Movatterモバイル変換

Network Working Group                                           JH. ChoiRequest for Comments: 4135                                   Samsung AITCategory: Informational                                         G. Daley                                                  CTIE Monash University                                                             August 2005Goals of Detecting Network Attachment in IPv6Status of This Memo   This memo provides information for the Internet community.  It does   not specify an Internet standard of any kind.  Distribution of this   memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2005).Abstract   When a host establishes a new link-layer connection, it may or may   not have a valid IP configuration for Internet connectivity.  The   host may check for link change (i.e., determine whether a link change   has occurred), and then, based on the result, it can automatically   decide whether its IP configuration is still valid.  During link   identity detection, the host may also collect necessary information   to initiate a new IP configuration if the IP subnet has changed.  In   this memo, this procedure is called Detecting Network Attachment   (DNA).  DNA schemes should be precise, sufficiently fast, secure, and   of limited signaling.Table of Contents1. Introduction ....................................................22. Problems in Detecting Network Attachment ........................32.1. Wireless Link Properties ...................................32.2. Link Identity Detection with a Single RA ...................32.3. Delays .....................................................43. Goals for Detecting Network Attachment ..........................53.1. Goals List .................................................64. Security Considerations .........................................65. Acknowledgements ................................................76. References ......................................................86.1. Normative References .......................................86.2. Informative References .....................................8Choi & Daley                 Informational                      [Page 1]

RFC 4135                       DNA Goals                     August 20051.  Introduction   When a host has established a new link-layer connection, it can send   and receive some IPv6 packets on the link, including those used for   configuration.  On the other hand, the host has Internet connectivity   only when it is able to exchange packets with off-link destinations.   When a link-layer connection is established or re-established, the   host may not know whether its existing IP configuration is still   valid for Internet connectivity.  A subnet change might have occurred   when the host changed its point of attachment.   In practice, the host doesn't know which of its addresses are valid   on the newly attached link.  It also doesn't know whether its   existing default router is on this link or whether its neighbor cache   entries are valid.  Correct configuration of each of these components   is necessary in order to send packets on and off the link.   To examine the status of the existing configuration, a host may check   whether a 'link change' has occurred.  In this document, the term   'link' is as defined inRFC 2461 [1].  The notion 'link' is not   identical with the notion 'subnet', as defined inRFC 3753 [2].  For   example, there may be more than one subnet on a link, and a host   connected to a link may be part of one or more of the subnets on the   link.   Today, a link change necessitates an IP configuration change.   Whenever a host detects that it has remained at the same link, it can   usually assume its IP configuration is still valid.  Otherwise, the   existing one is no longer valid, and a new configuration must be   acquired.  Therefore, to examine the validity of an IP configuration,   all that is required is that the host checks for link change.   In the process of checking for link change, a host may collect some   of the necessary information for a new IP configuration, such as on-   link prefixes.  So, when an IP subnet change has occurred, the host   can immediately initiate the process of getting a new IP   configuration.  This may reduce handoff delay and minimize signaling.   Rapid attachment detection is required for a device that changes   subnet while having on-going sessions.  This may be the case if a   host is connected intermittently, is a mobile node, or has urgent   data to transmit upon attachment to a link.   Detecting Network Attachment (DNA) is the process by which a host   collects the appropriate information and detects the identity of its   currently attached link to ascertain the validity of its IP   configuration.Choi & Daley                 Informational                      [Page 2]

RFC 4135                       DNA Goals                     August 2005   DNA schemes are typically run per interface.  When a host has   multiple interfaces, the host separately checks for link changes on   each interface.   It is important to note that DNA process does not include the actual   IP configuration procedure.  For example, with respect to DHCP, the   DNA process may determine that the host needs to get some   configuration information from a DHCP server.  However, the process   of actually retrieving the information from a DHCP server falls   beyond the scope of DNA.   This document considers the DNA procedure only from the IPv6 point of   view, unless explicitly mentioned otherwise.  Thus, the term "IP" is   to be understood to denote IPv6, by default.  For the IPv4 case,   refer to [7].2.  Problems in Detecting Network Attachment   A number of issues make DNA complicated.  First, wireless   connectivity is not as clear-cut as wired connectivity.  Second, it's   difficult for a single Router Advertisement (RA) message to indicate   a link change.  Third, the current Router Discovery specification   specifies that routers wait a random delay of 0-.5 seconds prior to   responding with a solicited RA.  This delay can be significant and   may result in service disruption.2.1.  Wireless Link Properties   Unlike in wired environments, what constitutes a wireless link is   variable both in time and space.  Wireless links do not have clear   boundaries.  This may be illustrated by the fact that a host may be   within the coverage area of multiple (802.11) access points at the   same time.  Moreover, connectivity on a wireless link can be very   volatile, which may make link identity detection hard.  For example,   it takes time for a host to check for link change.  If the host   ping-pongs between two links and doesn't stay long enough at a given   link, it can't complete the DNA procedure.2.2.  Link Identity Detection with a Single RA   Usually, a host gets the information necessary for IP configuration   from RA messages.  Based on the current definition [1], it's   difficult for a host to check for link change upon receipt of a   single RA.   To detect link identity, a host may compare the information in an RA,   such as router address or prefixes, with the locally stored   information.Choi & Daley                 Informational                      [Page 3]

RFC 4135                       DNA Goals                     August 2005   The host may use received router addresses to check for link change.   The router address in the source address field of an RA is of link-   local scope, however, so its uniqueness is not guaranteed outside a   link.  If it happens that two different router interfaces on   different links have the same link-local address, the host can't   detect that it has moved from one link to another by checking the   router address in RA messages.   The set of all global prefixes assigned to a link can represent link   identity.  The host may compare the prefixes in an incoming RA with   the currently stored ones.  An unsolicited RA message, however, can   omit some prefixes for convenience [1], and it's not easy for a host   to attain and retain all the prefixes on a link with certainty.   Therefore, neither the absence of a previously known prefix nor the   presence of a previously unknown prefix in the RA guarantees that a   link change has occurred.2.3.  Delays   The following issues cause DNA delay that may result in communication   disruption.   1) Delay for receiving a hint   A hint is an indication that a link change might have occurred.  This   hint itself doesn't confirm a link change, but initiates appropriate   DNA procedures to detect the identity of the currently attached link.   Hints come in various forms and differ in how they indicate a   possible link change.  They can be link-layer event notifications   [6], the lack of RA from the default router, or the receipt of a new   RA.  The time taken to receive a hint also varies.   As soon as a new link-layer connection has been made, the link layer   may send a link-up notification to the IP layer.  A host may   interpret the new link-layer connection as a hint for a possible link   change.  With link-layer support, a host can receive such a hint   almost instantly.   Mobile IPv6 [4] defines the use of RA Interval Timer expiry for a   hint.  A host keeps monitoring for periodic RAs and interprets the   lack of them as a hint.  It may implement its own policy to determine   the number of missing RAs needed to interpret that as a hint.  Thus,   the delay depends on the Router Advertisement interval.   Without schemes such as those above, a host must receive a new RA   from a new router to detect a possible link change.  The detection   time then also depends on the Router Advertisement frequency.Choi & Daley                 Informational                      [Page 4]

RFC 4135                       DNA Goals                     August 2005   Periodic RA beaconing transmits packets within an interval varying   randomly between MinRtrAdvInterval to MaxRtrAdvInterval seconds.   Because a network attachment is unrelated to the advertisement time   on the new link, hosts are expected to arrive, on average, halfway   through the interval.  This is approximately 1.75 seconds with   Neighbor Discovery [1] advertisement rates.   2) Random delay execution for RS/RA exchange   Router Solicitation and Router Advertisement messages are used for   Router Discovery.  According to [1], it is sometimes necessary for a   host to wait a random amount of time before it may send an RS, and   for a router to wait before it may reply with an RA.   According toRFC 2461 [1], the following apply:   -  Before a host sends an initial solicitation, it SHOULD delay the      transmission for a random amount of time between 0 and      MAX_RTR_SOLICITATION_DELAY (1 second).   -  Furthermore, any RA sent in response to a Router Solicitation MUST      be delayed by a random time between 0 and MAX_RA_DELAY_TIME (0.5      seconds).3.  Goals for Detecting Network Attachment   The DNA working group has been chartered to define an improved scheme   for detecting IPv6 network attachment.  In this section, we define   the goals that any such solution should aim to fulfill.   DNA solutions should correctly determine whether a link change has   occurred.  Additionally, they should be sufficiently fast so that   there would be no or at most minimal service disruption.  They should   neither flood the link with related signaling nor introduce new   security holes.   When defining new solutions, it is necessary to investigate the usage   of available tools, Neighbor Solicitation/Neighbor Advertisement   messages, RS/RA messages, link-layer event notifications [6], and   other features.  This will allow precise description of procedures   for efficient DNA Schemes.Choi & Daley                 Informational                      [Page 5]

RFC 4135                       DNA Goals                     August 20053.1.  Goals List   G1  DNA schemes should detect the identity of the currently attached       link to ascertain the validity of the existing IP configuration.       They should recognize and determine whether a link change has       occurred and initiate the process of acquiring a new       configuration if necessary.   G2  DNA schemes should detect the identity of an attached link with       minimal latency lest there should be service disruption.   G3  If a host has not changed a link, DNA schemes should not falsely       assume a link change, and an IP configuration change should not       occur.   G4  DNA schemes should not cause undue signaling on a link.   G5  DNA schemes should make use of existing signaling mechanisms       where available.   G6  DNA schemes should make use of signaling within the link       (particularly link-local scope messages), because communication       off-link may not be achievable in the case of a link change.   G7  DNA schemes should be compatible with security schemes such as       Secure Neighbor Discovery [3].   G8  DNA schemes should not introduce new security vulnerabilities.       The node supporting DNA schemes should not expose itself or other       nodes on a link to additional man-in-the-middle, identity-       revealing, or denial-of-service attacks.   G9  Nodes (such as routers or hosts) that support DNA schemes should       work appropriately with unmodified nodes that do not.   G10 Hosts, especially in wireless environments, may perceive routers       reachable on different links.  DNA schemes should take into       consideration the case where a host is attached to more than one       link at the same time.4.  Security Considerations   The DNA process is intimately related to the Neighbor Discovery   protocol [1] and its trust model and threats have much in common with   those presented inRFC 3756 [5].  Nodes connected over wireless   interfaces may be particularly susceptible to jamming, monitoring,   and packet-insertion attacks.Choi & Daley                 Informational                      [Page 6]

RFC 4135                       DNA Goals                     August 2005   With unsecured DNA schemes, it is inadvisable for a host to adjust   its security based on which network it believes it is attached to.   For example, it would be inappropriate for a host to disable its   personal firewall because it believed that it had connected to a home   network.   Even in the case where authoritative information (routing and prefix   state) are advertised, wireless network attackers may still prevent   soliciting nodes from receiving packets.  This may cause unnecessary   IP configuration change in some devices.  Such attacks may be used to   make a host preferentially select a particular configuration or   network access.   Devices receiving confirmations of reachability (for example, from   upper-layer protocols) should be aware that unless these indications   are sufficiently authenticated, reachability may falsely be asserted   by an attacker.  Similarly, even if such reachability tests are known   to originate from a trusted source, they should be ignored for   reachability confirmation if the packets are not fresh or have been   replayed.  This may reduce the effective window for attackers   replaying otherwise authentic data.   It may be dangerous to receive link-change notifications from the   link layer and network layer, if they are received from devices that   are insufficiently authenticated.  In particular, notifications that   authentication has completed at the link layer may not imply that a   security relationship is available at the network layer.  Additional   authentication may be required at the network layer to justify   modification of IP configuration.5.  Acknowledgements   Erik Nordmark has contributed significantly to work predating this   document.  Also Ed Remmell's comments on the inconsistency of RA   information were most illuminating.  The authors wish to express our   appreciation to Pekka Nikander for valuable feedback.  We gratefully   acknowledge the generous assistance we received from Shubhranshu   Singh for clarifying the structure of the arguments.  Thanks to Brett   Pentland, Nick Moore, Youn-Hee Han, JaeHoon Kim, Alper Yegin, Jim   Bound, and Jari Arkko for their contributions to this document.Choi & Daley                 Informational                      [Page 7]

RFC 4135                       DNA Goals                     August 20056.  References6.1.  Normative References   [1]  Narten, T., Nordmark, E., and W. Simpson, "Neighbor Discovery        for IP Version 6 (IPv6)",RFC 2461, December 1998.   [2]  Manner, J. and M. Kojo, "Mobility Related Terminology",RFC3753, June 2004.   [3]  Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure        Neighbor Discovery (SEND)",RFC 3971, March 2005.6.2.  Informative References   [4]  Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in        IPv6",RFC 3775, June 2004.   [5]  Nikander, P., Kempf, J., and E. Nordmark, "IPv6 Neighbor        Discovery (ND) Trust Models and Threats",RFC 3756, May 2004.   [6]  Yegin, A., "Link-layer Event Notifications for Detecting Network        Attachments", work in progress, July 2005.   [7]  Aboba, B., "Detecting Network Attachment (DNA) in IPv4", work in        progress, June 2005.Authors' Addresses   JinHyeock Choi   Samsung AIT   Communication & N/W Lab   P.O.Box 111 Suwon 440-600   KOREA   Phone: +82 31 280 9233   EMail: jinchoe@samsung.com   Greg Daley   CTIE Monash University   Centre for Telecommunications and Information Engineering   Monash University   Clayton 3800 Victoria   Australia   Phone: +61 3 9905 4655   EMail: greg.daley@eng.monash.edu.auChoi & Daley                 Informational                      [Page 8]

RFC 4135                       DNA Goals                     August 2005Full Copyright Statement   Copyright (C) The Internet Society (2005).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   This document and the information contained herein are provided on an   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the procedures with respect to rights in RFC documents can be   found inBCP 78 andBCP 79.   Copies of IPR disclosures made to the IETF Secretariat and any   assurances of licenses to be made available, or the result of an   attempt made to obtain a general license or permission for the use of   such proprietary rights by implementers or users of this   specification can be obtained from the IETF on-line IPR repository athttp://www.ietf.org/ipr.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights that may cover technology that may be required to implement   this standard.  Please address the information to the IETF at ietf-   ipr@ietf.org.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Choi & Daley                 Informational                      [Page 9]