be assigned
   ICMPv6 type numbers from the informational message range:

   o  The Delegation Chain Solicitation message, described in Section
      6.1.

   o  The Delegation Chain Advertisement message, described in Section
      6.2.

   This document defines two new Neighbor Discovery [6] options, which
   must be assigned Option Type values within the option numbering space
   for Neighbor Discovery messages:

   o  The Trusted Root option, described in Section 6.3.

   o  The Certificate option, described in Section 6.4.

   o  The Nonce option, described in Section 5.3.

   This document defines a new reserved SPI number in the Reserved SPI
   range 1-255 [3].

   This document defines a new IPSEC AH Transform Identifier for the
   IPsec DOI [4].  This identifier represents the AH_RSA_Sig transform
   from Section 7.1.

   This document defines a new name space for the Name Type field in the
   Trusted Root option.  Future values of this field can be allocated
   using standards action [5].

   Another new name space is allocated for the Cert Type field in the
   Certificate option.  Future values of this field can be allocated
   using standards action [5].















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Normative References

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

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

   [3]   Kent, S. and R. Atkinson, "IP Authentication Header", RFC 2402,
         November 1998.

   [4]   Piper, D., "The Internet IP Security Domain of Interpretation
         for ISAKMP", RFC 2407, November 1998.

   [5]   Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
         Considerations Section in RFCs", BCP 26, RFC 2434, October
         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]   Narten, T. and R. Draves, "Privacy Extensions for Stateless
         Address Autoconfiguration in IPv6", RFC 3041, January 2001.

   [10]  Bassham, L., Polk, W. and R. Housley, "Algorithms and
         Identifiers for the Internet X.509 Public Key Infrastructure
         Certificate and Certificate Revocation List (CRL) Profile", RFC
         3279, April 2002.

   [11]  Housley, R., Polk, W., Ford, W. and D. Solo, "Internet X.509
         Public Key Infrastructure Certificate and Certificate
         Revocation List (CRL) Profile", RFC 3280, April 2002.

   [12]  Farrell, S. and R. Housley, "An Internet Attribute Certificate
         Profile for Authorization", RFC 3281, April 2002.

   [13]  Hinden, R. and S. Deering, "Internet Protocol Version 6 (IPv6)
         Addressing Architecture", RFC 3513, April 2003.

   [14]  Lynn, C., "X.509 Extensions for IP Addresses and AS
         Identifiers", Internet-Draft (expired)



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         draft-ietf-pkix-x509-ipaddr-as-extn-00, February 2002.

   [15]  Perkins, C., Johnson, D. and J. Arkko, "Mobility Support in
         IPv6", draft-ietf-mobileip-ipv6-22 (work in progress), May
         2003.

   [16]  International Organization for Standardization, "The Directory
         - Authentication Framework", ISO Standard X.509, 2000.

   [17]  RSA Laboratories, "RSA Encryption Standard, Version 1.5", PKCS
         1, November 1993.

   [18]  National Institute of Standards and Technology, "Secure Hash
         Standard", FIPS PUB 180-1, April 1995, <http://
         www.itl.nist.gov/fipspubs/fip180-1.htm>.




































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Informative References

   [19]  Postel, J., "Internet Control Message Protocol", STD 5, RFC
         792, September 1981.

   [20]  Plummer, D., "Ethernet Address Resolution Protocol: Or
         converting network protocol addresses to 48.bit Ethernet
         address for transmission on Ethernet hardware", STD 37, RFC
         826, November 1982.

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

   [22]  Deering, S., Fenner, W. and B. Haberman, "Multicast Listener
         Discovery (MLD) for IPv6", RFC 2710, October 1999.

   [23]  Arkko, J., "Effects of ICMPv6 on IKE and IPsec Policies",
         draft-arkko-icmpv6-ike-effects-01 (work in progress), June
         2002.

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

   [25]  Droms, R., "Dynamic Host Configuration Protocol for IPv6
         (DHCPv6)", draft-ietf-dhc-dhcpv6-28 (work in progress),
         November 2002.

   [26]  Kent, S., "IP Encapsulating Security Payload (ESP)",
         draft-ietf-ipsec-esp-v3-04 (work in progress), March 2003.

   [27]  Aura, T., "Cryptographically Generated Addresses (CGA)",
         draft-ietf-send-cga-00.txt (work in progress), May 2003.

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

   [29]  Montenegro, G. and C. Castelluccia, "SUCV Identifiers and
         Addresses", draft-montenegro-sucv-03 (work in progress), July
         2002.

   [30]  O'Shea, G. and M. Roe, "Child-proof Authentication for MIPv6",
         Computer Communications Review, April 2001.

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



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   [32]  Arkko, J., Aura, T., Kempf, J., Mantyla, V., Nikander, P. and
         M. Roe, "Securing IPv6 Neighbor Discovery", Wireless Security
         Workshop, September 2002.

   [33]  Montenegro, G. and C. Castelluccia, "Statistically Unique and
         Cryptographically Verifiable (SUCV) Identifiers and Addresses",
         NDSS, February 2002.

   [34]  Institute of Electrical and Electronics Engineers, "Local and
         Metropolitan Area Networks: Port-Based Network Access Control",
         IEEE Standard 802.1X, September 2001.


Authors' Addresses

   Jari Arkko
   Ericsson
   Jorvas  02420
   Finland

   EMail: jari.arkko@ericsson.com


   James Kempf
   DoCoMo Communications Labs USA
   181 Metro Drive
   San Jose, CA  94043
   USA

   EMail: kempf@docomolabs-usa.com


   Bill Sommerfeld
   Sun Microsystems
   1 Network Drive UBUR02-212
   Burlington  01803
   USA

   EMail: sommerfeld@east.sun.com


   Brian Zill
   Microsoft
   USA

   EMail: bzill@microsoft.com





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   Pekka Nikander
   Ericsson
   Jorvas  02420
   Finland

   EMail: Pekka.Nikander@nomadiclab.com













































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Appendix A. Contributors

   Steven Bellovin was the first to suggest the use of IPsec in this
   manner for the protection of Neighbor Discovery.  Ran Atkinson and
   Brian Weis have in the past experimented with public-key based
   variants of AH for other purposes.  Vesa-Matti Mantyla was a
   co-author of an unpublished draft from which many of the details of
   this document have been inherited.  The theoretical foundations of
   protecting Neighbor Discovery were laid out in a paper [32] where
   Tuomas Aura, Vesa-Matti Mantyla, Pekka Nikander, and Mike Roe were
   co-authors.








































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Appendix B. Acknowledgements

   The authors would like to thank Erik Nordmark, Gabriel Montenegro,
   Tuomas Aura, Pekka Savola, and Alper Yegin for interesting
   discussions in this problem space.














































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Appendix C. IPR Considerations

   The optional CGA part of SEND uses public keys and hashes to prove
   address ownership.  Several IPR claims have been made about such
   methods.














































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