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Internet Engineering Task Force (IETF)                      B. CarpenterRequest for Comments: 6866                             Univ. of AucklandCategory: Informational                                         S. JiangISSN: 2070-1721                            Huawei Technologies Co., Ltd.                                                           February 2013Problem Statement for Renumbering IPv6 Hostswith Static Addresses in Enterprise NetworksAbstract   This document analyses the problems of updating the IPv6 addresses of   hosts in enterprise networks that, for operational reasons, require   static addresses.Status of This Memo   This document is not an Internet Standards Track specification; it is   published for informational purposes.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Not all documents   approved by the IESG are a candidate for any level of Internet   Standard; seeSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc6866.Copyright Notice   Copyright (c) 2013 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.  Code Components extracted from this document must   include Simplified BSD License text as described in Section 4.e of   the Trust Legal Provisions and are provided without warranty as   described in the Simplified BSD License.Carpenter & Jiang             Informational                     [Page 1]

RFC 6866              Renumbering Static Addresses         February 2013Table of Contents1. Introduction ....................................................22. Analysis ........................................................32.1. Static Addresses Imply Static Prefixes .....................32.2. Other Hosts Need Literal Address ...........................42.3. Static Server Addresses ....................................52.4. Static Virtual Machine Addresses ...........................62.5. Asset Management and Security Tracing ......................62.6. Primitive Software Licensing ...............................72.7. Network Elements ...........................................72.8. Access Control Lists .......................................72.9. Management Aspects .........................................83. Summary of Problem Statement ....................................84. Security Considerations .........................................95. Acknowledgements ...............................................106. Informative References .........................................101.  Introduction   A problem that is frequently mentioned in discussions of renumbering   enterprise networks [RFC5887] [RFC6879] [GAP-ANALYSIS] is that of   statically assigned addresses.  The scope of the present document is   to analyse the problems caused for enterprise networks during   renumbering by static addresses and to identify related gaps in   existing technology.  Some aspects also apply to small office and   home networks, but these are not the intended scope of the document.   A static address can be defined as an IP address that is intended by   the network manager to remain constant over a long period of time,   possibly many years, regardless of system restarts or any other   unpredictable events.  Static addressing often implies manual address   assignment, including manual preparation of configuration scripts.   An implication of hosts having static addresses is that subnets must   have static prefixes, which also requires analysis.   In a sense, the issue of static addresses is a result of history.  As   discussed inSection 3.2 of [RFC6250], various properties of IP   addresses that have long been assumed by programmers and operators   are no longer true today, although they were true when almost all   addresses were manually assigned.  In some cases, the resulting   operational difficulties are avoided by static addressing.   Although static addressing is, in general, problematic for   renumbering, hosts inside an enterprise may have static addresses for   a number of operational reasons:Carpenter & Jiang             Informational                     [Page 2]

RFC 6866              Renumbering Static Addresses         February 2013   o  For some reason, other hosts need to be configured with a literal      numeric address for the host in question, so its address must be      static.   o  Even if a site has local DNS support and this is normally used to      locate servers, some operators wish their servers to have static      addresses so that issues of address lifetime and DNS Time to Live      (TTL) cannot affect connectivity.   o  Some approaches to virtual server farms require static addressing.   o  On some sites, the network operations staff require hosts to have      static addresses for asset management purposes and for address-      based backtracking of security incidents.   o  Certain software licensing mechanisms are based on IP addresses.   o  Network elements, such as routers, are usually assigned static      addresses, which are also configured into network monitoring and      management systems.   o  Access Control Lists and other security mechanisms are often      configured using IP addresses.   Static addressing is not the same thing as manual addressing.  Static   addresses may be configured automatically, for example, by stateful   DHCPv6.  In that case, the database from which the static address is   derived may itself have been created automatically in some fashion,   or configured manually.  If a host's address is configured manually   by the host's administrator, it is by definition static.   This document analyses these issues in more detail and presents a   problem statement.  Where obvious alternatives to static addresses   exist, they are mentioned.2.  Analysis2.1.  Static Addresses Imply Static Prefixes   Host addresses can only be static if subnet prefixes are also static.   Static prefixes are such a long-established practice in enterprise   networks that it is hard to discern the reason for them.  Originally,   before DHCP became available, there was simply no alternative.  Thus   it became accepted practice to assign subnet prefixes manually and   build them into static router configurations.  Today, the static   nature of subnet prefixes has become a diagnostic tool in itself, atCarpenter & Jiang             Informational                     [Page 3]

RFC 6866              Renumbering Static Addresses         February 2013   least in the case of IPv4 where prefixes can easily be memorised.  If   several users sharing a subnet prefix report problems, the fault can   readily be localised.   This model is being challenged for the case of unmanaged home IPv6   networks, in which it is possible to assign subnet prefixes   automatically, at least in a cold start scenario [PREFIX].  For an   enterprise network, the question arises whether automatic subnet   prefix assignment can be made using the "without a flag day" approach   to renumbering.  [RFC4192] specifies that "the new prefix is added to   the network infrastructure in parallel with (and without interfering   with) the old prefix".  Any method for automatic prefix assignment   needs to support this.2.2.  Other Hosts Need Literal Address   This issue commonly arises in small networks without local DNS   support, for devices such as printers, that all other hosts need to   reach.  In this case, not only does the host in question have a   static address but that address is also configured in the other   hosts.  It is a long-established practice in small IPv4 enterprise   networks that printers, in particular, are manually assigned a fixed   address (typically, an [RFC1918] address) and that users are told to   manually configure printer access using that fixed address.  For a   small network, the work involved in doing this is much less than the   work involved in doing it "properly" by setting up DNS service,   whether local or hosted by an ISP, to give the printer a name.  Also,   although the Service Location Protocol (SLP) [RFC2608] is widely   available for tasks such as printer discovery, it is not widely used   in enterprise networks.  In consequence, if the printer is renumbered   for any reason, the manual configuration of all users' hosts must be   updated in many enterprises.   In the case of IPv6, exactly the same situation would be created by   numbering the printer statically under the site's Unique Local   Address (ULA) prefix [RFC4193].  Although this address would not   change if the site's globally routable prefix is changed, internal   renumbering for any other reason would be troublesome.  Additionally,   the disadvantage compared to IPv4 is that an IPv6 address is harder   to communicate reliably, compared to something as simple as   "10.1.1.10".  The process will be significantly more error-prone for   IPv6.   If such a host is numbered out of a globally routable prefix that is   potentially subject to renumbering, then a renumbering event will   require a configuration change in all hosts using the device in   question, and such configuration data are by no means stored in the   network layer.Carpenter & Jiang             Informational                     [Page 4]

RFC 6866              Renumbering Static Addresses         February 2013   At least two simple alternatives exist to avoid static numbering of   simple devices, such as printers, by giving them local names.  One is   the use of Multicast DNS (mDNS) [RFC6762] in combination with DNS   Service Discovery [RFC6763].  The other is the Service Location   Protocol [RFC2608].  Both of these solutions are widely implemented,   but seemingly not widely deployed in enterprise networks.2.3.  Static Server Addresses   On larger sites, it is safe to assume that servers of all kinds,   including printers, are identified in user configurations and   applications by DNS names.  However, it is very widespread   operational practice that servers have static IP addresses.  If they   did not, whenever an address assigned by stateless address   autoconfiguration [RFC4862] or DHCPv6 [RFC3315] expired, and if the   address actually changed for some extraneous reason, sessions in   progress might fail (depending on whether the address deprecation   period was long enough).   DNS aspects of renumbering are discussed in more detail in [RFC6879].   Here, we note that one reason for widespread use of static server   addresses is the lack of deployment of Secure Dynamic DNS update   [RFC3007], or some other method of prompt DNS updates, in enterprise   networks.  A separate issue is that even with such updates in place,   remote users of a server would attempt to use the wrong address until   the DNS TTL expired, as discussed in [RFC4192].   Server addresses can be managed centrally, even if they are static,   by using DHCPv6 in stateful mode to ensure that the same address is   always assigned to a given server.  Consistency with DNS can be   ensured by generating both DHCPv6 data and DNS data from a common   configuration database using a suitable configuration tool.  This   does normally carry the implication that the database also contains   the hardware (Media Access Control (MAC)) addresses of the relevant   LAN interfaces on the servers, so that the correct IPv6 address can   be delivered whenever a server requests an address.  Not every   operator wishes to maintain such a costly database, however, and some   sites are therefore likely today to fall back on manual configuration   of server addresses as a result.   In the event of renumbering the prefix covering such servers, the   situation should be manageable if there is a common configuration   database; the "without a flag day" procedure [RFC4192] could be   followed.  However, if there is no such database, a manual procedure   would have to be adopted.Carpenter & Jiang             Informational                     [Page 5]

RFC 6866              Renumbering Static Addresses         February 20132.4.  Static Virtual Machine Addresses   According to [PROBLEM], the placement and live migration of Virtual   Machines (VMs) in a physical network requires that their IP addresses   be fixed and static.  Otherwise, when a VM is migrated to a different   physical server, its IP address would change and transport sessions   in progress would be lost.  In effect, this is a special case of the   previous one.   If VMs are numbered out of a prefix that is subject to renumbering,   there is a direct conflict with application session continuity,   unless a procedure similar to [RFC4192] is followed.2.5.  Asset Management and Security Tracing   There are some large (campus-sized) sites that not only capture the   MAC addresses of servers in a configuration system, but also do so   for desktop client machines with wired connections that are then   given static IP addresses.  Such hosts are not normally servers, so   the two preceding cases do not apply.  One motivation for this   approach is straightforward asset management (Who has which   computer?, Connected to which cable?).  Another, more compelling,   reason is security incident handling.  If, as occurs with reasonable   frequency on any large network, a particular host is found to be   generating some form of unwanted traffic, it is urgent to be able to   track back from its IP address to its physical location so that an   appropriate intervention can be made.  A static binding between the   MAC address and the IPv6 address might be preferred for this purpose.   Such users will not, in most circumstances, be significantly   inconvenienced by prefix renumbering, as long as it follows the   [RFC4192] procedure.  The address deprecation mechanism would allow   for clean termination of current sessions, including those in which   their machine was actually operating as a server, e.g., for a peer-   to-peer application.  The only users who would be seriously affected   would be those running extremely long transport sessions that might   outlive the address deprecation period.   Note that such large campus sites generally allocate addresses   dynamically to wireless hosts, since (in an IPv4 world) addresses are   scarce and allocating static addresses to intermittent users is not   acceptable.  Also, a wireless user may appear on different subnets at   different times, so it cannot be given a single static address.   These users will, in most circumstances, only be slightly   inconvenienced, if at all, by prefix renumbering.Carpenter & Jiang             Informational                     [Page 6]

RFC 6866              Renumbering Static Addresses         February 20132.6.  Primitive Software Licensing   Although it has many disadvantages and cannot be recommended as a   solution, software licensing based on IP addresses or prefixes is   still quite widely used in various forms.  It is to be expected that   this practice will continue for IPv6.  If so, there is no alternative   to informing the licensing party of the new address(es) by whatever   administrative process is required.  In anRFC 4192 renumbering   procedure, the licenses for the old and new addresses or prefixes   would have to overlap.   If acceptable to the licensing mechanism, using addresses under an   enterprise's ULA prefix for software licensing would avoid this   problem.2.7.  Network Elements   Each interface of a router needs an IP address, and so do other   network elements, such as firewalls, proxies, and load balancers.   Since these are critical infrastructures, they must be monitored and   in some cases controlled by a network management system.  A   conventional approach to this is to assign the necessary IP addresses   statically, and to configure those addresses in the monitoring and   management systems.  It is common practice that some such addresses   will have no corresponding DNS entry.  If these addresses need to be   changed, there will be considerable ramifications.  A restart of the   network element might be needed, interrupting all user sessions in   progress.  Simultaneously, the monitoring and management system   configurations must be updated, and in the case of a default router,   its clients must be informed.  To avoid such disruption, network   elements must be renumbered according to an [RFC4192] procedure, like   any other host.   There is a school of thought that to minimise renumbering problems   for network elements and to keep the simplicity of static addressing   for them, network elements should all have static ULA addresses for   management and monitoring purposes, regardless of what other global   addresses they may have.2.8.  Access Control Lists   Access Control Lists (ACLs) and other security mechanisms are often   configured using static IP addresses.  This may occur in network   elements or hosts.  If they are not updated promptly during a   renumbering event, the result may be the opening of security   loopholes, the blocking of legitimate traffic, or both.  Such   security loopholes may never be detected until they are successfully   exploited.Carpenter & Jiang             Informational                     [Page 7]

RFC 6866              Renumbering Static Addresses         February 20132.9.  Management Aspects   As noted in the Introduction, static addressing and manual address   configuration are not the same thing.  In terms of managing a   renumbering event, static addressing derived automatically from a   central database, e.g., by stateful DHCPv6, is clearly better than   manual configuration by an administrator.  This remains true even if   the database itself requires manual changes, since, otherwise, an   administrator would have to log in to every host concerned, a time-   consuming and error-prone task.  In cases where static addresses   cannot be avoided, they could be assigned automatically from a   central database using a suitable protocol, such as stateful DHCPv6.   Clearly, the database needs to be supported by a suitable   configuration tool, to minimise manual updates and to eliminate   manual configuration of individual hosts.3.  Summary of Problem Statement   If subnet prefixes are statically assigned, various network elements   and the network management system must be updated when they are   renumbered.  To avoid loss of existing user sessions, the old   prefixes need to be removed only after a period of overlap.   If a printer or similar local server is statically addressed, and has   no DNS or mDNS name and no discovery protocol, renumbering will   require configuration changes in all hosts using that server.  Most   likely, these changes will be manual; therefore, this type of   configuration should be avoided except for very small networks.  Even   if the server is under a ULA prefix, any subnet rearrangement that   causes it to be renumbered will have the same effect.   If a server with a DNS name is statically addressed via a common   configuration database that supports both DHCPv6 and DNS, then it can   be renumbered "without a flag day" by followingRFC 4192.  However,   if there is no common configuration database, then present technology   requires manual intervention.  Similar considerations apply to   virtual servers with static addresses.   If client computers, such as desktops, are statically addressed via a   common configuration database and stateful DHCPv6, they can also be   renumbered "without a flag day."  But other statically addressed   clients will need manual intervention, so DHCPv6 should be used if   possible.   If address-based software licensing is unavoidable, requiring static   addresses, and ULAs cannot be used for this case, an administrative   procedure during renumbering seems unavoidable.Carpenter & Jiang             Informational                     [Page 8]

RFC 6866              Renumbering Static Addresses         February 2013   If network elements have static addresses, the network management   system and affected client hosts must be informed when they are   renumbered.  Even if a network element is under a ULA prefix, any   subnet rearrangement that causes it to be renumbered will have the   same effect.   ACLs configured with static addresses must be updated during   renumbering.   It appears that the majority of the above problems can be largely   mitigated if the following measures are taken:   1.  The site uses a general configuration management database and an       associated tool that manage all prefixes and all DHCPv6, DNS, and       router and security configurations in a consistent and integrated       way.  Even if static addresses are used, they are always       configured with this tool, and never manually.  Specification of       such a tool is out of scope for the present document.   2.  All printers and other local servers are always accessed via a       DNS or mDNS name, or via a discovery protocol.  User computers       are configured only with names for such servers and never with       their addresses.   3.  Internal traffic uses a ULA prefix, such that disturbance to such       traffic is avoided if the externally used prefix changes.   4.  If prefix renumbering is required, theRFC 4192 procedure is       followed.   Remaining open questions are:   1.  Is minor residual loss of extremely long-living transport       sessions during renumbering operationally acceptable?   2.  Can automatic network element renumbering be performed without       interrupting any user sessions?   3.  Do any software licensing systems require manual intervention?4.  Security Considerations   This document does not define a protocol, so it does not introduce   any new security exposures.  However, security configurations, such   as ACLs, are affected by the renumbering of static addresses.Carpenter & Jiang             Informational                     [Page 9]

RFC 6866              Renumbering Static Addresses         February 20135.  Acknowledgements   Valuable comments and contributions were made by Ran Atkinson, Ralph   Droms, Adrian Farrel, Wes George, Brian Haberman, Bing Liu, Pete   Resnick, and other participants in the 6renum WG.6.  Informative References   [GAP-ANALYSIS]  Liu, B., Jiang, S., Carpenter, B., Venaas, S., and W.                   George, "IPv6 Site Renumbering Gap Analysis", Work                   in Progress, December 2012.   [PREFIX]        Baker, F. and R. Droms, "IPv6 Prefix Assignment in                   Small Networks", Work in Progress, March 2012.   [PROBLEM]       Narten, T., Ed., Gray, E., Ed., Black, D., Dutt, D.,                   Fang, L., Kreeger, L., Napierala, M., and M.                   Sridharan, "Problem Statement: Overlays for Network                   Virtualization", Work in Progress, October 2012.   [RFC1918]       Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot,                   G., and E. Lear, "Address Allocation for Private                   Internets",BCP 5,RFC 1918, February 1996.   [RFC2608]       Guttman, E., Perkins, C., Veizades, J., and M. Day,                   "Service Location Protocol, Version 2",RFC 2608,                   June 1999.   [RFC3007]       Wellington, B., "Secure Domain Name System (DNS)                   Dynamic Update",RFC 3007, November 2000.   [RFC3315]       Droms, R., Bound, J., Volz, B., Lemon, T., Perkins,                   C., and M. Carney, "Dynamic Host Configuration                   Protocol for IPv6 (DHCPv6)",RFC 3315, July 2003.   [RFC4192]       Baker, F., Lear, E., and R. Droms, "Procedures for                   Renumbering an IPv6 Network without a Flag Day",RFC 4192, September 2005.   [RFC4193]       Hinden, R. and B. Haberman, "Unique Local IPv6                   Unicast Addresses",RFC 4193, October 2005.   [RFC4862]       Thomson, S., Narten, T., and T. Jinmei, "IPv6                   Stateless Address Autoconfiguration",RFC 4862,                   September 2007.Carpenter & Jiang             Informational                    [Page 10]

RFC 6866              Renumbering Static Addresses         February 2013   [RFC5887]       Carpenter, B., Atkinson, R., and H. Flinck,                   "Renumbering Still Needs Work",RFC 5887, May 2010.   [RFC6250]       Thaler, D., "Evolution of the IP Model",RFC 6250,                   May 2011.   [RFC6762]       Cheshire, S. and M. Krochmal, "Multicast DNS",RFC 6762, February 2013.   [RFC6763]       Cheshire, S. and M. Krochmal, "DNS-Based Service                   Discovery",RFC 6763, February 2013.   [RFC6879]       Jiang, S., Liu, B., and B. Carpenter, "IPv6                   Enterprise Network Renumbering Scenarios,                   Considerations, and Methods",RFC 6879,                   February 2013.Authors' Addresses   Brian Carpenter   Department of Computer Science   University of Auckland   PB 92019   Auckland,   1142   New Zealand   EMail: brian.e.carpenter@gmail.com   Sheng Jiang   Huawei Technologies Co., Ltd.   Q14, Huawei Campus   No.156 Beiqing Road   Hai-Dian District, Beijing  100095   P.R. China   EMail: jiangsheng@huawei.comCarpenter & Jiang             Informational                    [Page 11]