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Versions: (draft-gont-6man-nd-opt-validation) 00

IPv6 maintenance Working Group (6man)                            F. Gont
Internet-Draft                                    SI6 Networks / UTN-FRH
Updates: 4861 (if approved)                                    R. Bonica
Intended status: Standards Track                        Juniper Networks
Expires: September 9, 2015                                        W. Liu
                                                     Huawei Technologies
                                                           March 8, 2015


             Validation of IPv6 Neighbor Discovery Options
                  draft-ietf-6man-nd-opt-validation-00

Abstract

   This memo specifies validation rules for IPv6 Neighbor Discovery (ND)
   Options.  In order to avoid pathological outcomes, IPv6
   implementations validate incoming ND options using these rules.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 9, 2015.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of




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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Methodology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  The Source Link-Layer Address (SLLA) Option . . . . . . . . .   4
   5.  The Target Link-Layer Address (TLLA) Option . . . . . . . . .   5
   6.  The Prefix Information Option . . . . . . . . . . . . . . . .   6
   7.  The Redirected Header Option  . . . . . . . . . . . . . . . .   7
   8.  The MTU Option  . . . . . . . . . . . . . . . . . . . . . . .   7
   9.  The Route Information Option  . . . . . . . . . . . . . . . .   8
   10. The Recursive DNS Server (RDNSS) Option . . . . . . . . . . .   9
   11. The DNS Search List (DNSSL) Option  . . . . . . . . . . . . .  10
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   13. Security Considerations . . . . . . . . . . . . . . . . . . .  11
   14. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  11
   15. References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     15.1.  Normative References . . . . . . . . . . . . . . . . . .  12
     15.2.  Informative References . . . . . . . . . . . . . . . . .  12
   Appendix A.  Mapping an IPv6 Address to a Local Router's Own
                Link-layer Address . . . . . . . . . . . . . . . . .  12
   Appendix B.  Mapping a Unicast IPv6 Address to A Broadcast Link-
                Layer Address  . . . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

   IPv6 [RFC2460] nodes use Neighbor Discovery (ND) [RFC4861] to
   discover their neighbors and to learn their neighbors' link-layer
   addresses.  IPv6 hosts also use ND to find neighboring routers that
   can forward packets on their behalf.  Finally, IPv6 nodes use ND to
   verify neighbor reachability, and to detect link-layer address
   changes.

   ND defines the following ICMPv6 [RFC4443] messages:

   o  Router Solicitation (RS)

   o  Router Advertisement (RA)

   o  Neighbor Solicitation (NS)

   o  Neighbor Advertisement (NA)

   o  Redirect



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   ND messages can include options that convey additional information.
   Currently, the following ND options are specified:

   o  Source link-layer address(SLLA) [RFC4861]

   o  Target link-layer address (TLLA) [RFC4861]

   o  Prefix information [RFC4861]

   o  Redirected header [RFC4861]

   o  MTU [RFC4861]

   o  Route Information [RFC4191]

   o  Recursive DNS Server (RDNSS) [RFC6106]

   o  DNS Search List (DNSSL) [RFC6106]

   This memo specifies validation rules for the ND options mentioned
   above.  In order to avoid pathological outcomes (such as
   [FreeBSD-rtsold]), IPv6 implementations validate incoming ND options
   using these rules.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

3.  Methodology

   Section 4 through Section 11 of this document define validation rules
   for ND options.  These sections also specify actions that are to be
   taken when an implementation encounters an invalid option.  Possible
   actions are:

   o  The entire option MUST be ignored.  However, the rest of the ND
      message MAY be processed.

   o  The entire ND message MUST be ignored

   In the spirit of "being liberal in what you receive", the first
   action is always preferred.  However, when an option length attribute
   is invalid, it is not possible to parse the rest of the ND message,
   and therefore subsequent ND options should be ignored.





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   We note that an implementation SHOULD NOT assume a particular length
   of an option (based on the option type) when it moves to the next
   option (whether it handles or ignores the current option) and SHOULD
   always use the length field of the option.

4.  The Source Link-Layer Address (SLLA) Option

   The SLLA Option is employed with NS, RS, and RA messages.  If any
   other ND message contains an SLLA Option, the SLLA Option MUST be
   ignored.  However, the rest of the ND message MAY be processed.  (As
   per [RFC4861]).

   Figure 1 illustrates the SLLA Option:

      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     |    Link-Layer Address ...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 1: Source Link-Layer Address Option

   The Type field is set to 1.

   The Length field specifies the length of the option (including the
   Type and Length fields) in units of 8 octets.  The Length field MUST
   be valid for the underlying link layer.  For example, for IEEE 802
   addresses the Length field MUST be 1 [RFC2464].  If an incoming ND
   message does not pass this validation check, the entire ND message
   MUST be discarded.

   The Link-Layer Address field specifies the link-layer address of the
   packet's originator.  It MUST NOT be any of the following:

   o  a broadcast address (see Appendix B for rationale)

   o  a multicast address (see Appendix B for rationale)

   o  an address belonging to the receiving node (see Appendix A for
      rationale)

   If an incoming ND message does not pass this validation check, the
   SLLA Option MUST be ignored.  However, the rest of the ND message MAY
   be processed.

   An ND message that carries the SLLA Option MUST have a source address
   other than the unspecified address (0:0:0:0:0:0:0:0).  If an incoming
   ND message does not pass this validation check, the SLLA Option MUST



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   be ignored.  However, the rest of the ND message MAY be processed.
   (As per [RFC4861]).

5.  The Target Link-Layer Address (TLLA) Option

   NA and Redirect messages MAY contain a TLLA Option.  If any other ND
   message contains an TLLA Option, the TLLA Option MUST be ignored.
   However, the rest of the ND message MAY be processed.  (As per
   [RFC4861]).

   Figure 2 illustrates the Target link-layer address:

      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     |    Link-Layer Address ...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Figure 2: Target link-layer address option format

   The Type field is set to 2.

   The Length field specifies the length of the option (including the
   Type and Length fields) in units of 8 octets.  The Length field MUST
   be valid for the underlying link layer.  For example, for IEEE 802
   addresses the Length field MUST be 1 [RFC2464].  If an incoming ND
   message does not pass this validation check, the entire ND message
   MUST be discarded.

   An ND message that carries the TLLA option also includes a Target
   Address.  The TLLA Option Link-Layer Address maps to the Target
   Address.  The TLLA Option Link-Layer Address MUST NOT be any of the
   following:

   o  a broadcast address (see Appendix B for rationale)

   o  a multicast address (see Appendix B for rationale)

   o  an address belonging to the receiving node (see Appendix A for
      rationale)

   If an incoming ND message does not pass this validation check, the
   TLLA Option MUST be ignored.  However, the rest of the ND message MAY
   be processed.







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6.  The Prefix Information Option

   The RA message MAY contain a Prefix Information Option.  If any other
   ND message contains a Prefix Information Option, the Prefix
   Information Option MUST be ignored.  However, the rest of the ND
   message MAY be processed.  (As per [RFC4861]).

   Figure 3 illustrates the Prefix Information Option:

      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     | Prefix Length |L|A|R|Reserved1|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         Valid Lifetime                        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                       Preferred Lifetime                      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           Reserved2                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     +                                                               +
     |                                                               |
     +                            Prefix                             +
     |                                                               |
     +                                                               +
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 3: Prefix Information option format

   The Type field is set to 3.

   The Length field MUST be set to 4.  If an incoming ND message does
   not pass this validation check, the entire ND message MUST be
   discarded.

   As stated in [RFC4861] the Preferred Lifetime MUST be less than or
   equal to the Valid Lifetime.  If an incoming ND message does not pass
   this validation check, the Prefix Information Option MUST be ignored.
   However, the rest of the ND message MAY be processed.

   The Prefix Length contains the number of leading bits in the prefix
   that are to be considered valid.  It MUST be greater than or equal to
   0, and smaller than or equal to 128.  If the field does not pass this
   check, the Prefix Information Option MUST be ignored.  However, the
   rest of the ND message MAY be processed.




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   The Prefix field MUST NOT contain a link-local or multicast prefix.
   If an incoming ND message does not pass this validation check, the
   Prefix Information Option MUST be ignored.  However, the rest of the
   ND message MAY be processed.

7.  The Redirected Header Option

   The Redirect message MAY contain a Redirect Header Option.  If any
   other ND message contains an Redirect Header Option, the Redirect
   Header Option MUST be ignored.  However, the rest of the ND message
   MAY be processed.  (As per [RFC4861]).

   Figure 4 illustrates the Redirected Header option:

      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     |            Reserved           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           Reserved                            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     ~                       IP header + data                        ~
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 4: Redirected Header Option format

   The Type field is 4.

   The Length field specifies the option size (including the Type and
   Length fields) in units of 8 octets.  Its value MUST be greater than
   or equal to 6.  If an incoming ND message does not pass this
   validation check, the entire ND message MUST be discarded.

   The value 6 was chosen to accommodate mandatory fields (8 octets)
   plus the base IPv6 header (40 octets).

8.  The MTU Option

   The RA message MAY contain an MTU Option.  If any other ND message
   contains an MTU Option, the MTU Option MUST be ignored.  However, the
   rest of the ND message MAY be processed.  (As per [RFC4861]).

   Figure 5 illustrates the MTU option:






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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      |    Length     |           Reserved            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                              MTU                              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Figure 5: MTU Option Format

   The Type field identifies the kind of option and is set to 5.

   The Length field MUST BE set to 1 by the sender.  If an incoming ND
   message does not pass this validation check, the entire ND message
   MUST be discarded.

   The MTU field is a 32-bit unsigned integer that specifies the MTU
   value that should be used for this link.  [RFC2460] specifies that
   the minimum IPv6 MTU is 1280 octets.  Therefore, the MTU MUST be
   greater than or equal to 1280.  If an incoming ND message does not
   pass this validation check, the MTU Option MUST be ignored.  However,
   the rest of the ND message MAY be processed.

   Additionally, the advertised MTU MUST NOT exceed the maximum MTU
   specified for the link-type (e.g., [RFC2464] for Ethernet networks).
   If an incoming ND message does not pass this validation check, the
   MTU Option MUST be ignored.  However, the rest of the ND message MAY
   be processed.

9.  The Route Information Option

   The RA message MAY contain a Route Information Option.  If any other
   ND message contains a Route Information Option, the Route Information
   Option MUST be ignored.  However, the rest of the ND message MAY be
   processed.

   Figure 6 illustrates Route Information option:














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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      |    Length     | Prefix Length |Resvd|Prf|Resvd|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                        Route Lifetime                         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                   Prefix (Variable Length)                    |
     .                                                               .
     .                                                               .
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 6: Route Information Option Format

   The Type field is 24.

   The Length field contains the length of the option (including the
   Type and Length fields) in units of 8 octets.  Its value MUST be at
   least 1 and at most 3.  If an incoming ND message does not pass this
   validation check, the entire ND message MUST be discarded.

   The Prefix Length field indicates the number of significant bits in
   the Prefix field that are significant.  Its value MUST be less than
   or equal to 128.  If the field does not pass this check, the Route
   Information Option MUST be ignored.

   The Length field and the Prefix Length field are closely related, as
   the Length field constrains the possible values of the Prefix Length
   field.  If the Prefix Length is equal to 0, the Length MUST be equal
   to 1.  If the Prefix Length is greater than 0 and less than 65, the
   Length MUST be equal to 2.  If the Prefix Length is greater than 65
   and less than 129, the Length MUST be equal to 3.  If an incoming ND
   message does not pass this validation check, the entire ND message
   MUST be discarded.

   The Prefix field MUST NOT contain a link-local unicast prefix
   (fe80::/10) or a link-local multicast prefix (e.g., ff02::/64).  If
   an incoming ND message does not pass this validation check, the Route
   Information Option MUST be ignored.  However, the rest of the ND
   message MAY be processed.

10.  The Recursive DNS Server (RDNSS) Option

   The RA message MAY contain a Recursive DNS Server (RDNSS) Option.  If
   any other ND message contains an RDNSS Option, the RDNSS Option MUST
   be ignored.  However, the rest of the ND message MAY be processed.

   Figure 7 illustrates the syntax of the RDNSS option:



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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      |     Length    |           Reserved            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           Lifetime                            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     :            Addresses of IPv6 Recursive DNS Servers            :
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 7: Recursive DNS Server Option Format

   The Type field is 25.

   The Length field specifies the length of the option (including the
   Type and Length fields) in units of 8 octets.  Its value MUST be
   greater than or equal to 3.  Additionally the Length field MUST pass
   the following check:

                           (Length -1) % 2 == 0

                                 Figure 8

   If the option does not pass these validation checks, the entire ND
   message MUST be discarded.

   The RDNSS address list MUST NOT contain multicast addresses or the
   unspecified address.  If an incoming ND message does not pass this
   validation check, the RDNSS Option MUST be ignored.  However, the
   rest of the ND message MAY be processed.

11.  The DNS Search List (DNSSL) Option

   The RA message MAY contain a DNS Search List (DNSSL) Option.  If any
   other ND message contains a DNSSL Option, the DNSSL Option MUST be
   ignored.  However, the rest of the ND message MAY be processed.

   Figure 9 illustrates the syntax of the DNSSL option:











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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      |     Length    |           Reserved            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           Lifetime                            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     :                Domain Names of DNS Search List                :
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 9: DNS Search List Option Format

   The Type field is 31.

   The Length field specifies the length of the option (including the
   Type and Length fields) in units of 8 octets.  Its value MUST be
   greater than or equal to 2.  If an incoming ND message does not pass
   these validation checks, the entire ND message MUST be discarded.

   [RFC6106] specifies the valid format of domain suffixes.  If a suffix
   is not validly encoded as specified, the corresponding DNSSL option
   MUST be ignored.

12.  IANA Considerations

   There are no IANA registries within this document.  The RFC-Editor
   can remove this section before publication of this document as an
   RFC.

13.  Security Considerations

   This document specifies sanity checks to be performed on Neighbor
   Discovery options.  By enforcing the checks specified in this
   document, a number of pathological behaviors (including some leading
   to Denial of Service scenarios) are eliminated.

14.  Acknowledgements

   Thanks to Tomoyuki Sahara and Jinmei Tatuya for their careful review
   and comments.

15.  References







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15.1.  Normative References

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, November 1987.

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

   [RFC2464]  Crawford, M., "Transmission of IPv6 Packets over Ethernet
              Networks", RFC 2464, December 1998.

   [RFC4191]  Draves, R. and D. Thaler, "Default Router Preferences and
              More-Specific Routes", RFC 4191, November 2005.

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

   [RFC4443]  Conta, A., Deering, S., and M. Gupta, "Internet Control
              Message Protocol (ICMPv6) for the Internet Protocol
              Version 6 (IPv6) Specification", RFC 4443, March 2006.

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, December 1998.

   [RFC6106]  Jeong, J., Park, S., Beloeil, L., and S. Madanapalli,
              "IPv6 Router Advertisement Options for DNS Configuration",
              RFC 6106, November 2010.

15.2.  Informative References

   [FreeBSD-rtsold]
              FreeBSD, , "rtsold(8) remote buffer overflow
              vulnerability", 2014,
              <https://www.freebsd.org/security/advisories/FreeBSD-SA-
              14:20.rtsold.asc>.

Appendix A.  Mapping an IPv6 Address to a Local Router's Own Link-layer
             Address












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                         +----------+      +--------+
                    ...==| Router A |      | Host C |
                         +----------+      +--------+
                              ||               ||
                         =============================
                                  ||
                                  ||          Network 1
                             +----------+
                             | Attacker |
                             +----------+

                    Figure 10: Unicast Forwarding Loop

   In Figure 10, an on-link attacker sends Router A a crafted ND message
   that maps Host C's IPv6 address to the link-layer address of Router
   A's interface to Network 1.  The crafted ND message causes Router A
   to map Host C's IPv6 address to the link layer address of its own
   interface to Network 1 and sets up the scenario for a subsequent
   attack.

   A packet is sent to Router A with the IPv6 Destination Address of
   Host C.  Router A forwards the packet on Network 1, specifying its
   own Network 1 interface as the link-layer destination.  Because
   Router A specified itself as the link layer destination, Router A
   receives the packet and forwards it again.  This process repeats
   until the IPv6 Hop Limit is decremented to 0 (and hence the packet is
   discarded).  In this scenario, the amplification factor is equal to
   the Hop Limit minus one.

   An attacker can realize this attack by sending either of the
   following:

   o  An ND message whose SLLA maps an IPv6 address to the link layer
      address of the victim router's (Router A's in our case) interface
      to the local network (Network 1 in our case)

   o  An ND message whose TLLA maps an IPv6 address to the link layer
      address of the victim router's (Router A's in our case) interface
      to the local network (Network 1 in our case)

Appendix B.  Mapping a Unicast IPv6 Address to A Broadcast Link-Layer
             Address









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             +----------+      +--------+         +----------+
             | Router A |      | Host C |         | Router B |
             +----------+      +--------+         +----------+
                  ||               ||                  ||
              =================================================
                                ||
                                ||
                           +----------+
                           | Attacker |
                           +----------+

                   Figure 11: Broadcast Forwarding Loop

   In Figure 11, the Attacker sends one crafted ND message to Router A,
   and one crafted ND message to Router B.  Each crafted ND message
   contains the Target Address set to Host C's IPv6 address, and a TLLA
   option set to the Ethernet broadcast address (ff:ff:ff:ff:ff:ff).
   These ND messages causes each router to map Host C's IPv6 address to
   the Ethernet broadcast address.  This sets up the scenario for a
   subsequent attack.

   The Attacker sends a packet to the Ethernet broadcast address
   (ff:ff:ff:ff:ff:ff), with an IPv6 Destination Address equal to the
   IPv6 address of Host C.  Upon receipt, both Router A and Router C
   decrement the Hop Limit of the packet, and resend it to the Ethernet
   broadcast address.  As a result, both Router A and Router B receive
   two copies of the same packet (one sent by Router A, and another sent
   by Router B).  This would result in a "chain reaction" that would
   only disappear once the Hop Limit of each of the packets is
   decremented to 0.  The equation in Figure 12 describes the
   amplification factor for this scenario :

                                   HopLimit-1
                                      ---
                                      \          x
                         Packets =    /   Routers
                                      ---
                                      x=0

                  Figure 12: Maximum amplification factor

   This equation does not take into account ICMPv6 Redirect messages
   that each of the Routers could send, nor the possible ICMPv6 "time
   exceeded in transit" error messages that each of the routers could
   send to the Source Address of the packet when each of the "copies" of
   the original packet is discarded as a result of their Hop Limit being
   decremented to 0.




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Internet-Draft          Validation of ND options              March 2015


   An attacker can realize this attack by sending either of the
   following:

   o  An ND message whose SLLA maps an IPv6 address not belonging to the
      victim routers to the broadcast link-layer address

   o  An ND message whose TLLA maps an IPv6 address not belonging to the
      victim routers to the broadcast link-layer address

   An additional mitigation would be for routers to not forward IPv6
   packets on the same interface if the link-layer destination address
   of the received packet was a broadcast or multicast address.

Authors' Addresses

   Fernando Gont
   SI6 Networks / UTN-FRH
   Evaristo Carriego 2644
   Haedo, Provincia de Buenos Aires  1706
   Argentina

   Phone: +54 11 4650 8472
   Email: fgont@si6networks.com
   URI:   http://www.si6networks.com


   Ronald P. Bonica
   Juniper Networks
   2251 Corporate Park Drive
   Herndon, VA  20171
   US

   Phone: 571 250 5819
   Email: rbonica@juniper.net


   Will (Shucheng) Liu
   Huawei Technologies
   Bantian, Longgang District
   Shenzhen  518129
   P.R. China

   Email: liushucheng@huawei.com








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