[Docs] [txt|pdf] [Tracker] [Email] [Nits]

Versions: 00

IPv6 Working Group                                              F. Baker
Internet-Draft                                             Cisco Systems
Expires: October 9, 2003                                  April 10, 2003


     Procedures for Renumbering an IPv6 Network without a Flag Day
                 draft-baker-ipv6-renumber-procedure-00

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that other
   groups may also distribute working documents as Internet-Drafts.

   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."

   The list of current Internet-Drafts can be accessed at http://
   www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on October 9, 2003.

Copyright Notice

   Copyright (C) The Internet Society (2003). All Rights Reserved.

Abstract

   This document addresses the key procedural issues in renumbering an
   IPv6 network. In certain areas, it is necessarily incomplete; it
   points out those areas, however. It may be considered an update to
   RFC 2072. It presumes the use of IPv6 Autoconfiguration as described
   in RFC 2894.

Requirements Language

   This document is not intended to be a requirements document, but a
   starting point for a plan that a network operator might use to
   renumber a network. As such, one could argue that requirements
   language is inappropriate. However, a few recommendations in
   application design or in procedural execution arise, which suggest



Baker                   Expires October 9, 2003                 [Page 1]


Internet-Draft         Renumbering IPv6 Networks              April 2003


   requirements. In those contexts, requirements language is used.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in  RFC 2119 [1].

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Detailed review of procedure . . . . . . . . . . . . . . . . .  5
   2.1 Initial condition: stable using the old prefix . . . . . . . .  5
   2.2 Adding the new prefix  . . . . . . . . . . . . . . . . . . . .  5
   2.3 Stable routing both prefixes . . . . . . . . . . . . . . . . .  5
   2.4 Shutting down the use of the old prefix  . . . . . . . . . . .  6
   2.5 Removing the old prefix  . . . . . . . . . . . . . . . . . . .  7
   2.6 Final condition: stable using the new prefix . . . . . . . . .  7
   3.  "Find all the places..." . . . . . . . . . . . . . . . . . . .  8
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   5.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
       Normative References . . . . . . . . . . . . . . . . . . . . . 12
       Informative References . . . . . . . . . . . . . . . . . . . . 13
       Author's Address . . . . . . . . . . . . . . . . . . . . . . . 14
       Intellectual Property and Copyright Statements . . . . . . . . 15




























Baker                   Expires October 9, 2003                 [Page 2]


Internet-Draft         Renumbering IPv6 Networks              April 2003


1. Introduction

   The Prussian military theorist Carl von Clausewitz [13] wrote,
   "Everything is very simple in war, but the simplest thing is
   difficult. These difficulties accumulate and produce a friction,
   which no man can imagine exactly who has not seen war. ... So in war,
   through the influence of an infinity of petty circumstances, which
   cannot properly be described on paper, things disappoint us, and we
   fall short of the mark."  Operating a network is aptly compared to
   conducting a war. The difference is that the opponent, who would
   sometimes appear to be the customer who pays the bills, is the
   futility of the expectation that homo ignoramus will behave
   intelligently. A monograph on the subject by Hardin [14] calls this
   the "Tragedy of the Commons", it results when a shortcut is taken
   because of perceived immediate utility to the perpetrator and a lack
   of responsibility for the side effects or latent ramifications of the
   shortcut.

   This document addresses the key procedural issues in renumbering an
   IPv6 network. The procedure is straightforward  to describe, but
   operationally can be difficult to automate or execute due to issues
   of statically configured network state, which one might aptly
   describe as "an infinity of petty circumstances". As a result, in
   certain areas, this procedure is necessarily incomplete; it points
   out those areas, however. It may be considered an update to RFC 2072
   [6]. For this reason also, this document contains recommendations for
   application design and network management which, if taken seriously,
   may avoid or minimize the impact of the issues.

   RFC 2072 [6] describes the implications of renumbering in an IPv4
   network. A number of issues are raised, not the least of which is
   that while IPv4 in no sense precludes the configuration of more than
   one prefix on an interface in an equal sense, IPv4 equipment usually
   does not provide this capability. The net result is that changing a
   subnet's prefix calls for a "flag day" - an epochal point in time,
   before which one set of realities apply and after which another
   disjoint set of realities apply - on the subnet, and changing a
   network's base prefix calls for a flag day for the network. IPv6
   intentionally calls for and provides the ability to configure
   multiple prefixes on the same interface, and provides facilities for
   the direct renumbering of those interfaces; as a result, it is
   possible to reconfigure an IPv6 network without a flag day. However,
   doing so requires planning and serious attention to detail.

   The network, during renumbering, progresses through a series of
   states which must be carefully considered from a policy perspective
   to ensure that they are consistent at all times with the policies of
   the administration. The network may be viewed as being in one of six



Baker                   Expires October 9, 2003                 [Page 3]


Internet-Draft         Renumbering IPv6 Networks              April 2003


   phases:

   Stable using the old prefix: Initially, of course, the network is
      using a prefix for in its routing, for its servers, and for other
      systems in its network. This is a stable configuration.

   Adding the new prefix: It is necessary to add the new prefix, but
      while the new prefix is being added, it will of necessity not be
      working everywhere in the network. Routing to various sub-prefixes
      will be configured over a period of time varying from minutes to
      hours depending on the size of the network and the degree of
      automation used in reconfiguration.

   Stable routing two prefixes: Once the network has been configured
      with the new prefix and has had sufficient time to stabilize, it
      becomes a stable platform with two addresses for every device, one
      in the old prefix and one in the new. Sessions are opened with the
      addresses in the old prefix; the new is idle.

   Shutting down the use of the old prefix: DNS [3][4] is changed to
      reflect addresses in the new prefix, and any manual address
      configuration that used the old prefix must be modified to use the
      new prefix.

   Removing the old prefix: Once all sessions are deemed to have
      completed, there will be no dependence on the old prefix. It may
      be removed from the configuration of the system.

   Stable using the new prefix: Equivalent to the initial state, but
      using the new prefix.

   This procedure identifies the considerations involved in taking the
   network from phase to phase.


















Baker                   Expires October 9, 2003                 [Page 4]


Internet-Draft         Renumbering IPv6 Networks              April 2003


2. Detailed review of procedure

   In this discussion, we assume that an entire prefix is being replaced
   with another entire prefix.  It may be that only part of a prefix is
   being changed, or that more than one prefix is being changed to a
   single joined prefix. In such cases, the principles apply, but will
   need to be modified to address the exact situation. This procedure
   should be seen as a skeleton of the procedure that would in fact be
   applied.

2.1 Initial condition: stable using the old prefix

   Initially, the network is using a given prefix for in its routing,
   for its servers, and for other systems in its network. This is a
   stable configuration.

2.2 Adding the new prefix

   It is necessary to add the new prefix, but while the new prefix is
   being added, it will of necessity not be working everywhere in the
   network, and unless properly protected, it can be used to attack the
   network in those places where it is operational. Routing to various
   sub-prefixes will be configured over a period of time varying from
   minutes to hours depending on the size of the network and the degree
   of automation used in reconfiguration.

   "Adding the new prefix" involves, at minimum, configuring the
   relevant routers to use it and letting hosts autoconfigure new
   addresses in the new prefix using IPv6 Autoconfiguration [2].
   Practically speaking, networks often have other knowledge of
   addresses; they show up in route maps, access lists, access control
   files and databases on hosts, and so on. The action here is to "find
   all the places that the prefix has to be added, and add it."

   Note that, to the extent that it is practicable, it is desirable to
   use DNS [3][4] as the source of one's addresses, if only because it
   consolidates the places needing change.

   Advertisement of the prefix outside its network is the last thing to
   be configured during this phase. One wants to have all of one's
   defenses in place before advertising the prefix, if only because the
   prefix may come under immediate attack.

2.3 Stable routing both prefixes

   Once the network has been configured with the new prefix and has had
   sufficient time to stabilize, it becomes a stable platform with two
   addresses configured on each and every infrastructure component



Baker                   Expires October 9, 2003                 [Page 5]


Internet-Draft         Renumbering IPv6 Networks              April 2003


   interface (apart from serial interfaces that use only the link local
   address), and two addresses available for the use of any end system,
   one in the old prefix and one in the new. However, due to DNS [3][4]
   advertisement and history, sessions are opened with the addresses in
   the old prefix; the new is idle. This is a stable configuration.

2.4 Shutting down the use of the old prefix

   While in this stable routing state, DNS [3][4] is changed to reflect
   addresses in the new prefix, and any manual address configuration
   that used the old prefix must be modified to use the new prefix. This
   may include direct knowledge of addresses in neighboring networks,
   justified perhaps by a belief that the Domain Name Service can be
   unreliable at times, or in web pages. A key part of this conversion
   process is that the routers are instructed to advertise that the new
   prefix is preferred in autoconfiguration [2]; end systems may choose
   to form a new address only when the router indicates that the new
   prefix is preferred.

   The reconfiguration capabilities of network devices, to make this
   happen, must be well designed in advance; this is the Achilles Heel
   of this operation. Ideally, every address in the network that is not
   obtained using DNS (initial boot servers, name servers, call
   managers, extranet peers, etc) should be reconfigurable via DHCP [7],
   periodic configuration download, or another well defined procedure.
   Absent this, renumbering the network can become a very expensive
   manual process.

   All DNS records have a lifetime, and the process of reconfiguration
   takes time, so during this phase one must presume that some systems
   are opening connections to the old prefix and some to the new. Even
   after such information has aged out of the system, those sessions
   have a lifetime; the administrator must decide when sufficient
   sessions have completed that remaining sessions are unimportant.
   Systems which have been statically configured and whose
   reconfiguration has been overlooked will also continue using the old
   prefix. During a renumbering event, it would be worthwhile to "sniff"
   the network in front of key servers, looking for systems which are
   still using the old prefix, in order both to determine when such
   access has ceased and to identify unchanged systems. This will not
   detect passive use (such as in an access list), but will help
   identify active use.

   Note that, to the extent that it is practicable, it is desirable to
   use DNS as the source of one's addresses, if only because it
   consolidates the places needing change.





Baker                   Expires October 9, 2003                 [Page 6]


Internet-Draft         Renumbering IPv6 Networks              April 2003


2.5 Removing the old prefix

   Once all sessions are deemed to have completed, there will be no
   dependence on the old prefix. It may be removed from the
   configuration of the routing system, and from any static
   configurations that depend on it.

2.6 Final condition: stable using the new prefix

   This is equivalent to the first state, but using the new prefix.









































Baker                   Expires October 9, 2003                 [Page 7]


Internet-Draft         Renumbering IPv6 Networks              April 2003


3. "Find all the places..."

   The difficult operational issues in steps two (Section 2.2),  four
   (Section 2.4),  five (Section 2.5) are in dealing with the
   configurations of hosts which are not under the control of the
   network administrator or are manually configured. Examples of such
   devices include VoIP telephones with static configuration of boot or
   name servers, scanning devices used by manufacturing partners in
   support of "just in time" purchasing, manufacturing, or shipping
   activities, the boot servers of routers and switches, and so on.
   Application designers frequently take short-cuts to save memory or
   increase responsiveness, and a common short-cut is to use static
   configuration of IP addresses rather than DNS translation to obtain
   the same. The downside of such behavior should be apparent; such a
   poorly designed application cannot even add or replace a server
   easily, much less change servers or reorganize its address space. The
   short-cut ultimately becomes very expensive to maintain and very hard
   to replace.

   As a result, in view of the possibility that a network may need to be
   renumbered in the future, any application and any platform that runs
   on an IP stack, whether IPv4 or IPv6:

   o  SHOULD obtain its addresses from DNS by translating an appropriate
      name,

   o  MUST obtain a new translation if a new session is opened with the
      same service after the address lifetime expires,

   o  when addresses are configured rather than translated, MUST provide
      a convenient programmatic method (such as DHCP [7]) to reconfigure
      the addresses that can be executed using a script or its
      equivalent

   Application designers, equipment vendors, and the Open Source
   community should take note. There is an opportunity to serve their
   customers well in this area, and network operators should take note
   to either develop or purchase appropriate tools.













Baker                   Expires October 9, 2003                 [Page 8]


Internet-Draft         Renumbering IPv6 Networks              April 2003


4. Security Considerations

   The process of renumbering is straightforward in theory but can be
   difficult and dangerous in practice. The threats fall into two broad
   categories: those arising from misconfiguration and those which are
   actual attacks.

   Misconfigurations can easily arise if any system in the network
   "knows" the old prefix, or an address in it, a priori and is not
   configured with the new prefix, or if the new prefix is configured in
   a manner which replaces the old instead of being co-equal to it for a
   period of time. Simplistic examples include

   o  You forget to reconfigure a system which is using the old prefix
      in some static configuration. In this case, when the old prefix is
      removed from the network, whatever feature was so configured
      becomes inoperative - it is not configured for the new prefix, and
      the old prefix is irrelevant.

   o  You are configuring a system via SSH to its only IPv6 address. You
      change that address, simultaneously removing the old configuration
      and replacing it with the new. Clearly, the underlying TCP will
      now be unable to deliver segments to the system under
      configuration, and configuration will not be able to continue
      until it is possible to log into the system using its new address.

   o  Similarly, imagine that one removes the old configuration before
      supplying the new. In this case, it may be necessary to obtain
      on-site support or travel to the system and access it via its
      console.

   Clearly, taking the extra time to add the new prefix to the
   configuration, allow the network to settle, and then remove the old
   obviates this class of issue. A special consideration applies when a
   class of devices are only occasionally used and require this
   reconfiguration; the administration must allow suficiently long in
   step four (Section 2.4) to ensure that their liklihood of detection
   is sufficiently high.

   A subtle case of this type can result when the DNS is used to
   populate access control lists and similar security or QoS
   configurations. DNS names used to translate between system or service
   names and corresponding addresses are treated in this procedure as
   providing the address in the preferred prefix, which is either the
   old or the new prefix but not both. Such DNS names provide a means in
   step four (Section 2.4) to cause systems in the network to stop using
   the old prefix to access servers or peers and cause them to start
   using the new prefix. DNS names used for access control lists,



Baker                   Expires October 9, 2003                 [Page 9]


Internet-Draft         Renumbering IPv6 Networks              April 2003


   however, need to go through the same three step procedure used for
   other access control lists, having the new prefix added to them in
   step two (Section 2.2) and the old prefix removed in step five
   (Section 2.5).

   Attacks are also possible. Suppose, for example, that the new prefix
   has been presented by a service provider, and the service provider
   starts advertising the prefix before the customer network is ready.
   The new prefix might be targeted in a distributed denial of service
   attack, or a system might be broken into using an application that
   would not cross the firewall using the old prefix, before the
   network's defenses have been configured. Clearly, one wants to
   configure the defenses first and only then accessibility and routing.

   RFC 2894 [2] partially automates the renumbering of router interfaces
   in IPv6 networks, and the autoconfiguration procedure in RFC 2462 [9]
   build on that to renumber the hosts. Dynamic DNS [8][10] provides a
   capability for updating DNS accordingly. Managing configuration items
   apart from those procedures is most obviously straightforward if all
   such configurations are generated from a central configuration
   repository or database, or if they can all be read into a temporary
   database, changed using appropriate scripts, and applied to the
   appropriate systems. Any place where scripted configuration
   management is not possible or is not used must be tracked and managed
   manually. Here, there be dragons.


























Baker                   Expires October 9, 2003                [Page 10]


Internet-Draft         Renumbering IPv6 Networks              April 2003


5. Acknowledgements

   This document grew out of a discussion on the  IETF list. Jeroen
   Massar, Eliot Lear, and Michel Participated in that discussion.

   Commentary on the initial draft came from Craig Huegen, Peter Elford,
   Roland Dobbins, Dan Wing, Harald Tveit Alvestrand, Jeff Wells, John
   Schnizlein, Laurent Nicolas, Michael Thomas, Ole Troan, Sean Convery,
   Tony Hain, and Scott Bradner. Specifically, the first three named
   took it on themselves to convince the author that the concept of
   network renumbering as a normal or frequent procedure is daft. Their
   comments, if they result in improved address management practices in
   networks, may be the best contribution this note has to offer.






































Baker                   Expires October 9, 2003                [Page 11]


Internet-Draft         Renumbering IPv6 Networks              April 2003


Normative References

   [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.

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












































Baker                   Expires October 9, 2003                [Page 12]


Internet-Draft         Renumbering IPv6 Networks              April 2003


Informative References

   [3]   Mockapetris, P., "Domain names - concepts and facilities", STD
         13, RFC 1034, November 1987.

   [4]   Mockapetris, P., "Domain names - implementation and
         specification", STD 13, RFC 1035, November 1987.

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

   [6]   Berkowitz, H., "Router Renumbering Guide", RFC 2072, January
         1997.

   [7]   Droms, R., "Dynamic Host Configuration Protocol", RFC 2131,
         March 1997.

   [8]   Vixie, P., Thomson, S., Rekhter, Y. and J. Bound, "Dynamic
         Updates in the Domain Name System (DNS UPDATE)", RFC 2136,
         April 1997.

   [9]   Thomson, S. and T. Narten, "IPv6 Stateless Address
         Autoconfiguration", RFC 2462, December 1998.

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

   [11]  Lemon, T. and S. Cheshire, "Encoding Long Options in the
         Dynamic Host Configuration Protocol (DHCPv4)", RFC 3396,
         November 2002.

   [12]  Blanchet, M., "A flexible method for managing the assignment of
         bites of an IPv6  address block",
         draft-ietf-ipngwg-ipaddressassign-02 (work in progress), March
         2001.

   [13]  von Clausewitz, C., Howard, M., Paret, P. and D. Brodie, "On
         War, Chapter VII, 'Friction in War'", June 1989.

   [14]  Hardin, G., "The Tragedy of the Commons", Science
         162(1968):1243-1248, June 1989.









Baker                   Expires October 9, 2003                [Page 13]


Internet-Draft         Renumbering IPv6 Networks              April 2003


Author's Address

   Fred Baker
   Cisco Systems
   1121 Via Del Rey
   Santa Barbara, CA  93117
   US

   Phone: 408-526-4257
   Fax:   413-473-2403
   EMail: fred@cisco.com








































Baker                   Expires October 9, 2003                [Page 14]


Internet-Draft         Renumbering IPv6 Networks              April 2003


Intellectual Property Statement

   The IETF takes no position regarding the validity or scope of any
   intellectual property 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; neither does it represent that it
   has made any effort to identify any such rights. Information on the
   IETF's procedures with respect to rights in standards-track and
   standards-related documentation can be found in BCP-11. Copies of
   claims of rights made available for publication 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 implementors or users of this specification can
   be obtained from the IETF Secretariat.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights which may cover technology that may be required to practice
   this standard. Please address the information to the IETF Executive
   Director.


Full Copyright Statement

   Copyright (C) The Internet Society (2003). All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works. However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assignees.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION



Baker                   Expires October 9, 2003                [Page 15]


Internet-Draft         Renumbering IPv6 Networks              April 2003


   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.











































Baker                   Expires October 9, 2003                [Page 16]


Html markup produced by rfcmarkup 1.129b, available from https://tools.ietf.org/tools/rfcmarkup/