V6OPS B. Liu Internet-Draft S. Jiang Intended status: Informational Huawei Technologies Expires: November 3, 2015 X. Gong W. Wang BUPT University May 2, 2015 DHCPv6/SLAAC Interaction Problems on Address Auto-configuration draft-ietf-v6ops-dhcpv6-slaac-problem-04 Abstract The IPv6 Neighbor Discovery (ND) Protocol includes an ICMPv6 Router Advertisement (RA) message. The RA message contains three flags, indicating which auto-configuration mechanisms are available to on- link hosts. These are the M, O and A flags. The M and O flags are advisory, not prescriptive. This document describes divergent host behaviors observed in popular operating systems. It also describes operational problems that divergent behaviors might cause. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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." This Internet-Draft will expire on November 3, 2015. Copyright Notice Copyright (c) 2015 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents Liu, et al. Expires November 3, 2015 [Page 1] Internet-Draft draft-ietf-v6ops-dhcpv6-slaac-problem-04 May 2015 (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. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. The M, O and A Flags . . . . . . . . . . . . . . . . . . . . 3 2.1. M (Managed) Flag . . . . . . . . . . . . . . . . . . . . 3 2.2. O (Otherconfig) Flag . . . . . . . . . . . . . . . . . . 4 2.3. A (Autonomous) Flag . . . . . . . . . . . . . . . . . . . 4 3. Behavior Ambiguity Analysis . . . . . . . . . . . . . . . . . 4 4. Observed Divergent Host Behaviors . . . . . . . . . . . . . . 5 5. Operational Problems . . . . . . . . . . . . . . . . . . . . 6 5.1. Inappropriate Sources . . . . . . . . . . . . . . . . . . 6 5.2. Renumbering Issues . . . . . . . . . . . . . . . . . . . 6 6. Security Considerations . . . . . . . . . . . . . . . . . . . 7 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 9.1. Normative References . . . . . . . . . . . . . . . . . . 8 9.2. Informative References . . . . . . . . . . . . . . . . . 8 Appendix A. Test Results . . . . . . . . . . . . . . . . . . . . 8 A.1. Test Environment . . . . . . . . . . . . . . . . . . . . 8 A.2. Host Behavior in the Initial State . . . . . . . . . . . 9 A.3. Host Behavior in State Transitions . . . . . . . . . . . 11 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 1. Introduction IPv6 [RFC2460] hosts invoke Neighbor Discovery (ND) [RFC4861] procedures in order to discover which auto-configuration mechanisms are available to them. The following is a list of auto-configuration mechanisms: o DHCPv6 [RFC3315] o Stateless Address Autoconfiguration (SLAAC) [RFC4862] ND specifies an ICMPv6 [RFC4443] Router Advertisement (RA) message. Routers periodically broadcast the RA message to all on-link nodes. They also unicast RA messages in response to solicitations. The RA message contains: Liu, et al. Expires November 3, 2015 [Page 2] Internet-Draft draft-ietf-v6ops-dhcpv6-slaac-problem-04 May 2015 o an M (Managed) flag o an O (OtherConfig) flag o zero or more Prefix Information (PI) Options The M flag indicates that addresses are available from DHCPv6. The O flag indicates that other configuration information (e.g., DNS- related information) is available from DHCPv6. The PI Option includes a prefix, an A (Autonomous) flag and other fields. The A flag indicates that the prefix can be used for SLAAC. The M and O flags are advisory, not prescriptive (although A flag is also advisory in definition in standard, it is quite prescriptive in implementations). For example, the M flag indicates that addresses are available from DHCPv6. It does not indicate that hosts are required to acquire addresses from DHCPv6. Similar statements can be made about the O flag. Because of the advisory definition of the flags, in some cases different operating systems appear divergent behaviors. This document analyzes possible divergent host behaviors might happen (some of the possible divergent behaviors are already observed in popular operating systems) and the operational problems might caused by divergent behaviors. 2. The M, O and A Flags This section briefly reviews how the M, O and A flags are defined in [RFC4861]. 2.1. M (Managed) Flag The M flag indicates that addresses are available from DHCPv6. If the M flag is set, the O flag is redundant and can be ignored because DHCPv6 will return all available configuration information. M and A flag semantics are independent of one another. The M flag indicates that addresses are available from DHCPv6, regardless of the A flag setting. The following settings are all allowed: o M=0 A=0 o M=0 A=1 o M=1 A=0 o M=1 A=1 Liu, et al. Expires November 3, 2015 [Page 3] Internet-Draft draft-ietf-v6ops-dhcpv6-slaac-problem-04 May 2015 2.2. O (Otherconfig) Flag The O flag indicates that other configuration information (e.g., DNS- related information) is available from DHCPv6. If the M flag is set, the O flag is redundant and can be ignored because DHCPv6 will return all available configuration information. O and A flag semantics are independent of one another. The O flag indicates that other configuration is available from DHCPv6, regardless of the A flag setting. The following settings are all allowed: o O=0 A=0 o O=0 A=1 o O=1 A=0 o O=1 A=1 2.3. A (Autonomous) Flag The A flag indicates that the prefix that is also carried by the PI option can be used for SLAAC. A flag semantics are independent of M and O flag semantics. The A flag indicates that the prefix can be used by SLAAC, regardless of the M and O flag settings. 3. Behavior Ambiguity Analysis The flags definition ambiguity means, on interpreting the same messages, different hosts might behave differently. Thus it could be un-controlled or un-predictable for administrators on some operations. The ambiguity is summarized as the following aspects. 1) Dependency between DHCPv6 and RA In standards, behavior of DHCPv6 and Neighbor Discovery protocols is specified respectively. But it is not clear that whether there should be any dependency between them. More specifically, it is unclear whether RA (with M=1) is required to trigger DHCPv6; in other words, It is unclear whether hosts should initiate DHCPv6 by themselves If there are no RAs at all. 2) Interpretation on Flags Transition When flags are in transition, e.g. the host is already SLAAC- configured, then M flag changes from FALSE to TRUE, it is not clear whether the host should start DHCPv6 or not; or vise versa, Liu, et al. Expires November 3, 2015 [Page 4] Internet-Draft draft-ietf-v6ops-dhcpv6-slaac-problem-04 May 2015 the host is already both SLAAC/DHCPv6 configured, then M flag change from TRUE to FALSE, it is also not clear whether the host should turn DHCPv6 off or not. 3) Relationship between Address Configuring Method and Address Lifetime When one address configuration method is off, that is, the A flag or M flag changes from TRUE to FALSE, it is not clear whether the host should immediately release the corresponding address(es) or just retain it(them) until expired. 4) Dependencies between the Flags The semantics of the flags seems not totally independent, but the standards didn't clearly clarify it. For example, when both M and O flags are TRUE, it is not clear whether the host should initiate one stateful DHCPv6 session to get both address and info- configuration or initiate two independent sessions (one is dedicated for address configuration and the other is for information configuration). When A and M flags are FALSE and O flag is TRUE, it is not clear whether the host should initiate a stand-alone stateless DHCPv6 session. Divergent behaviors on all the four aspects have been observed among some popular operating systems as described in Section 4 below. 4. Observed Divergent Host Behaviors The authors tested several popular operating systems in order to determine what behaviors the M, O and A flag elicit. In some cases, the M, O and A flags elicit divergent behaviors. The table below characterizes those cases. For test details, please refer to Appendix A. Liu, et al. Expires November 3, 2015 [Page 5] Internet-Draft draft-ietf-v6ops-dhcpv6-slaac-problem-04 May 2015 Host State Input Behavior Host has not No RA Some popular operating systems acquire acquired any addresses from DHCPv6. Others do not. addresses Host has not RA Some popular operating systems acquire acquired any with other information from DHCPv6, regardless addresses M=0, of the A flag setting. Others do so, but O=1 only if A=1 Host has acquired RA Some operating systems release DHCPv6 addresses from with M addresses immediately. Some release DHCPv6 DHCPv6 only (M = =0 addresses when they expire. 1) Host has acquired RA Some operating systems acquire DHCPv6 addresses from with M addresses immediately. Others do so only if SLAAC only (A=1) = 1 their SLAAC addresses expire and cannot be refreshed. 5. Operational Problems This section describes operational issues caused by the divergent behaviors, described above. 5.1. Inappropriate Sources Some operating systems base their decision to acquire configuration information upon inappropriate sources. For example, some operating systems acquire other configuration information if M=0, O=1, and A=1, but not if M=0, O=1 and A=0. In other words, on some operating systems, it is impossible to acquire other information from DHCPv6 (stateless DHCPv6 configuration) unless addresses are acquired from either DHCPv6 or SLAAC. 5.2. Renumbering Issues According to [RFC6879] a renumbering exercise can include the following steps: o Causing hosts that have acquired addresses from one auto- configuration mechanism to release those addresses and acquire new addresses from another auto-configuration mechanism o Causing hosts that have acquired addresses from one auto- configuration mechanism to release those addresses and acquire new addresses from the same auto-configuration mechanism Liu, et al. Expires November 3, 2015 [Page 6] Internet-Draft draft-ietf-v6ops-dhcpv6-slaac-problem-04 May 2015 o Causing hosts that have acquired addresses from one auto- configuration mechanism to retain those addresses and acquire new addresses from another auto-configuration mechanism Ideally, these steps could be initiated by broadcasting RA message onto the subnetwork that is being renumbered. Sadly, this is not possible, because the RA message may elicit a different behavior from each host. According to Section 4, renumbering operations would have the following limitations: o When M flag is turned off, some operating systems release DHCPv6 acquired addresses immediately, while other will retain then until they expire. This means a flash switch from DHCPv6 to SLAAC would happen on some hosts. Normally, the "make-before-break" approach proposed in [RFC4192] is considered better than flash renumbering. o On some operating systems, if a host has acquired addresses from SLAAC, it is impossible to acquire additional addresses from DHCPv6. This may be required as part of a renumbering operation. 6. Security Considerations As this memo does not introduce any new protocols or procedures, it does not introduce any new security vulnerabilities. 7. IANA Considerations This draft does not request any IANA action. 8. Acknowledgements The authors wish to acknowledge BNRC-BUPT (Broad Network Research Centre in Beijing University of Posts and Telecommunications) for their testing efforts. Special thanks to Xudong Shi, Longyun Yuan and Xiaojian Xue for their extraordinary effort. Special thanks to Ron Bonica who made a lot of significant contribution to this draft, including draft editing and presentations which dramatically improved this work. The authors also wish to acknowledge Brian E Carpenter, Ran Atkinson, Mikael Abrahamsson, Tatuya Jinmei, Mark Andrews and Mark Smith for their helpful comments. Liu, et al. Expires November 3, 2015 [Page 7] Internet-Draft draft-ietf-v6ops-dhcpv6-slaac-problem-04 May 2015 9. References 9.1. Normative References [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998. [RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification", RFC 4443, March 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. 9.2. Informative References [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. [RFC3736] Droms, R., "Stateless Dynamic Host Configuration Protocol (DHCP) Service for IPv6", RFC 3736, April 2004. [RFC4192] Baker, F., Lear, E., and R. Droms, "Procedures for Renumbering an IPv6 Network without a Flag Day", RFC 4192, September 2005. [RFC6879] Jiang, S., Liu, B., and B. Carpenter, "IPv6 Enterprise Network Renumbering Scenarios, Considerations, and Methods", RFC 6879, February 2013. Appendix A. Test Results A.1. Test Environment Liu, et al. Expires November 3, 2015 [Page 8] Internet-Draft draft-ietf-v6ops-dhcpv6-slaac-problem-04 May 2015 /-----\ +---------+ // \\ | DHCPv6 | | Router | | server | \\ // +----+----+ \--+--/ | | | | | | ----+--+----------+----------+---+----- | | | | | | | | | +----+---+ +----+---+ +----+---+ | | | | | | | Host 1 | | Host 2 | | Host 3 | +--------+ +--------+ +--------+ Figure 1: Test Environment The test environment depicted Figure 1 in was replicated on a single server using VMware. For simplicity of operation, only one host was run at a time. Network elements were as follows: o Router: Quagga 0.99-19 soft router installed on Ubuntu 11.04 virtual host o DHCPv6 Server: Dibbler-server installed on Ubuntu 11.04 virtual host o Host 1: Window 7 / Window 8.1 Virtual Host o Host 2: Ubuntu 14.04 (Linux Kernel 3.12.0) Virtual Host o Host 3: Mac OS X v10.9 Virtual Host o Host 4: IOS 8.0 (model: Apple iPhone 5S, connected via wifi) A.2. Host Behavior in the Initial State The bullet list below describes host behavior in the initial state, when the host has not yet acquired any auto-configuration information. Each bullet item represents an input and the behavior elicited by that input. o A=0, M=0, O=0 * Windows 8.1 acquired addresses and other information from DHCPv6. Liu, et al. Expires November 3, 2015 [Page 9] Internet-Draft draft-ietf-v6ops-dhcpv6-slaac-problem-04 May 2015 * All other hosts acquired no configuration information. o A=0, M=0, O=1 * Windows 8.1 acquired addresses and other information from DHCPv6. * Windows 7, OSX 10.9 and IOS 8.0 acquired other information from DHCPv6. * Ubuntu 14.04 acquired no configuration information. o A=0, M=1, O=0 * All hosts acquired addresses and other information from DHCPv6. o A=0, M=1, O=1 * All hosts acquired addresses and other information from DHCPv6. o A=1, M=0, O=0 * Windows 8.1 acquired addresses from SLAAC and DHCPv6. It also acquired non-address information from DHCPv6. * All the other host acquired addresses from SLAAC o A=1, M=0, O=1 * Windows 8.1 acquired addresses from SLAAC and DHCPv6. It also acquired other information from DHCPv6. * All the other hosts acquired addresses from SLAAC and other information from DHCPv6. o A=1, M=1, O=0 * All hosts acquired addresses from SLAAC and DHCPv6. They also acquired other information from DHCPv6. o A=1, M=1, O=1 * All hosts acquired addresses from SLAAC and DHCPv6. They also acquired other information from DHCPv6. As showed above, four inputs result in divergent behaviors. Liu, et al. Expires November 3, 2015 [Page 10] Internet-Draft draft-ietf-v6ops-dhcpv6-slaac-problem-04 May 2015 A.3. Host Behavior in State Transitions The bullet list below describes behavior elicited during state transitions. The value x can represents both 0 and 1. o Old state (M = x, O = x, A = 1) , New state (M = x, O = x, A = 0) (This means a SLAAC-configured host, which is regardless of DHCPv6 configured or not, receiving A in transition from 1 to 0. ) * All the hosts retain SLAAC addresses until they expire o Old state (M = 0, O = x, A = 1), New state (M = 1, O = x, A = 1) (This means a SLAAC-only host receiving M in transition from 0 to 1.) * Windows 7 acquires addresses from DHCPv6, immediately. * Ubuntu 14.04/OSX 10.9/IOS 8.0 acquires addresses from DHCPv6 only if the SLAAC addresses are allowed to expire * Windows 8.1 was not tested because it always acquire addresses from DHCPv6 regardless of the M flag setting. o Old state (M = 1, O = x, A = x), New state (M = 0, O = x, A = x) (This means a DHCPv6-configured host receiving M in transition from 1 to 0.) * Windows 7 immediately released the DHCPv6 address * Windows 8.1/Ubuntu 14.04/OSX 10.9/IOS 8.0 keep the DHCPv6 addresses until they expire o Old state (M = 1, O = x, A = 0), New state (M = 1, O = x, A = 1) (This means a DHCPv6-only host receiving A in transition from 0 to 1.) * All host acquire addresses from SLAAC o Old state (M = 0, O = 1, A = x), New state (M = 1, O = 1, A = x) (This means a Stateless DHCPv6-configured host [RFC3736], which is regardless of SLAAC configured or not, receiving M in transition from 0 to 1 with keeping O=1 ) * Windows 7 acquires addresses and refreshes other information from DHCPv6 * Ubuntu 14.04/OSX 10.9/IOS 8.0 does nothing Liu, et al. Expires November 3, 2015 [Page 11] Internet-Draft draft-ietf-v6ops-dhcpv6-slaac-problem-04 May 2015 * Windows 8.1 was not tested because it always acquire addresses from DHCPv6 regardless of the M flag setting. o Old state (M = 1, O = 1, A = x), New state (M = 0, O = 1, A = x) (This means a Stateful DHCPv6-configured host, which is regardless of SLAAC configured or not, receiving M in transition from 0 to 1 with keeping O=1 ) * Windows 7 released all DHCPv6 addresses and refreshes all DHCPv6 other information. * Windows 8.1/Ubuntu 14.04/OSX 10.9/IOS 8.0 does nothing Authors' Addresses Bing Liu Huawei Technologies Q14, Huawei Campus, No.156 Beiqing Road Hai-Dian District, Beijing, 100095 P.R. China Email: leo.liubing@huawei.com Sheng Jiang Huawei Technologies Q14, Huawei Campus, No.156 Beiqing Road Hai-Dian District, Beijing, 100095 P.R. China Email: jiangsheng@huawei.com Xiangyang Gong BUPT University No.3 Teaching Building Beijing University of Posts and Telecommunications (BUPT) No.10 Xi-Tu-Cheng Rd. Hai-Dian District, Beijing P.R. China Email: xygong@bupt.edu.cn Liu, et al. Expires November 3, 2015 [Page 12] Internet-Draft draft-ietf-v6ops-dhcpv6-slaac-problem-04 May 2015 Wendong Wang BUPT University No.3 Teaching Building Beijing University of Posts and Telecommunications (BUPT) No.10 Xi-Tu-Cheng Rd. Hai-Dian District, Beijing P.R. China Email: wdwang@bupt.edu.cn Liu, et al. Expires November 3, 2015 [Page 13]