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Versions: 00 01 02

INTERNET-DRAFT                                          R. Hinden, Nokia
June 11, 2003                                    Brian Haberman, Caspian





              Globally Unique IPv6 Local Unicast Addresses

              <draft-hinden-ipv6-global-local-addr-01.txt>




Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026. Internet-Drafts are working
   documents of the Internet Engineering Task Force (IETF), its areas,
   and its working groups.  Note that other groups may also distribute
   working documents as Internet-Drafts.

   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."

   To view the list Internet-Draft Shadow Directories, see
   http://www.ietf.org/shadow.html.

   This internet draft expires on December 16, 2003.


Abstract

   This document defines an unicast address format that is globally
   unique and is intended for local communications, usually inside of a
   site.  They are not expected to be routable on the global Internet
   given current routing technology.












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1.0 Introduction

   This document defines an IPv6 unicast address format that is globally
   unique and is intended for local communications [IPV6].  They are not
   expected to be routable on the global Internet given current routing
   technology.  They are routable inside of a more limited area such as
   a site.  They may also be routed between a limited set of sites.

   Globally unique IPv6 local addresses have the following
   characteristics:

      - Globally unique prefix.
      - Well known prefix to allow for easy filtering at site
        boundaries.
      - Allows sites to be combined or privately interconnected without
        creating any address conflicts or require renumbering of
        interfaces using these prefixes.
      - Internet Service Provider independent and can be used for
        communications inside of a site without having any permanent or
        intermittent Internet connectivity.
      - If accidentally leaked outside of a site via routing or DNS,
        there is no conflict with any other addresses.
      - In practice, applications may treat these address like global
        scoped addresses.
      - These addresses are also candidates for end-to-end use in some
        classes of multihoming solutions.

   This document defines the format of Globally Unique IPv6 Local
   addresses, how to allocate them, and usage considerations including
   routing, site border routers, DNS, application support, VPN usage,
   and guidelines for how to use for local communication inside a site.

   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].


2.0 Acknowledgments

   The underlying idea of creating globally unique IPv6 local addresses
   describe in this document been proposed a number of times by a
   variety of people.  The authors of this draft does not claim
   exclusive credit.  Credit goes to Brian Carpenter, Christian Huitema,
   Aidan Williams, Andrew White, Michel Py, Charlie Perkins, and many
   others.  The authors would also like to thank Brian Carpenter,
   Charlie Perkins, Harald Alvestrand, Keith Moore, Margaret Wasserman,
   and Michel Py for their comments and suggestions on this draft.




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3.0 Globally Unique IPv6 Local Unicast Addresses

3.1 Format

   The globally unique IPv6 local addresses are created using a
   centrally allocated global ID.  They have the following format:

      |   n    |
      |  bits  |  m bits    |  16 bits  |          64 bits            |
      +--------+------------+-----------+-----------------------------+
      | prefix | global ID  | subnet ID |        interface ID         |
      +--------+------------+-----------+-----------------------------+

   Where:

      prefix            prefix to identify Globally Unique IPv6 Local
                        unicast addresses.

      global ID         global identifier used to create a globally
                        unique prefix. See section 3.2 for additional
                        information.

      subnet ID         16-bit subnet ID is an identifier of a subnet
                        within the site.

      interface ID      64-bit IID as defined in [ADDARCH].

   There are a range of choices available when choosing the size of the
   prefix and Global ID field length.  There is a direct tradeoff
   between having a Global ID field large enough to support foreseeable
   future growth and not using too much of the IPv6 address space
   needlessly.  A reasonable way of evaluating a specific field length
   is to compare it to a projected 2050 world population of 9.3 billion
   [POPUL] to compare the number of resulting /48 prefixes per person.
   A range of prefix choices is shown in the following table:

      Prefix   Global ID       Number /48         Prefixes     % of IPv6
               Length          Prefixes           per Person   Address Space

      /11      37               137,438,953,472      15        0.049%
      /10      38               274,877,906,944      30        0.098%
      /9       39               549,755,813,888      59        0.195%
      /8       40             1,099,511,627,776     118        0.391%
      /7       41             2,199,023,255,552     236        0.781%
      /6       42             4,398,046,511,104     473        1.563%

   A very high utilization ratio of these allocations can be assumed
   because no internal structure is required in the field nor is there



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   any reason to be able to aggregate the prefixes.

   The authors believes that a /7 prefix resulting in a 41 bit Global ID
   is a good choice.  It provides for a large number of assignments
   (i.e., 2.2 trillion) and at the same time uses less than .8% of the
   total IPv6 address space.  It is unlikely that this space will be
   exhausted.  If more than this was needed, then additional IPv6
   address space could be allocated for this purpose.

   For the rest of this document the FC00::/7 prefix and a 41-bit Global
   ID is used.


3.2 Global ID

   The allocation of global IDs should be pseudo-random [RANDOM].  They
   should not be assigned sequentially or with well known numbers.  This
   to ensure that there is not any relationship between allocations and
   to help clarify that these prefixes are not intended to be routed
   globally.  Specifically, these prefixes are designed to not
   aggregate.

   There are two ways to allocate Global IDs.  These are centrally by a
   allocation authority and locally by the site.  The Global ID is split
   into two parts for each type of allocation.  The prefixes for each
   type are:

      FC00::/8    Centrally assigned
      FD00::/8    Locally assigned

   Each results in a 40-bit space to allocate.

   Two assignment methods are included because they have different
   properties.  The centrally assigned global IDs have a much higher
   probability that they are unique and the assignments can be escrowed
   to resolve any disputes regarding duplicate assignments.  The local
   assignments are free and do not need any central coordination or
   assignment, but have a lower (but still adequate) probability of
   being unique.  It is expected that large managed sites will prefer
   central assignments and small or disconnected sites will prefer local
   assignments.  Sites are free to choice either approach.


3.2.1 Centrally Assigned Global IDs

   Centrally assigned global IDs MUST be generated with a pseudo-random
   algorithm consistent with [RANDOM].  They should not be assigned
   sequentially or by locality.  This to ensure that there is not any



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   relationship between allocations and to help clarify that these
   prefixes are not intended to be routed globally.  Specifically, these
   prefixes are designed to not aggregate.

   Global IDs should be assigned centrally by a single allocation
   authority because they are pseudo-random and without any structure.
   This is easiest to accomplish if there is a single source of the
   assignments.

   The requirements for centrally assigned global ID allocations are:

      - Available to anyone in an unbiased manner.
      - Permanent with no periodic fees.
      - One time non-refundable allocation fee in the order of 10 Euros
        per allocation.
      - The ownership of each individual allocation should be private,
        but should be escrowed.

   The allocation authority should permit allocations to be obtained
   without having any sort of internet connectivity.  For example in
   addition to web based registration they should support some methods
   like telephone, postal mail, fax, telex, etc.  They should also
   accept a variety of payment methods and currencies.

   The reason for the one time 10 Euro charge for each prefix is to
   provide a barrier to any hoarding of the these allocations but at the
   same time keep the cost low enough to not create a barrier to anyone
   needing one.  The charge is non-refundable in order to keep overhead
   low.

   The ownership of the allocations is not needed to be public since the
   resulting addresses are intended to be used for local communication.
   It is escrowed to insure there are no duplicate allocations and in
   case it is needed in the future (e.g., to resolve duplicate
   allocation disputes).

   An example of a allocation authority is a non-profit organization
   such as the Public Internet Registry (PIR) that the Internet Society
   has created to manage the .org domain.  They already know how to
   collect small sums efficiently and there are safeguards in place for
   the appropriate use of any excess revenue generated.

   Note, there are many possible ways of of creating an allocation
   authority.  It is important to keep in mind when reviewing
   alternatives that the goal is to pick one that can do the job.  It
   doesn't have to be perfect, only good enough to do the job at hand.
   The authors believe that PIR shows that this requirement can be
   satisfied, but this draft does not specifically recommend the choice



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   of PIR.


3.2.2 Locally Assigned Global IDs

   Global IDs can also be generated locally by an individual site.  This
   makes it easy to get a prefix with out the need to contact an
   assignment authority or internet service provider.  There is not as
   high a degree of assurance that the prefix will not conflict with
   another locally generated prefix, but the likelihood of conflict is
   small.  Sites that are not comfortable with this degree of
   uncertainty should use a centrally assigned global ID.

   Locally assigned global IDs MUST be generated with a pseudo-random
   algorithm consistent with [RANDOM].  Section 3.2.3 describes a
   suggested algorithm.  It is important to insure a reasonable
   likelihood uniqueness that all sites generating a Global IDs use a
   functionally similar algorithm.


3.2.3  Sample Code for Pseudo-Random Global ID Algorithm

   The algorithm described below is intended to be used for centrally
   and locally assigned Global IDs.  In each case the resulting global
   ID will be used in the appropriate prefix as defined in section 3.2.

     1) Obtain the current time of day in 64-bit NTP format [NTP].
     2) Obtain the birth date of the person running the algorithm (or
        one of his/her descendants or ancestors) in 64-bit NTP format.
     3) Concatenate the time of day with the birth date resulting in a
        128-bit value (i.e., TOD, Birthday).
     4) Compute an MD5 digest on the 128-bit value as specified in
        [MD5DIG].
     5) Use the least significant 40 bits as the Global ID.

   This algorithm will result in a global ID that is reasonably unique
   and can be used as a Global ID.


3.3 Scope Definition

   By default, the scope of these addresses is global.  That is, they
   are not limited by ambiguity like the site-local addresses defined in
   [ADDRARCH].  Rather, these prefixes are globally unique, and as such,
   their applicability exceeds the current site-local addresses.  Their
   limitation is in the routability of the prefixes, which is limited to
   a site and any explicit routing agreements with other sites to
   propagate them.  Also, unlike site-locals, these prefixes can overlap



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4.0 Routing

   Globally IPv6 Local address are designed to be routed inside of a
   site in the same manner as other types of unicast addresses.  They
   can be carried in any IPv6 routing protocol without any change.

   It is expected that they would share the same subnet IDs with
   provider based global unicast addresses if they were being used
   concurrently [GLOBAL].

   Any routing protocol that is used between sites is required to filter
   out any incoming or outgoing globally unique IPv6 local routes.  The
   exception to this is if specific /48 globally unique IPv6 local
   routes have been configured to allow for inter-site communication.

   If BGP is being used at the site border with an ISP, by default
   filters MUST be installed in the BGP configuration to keep any site-
   local prefixes from being advertised outside of the site or for site-
   local prefixes to be learned from another site.  The exception to
   this is if there are specific /48 routes created for one or more
   globally unique IPv6 local prefixes.


5.0 Renumbering and Site Merging

   The use of globally unique IPv6 local addresses in a site results in
   making communication using these addresses independent of renumbering
   a site's provider based global addresses.

   When merging multiple sites none of the addresses created with these
   prefixes need to be renumbered because all of the addresses are
   unique.  Routes for each specific prefix would have to be configured
   to allow routing to work correctly between the formerly separate
   sites.


6.0 Site Border Router and Firewall Filtering

   While no serious harm will be done if packets with these addresses
   are sent outside of a site via a default route, it is recommended
   that they be filtered to keep any packets with globally unique IPv6
   local destination addresses from leaking outside of the site and to
   keep any site prefixes from being advertised outside of their site.

   Site border routers SHOULD install a black hole route for the
   Globally Unique IPv6 Local prefix FC00::/7.  This will insure that
   packets with Globally Unique IPv6 Local destination addresses will
   not be forwarded outside of the site via a default route.



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   Site border routers and firewalls SHOULD NOT forward any packets with
   globally unique IPv6 local source or destination addresses outside of
   the site unless they have been explicitly configured with routing
   information about other globally unique IPv6 local prefixes.  The
   default behavior of these devices SHOULD be to filter them.


7.0 DNS Issues

   Globally Unique IPv6 Local addresses SHOULD NOT be installed in the
   global DNS.  They may be installed in a naming system local to the
   site or kept separate from the global DNS using techniques such as
   "two-faced" DNS.

   If globally unique IPv6 local address are configured in the global
   DNS, no harm is done because they are unique and will not create any
   confusion.  The may not be reachable, but this is a property that is
   common to all types of global IPv6 unicast addresses.

   For future study names with globally unique IPv6 local addresses may
   be resolved inside of the site using dynamic naming systems such as
   Multicast DNS.


8.0 Application and Higher Level Protocol Issues

   Application and other higher level protocols can treat globally
   unique IPv6 local addresses in the same manner as other types of
   global unicast addresses.  No special handling is required.  This
   type of addresses may not be reachable, but that is no different from
   other types of IPv6 global unicast addresses.  Applications need to
   be able to handle multiple addresses that may or may not be reachable
   any point in time.  In most cases this complexity should be hidden in
   APIs.

   From a host's perspective this difference shows up as different
   reachability than global unicast and could be handled by default that
   way.  In some cases it is better for nodes and applications to treat
   them differently from global unicast addresses.  A starting point
   might be to give them preference over global unicast, but fall back
   to global unicast if a particular destination is found to be
   unreachable.  Much of this behavior can be controlled by how they are
   allocated to nodes and put into the DNS.  However it is useful if a
   host can have both types of addresses and use them appropriately.

   Note that the address selection mechanisms of [ADDSEL], and in
   particular the policy override mechanism replacing default address
   selection, are expected to be used on a site where globally unique



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   IPv6 local addresses are configured.


9.0 Use of Globally Unique IPv6 Local Addresses for Local Communications

   IPv6 globally unique IPv6 local addresses, like global scope unicast
   addresses, are only assigned to nodes if their use has been enabled
   (via IPv6 address autoconfiguration [ADDAUTO], DHCPv6 [DHCP6], or
   manually) and configured in the DNS.  They are not created
   automatically the way that IPv6 link-local addresses are and will not
   appear or be used unless they are purposely configured.

   In order for hosts to autoconfigure globally unique IPv6 local
   addresses routers have to be configured to advertise globally unique
   IPv6 local /64 prefixes in router advertisements.  Likewise, a DHCPv6
   server must have been configured to assign them.  In order for a node
   to learn the globally unique IPv6 local address of another node, the
   globally unique IPv6 local address must have been installed in the
   DNS.  For these reasons, it is straight forward to control their
   usage in a site.

   To limit the use of globally unique IPv6 local addresses the
   following guidelines apply:

      - Nodes that are to only be reachable inside of a site, the local
        DNS should be configured to only include the globally unique
        IPv6 local addresses of these nodes.  Nodes with only globally
        unique IPv6 local addresses must not be installed in the global
        DNS.

      - Nodes that are to be limited to only communicate with other
        nodes in the site should be set to only autoconfigure globally
        unique IPv6 local addresses via [ADDAUTO] or to only receive
        globally unique IPv6 local addresses via [DHCP6].  Note: For the
        case where both global and globally unique IPv6 local prefixes
        are being advertised on a subnet, this will require a switch in
        the devices to only autoconfigure globally unique IPv6 local
        addresses.

      - Nodes that are to be reachable from inside of the site and from
        outside of the site, the DNS should be configured to include the
        global addresses of these nodes.  The local DNS may be
        configured to also include the globally unique IPv6 local
        addresses of these nodes.

      - Nodes that can communicate with other nodes inside of the site
        and outside of the site, should autoconfigure global addresses
        via [ADDAUTO] or receive global address via [DHCP6].  They may



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        also obtain globally unique IPv6 local addresses via the same
        mechanisms.


10.0 Use of Globally Unique IPv6 Local Addresses with VPNs

   Globally unique IPv6 local addresses can be used for inter-site
   Virtual Private Networks (VPN) if appropriate routes are set up.
   Because the addresses are unique these VPNs will work reliably and
   without the need for translation.  They have the additional property
   that they will continue to work if the individual sites are
   renumbered or merged.


11.0 Advantages and Disadvantages

11.1 Advantages

   This approach has the following advantages:

      - Provides globally unique local prefixes that can be used
        independently of any provider based IPv6 unicast address
        allocations.  This is useful for sites not always connected to
        the Internet or sites that wish to have a distinct prefix that
        can be used to localize traffic inside of the site.
      - Applications can treat these addresses in an identical manner as
        any other type of global IPv6 unicast addresses.
      - Sites can be merged without any renumbering of the globally
        unique IPv6 local addresses.
      - Sites can change their provider based IPv6 unicast address
        without disrupting any communication using globally unique IPv6
        local addresses.
      - Well known prefix that allows for easy filtering at site
        boundary.
      - Can be used for inter-site VPNs.
      - If accidently leaked outside of a site via routing or DNS, there
        is no conflict with any other addresses.

11.2 Disadvantages

   This approach has the following disadvantages:

      - Not possible to route globally unique IPv6 local prefixes on the
        global Internet with current routing technology.
        Consequentially, it is necessary to have the default behavior of






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        site border routers to filter these addresses.
      - There is a very low probability of non-unique locally assigned
        global IDs being generated by the algorithm in section 3.2.3.
        This risk can be ignored for all practical purposes, but it
        leads to a theoretical risk of clashing address prefixes.


12.0 Security Considerations

   Globally unique IPv6 local addresses do not provide any inherent
   security to the nodes that use them.  They may be used with filters
   at site boundaries to keep globally unique IPv6 local traffic inside
   of the site, but this is no more or less secure than filtering any
   other type of global IPv6 unicast addresses.

   Globally unique IPv6 local addresses do allow for address-based
   security mechanisms, including IPSEC, across end to end VPN
   connections.


13.0 IANA Considerations

   The IANA is instructed to allocate the FC00::/7 prefix for Globally
   Unique IPv6 Local addresses.

   The IANA is instructed to delegate, within a reasonable time, the
   prefix FC00::/8 to an allocation authority for Globally Unique IPv6
   Local prefixes of length /48.  This allocation authority shall comply
   with the requirements described in section 3.2 of this document,
   including in particular the charging of a modest one-time fee, with
   any profit being used for the public good in connection with the
   Internet.


14.0 Change Log

   Draft <draft-hinden-ipv6-global-local-addr-01.txt>

      o Added section on scope definition and updated application
        requirement section.
      o Clarified that, by default, the scope of these addresses is
        global.
      o Renumbered sections and general text improvements
      o Removed reserved global ID values
      o Added pseudo code for local allocation submitted by Brian
        Haberman and added him as an author.
      o Split Global ID values into centrally assigned and local
        assignments and added text to describe local assignments



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   Draft <draft-hinden-ipv6-global-local-addr-00.txt>

      o Initial Draft


REFERENCES

   Normative

   [ADDARCH] Hinden, R., S. Deering, S., "IP Version 6 Addressing
             Architecture", RFC3515, April 2003.

   [GLOBAL]  Hinden, R., S. Deering, E. Nordmark, "IPv6 Global Unicast
             Address Format", Internet Draft, <draft-ietf-ipv6-unicast-
             aggr-v2-02.txt>, February 2003.

   [IPV6]    Deering, S., R. Hinden, "Internet Protocol, Version 6
             (IPv6) Specification", RFC2460, December 1998.

   [MD5DIG]  Rivest, R., "The MD5 Message-Digest Algorithm", RFC1321,
             April 1992.

   [NTP]   Mills, David L., "Network Time Protocol (Version 3)
             Specification, Implementation and Analysis", RFC1305, March
             1992.

   [POPUL]   Population Reference Bureau, "World Population Data Sheet
             of the Population Reference Bureau 2002",  August 2002.

   [RANDOM]  Eastlake, D. 3rd, S. Crocker, J. Schiller, "Randomness
             Recommendations for Security", RFC1750, December 1994.

   [RFC2026] Bradner, S., "The Internet Standards Process -- Revision
             3", RFC2026, BCP00009, October 1996.

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", RFC2119, BCP14, March 1997.

   Non-Normative

   [ADDAUTO] Thomson, S., T. Narten, "IPv6 Stateless Address
             Autoconfiguration", RFC2462, December 1998.

   [DHCP6]   Droms, R., et. al., "Dynamic Host Configuration Protocol
             for IPv6 (DHCPv6)", Internet Draft, <draft-ietf-dhc-
             dhcpv6-28.txt>, November 2002.





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


AUTHOR'S ADDRESSES

   Robert M. Hinden
   Nokia
   313 Fairchild Drive
   Mountain View, CA 94043
   US

   phone: +1 650 625-2004
   email: bob.hinden@nokia.com


   Brian Haberman
   Caspian Networks
   1 Park Drive, Suite 300
   Research Triangle Park, NC  27709
   US

   phone: +1-929-949-4828
   email: brian@innovationslab.net



























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