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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: December 11, 2013                                B. Carpenter
                                                University of Auckland
                                                             S. Venaas
                                                         Cisco Systems
                                                             W. George
                                                     Time Warner Cable
                                                          June 9, 2013

                    IPv6 Site Renumbering Gap Analysis
                   draft-ietf-6renum-gap-analysis-08.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
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   at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on December 11, 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
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   (http://trustee.ietf.org/license-info) in effect on the date of
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   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. Its main
   content is a gap analysis that provides a basis for future works 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.



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 ..................................... 7
   4. Managing Prefixes ............................................ 7
      4.1. Prefix Delegation ....................................... 7
      4.2. Prefix Assignment ....................................... 8
   5. Address Configuration ........................................ 8
      5.1. Host Address Configuration .............................. 8
      5.2. Router Address Configuration ............................ 9
   6. Updating Address-relevant Entries ........................... 10
      6.1. DNS Records Update ..................................... 10
      6.2. In-host Server Address Update .......................... 11
      6.3. Address update in scattered configurations ............. 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. Gap Summary ................................................. 17
      9.1. Managing Prefixes ...................................... 17
      9.2. Address configuration .................................. 17
      9.3. Address relevant entries update ........................ 17
      9.4. Renumbering event management ........................... 18
      9.5. Miscellaneous .......................................... 19
   10. Gaps considered unsolvable ................................. 19


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      10.1. Address Configuration ................................. 19
      10.2. Address-relevant Entries Update ....................... 19
      10.3. Miscellaneous ......................................... 20
   11. Security Considerations .................................... 20
   12. IANA Considerations......................................... 21
   13. Acknowledgments ............................................ 21
   14. References ................................................. 22
      14.1. Normative References .................................. 22
      14.2. Informative References ................................ 23







































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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 [RFC4984]. It is thus desirable to develop
   tools and practices that may make renumbering a simpler process to
   reduce demand for IPv6 PI space.

   Building upon the IPv6 enterprise renumbering scenarios described in
   [RFC6879], 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
   according to 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. Renumbering event management is presented
   independently from the steps of a renumbering process, in order to
   identify some operational and administrative gaps in renumbering.

   This document starts from existing work in [RFC5887] and [RFC4192].
   It does further analysis and identifies the valuable and solvable
   issues, digs out of some undiscovered gaps, and gives some solution
   suggestions. This document considers make-before-break approach as a
   premise for the gap analysis, so readers should be familiar with
   [RFC4192].

   Renumbering nodes with static addresses has a particular set of
   problems, thus discussion of that space has been covered in a related
   document [RFC6866].

   This document does not cover the un-planned emergency renumbering
   cases.

2. Overall Requirements for Renumbering

   This section introduces the overall 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.


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   The automation can be divided into four aspects as follows. (Detailed
   analysis of the four aspects is presented respectively in section 4
   to section 7.)

   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.

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

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

   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 be solved within
   renumbering context only. However, with the [RFC4192] make-before-
   break approach, and  the address lifetime mechanisms in IPv6
   Stateless Address Autoconfiguration (SLAAC) and Dynamic Host
   Configuration Protocol for IPv6 (DHCPv6), a smooth transition
   mechanism from old to new prefixes is applicable. In most of the
   cases, since we can set the transition period long enough to cover
   the on-going sessions, we consider this mechanism sufficient for
   avoiding session brokenness issue in IPv6 site renumbering. (Please
   note that if multiple addresses are running simultaneously on hosts,
   the address selection [RFC6724] needs to be carefully handled.)

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.




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   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] obtain new
      addresses through the renewal process or when they receive the
      reconfiguration messages initiated by the DHCPv6 servers.

   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 we are not aware
      of it being used in real network deployment.

3.2. Management Tools

   Some renumbering operations 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 IP address management (IPAM) tools. There are both commercial and
      open-source solutions. IPAM tools are used to manage IP address
      plans, and usually integrate 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 Some organizations use third-party tools to push configuration to
      devices. This is sometimes used as a supplement to vendor specific
      solutions. A representative of such third-party tool is [cfengine].

   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.





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   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. It should be noted that the administrators need to
      carefully deal with the address selection issue while the old and
      new prefixes are both available during the overlapping period in
      [RFC4192] procedure. And the address selection policies might need
      to be updated after renumbering. So administrator could leverage
      the address selection policy distribution mechanism in
      [I-D.ietf-6man-addr-select-opt].

   o [RFC6879] 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 IPv6 enterprise site, the key procedural issue is
   switching the old prefix (es) to the new one(s). A new short prefix
   may be divided into longer ones for subnets. So we need to carefully
   manage the prefixes to ensure they are synchronized and coordinated
   in the whole network.

4.1. Prefix Delegation

   For big enterprises, the new short prefix(es) usually comes down
   through off-line human communication. But for the SOHO style SMEs
   (Small & Medium Enterprises), the prefixes might be dynamically
   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.

   The delegation routers might need to renumber themselves with the new
   delegated prefixes. So there should be a mechanism informing the
   router to renumber themselves by delegated prefixes; and there also



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   should be a mechanism for the routers to derive addresses
   automatically based on the delegated prefixes.

4.2. Prefix Assignment

   When subnet routers receive the longer prefixes, they can advertise a
   prefix on a link to which hosts are connected.  Host address
   configuration, rather than routers, is the primary concern for prefix
   assignment which is described in the following section 5.1.

5. Address Configuration

5.1. Host Address Configuration

   o SLAAC/DHCPv6 interaction problems

   Both of the DHCPv6 and Neighbor Discovery (ND) protocols have IP
   address configuration function. They are suitable for different
   scenarios. 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
   [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 additional complexity for both the
   hosts and the network management.

   With the flags defined in RA (ManagedFlag indicating the DHCPv6
   service available in the network; OtherConfigFlag indicating other
   configurations such as DNS/routing), the two separated address
   configuration modes are 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 flags.
   Different operating systems have followed different approaches. (For
   more details, please refer to [I-D.liu-bonica-dhcpv6-slaac-problem]
   and [I-D.liu-6renum-dhcpv6-slaac-switching].)

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

     - DHCPv6-configured hosts might not be able to be renumbered by RA

     It is unclear whether a DHCPv6 configured host will accept address
     configuration though RA messages, especially when M flag


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     transitioning from 1 to 0; this depends on the implementation of
     the operating system. It might not be possible for administrators
     to only use RA messages for renumbering, since renumbering might
     fail on some already DHCPv6-configured hosts. It means
     administrators have to use DHCPv6 reconfiguration for some DHCPv6-
     configured hosts. It is not convenient and DHCPv6 reconfiguration
     is not suitable for bulk usage as analyzed in below.

     - DHCPv6-configured hosts might not be able to learn new RA
       prefixes

     [RFC5887] mentioned that DHCPv6-configured hosts may want to learn
     about the upstream availability of new prefixes or loss of prior
     prefixes dynamically by deducing this from periodic RA messages.
     Relevant standards ([RFC4862],[RFC3315]) are ambiguous about what
     approach should be taken by a DHCPv6-configured host when it
     receives RA messages containing a new prefix. Current behavior
     depends on the operating system of the host and cannot be predicted
     or controlled by the network.

     - SLAAC-configured hosts might not be able to add DHCPv6 address(es)

     The behavior when the host receives RA messages with M flag set is
     unspecified.

     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.

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

   o Restart after renumbering



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   As [RFC2072] mentioned, some routers cache IP addresses in some
   situations, so routers might need to be restarted as a result of site
   renumbering. While most modern systems support a cache-clear function
   that eliminates the need for restarts, there are always exceptions
   that must be taken into account.

   o Router naming

   [RFC4192] suggests 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 currently it is present in most IPSec VPN
   implementations. However, many administrators may need to be alerted
   to the fact that it could be utilized to avoid manual modification
   during renumbering.

6. Updating Address-relevant Entries

   In conjunction with renumbering the nodes, any configuration or data
   store containing previous addresses must be updated as well. Some
   examples include DNS records and filters in various entities such as
   ACLs in firewalls/gateways.

6.1. DNS Records Update

   o Secure Dynamic DNS update

   In real network operations, DNS update is normally achieved 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 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
   implementations, but it hasn't been widely deployed. Normal hosts are
   not suitable to do the update mainly because of the complexity of key
   management issues inherited from secure DNS mechanisms, so current
   practices usually assign the DHCP servers to act as DNS clients to
   request the DNS server updating relevant records [RFC4704]. This
   server-oriented approach is applicable for large numbers of hosts'
   using secure DDNS. (In some commercial solutions, DNS service could
   be integrated with DHCP service provided by the same vendor so that
   the secure DDNS might be silently enabled as default.) However, there
   is still a gap here, since the DHCP servers have to learn the
   relevant hosts have changed their addresses and thus trigger the DDNS


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   update. If the hosts were numbered and also renumbered by DHCP, then
   it is easy for the DHCP servers to learn the address changes; but if
   the hosts were numbered by SLAAC, then there could be trouble.
   [I-D.ietf-dhc-addr-registration] proposed a address registration
   mechanism which could be used to address the latter issue; however,
   it has not been deployed yet.

6.2. In-host Server Address Update

   While DNS stores addresses of hosts in servers, hosts are also
   configured with addresses of servers such as DNS server, radius
   server. While renumbering, the hosts must update these addresses if
   the server addresses changed.

   In principle, the addresses of DHCPv6 servers do not need to be
   updated, since they could be dynamically discovered through DHCPv6
   relevant multicast messages. But in practice, most relay agents have
   the alternative of being configured with DHCPv6 server address rather
   than sending to a multicast address. So the DHCP server addresses
   update might be an issue in practice.

6.3. Address update in scattered configurations

   Besides the DNS records and the in-host server address entries, there
   are also many places in which IP addresses are configured, for
   example, filters such as ACL and routing policies. 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.

   In renumbering, it is annoying and error-prone to update the IP
   addresses in all the above mentioned places. We lack a "one-stop"
   mechanism to trigger the updates for all the subsystems on a
   host/server, and all the external databases that refer to the IP
   address update. We decompose the general "one-stop" gap into the
   following two aspects.

   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



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   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 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 refers to 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 Aggregation

     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, it is hard to get all the
     relevant configurations through one place.

     - Configuration Update Automation

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


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     configuration management system to leverage. Although there are
     some vendor-independent tools as mentioned in section 3.2, a
     standard and comprehensive way of uniformly updating configurations
     in multi-vendor devices is still 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 to hosts that a
      renumbering event has changed some DNS records in DNS servers
      (normally, in an enterprise it/they is/are (a) local recursive DNS
      server(s).), and then the hosts might want to refresh the DNS
      cache. That mechanism may also need to indicate that such a change
      will happen at a specific time in the future.

   o As suggested in [RFC4192], if the DNS service can be given prior
      notice about a renumbering event, then people could reduce the
      delay in the transition to new IPv6 addresses, thus improve the
      efficiency of renumbering.

   o Router awareness: in a site with multiple domains which are
      connected by border routers, all border routers should be aware of
      renumbering in one domain or multiple domains, and update the
      internal forwarding tables and the address/prefix based filters
      accordingly to correctly handle inbound packets.

   o Ingress filtering: ISPs normally enable ingress filter to drop
      packets with source addresses from other ISPs at the end site
      routers to prevent IP spoofing [RFC2827]. In a multihomed site
      with multiple PA prefixes, the ingress router of ISP A should be
      notified if the ISP B initiates a renumbering event in order to
      properly update its filters to permit the new legitimate prefix
      (es). For large enterprises, it might be applicable to indicate
      this new legitimate prefix information through human communication,
      however, for the millions of small enterprises, an automated
      notification mechanism is needed.




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   o In the NMS (network management system), logs collected through
      syslog, SNMP notification, IPFIX, etc. usually treat the UDP
      message source IP addresses as the host or router IDs. When one
      source IP address is changed, the log collectors will consider
      that a new device appeared in the network. So a mechanism is
      needed for the NMS applications to learn the renumbering event, so
      that they could correlate the old and new addresses in the logs.

7.2. Synchronization Management

   o DNS update synchronization

   The DNS changes must be coordinated with the changes of node address
   configuration. DNS has a latency issue of propagating information
   from the server to the resolver. The latency is mainly caused by TTL
   assigned to individual DNS records and the timing of updates from
   primary to secondary servers [RFC4192].

   Ideally, during a renumbering operation, the DNS TTLs should always
   be shorter than any other lifetime associated with an address. If the
   TTLs were set correctly, then the DNS latency could be well
   controlled. However, there might be some exceptional situations in
   which the DNS TTLs were already set too long for the time available
   to plan and execute a renumbering event. In these situations, there
   currently are no mechanisms to deal with the already configured long
   DNS TTLs.

7.3. Renumbering Monitoring

   While treating renumbering as a network event, mechanisms to monitor
   the renumbering process might be needed to inform the administrators
   whether the renumbering has been successfully done. Considering the
   address configuration operation might be stateless (if ND is used for
   renumbering), it is difficult for monitoring.

8. Miscellaneous

   Since multicast and mobility are special use cases which might not be
   included in routine/common renumbering operations, they are
   separately discussed as miscellaneous in this section.

8.1. Multicast

   In the perspective of interface renumbering operations, renumbering a
   multicast address is the same with renumbering a unicast address. So
   this section mainly discusses the issues from the perspective of the
   impact to the multicast application systems caused by renumbering.


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   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 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.

   o Renumbering of multicast addresses



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   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.

   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 is 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.

   In summary, currently the multicast renumbering issues are basically
   handled by application-specific methods. There is no standard way to
   guarantee multicast service could live across a renumbering event.

8.2. Mobility

   As described in [RFC5887], if a mobile node's home address changes
   unexpectedly, the node can be informed of the new global routing
   prefix used at the home site through the Mobile Prefix Solicitation
   and Mobile Prefix Advertisement ICMPv6 messages [RFC6275]. But if the
   mobile node is unfortunately disconnected at the time of home address
   renumbering, it will no longer know a valid subnet anycast address
   for its home agent, leaving it to deduce a valid address on the basis
   of DNS information.



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   So, for Mobile IP, we need a better mechanism to handle change of
   home agent address while mobile is disconnected.

9. Gap Summary

9.1. Managing Prefixes

   o A mechanism informing the router to renumber themselves by
      delegated prefixes

   o A mechanism for the routers to derive addresses automatically
      based on the delegated prefixes.

9.2. Address configuration

   o Host address configuration

     - DHCPv6-configured hosts might not able to be renumbered by RA on
        some of current implementations

     - DHCPv6-configured hosts might not able to learn new RA prefixes
        on some of current implementations

     - SLAAC-configured hosts might not able to add DHCPv6 address(es)
        on some of current implementations

   o Router address configuration

     - A mechanism for interior routers in multihomed site to learn
        which upstream providers and prefixes were currently reachable

     - Cache-clear might need restart (rarely in modern routers)

     - Using router domain names is not widely learned/deployed by
        administrators

9.3. Address relevant entries update

   o DNS records update

     - For key management scalable issue, secure dynamic DNS update is
        usually done by DHCP servers on behalf of the hosts, so it might
        not be applicable for SLAAC-configured hosts to do secure DDNS.

   o In-host server address update




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     - DHCP relays might be configured with DHCP server addresses
        rather than sending multicast messages to discover the DHCP
        server dynamically, so the DHCP server addresses update might be
        an issue in practice.

   o Address update in scattered configurations

     - Devices don't support parameterized configuration,
        administrators need to touch every places where IP addresses
        were configured

     - It is hard to get all the address-relevant configurations spread
        in various devices through one place

     - Uniformly update configurations in multi-vendor devices is a big
        gap currently

9.4. Renumbering event management

   o  Renumbering notification

     - A mechanism to indicate hosts local recursive DNS is going to be
        renumbered

     - A prior notice about a renumbering event for DNS

     - A mechanism for border routers to know internal partial
        renumbering

     - For multihomed sites, a mechanism to notify the egress router of
        ISPA that egress router connecting to ISPB initiates renumbering
        is needed.

     - A mechanism is needed for the NMS applications to learn the
        renumbering event, so that they could correlate the old and new
        addresses in the logs.

   o  Synchronization management

     - DNS information propagating latency issue

   o  Renumbering monitoring

     - Mechanisms to monitor the process and feedback of renumbering
        might be needed.




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9.5. Miscellaneous

   o  Multicast

     - Mechanism for SSM receivers to learn the source addresses when
        multicast sources are renumbered.

   o  Mobility

     - A better mechanism to handle change of home agent address while
        mobile is disconnected.

10. Gaps considered unsolvable

   This section lists gaps have been identified by other documents but
   are considered unsolvable.

10.1. 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.

10.2. Address-relevant Entries Update

   o DNS authority

   In an enterprise that hosts servers on behalf of collaborators and
   customers, it is often the case that DNS zones outside the
   administrative control of the hosting enterprise maintain resource
   records concerning addresses for hosted nodes within its address
   space. When the hosting enterprise renumbers, it does not have
   sufficient authority to change those records.

   This is an operational and policy issue. It is out of scope for this
   document to consider a technical solution or to propose an additional
   protocol or mechanism to standardize the interaction between DNS
   systems for authority negotiations.





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   o DNS entries commonly have matching Reverse DNS entries which will
      also need to be updated during renumbering. It might not be
      possible to combine forward and reverse DNS entries update in one
      procedure.

   o DNS data structure optimization

   [RFC2874] proposed an A6 record type for DNS recording of IPv6
   address and prefix. Several extensions to DNS query and processing
   were also proposed. A6 was designed to be a replacement for AAAA
   record. The changes were designed to facilitate network renumbering
   and multihoming. 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.

   However, the A6 record has not been widely used, and has been shown
   to have various problems and disadvantages (see section 2 in
   [RFC6563]). It has been deprecated and moved to historic status by
   [RFC6563]. The idea of a structured record to separate prefix and
   suffix is still potentially valuable for renumbering, but avoiding
   the problems of the A6 record would require a major development
   effort.

10.3. 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, in general, we can assert that any
      implementation is at risk from renumbering if it does not check
      whether an address is valid each time it starts session resumption
      (e.g. a laptop wakes from sleep state). It is also more of less
      risky when it opens a new communications session by using cached
      addresses.

   We considered the above two points (ID/Locator overloading in
   transport layer & address caching in app layer) are fundamental
   issues that might not be proper to deal with them just in terms of
   renumbering.

11. Security Considerations

   o Prefix Validation




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   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.

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

   o Influence on Security Controls

   During renumbering, security controls (e.g. ACLs) protecting
   legitimate resources should not be interrupted. For example, if some
   addresses are in a blacklist, they should not escape from the
   blacklist due to renumbering.

   If there are DHCPv6 authentication keys associated with an IP address
   then the keys need to be changed for continually working when the
   addresses are renumbered.

   Addresses in SEND certificates are going to need to get updated when
   renumbering. During the overlap between old and new addresses, both
   certificates must remain valid.

   o Security Protection for Renumbering Notification

   Section 7.1 mentions possible notification mechanisms to signal a
   change in the DNS system or in the border routers related to a
   renumbering event. Since DNS system and border routers are key
   elements in any network, and they might take action according to the
   notification, a security authentication for the renumbering
   notification is needed.

   o Security Protection for Configuration Update

   Automated configuration update approaches like [LEROY] would increase
   the risk since a bad actor with the right permission could cause
   havoc to the networks.

12. IANA Considerations

   This draft does not request any IANA actions.

13. Acknowledgments

   This work adopts significant amounts of content from [RFC5887] and
   particularly the "DNS Authority" topic in section 10.2 is from


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   [draft-chown-v6ops-renumber-thinkabout]. Both of the two documents
   are important input for this work, that some
   principles/considerations applied in this work are implicitly
   inherited from them. 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 Ted Lemon, Lee
   Howard, Robert Sparks, S. Moonesamy, Fred Baker, Sean Turner, Benoit
   Claise, Stephen Farrell, Brian Haberman, Joel Jaeggli, Eric Vyncke,
   Phillips Matthew, Benedikt Stockebrand, Gustav Reinsberger, Teco Boot
   and other members of 6renum WG.

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

14. References

14.1. Normative References

   [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.

   [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.






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14.2. Informative References

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

   [RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering:
             Defeating Denial of Service Attacks which employ IP Source
             Address Spoofing", RFC 2267, January 1998.

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

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

   [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.

   [RFC4704] Volz, B., "The Dynamic Host Configuration Protocol for IPv6
             (DHCPv6) Client Fully Qualified Domain Name (FQDN) Option",
             RFC 4704, October 2006.

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

   [RFC4984] Meyer, D., Ed., Zhang, L., Ed., and K. Fall, Ed., "Report
             from the IAB Workshop on Routing and Addressing", RFC 4984,
             September 2007.

   [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.

   [RFC6724] Thaler, D., Ed., Draves, R., Matsumoto, A., and T. Chown,
             "Default Address Selection for Internet Protocol Version 6
             (IPv6)", RFC 6724, September 2012.


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   [RFC6275] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
             in IPv6", RFC 3775, June 2004.

   [RFC6866] Carpenter, B. and S. Jiang, "Problem Statement for
             Renumbering IPv6 Hosts with Static Addresses in Enterprise
             Networks", RFC 6866, February 2013.

   [RFC6879] Jiang, S., Liu, B., and B. Carpenter, "IPv6 Enterprise
             Network Renumbering Scenarios, Considerations, and Methods",
             RFC 6879, February 2013.

   [I-D.ietf-6man-addr-select-opt]
             Matsumoto, A.M., Fujisaki T.F., and T. Chown, "Distributing
             Address Selection Policy using DHCPv6", Working in Progress,
             April 2013.

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

   [I-D.ietf-dhc-addr-registration]
             Jiang, S., Chen G., and S. Krishnan, "A Generic IPv6
             Addresses Registration Solution Using DHCPv6", working in
             progress, February 2013.

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

   [I-D.liu-bonica-dhcpv6-slaac-problem]
             Liu, B., and R. Bonica, "DHCPv6/SLAAC Address Configuration
             Interaction Problem Statement", Working in Progress,
             February 2013.

   [cfengine]http://cfengine.com/what-is-cfengine

   [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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   Wesley George
   Time Warner Cable
   13820 Sunrise Valley Drive
   Herndon, VA  20171
   USA

   Phone: +1 703-561-2540
   Email: wesley.george@twcable.com


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