Movatterモバイル変換

Internet Engineering Task Force (IETF)                      B. CarpenterRequest for Comments: 5887                             Univ. of AucklandCategory: Informational                                      R. AtkinsonISSN: 2070-1721                                         Extreme Networks                                                               H. Flinck                                                  Nokia Siemens Networks                                                                May 2010Renumbering Still Needs WorkAbstract   This document reviews the existing mechanisms for site renumbering   for both IPv4 and IPv6, and it identifies operational issues with   those mechanisms.  It also summarises current technical proposals for   additional mechanisms.  Finally, there is a gap analysis identifying   possible areas for future work.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/rfc5887.Copyright Notice   Copyright (c) 2010 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, et al.             Informational                     [Page 1]

RFC 5887              Renumbering Still Needs Work              May 2010Table of Contents1. Introduction ....................................................32. Existing Host-Related Mechanisms ................................52.1. DHCP .......................................................52.2. IPv6 Stateless Address Autoconfiguration ...................62.3. IPv6 ND Router/Prefix Advertisements .......................72.4. PPP ........................................................72.5. DNS Configuration ..........................................82.6. Dynamic Service Discovery ..................................93. Existing Router-Related Mechanisms ..............................93.1. Router Renumbering .........................................94. Existing Multi-Addressing Mechanism for IPv6 ...................105. Operational Issues with Renumbering Today ......................115.1. Host-Related Issues .......................................115.1.1. Network-Layer Issues ...............................115.1.2. Transport-Layer Issues .............................135.1.3. DNS Issues .........................................145.1.4. Application-Layer Issues ...........................145.2. Router-Related Issues .....................................165.3. Other Issues ..............................................175.3.1. NAT State Issues ...................................175.3.2. Mobility Issues ....................................185.3.3. Multicast Issues ...................................185.3.4. Management Issues ..................................195.3.5. Security Issues ....................................216. Proposed Mechanisms ............................................226.1. SHIM6 .....................................................226.2. MANET Proposals ...........................................226.3. Other IETF Work ...........................................236.4. Other Proposals ...........................................237. Gaps ...........................................................247.1. Host-Related Gaps .........................................247.2. Router-Related Gaps .......................................257.3. Operational Gaps ..........................................257.4. Other Gaps ................................................268. Security Considerations ........................................269. Acknowledgements ...............................................2710. Informative References ........................................27Appendix A.  Embedded IP Addresses ................................34Carpenter, et al.             Informational                     [Page 2]

RFC 5887              Renumbering Still Needs Work              May 20101.  Introduction   In early 1996, the IAB published a short RFC entitled "Renumbering   Needs Work" [RFC1900], which the reader is urged to review before   continuing.  Almost ten years later, the IETF published "Procedures   for Renumbering an IPv6 Network without a Flag Day" [RFC4192].  A few   other RFCs have touched on router or host renumbering: [RFC1916],   [RFC2071], [RFC2072], [RFC2874], [RFC2894], and [RFC4076].   In fact, since 1996, a number of individual mechanisms have become   available to simplify some aspects of renumbering.  The Dynamic Host   Configuration Protocol (DHCP) is available for IPv4 [RFC2131] and   IPv6 [RFC3315].  IPv6 includes Stateless Address Autoconfiguration   (SLAAC) [RFC4862], and this includes Router Advertisements (RAs) that   include options listing the set of active prefixes on a link.  The   Point-to-Point Protocol (PPP) [RFC1661] also allows for automated   address assignment for both versions of IP.   Despite these efforts, renumbering, especially for medium to large   sites and networks, is widely viewed as an expensive, painful, and   error-prone process, and is therefore avoided by network managers as   much as possible.  Some would argue that the very design of IP   addressing and routing makes automatic renumbering intrinsically   impossible.  In fact, managers have an economic incentive to avoid   having to renumber, and many have resorted to private addressing and   Network Address Translation (NAT) as a result.  This has the highly   unfortunate consequence that any mechanisms for managing the scaling   problems of wide-area (BGP4) routing that require occasional or   frequent site renumbering have been consistently dismissed as   unacceptable.  But none of this means that we can duck the problem,   because as explained below, renumbering is sometimes unavoidable.   This document aims to explore the issues behind this problem   statement, especially with a view to identifying the gaps and known   operational issues.   It is worth noting that for a very large class of users, renumbering   is not in fact a problem of any significance.  A domestic or small   office user whose device operates purely as a client or peer-to-peer   node is in practice renumbered at every restart (even if the address   assigned is often the same).  A user who roams widely with a laptop   or pocket device is also renumbered frequently.  Such users are not   concerned with the survival of very long-term application sessions   and are in practice indifferent to renumbering.  Thus, this document   is mainly concerned with issues affecting medium to large sites.Carpenter, et al.             Informational                     [Page 3]

RFC 5887              Renumbering Still Needs Work              May 2010   There are numerous reasons why such sites might need to renumber in a   planned fashion, including:   o  Change of service provider, or addition of a new service provider,      when provider-independent addressing is not an option.   o  A service provider itself has to renumber.   o  Change of site topology (i.e., subnet reorganisation).   o  Merger of two site networks into one, or split of one network into      two or more parts.   o  During IPv6 deployment, change of IPv6 access method (e.g., from      tunneled to native).   The most demanding case would be unplanned automatic renumbering,   presumably initiated by a site border router, for reasons connected   with wide-area routing.  There is already a degree of automatic   renumbering for some hosts, e.g., IPv6 "privacy" addresses [RFC4941].   It is certainly to be expected that as the pressure on IPv4 address   space intensifies in the next few years, there will be many attempts   to consolidate usage of addresses so as to avoid wastage, as part of   the "end game" for IPv4, which necessarily requires renumbering of   the sites involved.  However, strategically, it is more important to   implement and deploy techniques for IPv6 renumbering, so that as IPv6   becomes universally deployed, renumbering becomes viewed as a   relatively routine event.  In particular, some mechanisms being   considered to allow indefinite scaling of the wide-area routing   system might assume site renumbering to be a straightforward matter.   There is work in progress that, if successful, would eliminate some   of the motivations for renumbering.  In particular, some types of   solutions to the problem of scalable routing for multihomed sites   would likely eliminate both multihoming and switching to another ISP   as reasons for site renumbering.   Several proposed identifier/locator split schemes provide good   examples, including at least Identifier Locator Network Protocol   [ILNP], Locator/ID Separation Protocol [LISP], and Six/One [SIX-ONE]   (in alphabetical order).  The recent discussion about IPv6 Network   Address Translation (IPv6 NAT) provides a separate example [NAT66].   While remaining highly contentious, this approach, coupled with   unique local addresses or a provider-independent address prefix,   would appear to eliminate some reasons for renumbering in IPv6.   However, even if successful, such solutions will not eliminate all of   the reasons for renumbering.  This document does not take anyCarpenter, et al.             Informational                     [Page 4]

RFC 5887              Renumbering Still Needs Work              May 2010   position about development or deployment of protocols or technologies   that would make long-term renumbering unnecessary, but rather deals   with practical cases where partial or complete renumbering is   necessary in today's Internet.   IP addresses do not have a built-in lifetime.  Even when an address   is leased for a finite time by DHCP or SLAAC, or when it is derived   from a DNS record with a finite time to live (TTL) value, this   information is unavailable to applications once the address has been   passed to an upper layer by the socket interface.  Thus, a   renumbering event is almost certain to be an unpredictable surprise   from the point of view of any application software using the address.   Many of the issues listed below derive from this fact.2.  Existing Host-Related Mechanisms2.1.  DHCP   At a high level, DHCP [RFC2131] [RFC3315] offers similar support for   renumbering for both versions of IP.  A host requests an address when   it starts up, the request might be delivered to a local DHCP server   or via a relay to a central server, and if all local policy   requirements are met, the server will provide an address with an   associated lifetime, and various other network-layer parameters (in   particular, the subnet mask and the default router address).   From an operational viewpoint, the interesting aspect is the local   policy.  Some sites require pre-registration of MAC (Media Access   Control) addresses as a security measure, while other sites permit   any MAC address to obtain an IP address.  Similarly, some sites use   DHCP to provide the same IP address to a given MAC address each time   (this is sometimes called "Static DHCP"), while other sites do not   (this is sometimes called "Dynamic DHCP"), and yet other sites use a   combination of these two modes where some devices (e.g., servers,   Voice over IP (VoIP) handsets) have a relatively static IP address   that is provisioned via DHCP while other devices (e.g., portable   computers) have a different IP address each time they connect to the   network.  As an example, many universities in the United States and   United Kingdom require MAC address registration of faculty, staff,   and student devices (including handheld computers with wireless   connections).   These policy choices interact strongly with whether the site has what   might be called "strong" or "weak" asset management.  At the strong   extreme, a site has a complete database of all equipment allowed to   be connected, certainly containing the MAC address(es) for each host,   as well as other administrative information of various kinds.  Such a   database can be used to generate configuration files for DHCP, DNS,Carpenter, et al.             Informational                     [Page 5]

RFC 5887              Renumbering Still Needs Work              May 2010   and any access control mechanisms that might be in use.  For example,   only certain MAC addresses might be allowed to get an IP address on   certain subnets.  At the weak extreme, a site has no asset   management, any MAC address may get a first-come first-served IP   address on any subnet, and there is no network-layer access control.   The IEEE 802.1X standard [IEEE.802-1X] [IEEE.802-1X-REV] specifies a   connection mechanism for wired/wireless Ethernet that is often   combined with DHCP and other mechanisms to form, in effect, a network   login.  Using such a network login, the user of a device newly   connecting to the network must provide both identity and   authentication before being granted access to the network.  As part   of this process, the network control point will often configure the   point of network connection for that specific user with a range of   parameters -- such as Virtual LAN (VLAN), Access Control Lists   (ACLs), and Quality-of-Service (QoS) profiles.  Other forms of   network login also exist, often using an initial web page for user   identification and authentication.  The latter approach is commonly   used in hotels or cafes.   In principle, a site that uses DHCP can renumber its hosts by   reconfiguring DHCP for the new address range.  The issues with this   are discussed below.2.2.  IPv6 Stateless Address Autoconfiguration   SLAAC, although updated recently [RFC4862], was designed prior to   DHCPv6 and was intended for networks where unattended automatic   configuration was preferred.  Ignoring the case of an isolated   network with no router, which will use link-local addresses   indefinitely, SLAAC follows a bootstrap process.  Each host first   gives itself a link-local address, and then needs to receive a link-   local multicast Router Advertisement (RA) [RFC4861] that tells it the   routeable subnet prefix and the address(es) of the default router(s).   A node may either wait for the next regular RA or solicit one by   sending a link-local multicast Router Solicitation.  Knowing the link   prefix from the RA, the node may now configure its own address.   There are various methods for this, of which the basic one is to   construct a unique 64-bit identifier from the interface's MAC   address.   We will not describe here the IPv6 processes for Duplicate Address   Detection (DAD), Neighbour Discovery (ND), and Neighbour   Unreachability Discovery (NUD).  Suffice it to say that they work,   once the initial address assignment based on the RA has taken place.Carpenter, et al.             Informational                     [Page 6]

RFC 5887              Renumbering Still Needs Work              May 2010   The contents of the RA message are clearly critical to this process   and its use during renumbering.  An RA can indicate more than one   prefix, and more than one router can send RAs on the same link.  For   each prefix, the RA indicates two lifetimes: "preferred" and "valid".   Addresses derived from this prefix must inherit its lifetimes.  When   the valid lifetime expires, the prefix is dead and the derived   address must not be used any more.  When the preferred lifetime is   expired (or set to zero) the prefix is deprecated, and must not be   used for any new sessions.  Thus, setting a preferred lifetime that   is zero or finite is SLAAC's warning that renumbering will occur.   SLAAC assumes that the new prefix will be advertised in parallel with   the deprecated one, so that new sessions will use addresses   configured under the new prefix.2.3.  IPv6 ND Router/Prefix Advertisements   With IPv6, a Router Advertisement not only advertises the   availability of an upstream router, but also advertises routing   prefix(es) valid on that link (subnetwork).  Also, the IPv6 RA   message contains a flag indicating whether or not the host should use   DHCPv6 to configure.  If that flag indicates that the host should use   DHCPv6, then the host is not supposed to autoconfigure itself as   outlined inSection 2.2.  However, there are some issues in this   area, described inSection 5.1.1.   In an environment where a site has more than one upstream link to the   outside world, the site might have more than one valid routing   prefix.  In such cases, typically all valid routing prefixes within a   site will have the same prefix length.  Also, in such cases, it might   be desirable for hosts that obtain their addresses using DHCPv6 to   learn about the availability of upstream links dynamically, by   deducing from periodic IPv6 RA messages which routing prefixes are   currently valid.  This application seems possible within the IPv6   Neighbour Discovery architecture, but does not appear to be clearly   specified anywhere.  So, at present, this approach for hosts to learn   about availability of new upstream links or loss of prior upstream   links is unlikely to work with currently shipping hosts or routers.2.4.  PPP   "The Point-to-Point Protocol (PPP)" [RFC1661] includes support for a   Network Control Protocol (NCP) for both IPv4 and IPv6.   For IPv4, the NCP is known as IPCP [RFC1332] and allows explicit   negotiation of an IP address for each end.  PPP endpoints acquire   (during IPCP negotiation) both their own address and the address of   their peer, which may be assumed to be the default router if no   routing protocol is operating.  Renumbering events arise when IPCPCarpenter, et al.             Informational                     [Page 7]

RFC 5887              Renumbering Still Needs Work              May 2010   negotiation is restarted on an existing link, when the PPP connection   is terminated and restarted, or when the point-to-point medium is   reconnected.  Peers may propose either the local or remote address or   require the other peer to do so.  Negotiation is complete when both   peers are in agreement.  In practice, if no routing protocol is used,   as in a subscriber/provider environment, then the provider proposes   both addresses and requires the subscriber either to accept the   connection or to abort.  Effectively, the subscriber device is   renumbered each time it connects for a new session.   For IPv6, the NCP is IP6CP [RFC5072] and is used to configure an   interface identifier for each end, after which link-local addresses   may be created in the normal way.  In practice, each side can propose   its own identifier and renegotiation is only necessary when there is   a collision, or when a provider wishes to force a subscriber to use a   specific interface identifier.  Once link-local addresses are   assigned and IP6CP is complete, automatic assignment of global scope   addresses is performed by the same methods as with multipoint links,   i.e., either SLAAC or DHCPv6.  Again, in a subscriber/provider   environment, this allows renumbering per PPP session.2.5.  DNS Configuration   A site must provide DNS records for some or all of its hosts, and of   course these DNS records must be updated when hosts are renumbered.   Most sites will achieve this by maintaining a DNS zone file (or a   database from which it can be generated) and loading this file into   the site's DNS server(s) whenever it is updated.  As a renumbering   tool, this is clumsy but effective.  Clearly perfect synchronisation   between the renumbering of the host and the updating of its A or AAAA   record is impossible.  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.   There are widespread reports that the freely available BIND DNS   software (which is what most UNIX hosts use), Microsoft Windows (XP   and later), and Mac OS X all include support for Secure Dynamic DNS   Update.  So do many home gateways.  Further, there are credible   reports that these implementations are interoperable when configured   properly ([DNSBOOK] p. 228 and p. 506).   Commonly used commercial DNS and DHCP servers (e.g., Windows Server)   often are deployed with Secure Dynamic DNS Update also enabled.  In   some cases, merely enabling both the DNS server and the DHCP server   might enable Secure Dynamic DNS Update as an automatic side effect   ([DNSBOOK] p. 506).  So in some cases, sites might have deployedCarpenter, et al.             Informational                     [Page 8]

RFC 5887              Renumbering Still Needs Work              May 2010   Secure Dynamic DNS Update already, without realising it.  An   additional enhancement would be for DHCP clients to implement support   for the "Client FQDN" option (Option 81).   Since address changes are usually communicated to other sites via the   DNS, the latter's security is essential for secure renumbering.  The   Internet security community believes that the current DNS Security   (DNSsec) and Secure Dynamic DNS Update specifications are   sufficiently secure and has been encouraging DNSsec deployment   ([RFC3007] [RFC4033] [RFC4034] [RFC4035]).   As of this writing, there appears to be significantly more momentum   towards rapid deployment of DNS Security standards in the global   public Internet than previously.  Several country-code Top-Level   Domains (ccTLDs) have already deployed signed TLD root zones (e.g.,   Sweden's .SE).  Several other TLDs are working to deploy signed TLD   root zones by published near-term deadlines (e.g., .GOV, .MIL).  In   fact, it is reported that .GOV has been signed operationally since   early February 2009.  It appears likely that the DNS-wide root zone   will be signed in the very near future.  See, for example,   <http://www.dnssec-deployment.org/> and   <http://www.ntia.doc.gov/DNS/DNSSEC.html>.2.6.  Dynamic Service Discovery   The need for hosts to contain pre-configured addresses for servers   can be reduced by deploying the Service Location Protocol (SLP).  For   some common services, such as network printing, SLP can therefore be   an important tool for facilitating site renumbering.  See [RFC2608],   [RFC2610], [RFC3059], [RFC3224], [RFC3421], and [RFC3832].   Multicast DNS (mDNS) and DNS Service Discovery are already widely   deployed in BSD, Linux, Mac OS X, UNIX, and Windows systems, and are   also widely used for both link-local name resolution and for DNS-   based dynamic service discovery [MDNS] [DNSSD].  In many   environments, the combination of mDNS and DNS Service Discovery   (e.g., using SRV records [RFC3958]) can be important tools for   reducing dependency on configured addresses.3.  Existing Router-Related Mechanisms3.1.  Router Renumbering   Although DHCP was originally conceived for host configuration, it can   also be used for some aspects of router configuration.  The DHCPv6   Prefix Delegation options [RFC3633] are intended for this.  ForCarpenter, et al.             Informational                     [Page 9]

RFC 5887              Renumbering Still Needs Work              May 2010   example, DHCPv6 can be used by an ISP to delegate or withdraw a   prefix for a customer's router, and this can be cascaded throughout a   site to achieve router renumbering.   An ICMPv6 extension to allow router renumbering for IPv6 is specified   in [RFC2894], but there appears to be little experience with it.  It   is not mentioned as a useful mechanism by [RFC4192].   [RFC4191] extends IPv6 router advertisements to convey default router   preferences and more-specific routes from routers to hosts.  This   could be used as an additional tool to convey information during   renumbering, but does not appear to be used in practice.   [CPE] requires that a customer premises router use DHCPv6 to obtain   an address prefix from its upstream ISP and use IPv6 RA messages to   establish a default IPv6 route (when IPv6 is in use).4.  Existing Multi-Addressing Mechanism for IPv6   IPv6 was designed to support multiple addresses per interface and   multiple prefixes per subnet.  As described in [RFC4192], this allows   for a phased approach to renumbering (adding the new prefix and   addresses before removing the old ones).   As an additional result of the multi-addressing mechanism, a site   might choose to use Unique Local Addressing (ULA) [RFC4193] for all   on-site communication, or at least for all communication with on-site   servers, while using globally routeable IPv6 addresses for all off-   site communications.  It would also be possible to use ULAs for all   on-site network management purposes, by assigning ULAs to all   devices.  This would make these on-site activities immune to   renumbering of the prefix(es) used for off-site communication.   Finally, ULAs can be safely shared with peer sites with which there   is a VPN connection, which cannot be done with ambiguous IPv4   addresses [RFC1918]; such VPNs would not be affected by renumbering.   The IPv6 model also includes "privacy" addresses that are constructed   with pseudo-random interface identifiers to conceal actual MAC   addresses [RFC4941].  This means that IPv6 stacks and client   applications already need to be agile enough to handle frequent IP   address changes (e.g., in the privacy address), since in a privacy-   sensitive environment the address lifetime likely will be rather   short.Carpenter, et al.             Informational                    [Page 10]

RFC 5887              Renumbering Still Needs Work              May 20105.  Operational Issues with Renumbering Today   For IPv6, a useful description of practical aspects was drafted in   [THINK], as a complement to [RFC4192].  As indicated there, a primary   requirement is to minimise the disruption caused by renumbering.   This applies at two levels: disruption to site operations in general   and disruption to individual application sessions in progress at the   moment of renumbering.  In the IPv6 case, the intrinsic ability to   overlap use of the old and new prefixes greatly mitigates disruption   to ongoing sessions, as explained in [RFC4192].  This approach is in   practice excluded for IPv4, largely because IPv4 lacks a Stateless   Address Autoconfiguration (SLAAC) mechanism.5.1.  Host-Related Issues5.1.1.  Network-Layer Issues   For IPv4, the vast majority of client systems (PCs, workstations, and   handheld computers) today use DHCP to obtain their addresses and   other network-layer parameters.  DHCP provides for lifetimes after   which the address lease expires.  So it should be possible to devise   an operational procedure in which lease expiry coincides with the   moment of renumbering (within some margin of error).  In the simplest   case, the network administrator just lowers all DHCP address lease   lifetimes to a very short value (e.g., a few minutes).  It does this   long enough before a site-wide change that each node will   automatically pick up its new IP address within a few minutes of the   renumbering event.  In this case, it would be the DHCP server itself   that automatically accomplishes client renumbering, although this   would cause a peak of DHCP traffic and therefore would not be   instantaneous.  DHCPv6 could accomplish a similar result.   The FORCERENEW extension is defined for DHCP for IPv4 [RFC3203].   This is specifically unicast-only; a DHCP client must discard a   multicast FORCERENEW.  This could nevertheless be used to trigger the   renumbering process, with the DHCP server cycling through all its   clients issuing a FORCERENEW to each one.  DHCPv6 has a similar   feature, i.e., a unicast RECONFIGURE message, that can be sent to   each host to inform it to check its DHCPv6 server for an update.   These two features do not appear to be widely used for bulk   renumbering purposes.   Procedures for using a DHCP approach to site renumbering will be very   different depending on whether the site uses strong or weak asset   management.  With strong asset management, and careful operational   planning, the subnet addresses and masks will be updated in the   database, and a script will be run to regenerate the DHCP MAC-to-IP   address tables and the DNS zone file.  DHCP and DNS timers will beCarpenter, et al.             Informational                    [Page 11]

RFC 5887              Renumbering Still Needs Work              May 2010   set temporarily to small values.  The DHCP and DNS servers will be   fed the new files, and as soon as the previous DHCP leases and DNS   TTLs expire, everything will follow automatically, as far as the host   IP layer is concerned.  In contrast, with weak asset management, and   a casual operational approach, the DHCP table will be reconfigured by   hand, the DNS zone file will be edited by hand, and when these   configurations are installed, there will be a period of confusion   until the old leases and TTLs expire.  The DHCP FORCERENEW or   RECONFIGURE messages could shorten this confusion to some extent.   DHCP, particularly for IPv4, has acquired a very large number of   additional capabilities, with approximately 170 options defined at   the time of this writing.  Although most of these do not carry IP   address information, some do (for example, options 68 through 76 all   carry various IP addresses).  Thus, renumbering mechanisms involving   DHCP have to take into account more than the basic DHCP job of   leasing an address to each host.   SLAAC is much less overloaded with options than DHCP; in fact, its   only extraneous capability is the ability to convey a DNS server   address.  Using SLAAC to force all hosts on a site to renumber is   therefore less complex than DHCP, and the difference between strong   and weak asset management is less marked.  The principle of   synchronising the SLAAC and DNS updates, and of reducing the SLAAC   lease time and DNS TTL, does not change.   We should note a currently unresolved ambiguity in the interaction   between DHCPv6 and SLAAC from the host's point of view.  RA messages   include a 'Managed Configuration' flag known as the M bit, which is   supposed to indicate that DHCPv6 is in use.  However, it is   unspecified whether hosts must interpret this flag rigidly (i.e., may   or must only start DHCPv6 if it is set, or if no RAs are received) or   whether hosts are allowed or are recommended to start DHCPv6 by   default.  An added complexity is that DHCPv6 has a 'stateless' mode   [RFC3736] in which SLAAC is used to obtain an address, but DHCPv6 is   used to obtain other parameters.  Another flag in RA messages, the   'Other configuration' or O bit, indicates this.   Until this ambiguous behaviour is clearly resolved by the IETF,   operational problems are to be expected, since different host   operating systems have taken different approaches.  This makes it   difficult for a site network manager to configure systems in such a   way that all hosts boot in a consistent way.  Hosts will start SLAAC,   if so directed by appropriately configured RA messages.  However, if   one operating system also starts a DHCPv6 client by default, and   another one starts it only when it receives the M bit, systematic   address management is impeded.Carpenter, et al.             Informational                    [Page 12]

RFC 5887              Renumbering Still Needs Work              May 2010   Also, it should be noted that on an isolated LAN, neither RA nor   DHCPv6 responses will be received, and the host will remain with only   its self-assigned link-local address.  One could also have a   situation where a multihomed network uses SLAAC for one address   prefix and DHCPv6 for another, which would clearly create a risk of   inconsistent host behaviour and operational confusion.   Neither the SLAAC approach nor DHCP without pre-registered MAC   addresses will work reliably in all cases of systems that are   assigned fixed IP addresses for practical reasons.  Of course, even   systems with static addressing can be configured to use DHCP to   obtain their IP address(es).  Such use of "Static DHCP" usually will   ease site renumbering when it does become necessary.  However, in   other cases, manual or script-driven procedures, likely to be site-   specific and definitely prone to human error, are needed.  If a site   has even one host with a fixed, manually configured address,   completely automatic host renumbering is very likely to be   impossible.   The above assumes the use of typical off-the-shelf hardware and   software.  There are other environments, often referred to as   embedded systems, where DHCP or SLAAC might not be used and even   configuration scripts might not be an option; for example, fixed IP   addresses might be stored in read-only memory, or even set up using   Dual In-Line Package (DIP) switches.  Such systems create special   problems that no general-purpose solution is likely to address.5.1.2.  Transport-Layer Issues   TCP connections and UDP flows are rigidly bound to a given pair of IP   addresses.  These are included in the checksum calculation, and there   is no provision at present for the endpoint IP addresses to change.   It is therefore fundamentally impossible for the flows to survive a   renumbering event at either end.  From an operational viewpoint, this   means that a site that plans to renumber itself is obliged either to   follow the overlapped procedure described in [RFC4192] or to announce   a site-wide outage for the renumbering process, during which all user   sessions will fail.  In the case of IPv4, overlapping of the old and   new addresses is unlikely to be an option, and in any case is not   commonly supported by software.  Therefore, absent enhancements to   TCP and UDP to enable dynamic endpoint address changes (for example,   [HANDLEY]), interruptions to TCP and UDP sessions seem inevitable if   renumbering occurs at either session endpoint.  The same appears to   be true of Datagram Congestion Control Protocol (DCCP) [RFC4340].Carpenter, et al.             Informational                    [Page 13]

RFC 5887              Renumbering Still Needs Work              May 2010   In contrast, Stream Control Transmission Protocol (SCTP) already   supports dynamic multihoming of session endpoints, so SCTP sessions   ought not be adversely impacted by renumbering the SCTP session   endpoints [RFC4960] [RFC5061].5.1.3.  DNS Issues   The main issue is whether the site in question has a systematic   procedure for updating its DNS configuration.  If it does, updating   the DNS for a renumbering event is essentially a clerical issue that   must be coordinated as part of a complete plan, including both   forward and reverse mapping.  As mentioned in [RFC4192], the DNS TTL   will be manipulated to ensure that stale addresses are not cached.   However, if the site uses a weak asset management model in which DNS   updates are made manually on demand, there will be a substantial   period of confusion and errors will be made.   There are anecdotal reports that many small user sites do not even   maintain their own DNS configuration, despite running their own web   and email servers.  They point to their ISP's resolver, request the   ISP to install DNS entries for their servers, but operate internally   mainly by IP address.  Thus, renumbering for such sites will require   administrative coordination between the site and its ISP(s), unless   the DNS servers in use have Secure Dynamic DNS Update enabled.  Some   commercial DNS service firms include Secure Dynamic DNS Update as   part of their DNS service offering.   It should be noted that DNS entries commonly have matching Reverse   DNS entries.  When a site renumbers, these reverse entries will also   need to be updated.  Depending on a site's operational arrangements   for DNS support, it might or might not be possible to combine forward   and reverse DNS updates in a single procedure.5.1.4.  Application-Layer Issues   Ideally, we would carry out a renumbering analysis for each   application protocol.  To some extent, this has been done, in   [RFC3795].  This found that 34 out of 257 Standards-Track or   Experimental application-layer RFCs had explicit address   dependencies.  Although this study was made in the context of IPv4 to   IPv6 transition, it is clear that all these protocols might be   sensitive to renumbering.  However, the situation is worse, in that   there is no way to discover by analyzing specifications whether an   actual implementation is sensitive to renumbering.  Indeed, such   analysis might be quite impossible in the case of proprietary   applications.Carpenter, et al.             Informational                    [Page 14]

RFC 5887              Renumbering Still Needs Work              May 2010   The sensitivity depends on whether the implementation stores IP   addresses in such a way that it might refer back to them later,   without allowing for the fact that they might no longer be valid.  In   general, we can assert that any implementation is at risk from   renumbering if it does not check that an address is valid each time   it opens a new communications session.  This could be done, for   example, by knowing and respecting the relevant DNS TTL, or by   resolving relevant Fully-Qualified Domain Names (FQDNs) again.  A   common experience is that even when FQDNs are stored in configuration   files, they are resolved only once, when the application starts, and   they are cached indefinitely thereafter.  This is insufficient.  Of   course, this does not apply to all application software; for example,   several well-known web browsers have short default cache lifetimes.   There are even more egregious breaches of this principle, for   example, software license systems that depend on the licensed host   computer having a particular IP address.  Other examples are the use   of literal IP addresses in URLs, HTTP cookies, or application proxy   configurations.  (Also seeAppendix A.)   In contrast, there are also many application suites that actively   deal with connectivity failures by retrying with alternative   addresses or by repeating DNS lookups.  This places a considerable   burden of complexity on application developers.   It should be noted that applications are in effect encouraged to be   aware of and to store IP addresses by the very nature of the socket   API calls gethostbyname() and getaddrinfo().  It is highly   unfortunate that many applications use APIs that require the   application to see and use lower-layer objects, such as network-layer   addresses.  However, the BSD Sockets API was designed and deployed   before the Domain Name System (DNS) was created, so there were few   good options at the time.  This issue is made worse by the fact that   these functions do not return an address lifetime, so that   applications have no way to know when an address is no longer valid.   The extension of the same model to cover IPv6 has complicated this   problem somewhat.  An application using the socket API is obliged to   contain explicit logic if it wishes to benefit from the availability   of multiple addresses for a given remote host.  If a programming   model were adopted in which only FQDNs were exposed to applications,   and addresses were cached with appropriate lifetimes within the API,   most of these problems would disappear.  It should be noted that at   least the first part of this is already available for some   programming environments.  A common example is Java, where only FQDNs   need to be handled by application code in normal circumstances, and   no additional application logic is needed to deal with multiple   addresses, which are handled by the run-time system.  This is highly   beneficial for programmers who are not networking experts, andCarpenter, et al.             Informational                    [Page 15]

RFC 5887              Renumbering Still Needs Work              May 2010   insulates applications software from many aspects of renumbering.  It   would be helpful to have similarly abstract, DNS-oriented, Networking   APIs openly specified and widely available for C and C++.   Some web browsers intentionally violate the DNS TTL with a technique   called "DNS Pinning."  DNS Pinning limits acceptance of server IP   address changes, due to a JavaScript issue where repeated address   changes can be used to induce a browser to scan the inside of a   firewalled network and report the results to an outside attacker.   Pinning can persist as long as the browser is running, in extreme   cases perhaps months at a time.  Thus, we can see that security   considerations may directly damage the ability of applications to   deal with renumbering.   Server applications might need to be restarted when the host they   contain is renumbered, to ensure that they are listening on a port   and socket bound to the new address.  In an IPv6 multi-addressed   host, server applications need to be able to listen on more than one   address simultaneously, in order to cover an overlap during   renumbering.  Not all server applications are written to do this, and   a name-based API as just mentioned would have to provide for this   case invisibly to the server code.   As noted inSection 2.6, the Service Location Protocol (SLP), and   multicast DNS with SRV records for service discovery, have been   available for some years.  For example, many printers deployed in   recent years automatically advertise themselves to potential clients   via SLP.  Many modern client operating systems automatically   participate in SLP without requiring users to enable it.  These tools   appear not to be widely known, although they can be used to reduce   the number of places that IP addresses need to be configured.5.2.  Router-Related Issues   [RFC2072] gives a detailed review of the operational realities in   1997.  A number of the issues discussed in that document were the   result of the relatively recent adoption of classless addressing;   those issues can be assumed to have vanished by now.  Also, DHCP was   a relative newcomer at that time, and can now be assumed to be   generally available.  Above all, the document underlines that   systematic planning and administrative preparation are needed, and   that all forms of configuration file and script must be reviewed and   updated.  Clearly this includes filtering and routing rules (e.g.,   when peering with BGP, but also with intradomain routing as well).   Two particular issues mentioned in [RFC2072] are:   o  Some routers cache IP addresses in some situations.  So routers      might need to be restarted as a result of site renumbering.Carpenter, et al.             Informational                    [Page 16]

RFC 5887              Renumbering Still Needs Work              May 2010   o  Addresses might be used by configured tunnels, including VPN      tunnels, although at least the Internet Key Exchange (IKE)      supports the use of Fully-Qualified Domain Names instead.   On the latter point, the capability to use FQDNs as endpoint names in   IPsec VPNs is not new and is standard (see[RFC2407], Section 4.6.2.3   and[RFC4306], Section 3.5).  This capability is present in most   IPsec VPN implementations.  There does seem to be an "educational" or   "awareness" issue that many system/network administrators do not   realise that it is there and works well as a way to avoid manual   modification during renumbering.  (Of course, even in this case, a   VPN may need to be reconnected after a renumbering event, but most   products appear to handle this automatically.)   In IPv6, 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.5.3.  Other Issues5.3.1.  NAT State Issues   When a renumbering event takes place, entries in the state table of   any Network Address Translator that happen to contain the affected   addresses will become invalid and will eventually time out.  Since   TCP and UDP sessions are unlikely to survive renumbering anyway, the   hosts involved will not be additionally affected.  The situation is   more complex for multihomed SCTP [SCTPNAT], depending on whether a   single or multiple NATs are involved.   A NAT itself might be renumbered and might need a configuration   change during a renumbering event.  One of the authors has a NAT-   enabled home gateway that obtains its exterior address from the   residential Internet service provider by acting as a DHCP client.   That deployment has not suffered operational problems when the ISP   uses DHCP to renumber the gateway's exterior IP address.  A critical   part of that success has been configuring IKE on the home gateway to   use a "mailbox name" for the user's identity type (rather than using   the exterior IP address of the home gateway) when creating or   managing the IP Security Associations.Carpenter, et al.             Informational                    [Page 17]

RFC 5887              Renumbering Still Needs Work              May 20105.3.2.  Mobility Issues   A mobile node using Mobile IP that is not currently in its home   network will be adversely affected if either its current care-of   address or its home address is renumbered.  For IPv6, if the care-of   address changes, this will be exactly like moving from one foreign   network to another, and Mobile IP will re-bind with its home agent in   the normal way.  If its home address changes unexpectedly, it 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 [RFC3775].  The situation is more   tricky if the mobile node is detached at the time of the renumbering   event, since 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.   In contrast to Mobile IPv6, Mobile IPv4 does not support prefix   solicitation and prefix advertisement messages, limiting its   renumbering capability to well-scheduled renumbering events when the   mobile node is connected to its home agent and managed by the home   network administration.  Unexpected home network renumbering events   when the mobile node is away from its home network and not connected   to the home agent are supported only if a relevant Authentication,   Authorisation, and Accounting (AAA) system is able to allocate   dynamically a home address and home agent for the mobile node.5.3.3.  Multicast Issues   As discussed in [THINK], IPv6 multicast can be used to help rather   than hinder renumbering, for example, by using multicast as a   discovery protocol (as in IPv6 Neighbour Discovery).  On the other   hand, the embedding of IPv6 unicast addresses into multicast   addresses specified in [RFC3306] and the embedded-RP (Rendezvous   Point) in [RFC3956] will cause issues when renumbering.   For both IPv4 and IPv6, changing the unicast source address of a   multicast sender might also be an issue for receivers, especially for   Source-Specific Multicast (SSM).  Applications need to learn the new   source addresses and new multicast trees need to be built   For IPv4 or IPv6 with Any-Source Multicast (ASM), renumbering can be   easy.  If sources are renumbered, from the routing perspective,   things behave just as if there are new sources within the same   multicast group.  There may be application issues though.  Changing   the RP address is easy when using Bootstrap Router (BSR) [RFC5059]   for dynamic RP discovery.  BSR is widely used, but it is also common   to use static config of RP addresses on routers.  In that case,   router configurations must be updated too.Carpenter, et al.             Informational                    [Page 18]

RFC 5887              Renumbering Still Needs Work              May 2010   If any multicast ACLs are configured, they raise the same issue as   unicast ACLs mentioned elsewhere.5.3.4.  Management Issues   Today, static IP addresses are routinely embedded in numerous   configuration files and network management databases, including MIB   modules.  Ideally, all of these would be generated from a single   central asset management database for a given site, but this is far   from being universal practice.  It should be noted that for IPv6,   where multiple routing prefixes per interface and multiple addresses   per interface are standard practice, the database and the   configuration files will need to allow for this (rather than for a   single address per host, as is normal practice for IPv4).   Furthermore, because of routing policies and VPNs, a site or network   might well embed addresses from other sites or networks in its own   configuration data.  (It is preferable to embed FQDNs instead, of   course, whenever possible.)  Thus, renumbering will cause a ripple   effect of updates for a site and for its neighbours.  To the extent   that these updates are manual, they will be costly and prone to   error.  Synchronising updates between independent sites can cause   unpredictable delays.  Note thatSection 4 suggests that IPv6 ULAs   can mitigate this problem, but of course only for VPNs and routes   that are suitable for ULAs rather than globally routeable addresses.   The majority of external addresses to be configured will not be ULAs.   SeeAppendix A for an extended list of possible static or embedded   addresses.   Some address configuration data are relatively easy to find (for   example, site firewall rules, ACLs in site border routers, and DNS).   Others might be widely dispersed and much harder to find (for   example, configurations for building routers, printer addresses   configured by individual users, and personal firewall   configurations).  Some of these will inevitably be found only after   the renumbering event, when the users concerned encounter a problem.   The overlapped model for IPv6 renumbering, with old and new addresses   valid simultaneously, means that planned database and configuration   file updates will proceed in two stages -- add the new information   some time before the renumbering event, and remove the old   information some time after.  All policy rules must be configured to   behave correctly during this process (e.g., preferring the new   address as soon as possible).  Similarly, monitoring tools must be   set up to monitor both old and new during the overlap.Carpenter, et al.             Informational                    [Page 19]

RFC 5887              Renumbering Still Needs Work              May 2010   However, it should be noted that the notion of simultaneously   operating multiple prefixes for the same network, although natural   for IPv6, is generally not supported by operational tools such as   address management software.  It also increases the size of IGP   routing tables in proportion to the number of prefixes in use.  For   these reasons, and due to its unfamiliarity to operational staff, the   use of multiple prefixes remains rare.  Accordingly, the use of ULAs   to provide stable on-site addresses even if the off-site prefix   changes is also rare.   If both IPv4 and IPv6 are renumbered simultaneously in a dual-stack   network, additional complications could result, especially with   configured IP-in-IP tunnels.  This scenario should probably be   avoided.   Use of FQDNs rather than raw IP addresses wherever possible in   configuration files and databases will reduce/mitigate the potential   issues arising from such configuration files or management databases   when renumbering is required or otherwise occurs.  This is advocated   in [RFC1958] (point 4.1).  Just as we noted inSection 5.1.4 for   applications, this is insufficient in itself; some devices such as   routers are known to only resolve FQDNs once, at start-up, and to   continue using the resulting addresses indefinitely.  This may   require routers to be rebooted, when they should instead be resolving   the FQDN again after a given timeout.   By definition, there is at least one place (i.e., the DNS zone file   or the database from which it is derived) where address information   is nevertheless inevitable.   It is also possible that some operators may choose to configure   addresses rather than names, precisely to avoid a possible circular   dependency and the resulting failure modes.  This is arguably even   advocated in [RFC1958] (point 3.11).   It should be noted that the management and administration issues   (i.e., tracking down, recording, and updating all instances where   addresses are stored rather than looked up dynamically) form the   dominant concern of managers considering the renumbering problem.   This has led many sites to continue the pre-CIDR (Classless Inter-   Domain Routing) approach of using a provider-independent (PI) prefix.   Some sites, including very large corporate networks, combine PI   addressing with NAT.  Others have adopted private addressing and NAT   as a matter of choice rather than obligation.  This range of   techniques allows for addressing plans that are independent of the   ISP(s) in use, and allows a straightforward approach to multihoming.   The direct cost of renumbering is perceived to exceed the indirect   costs of these alternatives.  Additionally, there is a risk elementCarpenter, et al.             Informational                    [Page 20]

RFC 5887              Renumbering Still Needs Work              May 2010   stemming from the complex dependencies of renumbering: it is hard to   be fully certain that the renumbering will not cause unforeseen   service disruptions, leading to unknown additional costs.   A relevant example in a corporate context is VPN configuration data   held in every employee laptop, for use while on travel and connecting   securely from remote locations.  Typically, such VPNs are statically   configured using numeric IP addresses for endpoints and even with   prefix lists for host routing tables.  Use of VPN configurations with   FQDNs to name fixed endpoints, such as corporate VPN gateways, and   with non-address identity types would enable existing IP Security   with IKE to avoid address renumbering issues and work well for highly   mobile users.  This is all possible today with standard IPsec and   standard IKE.  It just requires VPN software to be configured with   names instead of addresses, and thoughtful network administration.   It should be noted that site and network operations managers are   often very conservative, and reluctant to change operational   procedures that are working reasonably well and are perceived as   reasonably secure.  They quite logically argue that any change brings   with it an intrinsic risk of perturbation and insecurity.  Thus, even   if procedural changes are recommended that will ultimately reduce the   risks and difficulties of renumbering (such as using FQDNs protected   by DNSsec where addresses are used today), these changes might be   resisted.5.3.5.  Security Issues   For IPv6, addresses are intended to be protected against forgery   during neighbour discovery by SEcure Neighbour Discovery (SEND)   [RFC3971].  This appears to be a very useful precaution during   dynamic renumbering, to prevent hijacking of the process by an   attacker.  Any automatic renumbering scheme has a potential exposure   to such hijacking at the moment that a new address is announced.   However, at present it is unclear whether or when SEND might be   widely implemented or widely deployed.   Firewall rules will certainly need to be updated, and any other cases   where addresses or address prefixes are embedded in security   components (access control lists, AAA systems, intrusion detection   systems, etc.).  If this is not done in advance, legitimate access to   resources might be blocked after the renumbering event.  If the old   rules are not removed promptly, illegitimate access might be possible   after the renumbering event.  Thus, the security updates will need to   be made in two stages (immediately before and immediately after the   event).Carpenter, et al.             Informational                    [Page 21]

RFC 5887              Renumbering Still Needs Work              May 2010   There will be operational and security issues if an X.509v3 Public   Key Infrastructure (PKI) Certificate includes a subjectAltName   extension that contains an iPAddress [RFC5280], and if the   corresponding node then undergoes an IP address change without a   concurrent update to the node's PKI Certificate.  For these reasons,   use of the dNSName rather than the iPAddress is recommended for the   subjectAltName extension.  Any other use of IP addresses in   cryptographic material is likely to be similarly troublesome.   If a site is, for some reason, listed by IP address in a white list   (such as a spam white list), this will need to be updated.   Conversely, a site that is listed in a black list can escape that   list by renumbering itself.   The use of IP addresses instead of FQDNs in configurations is   sometimes driven by a perceived security need.  Since the name   resolution process has historically lacked authentication,   administrators prefer to use raw IP addresses when the application is   security sensitive (firewalls and VPN are two typical examples).  It   might be possible to solve this issue in the next few years with   DNSsec (seeSection 2.5), now that there is strong DNS Security   deployment momentum.6.  Proposed Mechanisms6.1.  SHIM6   SHIM6, proposed as a host-based multihoming mechanism for IPv6, has   the property of dynamically switching the addresses used for   forwarding the actual packet stream while presenting a constant   address as the upper-layer identifier for the transport layer   [RFC5533].  At least in principle, this property could be used during   renumbering to alleviate the problem described inSection 5.1.2.   SHIM6 is an example of a class of solutions with this or a similar   property; others are Host Identity Protocol (HIP), IKEv2 Mobility and   Multihoming (MOBIKE), Mobile IPv6, SCTP, and proposals for multi-path   TCP.6.2.  MANET Proposals   The IETF working groups dealing with mobile ad hoc networks have been   working on a number of mechanisms for mobile routers to discover   available border routers dynamically, and for those mobile routers to   be able to communicate that information to hosts connected to those   mobile routers.Carpenter, et al.             Informational                    [Page 22]

RFC 5887              Renumbering Still Needs Work              May 2010   Recently, some MANET work has appeared on a "Border Router Discovery   Protocol (BRDP)" that might be useful work towards a more dynamic   mechanism for site interior router renumbering [BRDP].   At present, the IETF AUTOCONF WG   (http://www.ietf.org/html.charters/autoconf-charter.html) is working   on address autoconfiguration mechanisms for MANET networks that also   seem useful for ordinary non-mobile non-MANET networks [AUTOC].  This   work is extensively surveyed in [AUTOC2] and [AUTOC3].  Other work in   the same area, e.g., [RFC5558], might also be relevant.   MANETs are, of course, unusual in that they must be able to   reconfigure themselves at all times and without notice.  Hence, the   type of hidden static configurations discussed above inSection 5.3.4   are simply intolerable in MANETs.  Thus, it is possible that when a   consensus is reached on autoconfiguration for MANETs, the selected   solution(s) might not be suitable for the more general renumbering   problem.  However, it is certainly worthwhile to explore applying   techniques that work for MANETs to conventional networks also.6.3.  Other IETF Work   A DHCPv6 extension has been proposed that could convey alternative   routes, in addition to the default router address, to IPv6 hosts   [DHRTOPT].  Other DHCP options are also on the table that may offer   information about address prefixes and routing to DHCP or DHCPv6   clients, such as [DHSUBNET] and [DHMIFRT].  It is conceivable that   these might be extended as a way of informing hosts dynamically of   prefix changes.   In the area of management tools, Network Configuration (NETCONF)   Protocol [RFC4741] is suitable for the configuration of any network   element or server, so could in principle be used to support secure   remote address renumbering.   The DNSOP WG has considered a Name Server Control Protocol (NSCP)   based on NETCONF that provides means for consistent DNS management   including potential host renumbering events [DNSCONT].6.4.  Other Proposals   A proposal has been made to include an address lifetime as an   embedded field in IPv6 addresses, with the idea that all prefixes   would automatically expire after a certain period and become   unrouteable [CROCKER].  While this might be viewed as provocative, it   would force the issue by making renumbering compulsory.Carpenter, et al.             Informational                    [Page 23]

RFC 5887              Renumbering Still Needs Work              May 20107.  Gaps   This section seeks to identify technology gaps between what is   available from existing open specifications and what appears to be   needed for site renumbering to be tolerable.7.1.  Host-Related Gaps   It would be beneficial to expose address lifetimes in the socket API,   or any low-level networking API.  This would allow applications to   avoid using stale addresses.   The various current discussions of a name-based transport layer or a   name-based network API also have potential to alleviate the   application-layer issues noted in this document.  Application   development would be enhanced by the addition of a more abstract   network API that supports the C and C++ programming languages.  For   example, it could use FQDNs and Service Names, rather than SockAddr,   IP Address, protocol, and port number.  This would be equivalent to   similar interfaces already extant for Java programmers.   Moving to a FQDN-based transport layer might enhance the ability to   migrate the IP addresses of endpoints for TCP/UDP without having to   interrupt a session, or at least in a way that allows a session to   restart gracefully.   Having a single registry per host for all address-based configuration   (/etc/hosts, anyone?), with secure access for site network   management, might be helpful.  Ideally, this would be remotely   configurable, for example, leveraging the IETF's current work on   networked-device configuration protocols (NetConf).  While there are   proprietary versions of this approach, sometimes based on Lightweight   Directory Access Protocol (LDAP), a fully standardised approach seems   desirable.   Do we really need more than DHCP or SLAAC for regular hosts?  Do we   need an IPv4 equivalent of SLAAC?  How can the use of DHCP FORCERENEW   and DHCPv6 RECONFIGURE for bulk renumbering be deployed?  FORCERENEW   in particular requires DHCP authentication [RFC3118] to be deployed.   The IETF should resolve the 'IPv6 ND M/O flag debate' once and for   all, with default, mandatory and optional behaviours of hosts being   fully specified.   The host behaviour for upstream link learning suggested inSection 2.3 should be documented.Carpenter, et al.             Informational                    [Page 24]

RFC 5887              Renumbering Still Needs Work              May 2010   It would be helpful to have multi-path, survivable, extensions for   both UDP and TCP (or institutionalise some aspects of SHIM6).7.2.  Router-Related Gaps   A non-proprietary secure mechanism to allow all address-based   configuration to be driven by a central repository for site   configuration data.  NETCONF might be a good starting point.   A MANET solution that's solid enough to apply to fully operational   small to medium fixed sites for voluntary or involuntary renumbering.   A MANET-style solution that can be applied convincingly to large or   very large sites for voluntary renumbering.   A useful short-term measure would be to ensure that [RFC2894] and   [RFC3633] can be used in practice.7.3.  Operational Gaps   Since address changes are usually communicated via the DNS, the   latter's security is essential for secure renumbering.  Thus, we   should continue existing efforts to deploy DNSsec globally, including   not only signing the DNS root, DNS TLDs, and subsidiary DNS zones,   but also widely deploying the already available DNSsec-capable DNS   resolvers.   Similarly, we should document and encourage widespread deployment of   Secure Dynamic DNS Update both in DNS servers and also in both client   and server operating systems.  This capability is already widely   implemented and widely available, but it is not widely deployed at   present.   Deploy multi-prefix usage of IPv6, including Unique Local Addresses   (ULAs) to provide stable internal addresses.  In particular, address   management tools need to support the multi-prefix model and ULAs.   Ensure that network monitoring systems will function during   renumbering, in particular to confirm that renumbering has completed   successfully or that some traffic is still using the old prefixes.   Document and encourage systematic site databases and secure   configuration protocols for network elements and servers (e.g.,   NETCONF).  The database should store all the information about the   network; scripts and tools should derive all configurations from the   database.  An example of this approach to simplify renumbering is   given at [LEROY].Carpenter, et al.             Informational                    [Page 25]

RFC 5887              Renumbering Still Needs Work              May 2010   Document functional requirements for site renumbering tools or   toolkits.   Document operational procedures useful for site renumbering.   In general, document renumbering instructions as part of every   product manual.   Recommend strongly that all IPv6 deployment plans, for all sizes of   site or network, should include provision for future renumbering.   Renumbering should be planned from day one when the first lines of   the configuration of a network or network service are written.  Every   IPv6 operator should expect to have to renumber the network one day   and should plan for this event.7.4.  Other Gaps   Define a secure mechanism for announcing changes of site prefix to   other sites (for example, those that configure routers or VPNs to   point to the site in question).   For Mobile IP, define a better mechanism to handle change of home   agent address while mobile is disconnected.8.  Security Considerations   Known current issues are discussed inSection 5.3.5.  Security issues   related to SLAAC are discussed in [RFC3756].  DHCP authentication is   defined in [RFC3118].   For future mechanisms to assist and simplify renumbering, care must   be taken to ensure that prefix or address changes (especially changes   coming from another site or via public sources such as the DNS) are   adequately authenticated at all points.  Otherwise, misuse of   renumbering mechanisms would become an attractive target for those   wishing to divert traffic or to cause major disruption.  As noted inSection 5.1.4, this may result in defensive techniques such as "DNS   pinning", which create difficulty when renumbering.   Whatever authentication method(s) are adopted, key distribution will   be an important aspect.  Most likely, public key cryptography will be   needed to authenticate renumbering announcements passing from one   site to another, since one cannot assume a preexisting trust   relationship between such sites.Carpenter, et al.             Informational                    [Page 26]

RFC 5887              Renumbering Still Needs Work              May 20109.  Acknowledgements   Significant amounts of text have been adapted from [THINK], which   reflects work carried out during the 6NET project funded by the   Information Society Technologies Programme of the European   Commission.  The authors of that document have agreed to their text   being submitted under the IETF's current copyright provisions.   Helpful material about work following on from 6NET was also provided   by Olivier Festor of INRIA.   Useful comments and contributions were made (in alphabetical order)   by Jari Arkko, Fred Baker, Olivier Bonaventure, Teco Boot, Stephane   Bortzmeyer, Dale Carder, Gert Doering, Ralph Droms, Pasi Eronen,   Vijay Gurbani, William Herrin, Cullen Jennings, Eliot Lear, Darrel   Lewis, Masataka Ohta, Dan Romascanu, Dave Thaler, Iljitsch van   Beijnum, Stig Venaas, Nathan Ward, James Woodyatt, and others.10.  Informative References   [AUTOC]       Chakeres, I., Macker, J., and T. Clausen, "Mobile Ad                 hoc Network Architecture", Work in Progress,                 November 2007.   [AUTOC2]      Bernardos, C., Calderon, M., and H. Moustafa, "Survey                 of IP address autoconfiguration mechanisms for MANETs",                 Work in Progress, November 2008.   [AUTOC3]      Bernardos, C., Calderon, M., and H. Moustafa, "Ad-Hoc                 IP Autoconfiguration Solution Space Analysis", Work                 in Progress, November 2008.   [BRDP]        Boot, T. and A. Holtzer, "Border Router Discovery                 Protocol (BRDP) based Address Autoconfiguration", Work                 in Progress, July 2009.   [CPE]         Singh, H., Beebee, W., Donley, C., Stark, B., and O.                 Troan, Ed., "Basic Requirements for IPv6 Customer Edge                 Routers", Work in Progress, May 2010.   [CROCKER]     Crocker, S., "Renumbering Considered Normal", 2006,                 <http://www.arin.net/meetings/minutes/ARIN_XVIII/PDF/wednesday/Renumbering_Crocker.pdf>.   [DHMIFRT]     Sun, T. and H. Deng, "Route Configuration by DHCPv6                 Option for Hosts with Multiple Interfaces", Work                 in Progress, March 2009.Carpenter, et al.             Informational                    [Page 27]

RFC 5887              Renumbering Still Needs Work              May 2010   [DHRTOPT]     Dec, W. and R. Johnson,"DHCPv6 Route Option", Work                 in Progress, March 2010.   [DHSUBNET]    Johnson, R., Kumarasamy, J., Kinnear, K., and M. Stapp,                 "Subnet Allocation Option", Work in Progress, May 2010.   [DNSBOOK]     Albitz, P. and C. Liu, "DNS and BIND", 5th Edition,                 O'Reilly, 2006.   [DNSCONT]     Dickinson, J., Morris, S., and R. Arends, "Design for a                 Nameserver Control Protocol", Work in Protocol,                 October 2008.   [DNSSD]       Cheshire, S. and M. Krochmal, "DNS-Based Service                 Discovery", Work in Progress, March 2010.   [HANDLEY]     Handley, M., Wischik, D., and M. Bagnulo, "Multipath                 Transport, Resource Pooling, and implications for                 Routing", 2008,                 <http://www.ietf.org/proceedings/08jul/slides/RRG-2.pdf>.   [IEEE.802-1X] Institute of Electrical and Electronics Engineers,                 "Port-Based Network Access Control:  IEEE Standard for                 Local and Metropolitan Area Networks 802.1X-2004",                 December 2009.   [IEEE.802-1X-REV]                 Institute of Electrical and Electronics Engineers,                 "802.1X-REV - Revision of 802.1X-2004 - Port Based                 Network Access Control:  IEEE Standard for Local and                 Metropolitan Area Networks", 2009.   [ILNP]        Atkinson, R.,"ILNP Concept of Operations", Work                 in Progress, February 2010.   [LEROY]       Leroy, D. and O. Bonaventure, "Preparing network                 configurations for IPv6 renumbering", International                 Journal of Network Management, 2009, <http://inl.info.ucl.ac.be/system/files/dleroy-nem-2009.pdf>.   [LISP]        Farinacci, D., Fuller, V., Meyer, D., and D. Lewis,                 "Locator/ID Separation Protocol (LISP)", Work                 in Progress, April 2010.   [MDNS]        Cheshire, S. and M. Krochmal,"Multicast DNS", Work                 in Progress, March 2010.Carpenter, et al.             Informational                    [Page 28]

RFC 5887              Renumbering Still Needs Work              May 2010   [NAT66]       Wasserman, M. and F. Baker, "IPv6-to-IPv6 Network                 Address Translation (NAT66)", Work in Progress,                 March 2009.   [RFC1332]     McGregor, G., "The PPP Internet Protocol Control                 Protocol (IPCP)",RFC 1332, May 1992.   [RFC1661]     Simpson, W., "The Point-to-Point Protocol (PPP)",                 STD 51,RFC 1661, July 1994.   [RFC1900]     Carpenter, B. and Y. Rekhter, "Renumbering Needs Work",RFC 1900, February 1996.   [RFC1916]     Berkowitz, H., Ferguson, P., Leland, W., and P. Nesser,                 "Enterprise Renumbering: Experience and Information                 Solicitation",RFC 1916, February 1996.   [RFC1918]     Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G.,                 and E. Lear, "Address Allocation for Private                 Internets",BCP 5,RFC 1918, February 1996.   [RFC1958]     Carpenter, B., "Architectural Principles of the                 Internet",RFC 1958, June 1996.   [RFC2071]     Ferguson, P. and H. Berkowitz, "Network Renumbering                 Overview: Why would I want it and what is it anyway?",RFC 2071, January 1997.   [RFC2072]     Berkowitz, H., "Router Renumbering Guide",RFC 2072,                 January 1997.   [RFC2131]     Droms, R., "Dynamic Host Configuration Protocol",RFC 2131, March 1997.   [RFC2407]     Piper, D., "The Internet IP Security Domain of                 Interpretation for ISAKMP",RFC 2407, November 1998.   [RFC2608]     Guttman, E., Perkins, C., Veizades, J., and M. Day,                 "Service Location Protocol, Version 2",RFC 2608,                 June 1999.   [RFC2610]     Perkins, C. and E. Guttman, "DHCP Options for Service                 Location Protocol",RFC 2610, June 1999.   [RFC2874]     Crawford, M. and C. Huitema, "DNS Extensions to Support                 IPv6 Address Aggregation and Renumbering",RFC 2874,                 July 2000.Carpenter, et al.             Informational                    [Page 29]

RFC 5887              Renumbering Still Needs Work              May 2010   [RFC2894]     Crawford, M., "Router Renumbering for IPv6",RFC 2894,                 August 2000.   [RFC3007]     Wellington, B., "Secure Domain Name System (DNS)                 Dynamic Update",RFC 3007, November 2000.   [RFC3059]     Guttman, E., "Attribute List Extension for the Service                 Location Protocol",RFC 3059, February 2001.   [RFC3118]     Droms, R. and W. Arbaugh, "Authentication for DHCP                 Messages",RFC 3118, June 2001.   [RFC3203]     T'Joens, Y., Hublet, C., and P. De Schrijver, "DHCP                 reconfigure extension",RFC 3203, December 2001.   [RFC3224]     Guttman, E., "Vendor Extensions for Service Location                 Protocol, Version 2",RFC 3224, January 2002.   [RFC3306]     Haberman, B. and D. Thaler, "Unicast-Prefix-based IPv6                 Multicast Addresses",RFC 3306, August 2002.   [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.   [RFC3421]     Zhao, W., Schulzrinne, H., Guttman, E., Bisdikian, C.,                 and W. Jerome, "Select and Sort Extensions for the                 Service Location Protocol (SLP)",RFC 3421,                 November 2002.   [RFC3633]     Troan, O. and R. Droms, "IPv6 Prefix Options for                 Dynamic Host Configuration Protocol (DHCP) version 6",RFC 3633, December 2003.   [RFC3736]     Droms, R., "Stateless Dynamic Host Configuration                 Protocol (DHCP) Service for IPv6",RFC 3736,                 April 2004.   [RFC3756]     Nikander, P., Kempf, J., and E. Nordmark, "IPv6                 Neighbor Discovery (ND) Trust Models and Threats",RFC 3756, May 2004.   [RFC3775]     Johnson, D., Perkins, C., and J. Arkko, "Mobility                 Support in IPv6",RFC 3775, June 2004.   [RFC3795]     Sofia, R. and P. Nesser, "Survey of IPv4 Addresses in                 Currently Deployed IETF Application Area Standards                 Track and Experimental Documents",RFC 3795, June 2004.Carpenter, et al.             Informational                    [Page 30]

RFC 5887              Renumbering Still Needs Work              May 2010   [RFC3832]     Zhao, W., Schulzrinne, H., Guttman, E., Bisdikian, C.,                 and W. Jerome, "Remote Service Discovery in the Service                 Location Protocol (SLP) via DNS SRV",RFC 3832,                 July 2004.   [RFC3956]     Savola, P. and B. Haberman, "Embedding the Rendezvous                 Point (RP) Address in an IPv6 Multicast Address",RFC 3956, November 2004.   [RFC3958]     Daigle, L. and A. Newton, "Domain-Based Application                 Service Location Using SRV RRs and the Dynamic                 Delegation Discovery Service (DDDS)",RFC 3958,                 January 2005.   [RFC3971]     Arkko, J., Kempf, J., Zill, B., and P. Nikander,                 "SEcure Neighbor Discovery (SEND)",RFC 3971,                 March 2005.   [RFC4033]     Arends, R., Austein, R., Larson, M., Massey, D., and S.                 Rose, "DNS Security Introduction and Requirements",RFC 4033, March 2005.   [RFC4034]     Arends, R., Austein, R., Larson, M., Massey, D., and S.                 Rose, "Resource Records for the DNS Security                 Extensions",RFC 4034, March 2005.   [RFC4035]     Arends, R., Austein, R., Larson, M., Massey, D., and S.                 Rose, "Protocol Modifications for the DNS Security                 Extensions",RFC 4035, March 2005.   [RFC4076]     Chown, T., Venaas, S., and A. Vijayabhaskar,                 "Renumbering Requirements for Stateless Dynamic Host                 Configuration Protocol for IPv6 (DHCPv6)",RFC 4076,                 May 2005.   [RFC4191]     Draves, R. and D. Thaler, "Default Router Preferences                 and More-Specific Routes",RFC 4191, November 2005.   [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.   [RFC4306]     Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",RFC 4306, December 2005.Carpenter, et al.             Informational                    [Page 31]

RFC 5887              Renumbering Still Needs Work              May 2010   [RFC4340]     Kohler, E., Handley, M., and S. Floyd, "Datagram                 Congestion Control Protocol (DCCP)",RFC 4340,                 March 2006.   [RFC4741]     Enns, R., "NETCONF Configuration Protocol",RFC 4741,                 December 2006.   [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.   [RFC4941]     Narten, T., Draves, R., and S. Krishnan, "Privacy                 Extensions for Stateless Address Autoconfiguration in                 IPv6",RFC 4941, September 2007.   [RFC4960]     Stewart, R., "Stream Control Transmission Protocol",RFC 4960, September 2007.   [RFC5059]     Bhaskar, N., Gall, A., Lingard, J., and S. Venaas,                 "Bootstrap Router (BSR) Mechanism for Protocol                 Independent Multicast (PIM)",RFC 5059, January 2008.   [RFC5061]     Stewart, R., Xie, Q., Tuexen, M., Maruyama, S., and M.                 Kozuka, "Stream Control Transmission Protocol (SCTP)                 Dynamic Address Reconfiguration",RFC 5061,                 September 2007.   [RFC5072]     S.Varada, Haskins, D., and E. Allen, "IP Version 6 over                 PPP",RFC 5072, September 2007.   [RFC5280]     Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,                 Housley, R., and W. Polk, "Internet X.509 Public Key                 Infrastructure Certificate and Certificate Revocation                 List (CRL) Profile",RFC 5280, May 2008.   [RFC5533]     Nordmark, E. and M. Bagnulo, "Shim6: Level 3                 Multihoming Shim Protocol for IPv6",RFC 5533,                 June 2009.   [RFC5558]     Templin, F., "Virtual Enterprise Traversal (VET)",RFC 5558, February 2010.   [SCTPNAT]     Xie, Q., Stewart, R., Holdrege, M., and M. Tuexen,                 "SCTP NAT Traversal Considerations", Work in Progress,                 November 2007.Carpenter, et al.             Informational                    [Page 32]

RFC 5887              Renumbering Still Needs Work              May 2010   [SIX-ONE]     Vogt, C., "Six/One: A Solution for Routing and                 Addressing in IPv6", Work in Progress, October 2009.   [THINK]       Chown, T., "Things to think about when Renumbering an                 IPv6 network", Work in Progress, September 2006.Carpenter, et al.             Informational                    [Page 33]

RFC 5887              Renumbering Still Needs Work              May 2010Appendix A.  Embedded IP Addresses   This Appendix lists common places where IP addresses might be   embedded.  The list was adapted from [THINK].      Provider based prefix(es)      Names resolved to IP addresses in firewall at startup time      IP addresses in remote firewalls allowing access to remote      services      IP-based authentication in remote systems allowing access to      online bibliographic resources      IP address of both tunnel end points for IPv6 in IPv4 tunnel      Hard-coded IP subnet configuration information      IP addresses for static route targets      Blocked SMTP server IP list (spam sources)      Web .htaccess and remote access controls      Apache .Listen. directive on given IP address      Configured multicast rendezvous point      TCP wrapper files      Samba configuration files      DNS resolv.conf on Unix      Any network traffic monitoring tool      NIS/ypbind via the hosts file      Some interface configurations      Unix portmap security masks      NIS security masks      PIM-SM Rendezvous Point address on multicast routersCarpenter, et al.             Informational                    [Page 34]

RFC 5887              Renumbering Still Needs Work              May 2010Authors' Addresses   Brian Carpenter   Department of Computer Science   University of Auckland   PB 92019   Auckland  1142   New Zealand   EMail: brian.e.carpenter@gmail.com   Randall Atkinson   Extreme Networks   PO Box 14129   Suite 100, 3306 East NC Highway 54   Research Triangle Park, NC  27709   USA   EMail: rja@extremenetworks.com   Hannu Flinck   Nokia Siemens Networks   Linnoitustie 6   Espoo  02600   Finland   EMail: hannu.flinck@nsn.comCarpenter, et al.             Informational                    [Page 35]