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Versions: (draft-jiang-6renum-enterprise) 00 01 02 03 04 05 06 RFC 6879

Network Working Group                                        S. Jiang
Internet Draft                                                 B. Liu
Intended status: Informational             Huawei Technologies Co., Ltd
Expires: January 14, 2013                                 B. Carpenter
                                                University of Auckland
                                                         July 16, 2012

      IPv6 Enterprise Network Renumbering Scenarios and Guidelines
                  draft-ietf-6renum-enterprise-01.txt


Status of this Memo

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   This Internet-Draft will expire on January 14, 2013.

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Abstract

   This document analyzes enterprise renumbering events and describes
   the best current practice among the existing renumbering mechanisms.
   According to the different stages of renumbering events,
   considerations and best current practices are described in three
   categories: during network design, for preparation of renumbering,
   and during a renumbering operation.

Table of Contents

   1. Introduction ................................................. 3
   2. Enterprise Network Illustration for Renumbering .............. 3
   3. Enterprise Network Renumbering Scenario Categories ........... 4
      3.1. Renumbering caused by External Network Factors........... 5
      3.2. Renumbering caused by Internal Network Factors........... 5
   4. Network Renumbering Considerations and Best Current Practices. 5
      4.1. Considerations and Best Current Practices during Network
      Design ....................................................... 6
      4.2. Considerations and Best Current Practices for the Preparation
      of Renumbering ............................................... 9
      4.3. Considerations and Best Current Practices during Renumbering
      Operation ................................................... 10
   5. Security Considerations ..................................... 12
   6. IANA Considerations ......................................... 13
   7. Acknowledgements ............................................ 13
   8. Change Log [RFC Editor please remove] ....................... 13
   9. References .................................................. 13
      9.1. Normative References ................................... 13
      9.2. Informative References ................................. 14
   Author's Addresses ............................................. 16















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1. Introduction

   IPv6 site renumbering is considered difficult. Network managers
   currently prefer to use Provider Independent (PI) addressing for IPv6
   to attempt to minimize the need for future renumbering. However,
   widespread use of PI may create very serious BGP4 scaling problems
   and PI space is not always available for enterprise according to the
   RIR (Regional Internet Registry) policies. It is thus desirable to
   develop tools and practices that may make renumbering a simpler
   process to reduce demand for IPv6 PI space. In any case, renumbering
   may be necessary for other reasons.

   This document undertakes scenario descriptions, including
   documentation of current capabilities and existing BCPs, for
   enterprise networks. It takes [RFC5887] and other relevant documents
   as the primary input.

   The IPv4 and IPv6 are logically separated from the perspective of
   renumbering, regardless of overlapping of the IPv4/IPv6 networks or
   devices. This document focuses on IPv6 only, by leaving IPv4 out of
   scope. Dual-stack network or IPv4/IPv6 transition scenarios are out
   of scope, too.

   This document focuses on enterprise network renumbering, though most
   of the analysis is also applicable to ISP network renumbering.
   Renumbering in home networks is considered out of scope, though it
   may also benefit from the analysis in this document.

   The concept of enterprise network and a typical network illustration
   are introduced first. Then, according to the different stages of
   renumbering events, considerations and best current practices are
   described in three categories: during network design, for preparation
   of renumbering, and during renumbering operation. A gap inventory is
   listed at the end of this document.

2. Enterprise Network Illustration for Renumbering

   An Enterprise Network as defined in [RFC4057] is: a network that has
   multiple internal links, one or more router connections to one or
   more Providers, and is actively managed by a network operations
   entity.

   The enterprise network architecture is illustrated in the figure
   below. Those entities relevant to renumbering are highlighted.




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   Address reconfiguration is fulfilled either by DHCPv6 or ND
   protocols. During the renumbering event, the DNS records need to be
   synchronized while routing tables, ACLs and IP filtering tables in
   various gateways also need to be updated, too.

   Static address issue is described in a dedicated draft [I-
   D.carpenter-6renum-static-problem]. (Editor's note: some major
   conclusions would be included in this document if we can get
   consensus on the discussion of the static address problem.)

               Uplink 1            Uplink 2
                  |                   |
              +---+---+           +---+---+
        +---- |Gateway| --------- |Gateway| -----+
        |     +-------+           +-------+      |
        |          Enterprise Network            |
        |   +------+     +------+    +------+    |
        |   | APP  |     |DHCPv6|    |  DNS |    |
        |   |Server|     |Server|    +Server+    |
        |   +---+--+     +---+--+    +--+---+    |
        |       |            |          |        |
        |    ---+--+---------+------+---+-       |
        |          |                |            |
        |       +--+---+        +---+--+         |
        |       |Router|        |Router|         |
        |       +--+---+        +---+--+         |
        |          |                |            |
        |     -+---+----+-------+---+--+-        |
        |      |        |       |      |         |
        |    +-+--+  +--+-+  +--+-+  +-+--+      |
        |    |Host|  |Host|  |Host|  |Host|      |
        |    +----+  +----+  +----+  +----+      |
        +----------------------------------------+
         Figure 1  Enterprise network illustration

   It is assumed that IPv6 enterprise networks are IPv6-only, or dual-
   stack in which a logical IPv6 plane is independent from IPv4. The
   complicated IPv4/IPv6 co-existence scenarios are out of scope.

   This document focuses on the unicast addresses; site-local, link-
   local, multicast and anycast addresses are out of scope.

3. Enterprise Network Renumbering Scenario Categories

   In this section, we divide enterprise network renumbering scenarios
   into two categories defined by external and internal network factors,
   which require renumbering for different reasons.


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3.1. Renumbering caused by External Network Factors

   The most influential external network factor is the uplink ISP.

   o The enterprise network switches to a new ISP. Of course, the
      prefixes received from different ISPs are different. This is the
      most common scenario.

      Whether there is an overlap time between the old and new ISPs
      would also influence the possibility whether the enterprise can
      fulfill renumbering without a flag day [RFC4192].

   o The renumbering event may be initiated by receiving new prefixes
      from the same uplink. This might happen if the enterprise network
      is switched to a different location within the network topology of
      the same ISP due to various considerations, such as commercial,
      performance or services reasons, etc. Alternatively, the ISP
      itself might be renumbered due to topology changes or migration to
      a different or additional prefix. These ISP renumbering events
      would initiate enterprise network renumbering events, of course.

   o The enterprise network adds new uplink(s) for multihoming
      purposes. This may not a typical renumbering because the original
      addresses will not be changed. However, initial numbering may be
      considered as a special renumbering event. The enterprise network
      removes uplink(s) or old prefixes.

3.2. Renumbering caused by Internal Network Factors

   o As companies split, merge, grow, relocate or reorganize, the
      enterprise network architectures may need to be re-built. This
      will trigger the internal renumbering.

   o The enterprise network may proactively adopt a new address scheme,
      for example by switching to a new transition mechanism or stage of
      a transition plan.

   o The enterprise network may reorganize its topology or subnets.

4. Network Renumbering Considerations and Best Current Practices

   In order to carry out renumbering in an enterprise network,
   systematic planning and administrative preparation are needed.
   Carefully planning and preparation could make the renumbering process
   smoother.




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   This section tries to give the recommended solutions or strategies
   for the enterprise renumbering, chosen among existing mechanisms.
   There are known gaps analyzed by [I-D.liu-6renum-gap-analysis]. If
   these gaps are filled in the future, the enterprise renumbering may
   be processed more automatically, with fewer issues.

4.1. Considerations and Best Current Practices during Network Design

   This section describes the consideration or issues relevant to
   renumbering that a network architect should carefully plan when
   building or designing a new network.

      - Prefix Delegation

      In a large or a multi-site enterprise network, the prefix should
      be carefully managed, particularly during renumbering events.
      Prefix information needs to be delegated from router to router.
      The DHCPv6 Prefix Delegation options [RFC3633] [I-D.ietf-dhc-pd-
      exclude] provide a mechanism for automated delegation of IPv6
      prefixes. Normally, DHCPv6 PD options are used between the
      internal enterprise routers.

      - Usage of FQDN

      In general, Fully-Qualified Domain Names (FQDNs) are recommended
      to be used to configure network connectivity, such as tunnels,
      whenever possible. The capability to use FQDNs as endpoint names
      has been standardized in several RFCs, such as [RFC5996], although
      many system/network administrators do not realize that it is there
      and works well as a way to avoid manual modification during
      renumbering.

      Service Location Protocol [RFC2608] and multicast DNS with SRV
      records for service discovery can reduce the number of places that
      IP addresses need to be configured. But it should be noted that
      multicast DNS is link-local only.

      - Usage of ULA

      Unique Local Addresses (ULAs) are defined in [RFC4193] as
      provider-independent prefixes, and they are globally unique to
      avoid collision. For enterprise networks, using ULA along with PA
      can provide a logically local routing plane separated from the
      globally routing plane. The benefit is to ensure stable and
      specific local communication regardless of the ISP uplink failure.
      This benefit is especially meaningful for renumbering. It mainly
      includes three use cases as the following.


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      When renumbering, as RFC4192 suggested, it has a period to keep
      using the old prefix(es) before the new prefix(es) is(are) stable.
      In the process of adding new prefix(es) and deprecating old
      prefix(es), it is not easy to keep the local communication immune
      of global routing plane change. If we use ULA for the local
      communication, the separated local routing plane can isolate the
      affecting by global routing change.

      Enterprise administrators may want to avoid the need to renumber
      their internal-only, private nodes when they have to renumber the
      PA addresses of the whole network because of changing ISPs, ISPs
      restructure their address allocations, or any other reasons. In
      these situations, ULA is an effective tool for the internal-only
      nodes.

      For multicast, ULA may be a way of avoiding renumbering from
      having an impact on multicast. In most deployments multicast is
      only used internally (intra-domain), and the addresses used for
      multicast sources and Rendezvous-Points need not be reachable nor
      routable externally. Hence one may at least internally make use of
      ULA for multicast specific infrastructure.

      - Address Types

      This document focuses on the dynamically-configured global unicast
      addresses in enterprise networks. They are the targets of
      renumbering events.

      Manual-configured addresses are not scalable in medium to large
      sites, hence are out of scope. Manual-configured addresses/hosts
      should be avoided as much as possible.

      - Address configuration models

      In IPv6 networks, there are two auto-configuration models for
      address assignment: Stateless Address Auto-Configuration (SLAAC)
      by Neighbor Discovery (ND, [RFC4861, RFC4862]) and stateful
      address configuration by Dynamic Host Configuration Protocol for
      IPv6 (DHCPv6, [RFC3315]). In the latest work, DHCPv6 can also
      support host-generated address model by assigning a prefix through
      DHCPv6 messages [I-D.ietf-dhc-host-gen-id].

      ND is considered easier to renumber by broadcasting a Router
      Advertisement message with a new prefix. DHCPv6 can also trigger
      the renumbering process by sending unicast RECONFIGURE messages,
      though it may cause a large number of interactions between hosts
      and DHCPv6 server.


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      This document has no preference between ND and DHCPv6 address
      configuration models. It is network architects' job to decide
      which configuration model is employed. But it should be noticed
      that using DHCPv6 and ND together within one network, especially
      in one subnet, may cause operational issues. For example, some
      hosts use DHCPv6 as the default configuration model while some use
      ND. Then the hosts' address configuration model depends on the
      policies of operating systems and cannot be controlled by the
      network. Section 5.1 of [I-D.ietf-6renum-gap-analysis] discusses
      more details on this topic. So, in general, this document
      recommends using DHCPv6/SLAAC independently in different subnets.

      However, since DHCPv6 is also used to configure many other network
      parameters, there are ND and DHCPv6 co-existence scenarios.
      Combinations of address configuration models may coexist within a
      single enterprise network. [I-D.ietf-savi-mix] provides
      recommendations to avoid collisions and to review collision
      handling in such scenarios.

      - DNS

      It is recommended that the site have an automatic and systematic
      procedure for updating/synchronising its DNS records, including
      both forward and reverse mapping [RFC2874]. A manual on-demand
      updating model does not scale, and increases the chance of errors.

      Although the A6 DNS record model [RFC2874] was designed for easier
      renumbering, it has a lot of unsolved technical issues [RFC3364].
      Therefore, it has been moved to experimental status [RFC3363], and
      will move to historic status by [RFC6563] (Moving A6 to Historic
      Status). So A6 is not recommended.

      In order to simplify the operation procedure, the network
      architect should combine the forward and reverse DNS updates in a
      single procedure.

      Often, a small site depends on its ISP's DNS system rather than
      maintaining its own. When renumbering, this requires
      administrative coordination between the site and its ISP.

      The DNS synchronization may be completed through the Secure DNS
      Dynamic Update [RFC3007]. Dynamic DNS update can be provided by
      the DHCPv6 client or by the server on behalf of individual hosts.
      [RFC4704] defined a DHCPv6 option to be used by DHCPv6 clients and
      servers to exchange information about the client's FQDN and about
      who has the responsibility for updating the DNS with the
      associated AAAA and PTR RRs. For example, if a client wants the


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      server to update the FQDN-address mapping in the DNS server, it
      can include the Client FQDN option with proper settings in the
      SOLICIT with Rapid Commit, REQUEST, RENEW, and REBIND message
      originated by the client. When DHCPv6 server gets this option, it
      can use the dynamic DNS update on behalf of the client. In this
      document, we promote to support this FQDN option. But since it's a
      DHCPv6 option, it implies that only the DHCP-managed networks are
      suitable for this operation. In SLAAC mode, sometimes hosts also
      need to register addresses on a registration server, which could
      in fact be a DHCPv6 server (as described in [I-D.ietf-dhc-addr-
      registration]); then the server would update corresponding DNS
      records.

      - Security

      Any automatic renumbering scheme has a potential exposure to
      hijacking. Malicious entity in the network can forge prefixes to
      renumber the hosts. So proper network security mechanisms are
      needed.

      For ND, Secure Neighbor Discovery (SEND, [RFC3971]) is a possible
      solution, but it is complex and there's almost no real deployment
      so far. Comparing the non-trivial deployment of SEND, RA guard
      [RFC6105] is a light-weight alternative, however, it also hasn't
      been widely deployed since it hasn't been published for long.

      For DHCPv6, there are built-in secure mechanisms (like Secure
      DHCPv6 [I-D.ietf-dhc-secure-dhcpv6]), and authentication of DHCPv6
      messages [RFC3315] could be utilized. But these security
      mechanisms also haven't been verified by wide real deployment.

      - Miscellaneous

      A site or network should also avoid embedding addresses from other
      sites or networks in its own configuration data. Instead, the
      Fully-Qualified Domain Names should be used. Thus, these
      connections can survive after renumbering events at other sites.
      This also applies to host-based connectivities.

4.2. Considerations and Best Current Practices for the Preparation of
   Renumbering

   In ND, it is not possible to reduce a prefix's lifetime to below two
   hours. So, renumbering should not be an unplanned sudden event. This
   issue could only be avoided by early planning and preparation.




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   This section describes several recommendations for the preparation of
   enterprise renumbering event. By adopting these recommendations, a
   site could be renumbered more easily. However, these recommendations
   are not cost free. They might increase the daily burden of network
   operation. Therefore, only those networks that are expected to be
   renumbered soon or very frequently should adopt these recommendations,
   with balanced consideration between daily cost and renumbering cost.

      - Reduce the address preferred time or valid time or both.

      Long-lifetime addresses may cause issues for renumbering events.
      Particularly, some offline hosts may reconnect using these
      addresses after renumbering events. Shorter preferred lifetimes
      with relatively long valid lifetimes may allow short transition
      periods for renumbering events and avoid frequent address
      renewals.

      - Reduce the DNS record TTL on the local DNS server.

      The DNS AAAA resource record TTL on the local DNS server should be
      manipulated to ensure that stale addresses are not cached.

      - Reduce the DNS configuration lifetime on the hosts.

      Since the DNS server could be renumbered as well, the DNS
      configuration lifetime on the hosts should also be reduced if
      renumbering events are expected. The DNS configuration can be done
      through either ND [RFC6106] or DHCPv6 [RFC3646].

      - Identify long-living sessions

      Any applications which maintain very long transport connections
      (hours or days) should be identified in advance, if possible. Such
      applications will need special handling during renumbering, so it
      is important to know that they exist.

4.3. Considerations and Best Current Practices during Renumbering
   Operation

   Renumbering events are not instantaneous events. Normally, there is a
   transition period, in which both the old prefix and the new prefix
   are used in the site. Better network design and management, better
   pre-preparation and longer transition period are helpful to reduce
   the issues during renumbering operation.

      - Within/without a flag day



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      As is described in [RFC4192], "a 'flag day' is a procedure in
      which the network, or a part of it, is changed during a planned
      outage, or suddenly, causing an outage while the network
      recovers."

      If renumbering event is processed within a flag day, the network
      service/connectivity will be unavailable for a period until the
      renumbering event is completed. It is efficient and provides
      convenience for network operation and management. But network
      outage is usually unacceptable for end users and enterprises. A
      renumbering procedure without a flag day provides smooth address
      switching, but much more operational complexity and difficulty is
      introduced.

      - Transition period

      If renumbering transition period is longer than all address
      lifetimes, after which the address leases expire, each host will
      automatically pick up its new IP address. In this case, it would
      be the DHCPv6 server or Router Advertisement itself that
      automatically accomplishes client renumbering.

      Address deprecation should be associated with the deprecation of
      associated DNS records. The DNS records should be deprecated as
      early as possible, before the addresses themselves.

      - Network initiative enforced renumbering

      If the network has to enforce renumbering before address leases
      expire, the network should initiate DHCPv6 RECONFIGURE messages.
      For some operating systems such as Windows 7, if the hosts receive
      RA messages with ManagedFlag=0, they'll release the DHCPv6
      addresses and do SLAAC according to the prefix information in the
      RA messages, so this could be another enforcement method for some
      specific scenarios.

      - Impact to branch/main sites

      Renumbering in main/branch site may cause impact on branch/main
      site communication. The routes, ingress filtering of site's
      gateways, and DNS may need to be updated. This needs careful
      planning and organizing.

      - DNS record update and DNS configuration on hosts

      DNS records on the local DNS server should be updated if hosts are
      renumbered. If the site depends on ISP's DNS system, it should


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      report the new host's DNS records to its ISP. During the
      transition period, both old and new DNS records are valid. If the
      TTLs of DNS records are shorter than the transition period, an
      administrative operation may not be necessary.

      DNS configuration on hosts should be updated if local recursive
      DNS servers are renumbered. During the transition period, both old
      and new DNS server addresses may co-exist on the hosts. If the
      lifetime of DNS configuration is shorter than the transition
      period, name resolving failure may be reduced to minimum. A
      notification mechanism may be needed to indicate to the hosts that
      a renumbering event of local recursive DNS happens or is going to
      take place.

      [Bing]                       Gap  7.1

      - Tunnel concentrator renumbering

      A tunnel concentrator itself might be renumbered. This change
      should be reconfigured in relevant hosts or routers, unless the
      configuration of tunnel concentrator was based on FQDN.

      - Connectivity session survivability

      During the renumbering operations, connectivity sessions in IP
      layer would break if the old address is deprecated before the
      session ends. However, the upper layer sessions may survive by
      using session survivability technologies, such as SHIM6 [RFC5533].
      As mentioned above, some long-living applications may need to be
      handled specially.

5. Security Considerations

   As noted, a site that is listed by IP address in a black list can
   escape that list by renumbering itself.

   Any automatic renumbering scheme has a potential exposure to
   hijacking. Proper network security mechanisms are needed. Although
   there are existing security mechanisms such as SEND, RA guard, secure
   DHCPv6 etc., they haven't been widely deployed and haven't been
   verified whether they are suitable for ensuring security while not
   bringing too much operational complexity and cost.

   Dynamic DNS update may bring risk of DoS attack to the DNS server. So
   along with the update authentication, session filtering/limitation
   may also be needed.



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   The "make-before-break" approach of [RFC4192] requires the routers
   keep advertising the old prefixes for some time. But if the ISP
   changes the prefixes very frequently, the co-existence of old and new
   prefixes may cause potential risk to the enterprise routing system.
   However, enterprise scenarios may not involve the extreme situation;
   this issue needs to be identified in the future.

   The security configuration updates will need to be made in two stages
   (immediately before and immediately after the event).

6. IANA Considerations

   This draft does not request any IANA action.

7. Acknowledgements

   This work is illuminated by RFC5887, so thank for RFC 5887 authors,
   Randall Atkinson and Hannu Flinck. Useful ideas were also presented
   in by documents from Tim Chown and Fred Baker. The authors also want
   to thank Wesley George, Olivier Bonaventure and other 6renum members
   for valuable comments.

8. Change Log [RFC Editor please remove]

   draft-jiang-6renum-enterprise-00, original version, 2011-07-01

   draft-jiang-6renum-enterprise-01, Update according to IETF81 and mail
   list discussions, 2011-10-09

   draft-jiang-6renum-enterprise-02, Update according to IETF82
   discussions, 2011-12-06

   draft-ietf-6renum-enterprise-00, Update according to mail list
   discussions, 2012-02-06



9. References

9.1. Normative References

   [RFC2608] Guttman, E., Perkins, C., Veizades, J., and M. Day "Service
             Location Protocol, Version 2", RFC 2608, June 1999.

   [RFC3007] B. Wellington, "Secure Domain Name System (DNS) Dynamic
             Update", RFC 3007, November 2000.



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   [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and
             M. Carney, "Dynamic Host Configuration Protocol for IPv6
             (DHCPv6)", RFC 3315, July 2003.

   [RFC3633] Troan, O., and R. Droms, "IPv6 Prefix Options for Dynamic
             Host Configuration Protocol (DHCP) version 6", RFC 3633,
             December 2003.

   [RFC3646] R. Droms, "DNS Configuration options for Dynamic Host
             Configuration Protocol for IPv6 (DHCPv6)", RFC 3646,
             December 2003.

   [RFC3956] Savola, P., and B. Haberman, "Embedding the Rendezvous
             Point (RP) Address in an IPv6 Multicast Address", RFC 3956,
             November 2004

   [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander
             "SEcure Neighbor Discovery (SEND)", RFC 3971, March 2005

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

   [RFC4704] B. Volz, "The Dynamic Host Configuration Protocol for IPv6
             (DHCPv6) Client Fully Qualified Domain Name (FQDN) Option",
             RFC 4706, October 2006.

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

   [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
             Address Autoconfiguration", RFC 4862, September 2007.

   [RFC5996] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen, "Internet
             Key Exchange Protocol Version 2 (IKEv2)", RFC 5996,
             September 2010.

   [RFC6106] Jeong, J., Ed., Park, S., Beloeil, L., and S. Madanapalli
             "IPv6 Router Advertisement Option for DNS Configuration",
             RFC 6106, November 2011.

9.2. Informative References

   [RFC2874] Crawford, M., and C. Huitema, "DNS Extensions to Support
             IPv6 Address Aggregation and Renumbering", RFC 2874, July
             2000.



Jiang, et al.             January 14, 2013                   [Page 14]

Internet-Draft   draft-ietf-6renum-enterprise-00.txt         July 2012


   [RFC3363] R. Bush, A. Durand, B. Fink, O. Gudmundsson, T. Hain,
             "Representing Internet Protocol version 6 (IPv6) Addresses
             in the Domain Name System (DNS)", RFC 3363, August 2002.

   [RFC3364] R. Austein, "Tradeoffs in Domain Name System (DNS) Support
             for Internet Protocol version 6 (IPv6)", RFC 3364, August
             2002.

   [RFC4057]  J. Bound, Ed. "IPv6 Enterprise Network Scenarios", RFC
             4057, June 2005.

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

   [RFC4864] Van de Velde, G., T. Hain, R. Droms, B. Carpenter, E. Klein,
             Local Network Protection for IPv6", RFC 4864, May 2007.

   [RFC5533] Nordmark, E., and Bagnulo, M., "Shim6: Level 3 Multihoming
             Shim Protocol for IPv6", RFC 5533, June 2009.

   [RFC5887] Carpenter, B., Atkinson, R., and H. Flinck, "Renumbering
             Still Needs Work", RFC 5887, May 2010.

   [RFC6105] Levy-Abegnoli, E., Van de Velde, G., Popoviciu, C., and J.
             Mohacsi, "IPv6 Router Advertisement Guard", RFC 6105,
             February 2011.

   [RFC6563] Jiang, S., Conrad, D. and Carpenter, B., "Moving A6 to
             Historic Status", RFC 6563, May 2012.

   [I-D.ietf-dhc-secure-dhcpv6]
             Jiang, S., and S. Shen, "Secure DHCPv6 Using CGAs", working
             in progress.

   [I-D.ietf-dhc-host-gen-id]
             S. Jiang, F. Xia, and B. Sarikaya, "Prefix Assignment in
             DHCPv6", draft-ietf-dhc-host-gen-id (work in progress),
             April, 2011.

   [I-D.ietf-savi-mix]
             Bi, J., Yao, G., Halpern, J., and Levy-Abegnoli, E., "SAVI
             for Mixed Address Assignment Methods Scenario", working in
             progress.





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   [I-D.ietf-dhc-pd-exclude]
             J. Korhonen, T. Savolainen, S. Krishnan, O. Troan, "Prefix
             Exclude Option for DHCPv6-based Prefix Delegation", working
             in progress.

   [I-D.ietf-dhc-addr-registration]
             Jiang, S., Chen, G., "A Generic IPv6 Addresses Registration
             Solution Using DHCPv6", working in progress.

   [I-D.ietf-6renum-gap-analysis]
             Liu, B., and Jiang, S., "IPv6 Site Renumbering Gap
             Analysis", working in progress.

    [I-D.carpenter-6renum-static-problem]
             Carpenter, B. and S. Jiang., "Problem Statement for
             Renumbering IPv6 Hosts with Static Addresses", working in
             progress.

Author's Addresses

   Sheng Jiang
   Huawei Technologies Co., Ltd
   Huawei Q14 Building, No.156 Beiqing Rd.,
   Zhong-Guan-Cun Environmental Protection Park, Hai-Dian District
   EMail: jiangsheng@huawei.com

   Bing Liu
   Huawei Technologies Co., Ltd
   Huawei Q14 Building, No.156 Beiqing Rd.,
   Zhong-Guan-Cun Environmental Protection Park, Hai-Dian District
   EMail: leo.liubing@huawei.com

   Brian Carpenter
   D

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