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Versions: (draft-liu-6renum-gap-analysis) 00 01 02 03 04 05 06 07 08 RFC 7010

Network Working Group                                            B. Liu
Internet Draft                                                 S. Jiang
Intended status: Informational             Huawei Technologies Co., Ltd
Expires: April 14, 2013                                    B. Carpenter
                                                 University of Auckland
                                                              S. Venaas
                                                          Cisco Systems
                                                       October 15, 2012

                    IPv6 Site Renumbering Gap Analysis
                   draft-ietf-6renum-gap-analysis-04.txt


Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF). Note that other groups may also distribute working
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   at http://datatracker.ietf.org/drafts/current/.

   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."

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

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors. All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.







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Abstract

   This document briefly introduces the existing mechanisms that could
   be utilized for IPv6 site renumbering and tries to cover most of the
   explicit issues and requirements of IPv6 renumbering. Through the gap
   analysis, the document provides a basis for future works that
   identify and develop solutions or to stimulate such development as
   appropriate. The gap analysis is presented following a renumbering
   event procedure summary.



Table of Contents


   1. Introduction ................................................. 4
   2. Overall Requirements for Renumbering ......................... 4
   3. Existing Components for IPv6 Renumbering ..................... 5
      3.1. Relevant Protocols and Mechanisms ....................... 5
      3.2. Management Tools ........................................ 6
      3.3. Procedures/Policies ..................................... 6
   4. Managing Prefixes ............................................ 7
      4.1. Prefix Delegation ....................................... 7
      4.2. Prefix Assignment ....................................... 7
   5. Address Configuration ........................................ 7
      5.1. Host Address Configuration .............................. 7
      5.2. Router Address Configuration ............................ 9
      5.3. Static Address Configuration ........................... 10
   6. Updating Address-relevant Entries ........................... 10
      6.1. DNS Records Update ..................................... 10
      6.2. In-host Server Address Update .......................... 11
      6.3. Parameterized IP-specific Configuration ................ 11
   7. Renumbering Event Management ................................ 13
      7.1. Renumbering Notification ............................... 13
      7.2. Synchronization Management ............................. 14
      7.3. Renumbering Monitoring ................................. 14
   8. Miscellaneous ............................................... 14
      8.1. Multicast .............................................. 14
      8.2. Mobility ............................................... 16
   9. Gaps considered unsolvable .................................. 16
      9.1. Address Configuration .................................. 16
      9.2. Address-relevant Entries Update ........................ 16
      9.3. Miscellaneous .......................................... 17
   10. Security Considerations .................................... 17
   11. IANA Considerations......................................... 18


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   12. Acknowledgments ........................................... 18
   13. References ................................................ 18
      13.1. Normative References ................................. 18
      13.2. Informative References ............................... 19












































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1. Introduction

   As introduced in [RFC5887], renumbering, especially for medium to
   large sites and networks, is currently viewed as an expensive,
   painful, and error-prone process, avoided by network managers as much
   as possible. If IPv6 site renumbering continues to be considered
   difficult, network managers will 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 performs a gap analysis to provide a basis for future
   work to identify and develop solutions or to stimulate such
   development as appropriate. The gap analysis is organized by the main
   steps of a renumbering process, which include prefix management, node
   address (re)configuration, and updating address-relevant entries in
   various devices such as firewalls, routers and servers, etc. Besides
   these steps, the aspect of renumbering event management is also
   presented independently, which intends to identify some
   operational/administrative gaps in renumbering.

   This document starts from existing work in [RFC5887],
   [I-D.chown-v6ops-renumber-thinkabout] and [RFC4192]. This document
   does further analysis and identifies the valuable and solvable issues,
   digs out of some undiscovered gaps, and gives some solution
   suggestions.

2. Overall Requirements for Renumbering

   This section introduces the overall ultimate goals we want to achieve
   in a renumbering event. In general, we need to leverage renumbering
   automation to avoid human intervention as much as possible at
   reasonable cost. Some existing mechanisms have already provided
   useful ability. Further efforts may be achieved in the future.

   The automation can be divided into four aspects as follows.

   o Prefix delegation and delivery should be automatic and accurate in
      aggregation and coordination.

   o Address reconfiguration should be automatically achieved through
      standard protocols with minimum human intervention.



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   o Address-relevant entry updates should be performed integrally and
      without error.

   o Renumbering event management is needed to provide the functions of
      renumbering notification, synchronization, and monitoring .etc.

   Besides automation, session survivability is another important issue
   during renumbering since application outage is one of the most
   obvious impacts that make renumbering painful and expensive. Session
   survivability is a fundamental issue that cannot solved within
   renumbering context only; however, we have an enormous advantage in
   IPv6 which is the ability to overlap the old and new prefixes and to
   use the address lifetime mechanisms in stateless address
   autconfiguration (SLAAC) and DHCPv6. That is fully described in
   [RFC4192], which provides a smooth transition mechanism from old to
   new prefixes. In most of the cases, since we can set the transition
   period long enough to cover the on-going sessions, we consider this
   mechanism is sufficient for avoiding session brokenness issue in IPv6
   site renumbering.

3. Existing Components for IPv6 Renumbering

   Since renumbering is not a new issue, some protocols and mechanisms
   have already been utilized for renumbering. There were also some
   dedicated protocols and mechanisms developed for renumbering. This
   section briefly reviews these existing protocols and mechanisms to
   provide a basis for the gap analysis.

3.1. Relevant Protocols and Mechanisms

   o RA messages, defined in [RFC4861], are used to deprecate/announce
      old/new prefixes and to advertise the availability of an upstream
      router. In renumbering, it is one of the basic mechanisms for host
      configuration.

   o When renumbering a host, SLAAC [RFC4862] may be used for address
      configuration with the new prefix(es). Hosts receive RA messages
      which contain routable prefix(es) and the address(es) of the
      default router(s), then hosts can generate IPv6 address(es) by
      themselves.

   o Hosts that are configured through DHCPv6 [RFC3315] can reconfigure
      addresses by starting RENEW actions when the current addresses'
      lease time are expired or they receive the reconfiguration
      messages initiated by the DHCPv6 servers.




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   o DHCPv6-PD (Prefix Delegation) [RFC3633] enables automated
      delegation of IPv6 prefixes using the DHCPv6.

   o [RFC2894] defined standard ICMPv6 messages for router renumbering.
      This is a dedicated protocol for renumbering, but it has not been
      widely used.

3.2. Management Tools

   Some operations of renumbering could be automatically processed by
   management tools in order to make the renumbering process more
   efficient and accurate. The tools may be designed specifically for
   renumbering, or common tools could be utilized for some of the
   renumbering operations.

   Following are examples of these tools.

   o IPAM (IP address management) tools. There are both commercial and
      open-source solutions. An IPAM is basically used to manage an IP
      address plan, and it integrates the DHCPv6 and DNS services
      together as a whole solution. Many mature commercial tools can
      support management operations, but normally they do not have
      dedicated renumbering functions. However, the integrated
      DNS/DHCPv6 services and address management function can obviously
      facilitate the renumbering process.

   o [LEROY] proposed a mechanism of macros to automatically update the
      address-relevant entries/configurations inside the DNS, firewall,
      etc. The macros can be delivered though SOAP protocol from a
      network management server to the managed devices.

   o Asset management tools/systems. These tools may provide the
      ability of managing configuration files in nodes so that it is
      convenient to update the address-relevant configuration in these
      nodes.

3.3. Procedures/Policies

   o [RFC4192] proposed a procedure for renumbering an IPv6 network
      without a flag day. The document includes a set of operational
      suggestions which can be followed step by step by network
      administrators.







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   o [I-D.ietf-6renum-enterprise] analyzes the enterprise renumbering
      events and gives the recommendations among the existing
      renumbering mechanisms. According to the different stages,
      renumbering considerations are described in three categories:
      considerations and recommendations during network design, for
      preparation of enterprise network renumbering, and during
      renumbering operation

4. Managing Prefixes

   When renumbering an enterprise site, a short prefix may be divided
   into longer prefixes for subnets. So we need to carefully manage the
   prefixes for prefix delivery, delegation, aggregation,
   synchronization, coordination, etc.

4.1. Prefix Delegation

   Usually, the short prefix(es) come down from the operator(s) and are
   received by DHCPv6 servers or routers inside the enterprise networks.
   The short prefix(es) could be automatically delegated through DHCPv6-
   PD. Then the downlink DHCPv6 servers or routers can begin advertising
   the longer prefixes to the subnets.

   For the delegation routers, they may need to renumber themselves with
   the delegated prefixes. We need to consider the router renumbering
   issue, which cannot be covered by DHCP-PD only.

4.2. Prefix Assignment

   When subnet routers receive the longer prefixes, they can directly
   assign them to the hosts. The prefix assignment overlaps with the
   host address configuration, which is described in the following
   section 5.1.

5. Address Configuration

5.1. Host Address Configuration

   o SLAAC/DHCPv6 co-existence

        Both of the DHCPv6 and Neighbor Discovery (ND) protocols have an
        IP address configuration function. They are suitable for
        different scenarios respectively. During renumbering, the SLAAC-
        configured hosts can reconfigure IP addresses by receiving ND
        Router Advertisement (RA) messages containing new prefix
        information. It should be noted that, the prefix delivery could
        be achieved through DHCPv6 according to the new IETF DHC WG


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        document
        [I.D ietf-dhc-host-gen-id]. The DHCPv6-configured hosts can
        reconfigure addresses by initiating RENEW sessions when the
        current addresses' lease times are expired or when they receive
        reconfiguration messages initiated by the DHCPv6 servers.

        Sometimes the two address configuration modes may both be
        available in one network. This would add more or less additional
        complexity for both the hosts and the network management. In ND
        protocol, there is an M (ManagedFlag) flag defined in RA message,
        which indicates the hosts the DHCPv6 service status in the
        network. And there is another O "OtherConfigFlag" flag
        indicateing the host to configure information such as
        DNS/routing other than addresses.

        Using these flags, the two separated address configuration modes
        are somehow correlated. However, the ND protocol did not define
        the flags as prescriptive but only as advisory. This has led to
        variation in the behavior of hosts when interpreting the M flag.
        Different operating systems follow different approaches [I-
        D.liu-6renum-dhcpv6-slaac-switching].

        The impact of ambiguous M/O flags mainly includes the following
        aspects:

        - SLAAC/DHCPv6 preference

          Ideally, it should be possible to choose either SLAAC or
          DHCPv6 as the default address configuration mechanism when a
          host goes online, but this is not always available in reality.
          On some current operating systems, DHCPv6 procedure will not
          start until they receive RA messages with M=1. This has an
          implication that RA messages are required for DHCPv6
          management. This may cause operational issues since it needs
          additional complexity in ND/DHCPv6 co-existence to achieve
          unified management in a network.

        - DHCPv6-configured hosts receiving RA messages

          It is unclear whether a DHCPv6 configured host will accept
          configuration though RA messages; this depends on the policies
          in the host's operating system. If it ignores the RA messages
          and there are no DHCPv6 reconfiguration messages received
          either, renumbering would fail.

          [RFC5887] mentioned that DHCPv6-configured hosts may want to
          learn about the upstream availability of new prefixes or loss


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          of prior prefixes dynamically by deducing this from periodic
          RA messages. But there is no standard specifying what approach
          should be taken by a DHCPv6-configured host when it receives
          RA messages containing a new prefix. It depends on the
          operating system of the host and cannot be predicted or
          controlled by the network.

        -  SLAAC-configured hosts finding DHCPv6 in use

          It is unspecified what behavior should be taken when the host
          receives RA messages with "M" set.

          The host may start a DHCPv6 session and receive the DHCPv6
          address configuration, or it may just ignore the messages. If
          the network side wants the hosts to start DHCPv6 configuration,
          it is just out of control of the network side.

   o DHCPv6 reconfigure bulk usage

        [RFC5887] mentioned that "DHCPv6 reconfiguration doesn't appear
        to be widely used for bulk renumbering purposes".

        The reconfiguration defined in [RFC3315] needs to establish a
        session between DHCPv6 server and client. This could be
        considered as a stateful approach which needs much resource on
        the server to maintain the renumbering sessions. This is
        probably one of the reasons that DHCPv6 reconfiguration is not
        suitable for bulk usage.

        Another limitation of DHCPv6 reconfiguration is that it only
        allows the messages to be delivered to unicast addresses. So if
        we want to use it for bulk renumbering, stateless DHCPv6
        reconfiguration with multicast may be needed. However, this may
        involve protocol modification.

5.2. Router Address Configuration

   o Learning new prefixes

        As described in [RFC5887], "if a site wanted to be multihomed
        using multiple provider-aggregated (PA) routing prefixes with
        one prefix per upstream provider, then the interior routers
        would need a mechanism to learn which upstream providers and
        prefixes were currently reachable (and valid).  In this case,
        their Router Advertisement messages could be updated dynamically
        to only advertise currently valid routing prefixes to hosts.
        This would be significantly more complicated if the various


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        provider prefixes were of different lengths or if the site had
        non-uniform subnet prefix lengths."

   o Restart after renumbering

        As [RFC2072] mentioned, some routers cache IP addresses in some
        situations, so routers might need to be restarted as a result of
        site renumbering.

   o Router naming

        In [RFC4192], it is suggested that "To better support
        renumbering, switches and routers should use domain names for
        configuration wherever appropriate, and they should resolve
        those names using the DNS when the lifetime on the name
        expires." As [RFC5887] described, this capability is not new,
        and at least it is present in most IPSec VPN implementations.
        But many administrators do not realize that it could be utilized
        to avoid manual modification during renumbering.

        In enterprise scenario, the requirement of router naming is not
        as strong as that in ISP. So for the administrators, the
        motivation of using router naming for easing renumbering may be
        not strong.

5.3. Static Address Configuration

   There is another document dedicated to the static address issue.
   Please refer to [I-D.ietf-6renum-static-problem].

6. Updating Address-relevant Entries

   When nodes in a site have been renumbered, then all the entries in
   the site which contain the nodes' addresses must be updated. The
   entries mainly include DNS records and filters in various entities
   such as ACLs in firewalls/gateways.

6.1. DNS Records Update

   o Dynamic DNS update

        For DNS records update, the most popular DNS system, BIND, will
        achieve it by maintaining a DNS zone file and loading this file
        into the site's DNS server(s). Synchronization between host
        renumbering and the updating of its A6 or AAAA record is hard.
        [RFC5887] mentioned that an alternative is to use Secure Dynamic



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        DNS Update [RFC3007], in which a host informs its own DNS server
        when it receives a new address.

        Secure Dynamic DNS Update has been widely supported by the major
        DNS systems, but it hasn't been widely deployed, especially in
        the host. Current practices mainly involve the DHCP servers
        which act as clients to request the DNS server to update
        relevant records. Normal hosts are not suitable to do this
        mainly because of the complexity of key management issues
        inherited from secure DNS mechanisms. But for some commercial
        DNS systems, the Secure Dynamic DNS Update issue may be much
        easier, since it could be integrated with services like DHCP
        provided by the same vendor so that the dynamic DNS update could
        be silently enabled.

6.2. In-host Server Address Update

   While DNS records addresses of hosts in servers, hosts also record
   addresses of servers such as DNS server, radius server, etc. While
   renumbering, the hosts must update the records if the server
   addresses changed. Addresses of DHCPv6 servers do not need to be
   updated. They are dynamically discovered using DHCPv6 relevant
   multicast addresses.

   o The DNS server addresses for hosts are configured by DHCPv6. But
      current DHCPv6 messages do not indicate to hosts the lifetimes of
      DNS. If the DNS lifetime expired and a host has been renumbered,
      other hosts may still use the old addresses. DHCPv6 should be
      extended to indicate to hosts the associated DNS lifetimes when
      making DNS configuration. How the DHCP server could know about the
      DNS lifetime is another issue.

6.3. Parameterized IP-specific Configuration

   Besides the DNS records and the in-host server address entries, there
   are also many places in which the IP addresses are configured, for
   example, filters such as ACL and routing policies, etc. There are
   even more sophisticated cases where the IP addresses are used for
   deriving values, for example, using the unique portion of the
   loopback address to generate an ISIS net ID.

   Ideally, a layer of abstraction for IP-specific configuration within
   various devices (routers, switches, hosts, servers, etc.) is needed.
   However, this cannot be achieved in one step. One possible
   improvement is to make the IP-specific configuration parameterized.
   Two aspects of parameterized configuration could be considered to
   achieve this.


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   o Self-contained Configuration in Individual device

        In an ideal way, the IP addresses can be defined as a value once,
        and then the administrators can use either keywords or variables
        to call the value in other places such as a sort of internal
        inheritance in CLI (command line interface) or other local
        configurations. This makes it easier to manage a renumbering
        event by reducing the number of places where a device's
        configuration  must be updated. However, it still means that
        every device needs to be touched, but only once instead of
        having to inspect the whole configuration to ensure that none of
        the separate places that a given IP address occurs is missed.

        Among the real current devices, some routers support defining
        multiple loopback interfaces which can be called in other
        configurations. For example, when defining a tunnel, it can call
        the defined loopback interface to use its address as the local
        address of the tunnel. This can be considered as a kind of
        parameterized self-contained configuration. But this only
        applies certain use cases; it is impossible to use the loopback
        interfaces to represent external devices and it is not always
        possible to call loopback interfaces in many other
        configurations. Parameterized self-contained configuration is
        still a gap for current devices.

   o Unified Configuration Management among Devices

        This is a more formalized central configuration management
        system, where all changes are made in one place and the system
        manages how to push the changes to the individual devices. This
        issue contains two aspects as the following.

        - Configuration AggregationL

          Configuration based on addresses or prefixes are usually
          spread in various devices. As [RFC5887] described, some
          address configuration data might be widely dispersed and much
          harder to find, even will inevitably be found only after the
          renumbering event. So there's a big gap for configuration
          aggregation.

        - Configuration Update Automation

          As mentioned in section 3.2, [LEROY] proposed a mechanism
          which can automatically update the entries. The mechanism
          utilizes macros suitable for various devices such as routers,
          firewalls etc. to update the entries based on the new prefix.


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          Such automation tool is valuable for renumbering because it
          can reduce manual operation which is error-prone and
          inefficiency.

          Besides the macros, [LEROY] also proposed to use SOAP to
          deliver the macros to the devices. As well as SOAP we may
          consider whether it is possible and suitable to use other
          standardized protocols such as NETCONF [RFC4714].

          But in current real networks, most of the devices use vendor-
          private protocols to update configurations, so it is not
          necessarily valid to assume that there is going to be a
          formalized configuration management system to leverage. It is
          a big gap currently.

7. Renumbering Event Management

   From the perspective of network management, renumbering is a kind of
   event which may need additional process to make it more easy and
   manageable.

7.1. Renumbering Notification

   If hosts or servers are aware of a renumbering event happening, it
   may benefit the relevant process. Following are several examples of
   such additional process that may ease the renumbering.

   o 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.

   o [RFC4192] suggests that "reducing the delay in the transition to
      new IPv6 addresses applies when the DNS service can be given prior
      notice about a renumbering event." Reducing delay could improve
      the efficiency of renumbering.

   o 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.

   o 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 connecting to ISP B initiates a renumbering
      event in order to properly update its filter function.



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7.2. Synchronization Management

   o DNS update synchronization

        DNS update synchronization focuses on the coordinating between
        DNS and other entities/mechanisms, for example, as described in
        [RFC5887], synchronizing the SLAAC and DNS updates, and of
        reducing the SLAAC lease time and DNS TTL.

7.3. Renumbering Monitoring

   While treating renumbering as a network event, mechanisms to monitor
   the renumbering process may be needed. Considering the address
   configuration operation may be stateless (if ND is used for
   renumbering), it is difficult for monitoring. But for the DNS and
   filter update, it is quite possible to monitor the whole process.

8. Miscellaneous

8.1. Multicast

   Renumbering also has an impact on multicast. Renumbering of unicast
   addresses affects multicast even if the multicast addresses are not
   changed. There may also be cases where the multicast addresses need
   to be renumbered.

   o Renumbering of multicast sources

        If a host that is a multicast source is renumbered, the
        application on the host may need to be restarted for it to
        successfully send packets with the new source address.

        For ASM (Any-Source Multicast) the impact on a receiver is that
        a new source appears to start sending, and it no longer receives
        from the previous source. Whether this is an issue depends on
        the application, but we believe it is likely to not be a major
        issue.

        For SSM (Source-Specific Multicast) however, there is one
        significant problem. The receiver needs to learn which source
        addresses it must join. Some applications may provide their own
        method for learning sources, where the source application may
        somehow signal the receiver.

        Otherwise, the receiver may e.g. need to get new SDP information
        with the new source address. This is similar to how to learn a



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        new group address, see the "Renumbering of multicast addresses"
        topic below.

   o Renumbering of Rendezvous-Point

        If the unicast addresses of routers in a network are renumbered,
        then the RP (Rendezvous-Point) address is also likely to change
        for at least some groups. An RP address is needed by PIM-SM for
        providing ASM, and for Bidir PIM. Changing the RP address is not
        a major issue, except that the multicast service may be impacted
        while the new RP addresses are configured. If dynamic protocols
        are used for distributing group-to-RP mappings, the change can
        be fairly quick, and any impact should be only for a very brief
        time. However, if routers are statically configured, this
        depends on how long it takes to update all the configurations.

        For PIM-SM one typically switches to SPT (Shortest-Path-Tree)
        when the first packet is received by the last-hop routers.
        Forwarding on the SPT should not be impacted by change of IP
        address. Network operator should be careful not deprecate the
        previous mapping before configuring a new one, because
        implementations may revert to Dense Mode if no RP is configured.

        The impact of this is minimal. The main concern is that while
        the peering is unavailable, one may not receive updates about
        new sources.

        It may help to configure a new peering before taking down the
        existing one.

   o Renumbering of multicast addresses

        In general multicast addresses can be chosen independently of
        the unicast addresses, and the multicast addresses can remain
        fixed even if the unicast addresses are renumbered. However, for
        IPv6 there are useful ways of deriving multicast addresses from
        unicast addresses, such as Unicast-Prefix-based IPv6 Multicast
        Addresses [RFC3306] and Embedded-RP IPv6 Multicast Addresses
        [RFC3956]. In that case the multicast addresses used may have to
        be renumbered.

        Renumbering group addresses may be complicated. For multicast,
        it is common to use literal addresses, and not DNS. When
        multicast addresses are changed, source applications need to be
        reconfigured and restarted.




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        Multicast receivers need to learn the new group addresses to
        join.

        Note that for SSM, receivers need to learn which multicast
        channels to join. A channel is a source and group pair. This
        means that for an SSM application, a change of source address is
        likely to have the same effect as a change of group address.

        Some applications may have dynamic methods of learning which
        groups (and possibly sources) to join. If not, the application
        may have to be reconfigured and restarted.

        One common way for receivers to learn the necessary parameters
        are by use of SDP. SDP information may be distributed via
        various application protocols, or it may be from a file. An SDP
        file may be distributed via HTTP, email etc. If a user is using
        a web browser and clicking on a link to launch the application
        with the necessary data, it may be a matter of closing the
        current application, and re-clicking the link.

8.2. Mobility

   As [RFC5887] suggested, for Mobile IP, we need a better mechanism to
   handle change of home agent address while mobile is disconnected.

9. Gaps considered unsolvable

   This section lists gaps have been documented but are considered
   unsolvable or out of the scope of this document.

9.1. Address Configuration

   o RA prefix lifetime limitation

        In section 5.5.3 of [RFC4862], it is defined that "If the
        received Valid Lifetime is greater than 2 hours or greater than
        RemainingLifetime, set the valid lifetime of the corresponding
        address to the advertised Valid Lifetime." So when renumbering,
        if the previous RemainingLifetime is longer than two hours, it
        is impossible to reduce a prefix's lifetime less than two hours.
        This limitation is to prevent denial-of-service attack.


9.2. Address-relevant Entries Update

   o DNS entries commonly have matching Reverse DNS entries which will
      also need to be updated during renumbering.


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   o DNS data structure optimization

        [RFC2874] proposed an  experimental A6 record type for DNS
        recording of IPv6 address and prefix. Several extensions to DNS
        query and processing were also proposed. With the A6 record and
        the extensions, an IPv6 address could be defined by using
        multiple DNS records. This feature would increase the complexity
        of resolvers but reduce the cost of zone file maintenance, so
        renumbering could be easier than with the AAAA record. But the
        A6 record has not been widely used, and it has been moved to
        historic status [RFC6563].

   o DNS authority

        As described in [I-D.chown-v6ops-renumber-thinkabout], "it is
        often the case in enterprises that host web servers and
        application servers on behalf of collaborators and customers
        that DNS zones out of the administrative control of the host
        maintain resource records concerning addresses for nodes out of
        their control. When the service host renumbers, they do not have
        sufficient authority to change the records. "

        It is an operational and policy issue and this document
        considers it not suitable to be solved through technical
        approach or bring additional protocol/mechanism to standardize
        the interaction between DNS systems for authority negotiations.

9.3. Miscellaneous

   o For transport layer, [RFC5887] said that TCP connections and UDP
      flows are rigidly bound to a given pair of IP addresses.

   o For application layer, as [RFC5887] said, in general, we can
      assert that any implementation is at risk from renumbering if it
      does not check that an address is valid each time it opens a new
      communications session.

10. Security Considerations

   o Prefix Validation

   Prefixes from the ISP may need authentication to prevent prefix
   fraud. Announcing changes of site prefix to other sites (for example,
   those that configure routers or VPNs to point to the site in
   question) also need validation.




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   In the LAN, Secure DHCPv6 ([I-D.ietf-dhc-secure-dhcpv6]) or SEND
   ([RFC3971], SEcure Neighbor Discovery) deployment may need to
   validate prefixes.

   o Influence on Security Controls

   During renumbering, security controls (e.g. ACLs) blocking access to
   legitimate resources should not be interrupted.

11. IANA Considerations

   This draft does not request any IANA action.

12. Acknowledgments

   This work adopts significant amounts of content from [RFC5887] and
   [I-D.chown-v6ops-renumber-thinkabout], so thanks go to Randall
   Atkinson, Hannu Flinck, Tim Chown, Mark Thompson, and Alan Ford. Some
   useful materials were provided by Oliver Bonaventure and his student
   Damien Leroy.

   Many useful comments and contributions were made by Lee Howard,
   Wesley George, and members of 6renum WG.

   This document was prepared using 2-Word-v2.0.template.dot.



13. References

13.1. Normative References

   [RFC2894] M. Crawford, "Router Renumbering for IPv6", RFC 2894,
             August 2000.

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

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

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




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

   [RFC3956] P. Savola, 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.

   [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.

13.2. Informative References

   [RFC2072] H. Berkowitz, "Router Renumbering Guide", RFC2072, January
             1997.

   [RFC3306] B. Haberman, D. Thaler, "Unicast-Prefix-based IPv6
             Multicast Addresses", RFC 3306, August 2002.

   [RFC3956] P. Savola, B. Haberman, "Embedding the Rendezvous Point (RP)
             Address in an IPv6 Multicast Address", RFC 3965, November
             2004.

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

   [RFC4714] Enns, R., "NETCONF Configuration Protocol", RFC 4714,
             December 2006.

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

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

   [I-D.ietf-dhc-secure-dhcpv6]
             Jiang, S., and Shen S., "Secure DHCPv6 Using CGAs", working
             in progress, March 2012.



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   [I-D.ietf-6renum-enterprise]
             Jiang, S., and B. Liu, "IPv6 Enterprise Network Renumbering
             Scenarios and Guidelines ", Working in
             Progress, July 2011.

   [I-D.chown-v6ops-renumber-thinkabout]
             Chown, T., "Things to think about when Renumbering an IPv6
             network", Work in Progress, September 2006.

   [I-D.ietf-6renum-static-problem]
             Carpenter, B., and S. Jiang, "Problem Statement for
             Renumbering IPv6 Hosts with Static Addresses", Working in
             Progress, August 2012.

   [I-D.liu-6renum-dhcpv6-slaac-switching]
             Liu, B., "DHCPv6/SLAAC Address Configuration Switching for
             Host Renumbering", Working in Progress, July 2012

   [LEROY]   Leroy, D. and O. Bonaventure, "Preparing network
             configurations for IPv6 renumbering", International of
             Network Management, 2009, <http://
             inl.info.ucl.ac.be/system/files/dleroy-nem-2009.pdf>


























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Authors' Addresses

   Bing Liu
   Huawei Technologies Co., Ltd
   Q14, Huawei Campus
   No.156 Beiqing Rd.
   Hai-Dian District, Beijing  100095
   P.R. China

   Email: leo.liubing@huawei.com


   Sheng Jiang
   Huawei Technologies Co., Ltd
   Q14, Huawei Campus
   No.156 Beiqing Rd.
   Hai-Dian District, Beijing  100095
   P.R. China

   Email: jiangsheng@huawei.com


   Brian Carpenter
   Department of Computer Science
   University of Auckland
   PB 92019
   Auckland, 1142
   New Zealand

   EMail: brian.e.carpenter@gmail.com

   Stig Venaas
   Cisco Systems
   Tasman Drive
   San Jose, CA  95134
   USA

   Email: stig@cisco.com


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