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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: May 14, 2007                                          R. Hiromi
                                                             K. Kanayama
                                                           Intec Netcore
                                                       November 10, 2006


     Problem Statement of Default Address Selection in Multi-prefix
        Environment: Operational Issues of RFC3484 Default Rules
                 draft-ietf-v6ops-addr-select-ps-00.txt

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
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Copyright Notice

   Copyright (C) The Internet Society (2006).

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 the communication.  RFC 3484 defines both the source
   and destination address selection algorithms, but the multi-prefix
   environment considered here needs additional rules beyond 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  . . . . . . . . . . . . .  6
       2.1.4.  Combined Use of Global and ULA . . . . . . . . . . . .  7
       2.1.5.  Site Renumbering . . . . . . . . . . . . . . . . . . .  8
       2.1.6.  Multicast Source Address Selection . . . . . . . . . .  8
       2.1.7.  Temporary Address Selection  . . . . . . . . . . . . .  8
     2.2.  Destination Address Selection  . . . . . . . . . . . . . .  9
       2.2.1.  IPv4 or IPv6 prioritization  . . . . . . . . . . . . .  9
       2.2.2.  ULA and IPv4 dual-stack environment  . . . . . . . . . 10
       2.2.3.  ULA or Global Prioritization . . . . . . . . . . . . . 10
   3.  Solutions  . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     3.1.  More Specific Routes (RFC 4191)  . . . . . . . . . . . . . 11
     3.2.  Policy Table Manipulation  . . . . . . . . . . . . . . . . 11
     3.3.  Revising RFC 3484  . . . . . . . . . . . . . . . . . . . . 12
   4.  Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 12
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 12
     7.2.  Informative References . . . . . . . . . . . . . . . . . . 13
   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 ULA [RFC4193] and
   Global scope networks, an end-host has multiple IP addresses.  These
   are examples of the 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 or filtering by a router on the way
   back or discard due to there being no route to the host.

   Considering a multi-prefix environment, the destination address
   selection is also important for correct communication establishment.
   The key to the appropriate process will come from the way to
   configure the source address and destination address to the
   interfaces at the end-hosts by the network policy of the site.

   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.  But there
   are still problematic cases such as when multiple default routes are
   supplied.  This document describes such possibilities of false
   dropping during address selection.

   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 it makes no mention of the provisions of
   address policy and does not define how to set it except manually.

1.1.  Scope of this document

   There has been a lot of discussion about "multiple addresses/
   prefixes" but the multi-homing issues for 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::/32 |          | 3ffe:1800::/32
                        +----+-+      +-+----+
                        | ISP1 |      | ISP2 |
                        +----+-+      +-+----+
                             |          |
             2001:db8:a::/48 |          | 3ffe:1800:a::/48
                      +------+---+ +----+-----+
                      | Gateway1 | | Gateway2 |
                      +--------+-+ +-+--------+
                               |     |
             2001:db8:a:1::/64 |     | 3ffe:1800:a:1::/64
                               |     |
                        -----+-+-----+------
                             |
                           +-+----+ 2001:db8:a:1:EUI64
                           | Host | 3ffe:1800:a:1:EUI64
                           +------+

                                [Fig. 1]

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

   To solve this case, one approach is to configure correctly both the
   routing configuration and address selection policy at Host.  You can
   use RFC 4191 [RFC4191] to deliver routing information to hosts.
   Another approach is to configure the gateways to make use of packet
   redirection between the gateways.













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2.1.2.  Ingress Filtering Problem

                        ==================
                        |    Internet    |
                        ==================
                             |       |
               2001:db8::/32 |       | 3ffe:1800::/32
                        +----+-+   +-+----+
                        | ISP1 |   | ISP2 |
                        +----+-+   +-+----+
                             |       |
             2001:db8:a::/48 |       | 3ffe:1800:a::/48
                            ++-------++
                            | Gateway |
                            +----+----+
                                 |  2001:db8:a:1::/64
                                 |  3ffe:1800:a:1::/64
                       ------+---+----------
                             |
                           +-+----+ 2001:db8:a:1:EUI64
                           | Host | 3ffe:1800:a: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 and
   more popular among ISPs in order 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:a:1::EUI64 as the source address for
   packets sent to a host(2001:fa8::1) somewhere in the Internet, the
   packets may be dropped at ISP2 because of Ingress Filtering.

   One possible solution for this problem is to adopt source-address-
   based routing at the customer site's gateway, but this manner of
   routing is not very popular at the moment.







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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 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.

                           +--------+
                           | Host-C | 3ffe:503:c:1:EUI64
                           +-----+--+
                                 |
                        ==============  +--------+
                        |  Internet  |  | Host-B | 3ffe:1800::EUI64
                        ==============  +--------+
                             |           |
               2001:db8::/32 |           | 3ffe:1800::/32
                        +----+-+   +-+---++
                        | ISP1 |   | ISP2 | (Closed Network/VPN tunnel)
                        +----+-+   +-+----+
                             |       |
             2001:db8:a::/48 |       | 3ffe:1800:a::/48
                            ++-------++
                            | Gateway |
                            +----+----+
                                 |  2001:db8:a:1::/64
                                 |  3ffe:1800:a:1::/64
                       ------+---+----------
                             |
                          +--+-----+ 2001:db8:a:1:EUI64
                          | Host-A | 3ffe:1800:a:1:EUI64
                          +--------+

                                [Fig. 3]

   You don't need two physical network connection here.  The connection
   from 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 sending packet will be the one delegated from ISP2, that
   is 3ffe:1800:a:1:EUI64, because of rule 8 (longest matching prefix)
   in RFC 3484.

   Host-C is located somewhere in the Internet and has an IPv6 address
   3ffe:503:c:1:EUI64.  When Host-A sends a packet to Host-C, the
   longest matching algorithm chooses 3ffe:1800:a:1:EUI64 for the source



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   address.  In this case, the packet goes through ISP1 and may be
   filtered by ISP1's ingress filter.  Even if the packet is fortunately
   not filtered by ISP1, a return packet from Host-C cannot possibly be
   delivered to Host-A because the return packet is destined for 3ffe:
   1800:a:1:EUI64, which is closed from the Internet.

   In this case, source-address-based routing alone described in the
   previous section does not solve the problem.  What is important is
   that each host chooses a correct source address for a given
   destination address as far as NAT does not exist in the IPv6 world.

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 ULA may be beneficial in
   some scenarios.  If ULA is used for internal communication, packets
   with ULA addresses need to be filtered at Gateway.

   There is no serious problem related to address selection in this
   case, thanks to the unlikeness of ULA and Global Unicast Address for
   now.  RFC 3484's longest matching rule 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: the moment the assignment of



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   those Global Unicast Addresses whose beginning bit is 1 starts.  In
   RFC 4291 [RFC4291], almost all the space of IPv6, including those
   with beginning bit 1, is 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 auto-configured address has
   a lifetime, so by stopping advertisement of the old prefix it is
   eventually invalidated.

   However, it takes a long time to invalidate the old prefix.  You
   cannot stop routing to the old prefix as long as the old prefix is
   not deprecated.  This issue can be a tough issue for ISP network
   administrator.

                              +-----+---+
                              | 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 address 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
   Temporary Address has both pros and cons.  It is good for viewing
   web-pages or communicating with the general public, but it is bad for
   a service that uses address-based authentication and for logging
   purpose.

   It would be better if you could turn the temporary address on and
   off.  It would also be better if you could switch its usage per
   service(destination address).  The same situation can be found when



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   using HA and CoA in 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.

                            +---------+
                            | 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.





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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, 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 ULA for the
   source address.  This will clearly result in a connection failure.

                           +--------+
                           | Host-C | AAAA = 2001:db8::80
                           +-----+--+ A    = 192.47.163.1
                                 |
                        ============
                        | Internet |
                        ============
                             |  no IPv6 connectivity
                        +----+----+
                        | Gateway |
                        +----+----+
                             |
                             | fd01:2:3::/48 (ULA)
                             | 192.0.2.0/24
                            ++--------+
                            | 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

   It is very common to differentiate services by the client's source
   address.  IP-address-based authentication is an extreme 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, ULA and IPv6 global address both have global scope, and RFC



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   3484 default rules do not specify which address should be given
   priority.  This point makes IPv6 implementation of address-based
   service differentiation a bit harder.

                            +------+
                            | 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.  Solutions

3.1.  More Specific Routes (RFC 4191)

   This method enables network administrator to distribute routing
   information to end-hosts.  It can solve only two problems in this
   document, that is 2.1.1, 2.2.2.  Routing information doesn't
   determine the source address when multiple addresses are attached to
   the outgoing network interface.  So, it cannot be used for every
   cases here.

3.2.  Policy Table Manipulation

   Almost all the problem cases raised in this document can be solved by
   configuring the policy table at end-hosts.  The problem for a site-



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   administrator is that he does not have the means to deliver policies
   to end-hosts.  Therefore, we proposed a method for policy
   distribution in the form of DHCPv6 option
   [I-D.fujisaki-dhc-addr-select-opt].  The usage of this mechanisim is
   illustrated in another I-D [I-D.arifumi-ipv6-policy-dist].

3.3.  Revising RFC 3484

   Revising address selection rules defined in RFC 3484 in another idea.
   These problems are, however, too network-environment-specific, so
   it's not easy to have all-purpose rule set.


4.  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.


5.  Security Considerations

   Address false-selection can lead to serious security problem, such as
   session hijack.  However, it should be noted that address selection
   is eventually up to end-hosts.  We have no means to enforce one
   specific address selection policy to every end-host.  So, a network
   administrator has to take countermeasures for unexpected address
   selection.


6.  IANA Considerations

   This document has no actions for IANA.


7.  References

7.1.  Normative References

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



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

7.2.  Informative References

   [I-D.arifumi-ipv6-policy-dist]
              Matsumoto, A., "Practical Usages of Address Selection
              Policy Distribution", draft-arifumi-ipv6-policy-dist-01
              (work in progress), June 2006.

   [I-D.fujisaki-dhc-addr-select-opt]
              Fujisaki, T., "Distributing Default Address Selection
              Policy using DHCPv6",
              draft-fujisaki-dhc-addr-select-opt-02 (work in progress),
              June 2006.

   [I-D.ietf-v6ops-nap]
              Velde, G., "Network Architecture Protection for IPv6",
              draft-ietf-v6ops-nap-04 (work in progress), October 2006.

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

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

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

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


Appendix A.  Appendix. Revision History

   01:
      Authors' addresses corrected.
      Solutions section added.
      Security Considerations section fully rewritten.
      Some editorial changes.









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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@syce.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


   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 Internet Society (2006).

   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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Matsumoto, et al.         Expires May 14, 2007                 [Page 15]


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