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Network Working Group                                           T. ChownRequest for Comments: 4076                     University of SouthamptonCategory: Informational                                        S. Venaas                                                                 UNINETT                                                        A. Vijayabhaskar                                   Cisco Systems (India) Private Limited                                                                May 2005Renumbering Requirements for StatelessDynamic Host Configuration Protocol for IPv6 (DHCPv6)Status of This Memo   This memo provides information for the Internet community.  It does   not specify an Internet standard of any kind.  Distribution of this   memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2005).Abstract   IPv6 hosts using Stateless Address Autoconfiguration are able to   configure their IPv6 address and default router settings   automatically.  However, further settings are not available.  If   these hosts wish to configure their DNS, NTP, or other specific   settings automatically, the stateless variant of the Dynamic Host   Configuration Protocol for IPv6 (DHCPv6) could be used.  This   combination of Stateless Address Autoconfiguration and stateless   DHCPv6 could be used quite commonly in IPv6 networks.  However, hosts   using this combination currently have no means by which to be   informed of changes in stateless DHCPv6 option settings; e.g., the   addition of a new NTP server address, a change in DNS search paths,   or full site renumbering.  This document is presented as a problem   statement from which a solution should be proposed in a subsequent   document.Chown, et al.                Informational                      [Page 1]

RFC 4076            Renumbering for Stateless DHCPv6            May 2005Table of Contents1.  Introduction ...................................................22.  Problem Statement ..............................................33.  Renumbering Scenarios ..........................................33.1.  Site Renumbering .........................................43.2.  Changes to a DHCPv6-assigned Setting .....................44.  Renumbering Requirements .......................................45.  Considerations in Choosing a Solution ..........................46.  Solution Space .................................................57.  Summary ........................................................58.  Security Considerations ........................................69.  Acknowledgements ...............................................610. References .....................................................610.1. Normative References .....................................610.2. Informative References ...................................61.  Introduction   IPv6 hosts using Stateless Address Autoconfiguration [2] are able to   configure their IPv6 address and default router settings   automatically.  Although Stateless Address Autoconfiguration for IPv6   allows automatic configuration of these settings, it does not provide   a mechanism for additional non IP-address settings to be configured   automatically.   The full version of the Dynamic Host Configuration Protocol for IPv6   (DHCPv6) [3] is designed to provide both stateful address assignment   to IPv6 hosts, as well as additional (non IP-address) configuration   including DNS, NTP, and other specific settings.  A full stateful   DHCPv6 server allocates the addresses and maintains the clients'   bindings to keep track of client leases.   If hosts using Stateless Address Autoconfiguration for IPv6 wish to   configure their DNS, NTP, or other specific settings automatically,   the stateless variant [4] of DHCPv6 could be used.  This variant is   more lightweight.  It does not do address assignment; instead, it   only provides additional configuration parameters, such as DNS   resolver addresses.  It does not maintain dynamic state about the   information assigned to clients, and therefore there is no need to   maintain dynamic per-client state on the server.   This combination of Stateless Address Autoconfiguration and stateless   DHCPv6 could be used quite commonly in IPv6 networks.Chown, et al.                Informational                      [Page 2]

RFC 4076            Renumbering for Stateless DHCPv6            May 20052.  Problem Statement   A problem, however, lies in the ability, or lack of ability, of   clients using this combination to be informed of (or to deduce)   changes in DHCPv6-assigned settings.   While a DHCPv6 server unicasts Reconfigure messages to individual   clients to trigger them to initiate Information-request/reply   configuration exchanges to update their configuration settings, the   stateless variant of DHCPv6 cannot use the Reconfigure mechanism   because it does not maintain a list of IP addresses (leases) to send   the unicast messages to.  Note that in DHCPv6, Reconfigure messages   must be unicast; multicast is not allowed.   Thus, events including the following cannot be handled:   o  Full site renumbering   o  DNS server change of address   o  NTP server change of address   o  A change in DNS search paths   It would be highly desirable that a host using the combination of   Stateless Address Autoconfiguration and stateless DHCPv6 could handle   a renumbering or reconfiguration event, whether planned or unplanned   by the network administrator.   Note that the scope of the problem could extend beyond Stateless   DHCPv6, since only IP address options have a lifetime; i.e., there is   no mechanism even in the full DHCPv6 that "expires" old information   or otherwise forces a client to recheck that new/updated information   is available.  However, with full DHCPv6, a node may learn of updates   to non-address options when renewing its address lease.3.  Renumbering Scenarios   There are two main scenarios for changes to DHCPv6-assigned settings   that would require the client to initiate an Information-request/   reply exchange to update the configuration.Chown, et al.                Informational                      [Page 3]

RFC 4076            Renumbering for Stateless DHCPv6            May 20053.1.  Site Renumbering   One of the fundamental principles of IPv6 is that sites receive their   IPv6 address allocations from an ISP using provider-assigned (PA)   address space.  There is currently no provider-independent (PI)   address space in IPv6.  Therefore, a site changing its ISP must   renumber its network.  Any such site renumbering will require hosts   to reconfigure both their own address and default router settings and   their stateless DHCPv6-assigned settings.3.2.  Changes to a DHCPv6-assigned Setting   An administrator may need to change one or more stateless   DHCPv6-assigned settings; e.g., an NTP server, DNS server, or the DNS   search path.  This may be required if a new, additional DNS server is   brought online and is moved to a new network (prefix), or if an   existing server is decommissioned or known to be unavailable.4.  Renumbering Requirements   Ideally, any of the above scenarios should be handled automatically   by the hosts on the network.  For this to be realised, a method is   required whereby the hosts are informed that they should request new   stateless DHCPv6-assigned setting information.   The solution to the problem may depend on whether the renumbering or   configuration change is planned or unplanned, from the perspective of   the network administrator.  There is already work underway toward   understanding the planned renumbering [5] scenario for IPv6 networks.   However, there is currently no mechanism in stateless DHCPv6 for   handling planned renumbering events.5.  Considerations in Choosing a Solution   A number of considerations could be listed for a desirable solution:   o  The solution should support planned renumbering; it is desirable      that it also supports unplanned renumbering.   o  Security is important.  No new security concerns should be      introduced to Stateless DHCPv6 by the solution.   o  It must be possible to update options, even if the network is not      renumbered.   o  It is desirable to maintain the "stateless" property; i.e., no      per-client state should need to be kept in the server.Chown, et al.                Informational                      [Page 4]

RFC 4076            Renumbering for Stateless DHCPv6            May 20056.  Solution Space   Solutions should be designed and presented in a separate document.   An initial brief set of candidate solutions might include the   following:   o  Add a Reconfigure message mechanism that would work in the      stateless DHCPv6 environment.  This could enable planned or      unplanned events, but may require a multicast mechanism in order      to be realised.   o  Convey a valid lifetime timer to clients for stateless DHCPv6-      assigned settings.  This could primarily enable planned events,      but with a small time-out it could handle unplanned events to some      extent at the expense of the additional request traffic.  The      selection of recommended lifetime values/ranges would be the      subject of future work.   o  Use some form of Router Advertisement (RA) [1] as a hint to      request new stateless DHCPv6-assigned settings.  Using only an      observed new RA prefix as a hint to re-request settings would not      handle changes that are purely to NTP, DNS, or other options.      Other possible means of detection of network (re)attachment could      also be used as cues (e.g., see Goals of Detecting Network      Attachment (DNA) in IPv6 [6]).   o  Change the semantics of the 'O' flag in RAs [2] so that toggling      its value may trigger an Information-request message.   There will also be conditions under which a client should send an   Information-request, such as reconnection to a link.  Recommendations   for these cases are outside the scope of this document, but we expect   ongoing work in the DNA WG (as scoped in Goals of Detecting Network   Attachment (DNA) in IPv6 [6]) to yield recommendations.7.  Summary   This document presents a problem statement for how IPv6 hosts that   use the combination of Stateless Address Autoconfiguration and   stateless DHCPv6 may be informed of renumbering events or other   changes to the settings that they originally learned through   stateless DHCPv6.  A short list of candidate solutions is presented,   which the authors hope will be expanded upon in subsequent documents.Chown, et al.                Informational                      [Page 5]

RFC 4076            Renumbering for Stateless DHCPv6            May 20058.  Security Considerations   There are no security considerations in this problem statement per   se.  However, whatever mechanism is designed or chosen to address   this problem should avoid introducing new security concerns for   (stateless) DHCPv6.   The issues of maintaining appropriate security through a renumbering   event are outside the scope of this document (if specific servers   within the network are being added or removed, firewall   configurations and ACLs, for example, will need to reflect this).   However, this is an important area for further work.9.  Acknowledgements   The authors would like to thank Ralph Droms, Bernie Volz, and other   individuals on the DHC mail list for their comments on this document,   as well as colleagues on the 6NET project.  We also thank the review   comments, particularly those from Thomas Narten.10.  References10.1.  Normative References   [1]  Narten, T., Nordmark, E., and W. Simpson, "Neighbor Discovery        for IP Version 6 (IPv6)",RFC 2461, December 1998.   [2]  Thomson, S. and T. Narten, "IPv6 Stateless Address        Autoconfiguration",RFC 2462, December 1998.   [3]  Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M.        Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",RFC 3315, July 2003.   [4]  Droms, R., "Stateless Dynamic Host Configuration Protocol (DHCP)        Service for IPv6",RFC 3736, April 2004.10.2.  Informative References   [5]  Baker, F., Lear, E. and R. Droms, "Procedures for Renumbering an        IPv6 Network without a Flag Day", Work in Progress, July 2004.   [6]  Choi, J.,"Goals of Detecting Network Attachment (DNA) in IPv6",        Work in Progress, October 2004.Chown, et al.                Informational                      [Page 6]

RFC 4076            Renumbering for Stateless DHCPv6            May 2005Authors' Addresses   Tim Chown   University of Southampton   School of Electronics and Computer Science   Southampton, Hampshire  SO17 1BJ   United Kingdom   EMail: tjc@ecs.soton.ac.uk   Stig Venaas   UNINETT   Trondheim  NO 7465   Norway   EMail: venaas@uninett.no   Vijayabhaskar A Kalusivalingam   Cisco Systems (India) Private Limited   9, Brunton Road   Bangalore  560025   India   EMail: vibhaska@cisco.comChown, et al.                Informational                      [Page 7]

RFC 4076            Renumbering for Stateless DHCPv6            May 2005Full Copyright Statement   Copyright (C) The Internet Society (2005).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   This document and the information contained herein are provided on an   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the procedures with respect to rights in RFC documents can be   found inBCP 78 andBCP 79.   Copies of IPR disclosures made to the IETF Secretariat and any   assurances of licenses to be made available, or the result of an   attempt made to obtain a general license or permission for the use of   such proprietary rights by implementers or users of this   specification can be obtained from the IETF on-line IPR repository athttp://www.ietf.org/ipr.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights that may cover technology that may be required to implement   this standard.  Please address the information to the IETF at ietf-   ipr@ietf.org.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Chown, et al.                Informational                      [Page 8]