DNA WG JinHyeock Choi Internet-Draft Samsung AIT Expires: December 10, 2004 Greg Daley CTIE Monash University June 11, 2004 Detecting Network Attachment in IPv6 Goals draft-ietf-dna-goals-00.txt Status of this Memo By submitting this Internet-Draft, I certify that any applicable patent or other IPR claims of which I am aware have been disclosed, and any of which I become aware will be disclosed, in accordance with RFC 3668. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on December 10, 2004. Copyright Notice Copyright (C) The Internet Society (2004). All Rights Reserved. Abstract At the time 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 or not. While checking for link change, the host may also collect necessary information to initiate a new IP configuration for the case that the IP subnet has changed. In this memo, this procedure is called Choi & Daley Expires December 10, 2004 [Page 1] Internet-Draft DNA Goals June 2004 Detecting Network Attachment (DNA). Rapid attachment detection is required when a host has on-going data traffic. Current DNA schemes are inadequate to support real-time applications. The existing procedures for advertising network information incur reception delays and do not provide enough information to properly determine the identity of links. For to-be-defined, efficient DNA schemes, a way to correctly represent a link change, a complete and consistent procedure for network information advertisement and a rapid delivery of the advertisements will be necessary. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Detecting Network Attachment in Existing IPv6 Systems . . . . 5 3. Problems in Detecting Network Attachment . . . . . . . . . . . 7 3.1 Wireless link properties . . . . . . . . . . . . . . . . . 7 3.2 Inadequacies in RA information . . . . . . . . . . . . . . 7 3.3 Delays . . . . . . . . . . . . . . . . . . . . . . . . . . 8 4. Goals for Detecting Network Attachment . . . . . . . . . . . . 10 4.1 Goals list . . . . . . . . . . . . . . . . . . . . . . . . 10 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 6. Security Considerations . . . . . . . . . . . . . . . . . . . 13 7. Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . 14 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15 8.1 Normative References . . . . . . . . . . . . . . . . . . . . 15 8.2 Informative References . . . . . . . . . . . . . . . . . . . 15 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 16 Intellectual Property and Copyright Statements . . . . . . . . 17 Choi & Daley Expires December 10, 2004 [Page 2] Internet-Draft DNA Goals June 2004 1. Introduction When a host has established a new link-layer connection, it can send and receive some IP packets at the link, particularly those used for configuration. On the other hand, the host has full Internet connectivity only when it is able to exchange packets with arbitrary destinations. When a link-layer connection is established or re-established, the host doesn't know whether its existing IP configuration is still valid for Internet connectivity. A subnet change might have occurred when the host changed its attachment point. In practice, the host doesn't know which of its addresses are valid on the newly attached link. A host knows neither if its existing default router is on this link, nor whether its neighbor cache entries are valid. Correct configuration of each of these components are necessary in order to send packets on and off the link. While other information for IP connectivity (such as DNS server configuration) is also important, obtaining most of such information depends on the determination of correct global addressing and valid default router configuration. Hence, to determine the need of a further configuration, a host needs to check at least that: 1) Whether it knows a (partially) reachable default router. 2) Whether it possesses a valid IP address. Partial reachability indicates that the host is able to receive packets from the router, but not necessarily vice versa. To examine the status of the existing configuration, a host may check whether a 'link change' has occurred. Today a link change necessitates an IP configuration change. Whenever the 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. Hence a host only needs to check for link change to examine the validity of its IP configuration. In the process of checking for link change, a host may collect some of the necessary information for a new IP configuration, for example on-link prefixes. So, when an IP subnet change has occurred, a host can immediately initiate the process of getting a new IP configuration. This may reduce handoff delay and minimize signaling. Choi & Daley Expires December 10, 2004 [Page 3] Internet-Draft DNA Goals June 2004 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. The process by which a host collects the appropriate information, detects the identity of its currently attached link, and ascertains the validity of its IP configuration, is called Detecting Network Attachment (DNA). 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. Choi & Daley Expires December 10, 2004 [Page 4] Internet-Draft DNA Goals June 2004 2. Detecting Network Attachment in Existing IPv6 Systems When a host changes its attachment point, for efficiency, a host should examine whether its IP configuration is still valid before initiating the process of acquiring a new IP configuration. DNA process aims to examine whether a host's current IP configuration is still valid. To achieve this goal, DNA process checks whether the host is still at the same link. Also, DNA process collects necessary information for a new IP configuration. For this, the following mechanisms and data are available to hosts: 1) Router Solicitation/Router Advertisement (RS/RA) messages 2) Neighbor Solicitation/Neighbor Advertisement (NS/NA) messages 3) Information provided by the link-layer Currently there is no way to represent the identity of links such that link changes can be detected instantly. The information in the above messages cannot be used to unambiguously identify links. Section 3 gives the detail. Though the set of all the assigned prefixes may be used to represent a link identity, it is difficult for a host to attain and retain all the prefixes with certainty. Moreover there may be links without any advertised prefix. Hence, to check for link change, as of today, a host must resort to guessing, based on Router Discovery and Neighbor Unreachability Detection (NUD). A host can examines whether 1) its existing default router is still reachable and 2) its IP addresses are still valid. After a network attachment, a host receives new (solicited or unsolicited) RAs and compares them with the previously received ones. It checks whether the information in the new RAs, the prefixes and the router addresses, matches with the stored ones, the configured IP addresses and the default router addresses. If Router Discovery fails to update the existing router's information, it indicates that the router is unreachable and should not be used. For Internet connectivity, a host needs to have an IP address whose prefix is assigned on the current link. To check the validity of its IP addresses, a host examines whether the prefix of its IP addresses are present in the Prefix Information Option of received RAs. Even if an address prefix is valid, an individual address is known to Choi & Daley Expires December 10, 2004 [Page 5] Internet-Draft DNA Goals June 2004 be valid only after the Duplicate Address Detection (DAD) procedure [5] has been completed. If RAs indicate that a subnet change has occured, the invalidity of other IP subnet information is implied. At the same time, from the received RAs, a host may collect some of the necessary information for a new configuration: a prefix to form a new IP address and router addresses to select a new default router. For rapid attachment detection, it is necessary for a host to receive an RA quickly enough. A host may also use NS/NA exchange to examine the reachability of the existing default router. Upon detecting a new link-layer connection, the host may probe the router with an NS message. If it receives an appropriate NA message, the router is still reachable. Otherwise, if the host receives no replies to Neighbor Solicitations, it may assume that its default router is no longer reachable. If a host receives a message from a router with which it has previously been able to exchange packets, then the Neighbor Discovery procedure may be used to establish full bi-directional reachability. In some environments, link-layer information regarding IP connectivity may be considered as a strong hint that change of link-layer attachment implies change of IP subnet. While this is sometimes the case, not all IP implementations at the network layer will be able to understand the indication from the link-layers, nor will those indications necessarily be always sufficient to make a proper decision. If the information from the link layer is available, but it is not considered authoritative, the information may still be used as a 'Link-layer hint'. Link-layer hints are indications from lower layers that IP connectivity may have changed. With suitable hysteresis, these hints may be used to initiate IP based reachability checks. Choi & Daley Expires December 10, 2004 [Page 6] Internet-Draft DNA Goals June 2004 3. Problems in Detecting Network Attachment There are a number of issues that make DNA complicated. First, wireless connectivity is not as clear-cut as wired one. Second the information contained in RA messages is not adequate for efficient DNA. Third, Router Discovery or NUD may take too long and result in service disruption. 3.1 Wireless link properties 1) Unclear boundary Unlike wired environments, what constitutes wireless link is variable in both time and space. It doesn't have clear boundaries. This may be illustrated by the fact that a host may contact multiple (802.11) access points at the same time. Moreover reachability on a wireless link is very volatile, which may make link detection hard. 2) Asymmetric reachability In some wireless environments, it may be possible to receive periodically multicast advertisement information without being able to send IP packets to the network. In these cases, it is insufficient to rely upon reception of unsolicited advertisement information as confirmation of router reachability. 3.2 Inadequacies in RA information Usually a host receives the information necessary for IP configuration from RA messages. Based on the current definition [4], the information contained in RA messages is inadequate to represent a link change. RA messages are not designed to represent link identities and have inherent ambiguities. 1) Link local scope of Router Address Usually a router address is contained in the source address field of RA messages. That router address is link-local scope and its uniqueness can't be guaranteed out side of a link. So if it happens that two different router interfaces have the same link-local address, a host can't detect that it has moved from one interface to another by checking the router address in RA messages. On the other hand, a host can't be sure that its default router is reachable, even if it can communicate with the router that has the same address as its existing router address. That router may be a different one, which happens to have the same link-local address as Choi & Daley Expires December 10, 2004 [Page 7] Internet-Draft DNA Goals June 2004 its default router address. 2) Omission of Prefix Information Option To check the validity of its IP address, a host should examine whether the prefix of its IP address is advertised on the link to which it is currently attached. The host checks whether the prefix of its IP addresses are present in the Prefix Information Option of incoming RA messages. But an unsolicited RA message can omit some prefixes for convenience, for example to save bandwidth [4]. Hence, the host can't be sure that the prefix of its current IP address is not supported on the current link, even though the prefix is not contained in a received RA. 3.3 Delays The following issues cause DNA delay that may result in communication disruption. 1) Delay for receiving a hint For rapid attachment detection, hints can be used to tell a host that a link change might have happened. This hint itself doesn't confirm a link change, but can be used to initiate the appropriate procedures. Hints come in various forms, and differ in how they indicate a new attachment. They can be link-layer indications, 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 a new network attachment as a hint for a possible link change. With link-layer support, a host can receive a hint almost instantly. [9] defines the use of RA Interval Timer expiry for a hint. A host keeps monitoring periodic RAs and interprets the lack of them as a hint. It may implement its own policy to determine the number of missing RAs for a hint. Hence the delay depends on the Router Advertisement interval. Without the schemes such as above, a host must receive a new RA from a new router to detect a possible link change. The detection time Choi & Daley Expires December 10, 2004 [Page 8] Internet-Draft DNA Goals June 2004 then also depends on the Router advertisement frequency. 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, the host is expected to arrive on average half way through the interval. This is approximately 1.75 seconds with [4] advertisement rates. 2) Delay for checking current default router Unreachability When a host examines the reachability of the current default router, a certain delay occurs if the current default router is not reachable. Usually it's easier to detect a node's presence than its absence. A host sends a solicitation message and, upon the receipt of a reply, it can assume that it's there. To be sure that a node is absent, time needs to be taken to ensure that the lack of a reply is not due to another reasons (for example, packet loss, MAC latency, or processing delay). So it takes time to verify the unreachability of the current router. After a host moves to another link, if it uses NUD for detection, it will take more than 3 seconds to recognize that the current router is no longer reachable [4]. 3) Random delay execution for RS/ RA exchange Router Solicitation and Router Advertisement messages are used for Router Discovery. According to [4], it is sometimes necessary for a host to wait a random amount of time to send an RS and for a router to wait to reply an RA. 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). Also Router Advertisements sent in response to a Router Solicitation MUST be delayed by a random time between 0 and MAX_RA_DELAY_TIME (0.5 seconds). Choi & Daley Expires December 10, 2004 [Page 9] Internet-Draft DNA Goals June 2004 4. Goals for Detecting Network Attachment DNA solutions should be 1) Precise, 2) Sufficiently fast and 3) Of limited signaling. The solutions should correctly determine whether a link change has occurred. They also should be sufficiently fast lest there should be service disruption. They should not flood the link with related signaling. It will be necessary to investigate the usage of available tools, NS/ NA messages, RS/RA messages, link-layer hints and other features. This will allow precise description of procedures for efficient DNA Schemes. 4.1 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 When upper-layer protocol sessions are being supported, DNA schemes should detect the identity of an attached link rapidly, with minimal latency. G3 In the case where a host has not changed a link or subnet, 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), since 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 Neighbour Discovery [8] and IPSec [7]. G8 A host configured for DNA should not expose itself to additional man in the middle or identity revealing attacks. G9 A host or router configured for DNA should not expose itself or other devices on the link to additional denial of service attacks. Choi & Daley Expires December 10, 2004 [Page 10] Internet-Draft DNA Goals June 2004 G10 The Routers supporting DNA should work appropriately with hosts using unmodified configuration schemes, such as [4] and [6]. G11 The Hosts supporting DNA should be able to work with unmodified routers and hosts which do not support DNA schemes. Choi & Daley Expires December 10, 2004 [Page 11] Internet-Draft DNA Goals June 2004 5. IANA Considerations No new message formats or services are defined in this document. Choi & Daley Expires December 10, 2004 [Page 12] Internet-Draft DNA Goals June 2004 6. Security Considerations Because DNA schemes are based on Neighbor Discovery, its trust models and threats are similar to the ones presented in [10]. Nodes connected over wireless interfaces may be particularly susceptible to jamming, monitoring and packet insertion attacks. Use of [8] to secure Neighbor Discovery are important in achieving reliable detection of network attachment. DNA schemes SHOULD incorporate the solutions developed in IETF SEND WG if available, where assessment indicates such procedures are required. 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, such reachability tests, even if known to originate from a trusted source should be ignored for reachability confirmation if duplicates or stale. This may reduce the effective window for attackers replaying otherwise authentic data. It may be dangerous to receive link-change indications from link-layer and network-layer, if they are received from devices which are insufficiently authenticated. In particular, indications 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. Choi & Daley Expires December 10, 2004 [Page 13] Internet-Draft DNA Goals June 2004 7. Acknowledgment Erik Nordmark has contributed significantly [11] to work predating this draft. 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 and Alper Yegin for their contributions to this draft. Choi & Daley Expires December 10, 2004 [Page 14] Internet-Draft DNA Goals June 2004 8. References 8.1 Normative References [1] Bradner, S., "IETF Rights in Contributions", BCP 78, RFC 3667, February 2004. [2] Bradner, S., "Intellectual Property Rights in IETF Technology", BCP 79, RFC 3668, February 2004. [3] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [4] Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery for IP Version 6 (IPv6)", RFC 2461, December 1998. [5] Thomson, S. and T. Narten, "IPv6 Stateless Address Autoconfiguration", RFC 2462, December 1998. [6] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C. and M. Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3315, July 2003. [7] Thayer, R., Doraswamy, N. and R. Glenn, "IP Security Document Roadmap", RFC 2411, November 1998. [8] Arkko, J., Kempf, J., Sommerfeld, B., Zill, B. and P. Nikander, "SEcure Neighbor Discovery (SEND)", draft-ietf-send-ndopt-05 (work in progress), April 2004. 8.2 Informative References [9] Johnson, D., Perkins, C. and J. Arkko, "Mobility Support in IPv6", RFC 3775, June 2004. [10] Nikander, P., Kempf, J. and E. Nordmark, "IPv6 Neighbor Discovery (ND) Trust Models and Threats", RFC 3756, May 2004. [11] Nordmark, E., "MIPv6: from hindsight to foresight?", draft-nordmark-mobileip-mipv6-hindsight-00 (work in progress), November 2001. Choi & Daley Expires December 10, 2004 [Page 15] Internet-Draft DNA Goals June 2004 Authors' Addresses JinHyeock Choi Samsung AIT i-Networking 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.au Choi & Daley Expires December 10, 2004 [Page 16] Internet-Draft DNA Goals June 2004 Intellectual Property Statement 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 in BCP 78 and BCP 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 at http://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. Disclaimer of Validity 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. Copyright Statement Copyright (C) The Internet Society (2004). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Choi & Daley Expires December 10, 2004 [Page 17]