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Versions: 00 01 02 03 draft-ietf-6man-rfc3484-revise

Network Working Group                                       A. Matsumoto
Internet-Draft                                               T. Fujisaki
Intended status: Standards Track                                     NTT
Expires: April 22, 2010                                        R. Hiromi
                                                           Intec Netcore
                                                        October 19, 2009


             Things To Be Considered for RFC 3484 Revision
                draft-arifumi-6man-rfc3484-revise-02.txt

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   Copyright (c) 2009 IETF Trust and the persons identified as the
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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents in effect on the date of
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   Please review these documents carefully, as they describe your rights
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Abstract

   RFC 3484 has several known issues to be fixed mainly because of the
   deprecation of IPv6 site-local unicast address and the coming of ULA.
   Additionally, the rule 9 of the destination address selection rules,
   namely the longest matching rule, is known for its adverse effect on
   the round robin DNS technique.  This document covers these essential
   points to be modified and proposes possible useful changes to be
   included in the revision of RFC 3484.


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
     1.1.  Problem Example . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Proposed Changes to RFC 3484  . . . . . . . . . . . . . . . . . 4
     2.1.  To remove site-local unicast address  . . . . . . . . . . . 4
     2.2.  To change default policy table  . . . . . . . . . . . . . . 5
     2.3.  To change ULA address scope to site-local . . . . . . . . . 5
     2.4.  To add descriptions for source address selection for
           multicast packet  . . . . . . . . . . . . . . . . . . . . . 6
     2.5.  To make address type dependent control possible . . . . . . 6
     2.6.  To disable or restrict RFC 3484 Section 6 Rule 9  . . . . . 6
     2.7.  To change private IPv4 address scope  . . . . . . . . . . . 7
   3.  Conclusion  . . . . . . . . . . . . . . . . . . . . . . . . . . 8
   4.  Security Considerations . . . . . . . . . . . . . . . . . . . . 8
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 8
     6.1.  Normative References  . . . . . . . . . . . . . . . . . . . 8
     6.2.  Informative References  . . . . . . . . . . . . . . . . . . 9
   Appendix A.  Appendix. Revision History . . . . . . . . . . . . . . 9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 9













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1.  Introduction

   RFC 3484 [RFC3484] defines default address selection rules for IPv6
   and IPv4.  Because of the deprecation of IPv6 site-local unicast
   address and the coming of ULA, [RFC4193] these rules in RFC 3484 are
   known to cause communication failures depending on the network
   environment.

   Additionally, there was a discussion at v6ops and ietf mailing lists
   that the rule 9 of the destination address selection has a serious
   adverse effect on the round robin DNS technique.  [RFC1794] RFC 3484
   defines that the destination address selection rule 9 should be
   applied to both IPv4 and IPv6, which spoils the DNS based load
   balancing technique that is widely used in the IPv4 Internet today.

   Remi Denis-Courmont summarized NAT related address selection problems
   and possible solutions in [I-D.denis-v6ops-nat-addrsel].

   Problems related to IPv6 and IPv4 address selection are described in
   RFC 5220 [RFC5220].  Some of them can be fixed by updating RFC 3484,
   and some of the others are solved by address selection design team's
   proposal [I-D.chown-addr-select-considerations].

   This document covers these essential points to be modified and
   proposes possible useful changes to be included in the revision of
   RFC 3484.

1.1.  Problem Example

   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.














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                           +--------+
                           | 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. 1]

   This problem can be solved by changing the scope of ULA to site-
   local, or by adding one entry to the default policy table that sets
   lower priority for ULA than IPv4 address.

   This problem was mentioned at ipv6 mailing lists by Pekka Savola.


2.  Proposed Changes to RFC 3484

2.1.  To remove site-local unicast address

   RFC3484 contains a few "site-local unicast" and "fec::" description.
   It's better to remove examples related to site-local unicast address,
   or change examples to use ULA.  Possible points to be re-written are
   below.
      - 2nd paragraph in Section 3.1 describes scope comparison
      mechanism.







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      - Section 10 contains examples for site-local address.

2.2.  To change default policy table

   The default rule today is:

         Prefix        Precedence Label
         ::1/128               50     0
         ::/0                  40     1
         2002::/16             30     2
         ::/96                 20     3
         ::ffff:0:0/96         10     4

   The changes that should be included into the default policy table are
   those rules that are universally useful and do no harm in every
   reasonable network envionment.  The changes we should consider for
   the default policy table are as follows.  The policy table is defined
   to be configurable.  The changes that are useful not universally but
   locally can be put into the policy table manually or by using the
   auto-configuration mechanism proposed as a DHCP option
   [I-D.fujisaki-dhc-addr-select-opt].
      - IPv4-compatible IPv6 address is deprecated.  [RFC4291] (However,
      should we keep this entry for the sake of backward compatibility
      ?)
      - Teredo [RFC4380] is defined and has 2001::/32.  Teredo's
      priority should be less or equal to 6to4, considering its
      characteristic of tunnel mechanism.  About Windows, this point is
      already in the implementation.

   When we apply these changes, the default policy table looks like
   this.

         Prefix        Precedence Label
         ::1/128               50     0
         ::/0                  30     2
         2002::/16             20     3
         ::ffff:0:0/96         10     4
         2001::/32              5     5   (For Teredo)

   Teredo has the worst precedence.  This means that, for IPv4-IPv6
   dual-stack host, Teredo address will be used only when the
   destination host has an IPv6 address only.

2.3.  To change ULA address scope to site-local

   RFC 5220 Section 2.1.4, 2.2.2, and 2.2.3 describes address selection
   problems related to ULA.  These problems can be solved by changing
   the scope of ULA to site-local.



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2.4.  To add descriptions for source address selection for multicast
      packet

   For example, we have to pay attention to source address selection for
   a multicast packet.  As described in RFC 5220 Section 2.1.6, by
   default, ULA will be chosen for a multicast packet of any scope.

   This issue cannot be solved by changing a RFC 3484 rule.  This is
   because, multicast and unicast have different sets of scope and it is
   site-dependent which unicast address scope is appropriate for the
   site's multicast scope.  Therefore, this issue can be solved, for
   example, by configuring the policy table per-site.

2.5.  To make address type dependent control possible

   It is hard to define default preferences for these address types, RA-
   based, DHCP-based, manual-based, and privacy extention address,
   because the appropriate preference value depends on the usage of
   these addresses, but not on address types themselves.  It is the
   policy table where you can control host's address selection behavior.

   For example, You can set priority on RFC 4941 [RFC4941] address
   (privacy extension) by putting a line in policy table specifying RFC
   4941 address by 128-bit prefixlen and continuing to update policy
   table according to RFC 4941 address re-generation.  But, this is
   surely troublesome for users and implementers.

   One idea is to update RFC 3484 policy table definition so that it can
   handle meta addresses like privacy, DHCPv6 generated, RA generated,
   manually generated (and even Home Address ?)

   To prefer privacy address by default, and to prefer RA-generated
   address for site internal, the policy table will look like this.

           Prefix                         Pref   Label
           2001:db8:1234::(PRIVACY)/128   30     2
           ::/0                           10     2
           2001:db8:1234::(RA):/128       30     1
           2001:db8::/48                  20     1

2.6.  To disable or restrict RFC 3484 Section 6 Rule 9

   There was a discussion at v6ops and ietf@ietf.org mailing lists that
   the rule 9 of the destination address selection has a serious adverse
   effect on the round robin DNS technique.  RFC 3484 defines that the
   destination address selection rule 9 should be applied to both IPv4
   and IPv6, which spoils the DNS based load balancing technique that is
   widely used in the IPv4 Internet today.



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   When the destination address acquired from one FQDN are two or more,
   the Rule 9 defines that the longest matching destination and source
   address pair should be chosen.  As in RFC 1794, the DNS based load
   balancing technique is achived by not re-ordering the destination
   addresses returned from the DNS server.  The Rule 9 defines
   deterministic rule for re-ordering at hosts, hence the technique of
   RFC 1794 is not available anymore.

   Regarding this problem, there was a lot of discussion in IETF and
   other places like below.
      http://drplokta.livejournal.com/109267.html
      http://www.ietf.org/mail-archive/web/ietf/current/msg51874.html
      http://www.ietf.org/mail-archive/web/discuss/current/msg01035.html
      http://www.ietf.org/mail-archive/web/dnsop/current/msg05847.html
      http://lists.debian.org/debian-ctte/2007/11/msg00029.html
      http://www.ietf.org/mail-archive/web/ietf/current/msg55991.html

   Possible changes to RFC 3484 are as follows:

   1.  To delete Rule 9 completely.
   2.  To apply Rule 9 only for IPv6 and not for IPv4.  In IPv6,
       hiearchical address assignment is general principle, hence the
       longest matchin rule is beneficial in many cases.  In IPv4, as
       stated above, the DNS based load balancing technique is widely
       used.
   3.  To apply Rule 9 for IPv6 conditionally and not for IPv4.  When
       the length of matching bits of the destination address and the
       source address is longer than N, the rule 9 is applied.
       Otherwise, the order of the destination addresses do not change.
       The N should be configurable and it should be 32 by default.
       This is simply because the two sites whose matching bit length is
       longer than 32 are probably adjacent.

   Now that IPv6 PI address is admitted in some RIRs, hierachical
   address assignment is not maintained anymore.  It seems that the
   longest matching algorithm is not worth the adverse effect of
   disalbing the DNS based load balance technique.  Therefore, the
   proposal 1 or 3 seems to be preferable.

2.7.  To change private IPv4 address scope

   As detailed in Remi's draft [I-D.denis-v6ops-nat-addrsel], when a
   host is in NATed site, and has a private IPv4 address and
   transitional addresses like 6to4 and Teredo, the host chooses
   transitional IPv6 address to access most of the dual-stack servers.

   This is because private IPv4 address is defined to be site-local
   scope, and as in RFC 3484, the scope matching rules (Rule 2) set



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   lower priority for private IPv4 address.

   By changing the address scope of private IPv4 address to global, this
   problem can be solved.


3.  Conclusion

   This document lists up several issues that should be included in the
   revision of RFC 3484, which are useful universally and do no harm in
   reasonable network environments.

   The address selection rules that are useful locally can be
   implemented, for example, by configuring the policy table.  The
   policy distribution mechanism [I-D.fujisaki-dhc-addr-select-opt] may
   be useful to configure a lot of hosts at a time.

   The destination address selection rule 9 will spoil the DNS based
   load balancing technique that is widely deployed at least in IPv4.
   To keep this functionality in IPv6, the rule 9 have to be deleted or
   restricted.


4.  Security Considerations

   No security risk is found that degrades RFC 3484.


5.  IANA Considerations

   Address type number for the policy table may have to be assigned by
   IANA.


6.  References

6.1.  Normative References

   [RFC1794]  Brisco, T., "DNS Support for Load Balancing", RFC 1794,
              April 1995.

   [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.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing



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              Architecture", RFC 4291, February 2006.

   [RFC4380]  Huitema, C., "Teredo: Tunneling IPv6 over UDP through
              Network Address Translations (NATs)", RFC 4380,
              February 2006.

6.2.  Informative References

   [I-D.chown-addr-select-considerations]
              Chown, T., "Considerations for IPv6 Address Selection
              Policy Changes", draft-chown-addr-select-considerations-03
              (work in progress), July 2009.

   [I-D.denis-v6ops-nat-addrsel]
              Denis-Courmont, R., "Problems with IPv6 source address
              selection and IPv4 NATs", draft-denis-v6ops-nat-addrsel-00
              (work in progress), February 2009.

   [I-D.fujisaki-dhc-addr-select-opt]
              Fujisaki, T., Matsumoto, A., and R. Hiromi, "Distributing
              Address Selection Policy using DHCPv6",
              draft-fujisaki-dhc-addr-select-opt-08 (work in progress),
              October 2009.

   [RFC4941]  Narten, T., Draves, R., and S. Krishnan, "Privacy
              Extensions for Stateless Address Autoconfiguration in
              IPv6", RFC 4941, September 2007.

   [RFC5220]  Matsumoto, A., Fujisaki, T., Hiromi, R., and K. Kanayama,
              "Problem Statement for Default Address Selection in Multi-
              Prefix Environments: Operational Issues of RFC 3484
              Default Rules", RFC 5220, July 2008.


Appendix A.  Appendix. Revision History

   02:
      The reference to RFC3041 was updated to RFC4941.
      Added the reference to address selection design team's proposal.

   01:
      The issue of private IPv4 address scope was added.
      The issue of ULA address scope was added.
      Discussion of longest matching rule was expanded.







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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





















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