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Versions: (draft-arifumi-v6ops-addr-select-ps) 00 01 02 03 04 05 06 07 08 09 RFC 5220

IPv6 Operations Working Group                               A. Matsumoto
Internet-Draft                                               T. Fujisaki
Intended status: Standards Track                                     NTT
Expires: April 13, 2008                                        R. Hiromi
                                                             K. Kanayama
                                                           Intec Netcore
                                                        October 11, 2007


     Problem Statement of Default Address Selection in Multi-prefix
        Environment: Operational Issues of RFC3484 Default Rules
                 draft-ietf-v6ops-addr-select-ps-02.txt

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
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   This Internet-Draft will expire on April 13, 2008.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   One physical network can carry multiple logical networks.  Moreover,
   we can use multiple physical networks at the same time in a host.  In
   that environment, end hosts might have multiple IP addresses and be
   required to use them selectively.  Without an appropriate source/



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   destination address selection mechanism, the host will experience
   some trouble in communication.  RFC 3484 defines both the source and
   destination address selection algorithms, but the multi-prefix
   environment considered here needs additional rules beyond those of
   the default operation.  This document describes the possible problems
   that end hosts could encounter in an environment with multiple
   logical networks.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Scope of this document . . . . . . . . . . . . . . . . . .  3
   2.  Problem Statement  . . . . . . . . . . . . . . . . . . . . . .  3
     2.1.  Source Address Selection . . . . . . . . . . . . . . . . .  3
       2.1.1.  Multiple Routers on Single Interface . . . . . . . . .  4
       2.1.2.  Ingress Filtering Problem  . . . . . . . . . . . . . .  5
       2.1.3.  Half-Closed Network Problem  . . . . . . . . . . . . .  5
       2.1.4.  Combined Use of Global and ULA . . . . . . . . . . . .  7
       2.1.5.  Site Renumbering . . . . . . . . . . . . . . . . . . .  7
       2.1.6.  Multicast Source Address Selection . . . . . . . . . .  8
       2.1.7.  Temporary Address Selection  . . . . . . . . . . . . .  8
     2.2.  Destination Address Selection  . . . . . . . . . . . . . .  8
       2.2.1.  IPv4 or IPv6 prioritization  . . . . . . . . . . . . .  8
       2.2.2.  ULA and IPv4 dual-stack environment  . . . . . . . . .  9
       2.2.3.  ULA or Global Prioritization . . . . . . . . . . . . . 10
   3.  Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 11
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
   6.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     6.1.  Normative References . . . . . . . . . . . . . . . . . . . 12
     6.2.  Informative References . . . . . . . . . . . . . . . . . . 12
   Appendix A.  Appendix. Revision History  . . . . . . . . . . . . . 13
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
   Intellectual Property and Copyright Statements . . . . . . . . . . 15
















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1.  Introduction

   One physical network can carry multiple logical networks.  In that
   case, an end-host has multiple IP addresses.  In the IPv4-IPv6 dual
   stack environment or in a site connected to both a ULA [RFC4193] and
   Global scope networks, an end-host has multiple IP addresses.  These
   are examples of networks that we focus on in this document.  In such
   an environment, an end-host will encounter some communication
   trouble.

   Inappropriate source address selection at the end-host causes
   unexpected asymmetric routing, filtering by a router or discarding of
   packets bacause there is no route to the host.

   Considering a multi-prefix environment, destination address selection
   is also important for correct or better communication establishment.

   RFC 3484 [RFC3484] defines both source and destination address
   selection algorithms.  In most cases, the host will be able to
   communicate with the targeted host using the algorithms.  However,
   there are still problematic cases such as when multiple default
   routes are supplied.  This document describes such possibilities of
   incorrect address selection, which leads to dropping packets and
   communication failure.

   In addition, the provision of an address policy table is an important
   matter.  RFC 3484 describes all the algorithms for setting the
   address policy table but address policy provisions are not mentioned.
   RFC 3484 only defines how to configure the address policy table
   manually.

1.1.  Scope of this document

   There has been a lot of discussion about "multiple addresses/
   prefixes" but the multi-homing techniques for achieving redundancy
   are out of our scope.  Cooperation with a mechanism like shim6 is
   rather desirable.  We focus on an end-site network environment.  The
   scope of this document is to sort out problematic cases of false
   dropping of the address selection within a multi-prefix environment.


2.  Problem Statement

2.1.  Source Address Selection







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2.1.1.  Multiple Routers on Single Interface

                          ==================
                          |    Internet    |
                          ==================
                             |          |
          2001:db8:1000::/36 |          | 2001:db8:8000::/36
                        +----+-+      +-+----+
                        | ISP1 |      | ISP2 |
                        +----+-+      +-+----+
                             |          |
         2001:db8:1000:::/48 |          | 2001:db8:8000::/48
                      +------+---+ +----+-----+
                      | Gateway1 | | Gateway2 |
                      +--------+-+ +-+--------+
                               |     |
          2001:db8:1000:1::/64 |     | 2001:db8:8000:1::/64
                               |     |
                        -----+-+-----+------
                             |
                           +-+----+ 2001:db8:1000:1::EUI64
                           | Host | 2001:db8:8000:1::EUI64
                           +------+

                                [Fig. 1]

   Generally speaking, there is no interaction between next-hop
   determination and address selection.  In this example, when a Host
   sends a packet via Gateway1, the Host does not necessarily choose
   address 2001:db8:1000:1::EUI64 given by Gateway1 as the source
   address.  This causes the same problem as described in the next
   section 'Ingress Filtering Problem'.



















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2.1.2.  Ingress Filtering Problem

                        ==================
                        |    Internet    |
                        ==================
                             |       |
          2001:db8:1000::/36 |       | 2001:db8:8000::/36
                        +----+-+   +-+----+
                        | ISP1 |   | ISP2 |
                        +----+-+   +-+----+
                             |       |
         2001:db8:1000:::/48 |       | 2001:db8:8000::/48
                            ++-------++
                            | Gateway |
                            +----+----+
                                 |  2001:db8:1000:1::/64
                                 |  2001:db8:8000:1::/64
                       ------+---+----------
                             |
                           +-+----+ 2001:db8:1000:1::EUI64
                           | Host | 2001:db8:8000:1::EUI64
                           +------+

                                [Fig. 2]

   When a relatively small site, which we call a "customer network", is
   attached to two upstream ISPs, each ISP delegates a network address
   block, which is usually /48, and a host has multiple IPv6 addresses.

   When the source address of an outgoing packet is not the one that is
   delegated by an upstream ISP, there is a possibility that the packet
   will be dropped at the ISP by its Ingress Filter.  Ingress
   filtering(uRPF: unicast Reverse Path Forwarding) is becoming more
   popular among ISPs to mitigate the damage of DoS attacks.

   In this example, when the Gateway chooses the default route to ISP2
   and the Host chooses 2001:db8:1000:1::EUI64 as the source address for
   packets sent to a host (2001:db8:2000::1) somewhere on the Internet,
   the packets may be dropped at ISP2 because of Ingress Filtering.

2.1.3.  Half-Closed Network Problem

   You can see a second typical source address selection problem in a
   multihome site with global-closed mixed connectivity like in the
   figure below.  In this case, Host-A is in a multihomed network and
   has two IPv6 addresses, one delegated from each of the upstream ISPs.
   Note that ISP2 is a closed network and does not have connectivity to
   the Internet.



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                           +--------+
                           | Host-C | 2001:db8:a000::1
                           +-----+--+
                                 |
                        ==============  +--------+
                        |  Internet  |  | Host-B | 2001:db8:8000::1
                        ==============  +--------+
                             |           |
           2001:db8:1000:/36 |           | 2001:db8:8000::/36
                        +----+-+   +-+---++
                        | ISP1 |   | ISP2 | (Closed Network/VPN tunnel)
                        +----+-+   +-+----+
                             |       |
           2001:db8:1000:/48 |       | 2001:db8:8000::/48
                            ++-------++
                            | Gateway |
                            +----+----+
                                 |  2001:db8:1000:1::/64
                                 |  2001:db8:8000:1::/64
                       ------+---+----------
                             |
                          +--+-----+ 2001:db8:1000:1::EUI64
                          | Host-A | 2001:db8:8000:1::EUI64
                          +--------+

                                [Fig. 3]

   You do not need two physical network connections here.  The
   connection from the Gateway to ISP2 can be a logical link over ISP1
   and the Internet.

   When Host-A starts the connection to Host-B in ISP2, the source
   address of a packet that has been sent will be the one delegated from
   ISP2, that is 2001:db8:8000:1::EUI64, because of rule 8 (longest
   matching prefix) in RFC 3484.

   Host-C is located somewhere on the Internet and has IPv6 address
   2001:db8:a000::1.  When Host-A sends a packet to Host-C, the longest
   matching algorithm chooses 2001:db8:8000:1::EUI64 for the source
   address.  In this case, the packet goes through ISP1 and may be
   filtered by ISP1's ingress filter.  Even if the packet is not
   filtered by ISP1, a return packet from Host-C cannot possibly be
   delivered to Host-A because the return packet is destined for 2001:
   db8:8000:1::EUI64, which is closed from the Internet.

   The important point is that each host chooses a correct source
   address for a given destination address as long as NAT does not exist
   in the IPv6 world.



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2.1.4.  Combined Use of Global and ULA

                        ============
                        | Internet |
                        ============
                              |
                              |
                         +----+----+
                         |   ISP   |
                         +----+----+
                              |
              2001:db8:a::/48 |
                         +----+----+
                         | Gateway |
                         +-+-----+-+
                           |     | 2001:db8:a:100::/64
          fd01:2:3:200:/64 |     | fd01:2:3:100:/64
                   -----+--+-   -+--+----
                        |           |
    fd01:2:3:200::EUI64 |           |      2001:db8:a:100::EUI64
                   +----+----+    +-+----+ fd01:2:3:100::EUI64
                   | Printer |    | Host |
                   +---------+    +------+

                                [Fig. 4]

   As NAP [I-D.ietf-v6ops-nap] describes, using a ULA may be beneficial
   in some scenarios.  If the ULA is used for internal communication,
   packets with ULA need to be filtered at the Gateway.

   There is no serious problem related to address selection in this
   case, because of the dissimilarity between the ULA and the Global
   Unicast Address.  The longest matching rule of RFC 3484 chooses the
   correct address for both intra-site and extra-site communication.

   In a few years, however, the longest matching rule will not be able
   to choose the correct address anymore.  That is the moment when the
   assignment of those Global Unicast Addresses starts, where the first
   bit is 1.  In RFC 4291 [RFC4291], almost all address spaces of IPv6,
   including those whose first bit is 1, are assigned as Global Unicast
   Addresses.

2.1.5.  Site Renumbering

   RFC 4192 [RFC4192] describes a recommended procedure for renumbering
   a network from one prefix to another.  An autoconfigured address has
   a lifetime, so by stopping advertisement of the old prefix, the
   autoconfigured address is eventually invalidated.



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   However, invalidating the old prefix takes a long time.  You cannot
   stop routing to the old prefix as long as the old prefix is not
   removed from the host.  This can be a tough issue for ISP network
   administrators.

                              +-----+---+
                              | Gateway |
                              +----+----+
                                   |  2001:db8:b::/64  (new)
                                   |  2001:db8:a::/64 (old)
                         ------+---+----------
                               |
                            +--+-----+ 2001:db8:b::EUI64  (new)
                            | Host-A | 2001:db8:a::EUI64 (old)
                            +--------+

                                [Fig. 5]

2.1.6.  Multicast Source Address Selection

   This case is an example of Site-local or Global prioritization.  When
   you send a multicast packet across site-borders, the source address
   of the multicast packet must be a global scope address.  The longest
   matching algorithm, however, selects a ULA if the sending host has
   both a ULA and a global address.

2.1.7.  Temporary Address Selection

   RFC 3041 [RFC3041] defines a Temporary Address.  The usage of a
   Temporary Address has both pros and cons.  That is good for viewing
   web pages or communicating with the general public, but that is bad
   for a service that uses address-based authentication and for logging
   purposes.

   If you could turn the temporary address on and off, that would be
   better.  If you could switch its usage per service(destination
   address), that would also be better.  The same situation can be found
   when using HA and CoA in a MobileIP network.

2.2.  Destination Address Selection

2.2.1.  IPv4 or IPv6 prioritization

   The default policy table gives IPv6 addresses higher precedence than
   IPv4 addresses.  There seem to be many cases, however, where network
   administrators want to control the address selection policy of end-
   hosts the other way around.




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                            +---------+
                            | Tunnel  |
                            | Service |
                            +--+---++-+
                               |   ||
                               |   ||
                        ===========||==
                        | Internet || |
                        ===========||==
                             |     ||
                192.0.2.0/24 |     ||
                        +----+-+   ||
                        | ISP  |   ||
                        +----+-+   ||
                             |     ||
               IPv4 (Native) |     || IPv6 (Tunnel)
                192.0.2.0/26 |     ||
                            ++-----++-+
                            | Gateway |
                            +----+----+
                                 |  2001:db8:a:1::/64
                                 |  192.0.2.0/28
                                 |
                       ------+---+----------
                             |
                           +-+----+ 2001:db8:a:1:EUI64
                           | Host | 192.0.2.2
                           +------+

                                [Fig. 6]

   In the figure above, a site has native IPv4 and tunneled-IPv6
   connectivity.  Therefore, the administrator may want to set a higher
   priority for using IPv4 than using IPv6 because the quality of the
   tunnel network seems to be worse than that of the native transport.

2.2.2.  ULA and IPv4 dual-stack environment

   This is a special form of IPv4 and IPv6 prioritization.  When an
   enterprise has IPv4 Internet connectivity but does not yet have IPv6
   Internet connectivity, and the enterprise wants to provide site-local
   IPv6 connectivity, a ULA is the best choice for site-local IPv6
   connectivity.  Each employee host will have both an IPv4 global or
   private address and a ULA.  Here, when this host tries to connect to
   Host-C that has registered both A and AAAA records in the DNS, the
   host will choose AAAA as the destination address and the ULA for the
   source address.  This will clearly result in a connection failure.




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                           +--------+
                           | Host-C | AAAA = 2001:db8::80
                           +-----+--+ A    = 192.0.2.1
                                 |
                        ============
                        | Internet |
                        ============
                             |  no IPv6 connectivity
                        +----+----+
                        | Gateway |
                        +----+----+
                             |
                             | fd01:2:3::/48 (ULA)
                             | 192.0.2.128/25
                            ++--------+
                            | Router  |
                            +----+----+
                                 |  fd01:2:3:4::/64 (ULA)
                                 |  192.0.2.240/28
                       ------+---+----------
                             |
                           +-+----+ fd01:2:3:4::100 (ULA)
                           | Host | 192.0.2.245
                           +------+

                                [Fig. 7]

2.2.3.  ULA or Global Prioritization

   Differentiating services by the client's source address is very
   common.  IP-address-based authentication is an typical example of
   this.  Another typical example is a web service that has pages for
   the public and internal pages for employees or involved parties.  Yet
   another example is DNS zone splitting.

   However, a ULA and IPv6 global address both have global scope, and
   RFC3484 default rules do not specify which address should be given
   priority.  This point makes IPv6 implementation of address-based
   service differentiation a bit harder.












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                            +------+
                            | Host |
                            +-+--|-+
                              |  |
                      ===========|==
                      | Internet | |
                      ===========|==
                            |    |
                            |    |
                       +----+-+  +-->+------+
                       | ISP  +------+  DNS | 2001:db8:a::80
                       +----+-+  +-->+------+ fc12:3456:789a::80
                            |    |
            2001:db8:a::/48 |    |
        fc12:3456:789a::/48 |    |
                       +----+----|+
                       | Gateway ||
                       +---+-----|+
                           |     |    2001:db8:a:100::/64
                           |     |    fc12:3456:789a:100::/64
                         --+-+---|-----
                             |   |
                           +-+---|+ 2001:db8:a:100::EUI64
                           | Host | fc12:3456:789a:100::EUI64
                           +------+

                                [Fig. 7]


3.  Conclusion

   We have covered problems related to destination or source address
   selection.  These problems have their roots in the situation where
   end-hosts have multiple IP addresses.  In this situation, every end-
   host must choose an appropriate destination and source address, which
   cannot be achieved only by routers.

   It should be noted that end-hosts must be informed about routing
   policies of their upstream networks for appropriate address
   selection.  A site administrator must consider every possible address
   false-selection problem and take countermeasures beforehand.


4.  Security Considerations

   When an intermediate router performs policy routing (e.g. source
   address based routing), inappropriate address selection causes
   unexpected routing.  For example, in the network described in 2.1.3,



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   when Host-A uses a default address selection policy and chooses an
   inappropriate address, a packet sent to VPN can be delivered to a
   location via the Internet.  This issue can lead to packet
   eavesdropping or session hijack.

   As documented in the security consideration section in RFC 3484,
   address selection algorithms expose a potential privacy concern.
   When a malicious host can make a target host perform address
   selection, the malicious host can know multiple addresses attached to
   the target host.  In a case like 2.1.4, if an attacker can make Host
   to send a multicast packet and the Host performs the default address
   selection algorithm, the attacker may be able to determine the ULAs
   attached to the Host.

   These security risks have roots in inappropriate address selection.
   Therefore, if a countermeasure is taken, and hosts always select an
   appropriate address that is suitable to a site's network structure
   and routing, these risks can be avoided.


5.  IANA Considerations

   This document has no actions for IANA.


6.  References

6.1.  Normative References

   [RFC3484]  Draves, R., "Default Address Selection for Internet
              Protocol version 6 (IPv6)", RFC 3484, February 2003.

   [RFC4193]  Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
              Addresses", RFC 4193, October 2005.

6.2.  Informative References

   [I-D.ietf-v6ops-nap]
              Velde, G., "Local Network Protection for IPv6",
              draft-ietf-v6ops-nap-06 (work in progress), January 2007.

   [RFC3041]  Narten, T. and R. Draves, "Privacy Extensions for
              Stateless Address Autoconfiguration in IPv6", RFC 3041,
              January 2001.

   [RFC4192]  Baker, F., Lear, E., and R. Droms, "Procedures for
              Renumbering an IPv6 Network without a Flag Day", RFC 4192,
              September 2005.



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   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, February 2006.


Appendix A.  Appendix. Revision History

   01:
      IP addresse notations changed to docmentation address.
      Descriptoin of solutions deleted.
   02:
      Security considerations section rewritten according to comments
      from SECDIR.


Authors' Addresses

   Arifumi Matsumoto
   NTT PF Lab
   Midori-Cho 3-9-11
   Musashino-shi, Tokyo  180-8585
   Japan

   Phone: +81 422 59 3334
   Email: arifumi@nttv6.net


   Tomohiro Fujisaki
   NTT PF Lab
   Midori-Cho 3-9-11
   Musashino-shi, Tokyo  180-8585
   Japan

   Phone: +81 422 59 7351
   Email: fujisaki@nttv6.net


   Ruri Hiromi
   Intec Netcore, Inc.
   Shinsuna 1-3-3
   Koto-ku, Tokyo  136-0075
   Japan

   Phone: +81 3 5665 5069
   Email: hiromi@inetcore.com







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   Ken-ichi Kanayama
   Intec Netcore, Inc.
   Shinsuna 1-3-3
   Koto-ku, Tokyo  136-0075
   Japan

   Phone: +81 3 5665 5069
   Email: kanayama@inetcore.com











































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Full Copyright Statement

   Copyright (C) The IETF Trust (2007).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on an
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Acknowledgment

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   Administrative Support Activity (IASA).





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