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Versions: 00 01 02 draft-ietf-6renum-enterprise

Network Working Group                                         S. Jiang
Internet Draft                                                  B. Liu
Intended status: Best Current Practice    Huawei Technologies Co., Ltd
Expires: January 03, 2012                                 B. Carpenter
                                                University of Auckland
                                                         July 01, 2011

      IPv6 Enterprise Network Renumbering Scenarios and Guidelines
                  draft-jiang-6renum-enterprise-00.txt


Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on January 03, 2012.

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   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors. All rights reserved.

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   described in the Simplified BSD License.



Abstract

   This document analyzes the enterprise renumbering events and gives
   the recommendations among the existing renumbering mechanisms.
   According to the different stages of renumbering events,



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   considerations and best current recommendations 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.

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........... 4
      3.2. Renumbering caused by Internal Network Factors........... 5
   4. Network Renumbering Considerations and Best Current
   Recommendations ................................................. 5
      4.1. Considerations and Recommendations during Network Design. 6
      4.2. Considerations and Recommendations for the Preparation of
      Renumbering .................................................. 8
      4.3. Considerations and Recommendations during Renumbering
      Operation .................................................... 9
   5. Gap Inventory ............................................... 11
   6. Security Considerations ..................................... 12
   7. IANA Considerations ......................................... 12
   8. Acknowledgements ............................................ 12
   9. Change Log [RFC Editor please remove] ....................... 12
   10. References ................................................. 13
      10.1. Normative References .................................. 13
      10.2. Informative References ................................ 14
   Author's Addresses ............................................. 15




















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1. Introduction

   IPv6 site renumbering is considered difficult. Network managers would
   turn to 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. It is thus
   desirable to develop tools and practices that may make renumbering a
   simpler process to reduce demand for IPv6 PI space.

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

   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.

   According to the different stages of renumbering events,
   considerations and best current recommendations 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

   The enterprise network architecture is illustrated as the figure
   below. From the renumbering perspective of view, these entities
   relevant to renumbering are highlighted.

   Address reconfiguration is fulfilled either by DHCPv6 or ND
   protocols. Static address assignment is not considered in this
   version. 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.












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               Uplink 1            Uplink 2
                  |                   |
              +---+---+           +---+---+
        +---- |Gateway| --------- |Gateway| -----+
        |     +-------+           +-------+      |
        |          Enterprise Network            |
        |   +------+     +------+    +------+    |
        |   | APP  |     | DHCP |    |  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-existing 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 category enterprise network renumbering scenarios
   mainly according to different reasons. Some of renumbering reasons
   described in [RFC2071] has out of date, or not suitable in IPv6, or
   not suitable for enterprise networks.

3.1. Renumbering caused by External Network Factors

   The most influential external network factor is the uplink ISP.







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   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. The typical scenario is that the DHCP server
      in ISP delegates a new prefix to the enterprise network. Or the
      enterprise network may be 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. The ISP itself may also be renumbered due to
      topology change 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
      purpose. 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. If the administrators
      only want part of the network to have multiple prefixes, the
      renumbering process should be carefully managed.

3.2. Renumbering caused by Internal Network Factors

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

4. Network Renumbering Considerations and Best Current Recommendations

   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.

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





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4.1. Considerations and Recommendations during Network Design

   This section describes the renumbering relevant considerations or
   issues that a network architect should carefully plan when he builds
   or designs 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] provide a mechanism
      for automated delegation of IPv6 prefixes. DHCPv6 PD options may
      also be used between the enterprise routers and their upstream
      ISPs.

      - Usage of FQDN

      It is recommended that Fully-Qualified Domain Names (FQDNs) should
      be used to configure network connectivity, such as tunnels. 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.

      - Address Types

      This document focuses on the dynamic-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 be out of scope. However, some hosts such as servers
      may need static addresses. Manual-configured addresses/hosts
      should be avoided as much as possible.

      [Open Question to WG] What we can do regarding to manual
      configured hosts and static addresses, which do need to be
      changed?

      Unique Local Address (ULA, [RFC4193]) may be used on local routers
      or servers, which only intends for local communications, usually



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      inside of enterprise networks. Normally, they do NOT need to be
      changed during the renumbering event.

      [Open Question to WG] Is anyone actually using ULAs?

      - Address configuration models

      In IPv6 networks, there are two auto-configuration models for
      address assignment: the Stateless Address Auto-Configuration
      (SLAAC) by Neighbor Discovery (ND, [RFC4861, RFC4862]) and the
      stateful address configuration by Dynamic Host Configuration
      Protocol for IPv6 (DHCPv6, [RFC3315]). In the latest work, DHCPv6
      can also support host-generate address model by assigning 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.

      In principle, a network should choose only one address
      configuration model and employs either ND or DHCPv6. This document
      has no preference between ND and DHCPv6 address configuration
      models.

      However, since DHCPv6 is also used to configure many other network
      parameters, there are ND and DHCPv6 co-existing scenarios. The
      current protocols do not effectively prevent that both SLAAC and
      DHCPv6 address assignment are used in the same network (see M bit
      analysis in section 5.1.1 [RFC5887]). It is network architects'
      job to make sure only one configuration model is employed. Even in
      a large network that contains several subnet works, it is
      recommended not to mix the two address configuration models though
      isolately using them in different subnet works may reduce the risk
      partly.

      - 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]. Manually on-demand
      updating model is considered as a harmful problem creator in
      renumbering event.

      A6 DNS record model is recommended over AAAA record model for
      renumbering purpose [RFC2874, RFC3364].


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

      If a small site depends on its ISP's DNS system rather than
      maintains its own one. When renumbering, it requires
      administrative coordination between the site and its ISP.
      Alternatively, the DNS synchronizing may be completed through the
      Secure Dynamic DNS Update.

      - Security

      Any automatic renumbering scheme has a potential exposure to
      hijacking at the moment that a new address is announced. Proper
      network security mechanisms should be employed. Secure Neighbor
      Discovery (SEND, [RFC3971]), which does not widely deployed, is
      recommended to replace ND. Alternatively, certain lightweight
      renumbering specific security mechanism may be developed in the
      future. DHCPv6 build-in secure mechanisms, like Secure DHCPv6
      [I-D.ietf-dhc-secure-dhcpv6] or authentication of DHCPv6 messages
      [RFC3315] are recommended.

      - Miscellaneous

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

4.2. Considerations and Recommendations for the Preparation of
   Renumbering

   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.

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

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


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      Long-lifetime addresses may cause issues for renumbering events.
      Particularly, some offline hosts may reconnect back using these
      addresses after renumbering events. Shorter preferred lifetime
      with relevant long valid lifetime may get short transition period
      for renumbering event and avoid address renew too frequent.

      - Reduce the DNS record TTL.

      The DNS 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]. However, DHCPv6
      DNS option does not include associated lifetime. It should be
      updated.

4.3. Considerations and Recommendations 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

      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 outage for a period till the
      renumbering event is completed. It is efficient and provides
      convenient for network operation and management. But network
      outage is usually unacceptable for end users and the enterprises.
      Renumbering procedure without a flag day provides smooth addresses
      switching, but much more operational complexity and difficulty is
      introduced.

      - Transition period




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

      - Network initiative enforced renumbering

      If the network has to enforce renumbering before addresses lease
      expire, the network should initiate enforcement messages, either
      in Router Advertisement messages or DHCPv6 RECONFIGURE messages.

      - 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 carefully
      planning and organizing.

      - DNS record update and DNS configuration on hosts

      DNS records should be updated if hosts are renumbered. If the site
      depends on ISP's DNS system, it should report the new host's DNS
      records to its ISP. During the transition period, both old and new
      DNS records are valid. If the TTL of DNS records is shorter than
      the transition period, 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 addresses may co-exist on the hosts. If the lifetime
      of DNS configuration is shorter than the transition period, name
      resolving failure may not be reduced to minimum. A notification
      mechanism may be needed to indicate the hosts that a renumbering
      event of local recursive DNS happens or is going to take place.

      - Router awareness

      In a site with multiple border routers, all border routers should
      be aware of partial renumbering in order to correctly handle
      inbound packets. Internal forwarding tables need to be updated.

      - Border filtering

      In a multihomed site, an egress router to ISP A could normally
      filter packets with source addresses from other ISPs. The egress
      router connecting to ISP A should be notified if the egress router


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      connecting to ISP B initiates a renumbering event in order to
      properly act filter function.

      - Tunnel concentrator renumbering

      Tunnel concentrator itself might be renumbered. This change should
      be reconfigured to relevant hosts or router, unless the
      configuration of tunnel concentrator was based on FQDN.

5. Gap Inventory

   This section lists a few issues that still remain unsolvable. Some of
   them may be inherently unsolvable.

      -  Manual or script-driven procedures will break the completely
         automatic host renumbering.

      -  Some environments like embedded systems might not use DHCP or
         SLAAC and even configuration scripts might not be an option.
         This creates special problems that no general-purpose solution
         is likely to address.

      -  TCP and UDP flows can't survive at renumbering event at either
         end.

      -  Some address configuration data might be widely dispersed and
         much harder to find, even will inevitably be found only after
         the renumbering event.

      -  The embedding of IPv6 unicast addresses into multicast
         addresses and the embedded-RP (Rendezvous Point) [RFC3956] will
         cause issues when renumbering.

      -  Changing the unicast source address of a multicast sender might
         also be an issue for receivers.

      -  When a renumbering event takes place, entries in the state
         table of tunnel concentrator that happen to contain the
         affected addresses will become invalid and will eventually time
         out. However, this can be considered as harmless though it
         takes sources on these devices for a while.

      -  A site that is listed in a black list can escape that list by
         renumbering itself. The site itself of course will not
         initiatively to report its renumbering and the black list may
         not be able to monitor or discover the renumbering event.



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      -  Multihomed site, using SLAAC for one address prefix and DHCPv6
         for another, would clearly create a risk of inconsistent host
         behaviour and operational confusion.

      -  The impact of portion renumbering may need to be analyzed
         further.

   Some of these issues can be considered as harmless or have minimum
   impacts.

6. Security Considerations

   A site that is listed in a black list can escape that list by
   renumbering itself.

   Any automatic renumbering scheme has a potential exposure to
   hijacking at the moment that a new address is announced. Proper
   network security mechanisms should be employed. SEND is recommended
   to replace ND. Alternatively, certain lightweight renumbering
   specific security mechanism may be developed in the future. DHCPv6
   build-in secure mechanisms, like Secure DHCPv6
   [I-D.ietf-dhc-secure-dhcpv6] or authentication of DHCPv6 messages
   [RFC3315] are recommended.

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

   [Editor note: this section needs further work.]

7. IANA Considerations

   This draft does not request any IANA action.

8. Acknowledgements

   This work is illumined by RFC5887, so thank for RFC 5887 authors,
   Randall Atkinson and Hannu Flinck. Useful ideas were also illumined
   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.

9. Change Log [RFC Editor please remove]

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





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10. References

10.1. Normative References

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

   [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.

   [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.






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10.2. Informative References

   [RFC2071] Ferguson, P., and H. Berkowitz., "Network Renumbering
             Overview: Why would I want it and what is it anyway?", RFC
             2071, January 1997.

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

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

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

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

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















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Author's Addresses

   Sheng Jiang
   Huawei Technologies Co., Ltd
   Huawei Building, No.3 Xinxi Rd.,
   Shang-Di Information Industry Base, Hai-Dian District, Beijing
   P.R. China
   EMail: jiangsheng@huawei.com

   Bing Liu
   Huawei Technologies Co., Ltd
   Huawei Building, No.3 Xinxi Rd.,
   Shang-Di Information Industry Base, Hai-Dian District, Beijing
   P.R. China
   EMail: leo.liubing@huawei.com

   Brian Carpenter
   Department of Computer Science
   University of Auckland
   PB 92019
   Auckland, 1142
   New Zealand
   EMail: brian.e.carpenter@gmail.com

























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