V6OPS B. Liu Internet-Draft Huawei Technologies Co., Ltd Intended status: Informational R. Bonica Expires: May 30, 2014 Juniper Networks S. Jiang Huawei Technologies Co., Ltd X. Gong W. Wang BUPT University November 26, 2013 DHCPv6/SLAAC Address Configuration Interaction Problem Statement draft-ietf-v6ops-dhcpv6-slaac-problem-00 Abstract This document analyzes the DHCPv6/SLAAC interaction issue on host. More specifically, the interaction is regarding with the A, M, and O flags defined in ND protocol. Test results identify that current implementations in operating systems have varied on interpreting these flags. The variation might cause some operational issues as described in the document. 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 May 30, 2014. Copyright Notice Copyright (c) 2013 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 May 30, 2014 [Page 1] Internet-Draft DHCPv6/SLAAC PS November 2013 (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. Host Behavior of DHCPv6/SLAAC Interaction . . . . . . . . . . 3 2.1. Relevant RA Flags Defined in Standards . . . . . . . . . 3 2.1.1. A (Autonomous) Flag . . . . . . . . . . . . . . . . . 3 2.1.2. M (Managed) Flag . . . . . . . . . . . . . . . . . . 3 2.1.3. O (Otherconfig) Flag . . . . . . . . . . . . . . . . 4 2.2. Behavior of Current Implementations . . . . . . . . . . . 4 2.2.1. A flag . . . . . . . . . . . . . . . . . . . . . . . 5 2.2.2. M flag . . . . . . . . . . . . . . . . . . . . . . . 5 2.2.3. O flag . . . . . . . . . . . . . . . . . . . . . . . 5 3. Possible Operational Issues of DHCPv6/SLAAC Interaction . . . 5 3.1. Renumbering . . . . . . . . . . . . . . . . . . . . . . . 5 3.2. Cold Start Problems . . . . . . . . . . . . . . . . . . . 6 3.3. Strong Management . . . . . . . . . . . . . . . . . . . . 6 4. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 6 5. Security Considerations . . . . . . . . . . . . . . . . . . . 7 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 8.1. Normative References . . . . . . . . . . . . . . . . . . 7 8.2. Informative References . . . . . . . . . . . . . . . . . 7 Appendix A. Test Details of Host Behaviors . . . . . . . . . . . 8 A.1. Host Transition Behavior . . . . . . . . . . . . . . . . 10 A.2. Host Stateful/Stateless DHCPv6 Behavior . . . . . . . . . 11 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 1. Introduction In IPv6, both of the DHCPv6 [RFC3315] and Neighbor Discovery [RFC4861] protocols could be utilized for automatic IP address configuration for the hosts. They are known as stateful address auto-configuration and stateless address auto-configuration (SLAAC (, [RFC4862]). Sometimes the two address configuration methods might be both available in one network. In ND protocol, there is an M (Managed) flag defined in RA message, indicating the hosts there is DHCPv6 service available when the flag is set. And there is an O (OtherConfig) flag indicating configure Liu, et al. Expires May 30, 2014 [Page 2] Internet-Draft DHCPv6/SLAAC PS November 2013 information other than addresses (e.g. DNS, Route .etc) is available through DHCPv6 configuration when it is set. Moreover, there's another A (Autonomous) flag defined in ND, which indicating the hosts to do SLAAC. So with these flags, the two address configuration methods are correlated. But for some reasons, the ND protocol didn't define the flags as prescriptive but only advisory. This means the definition is more or less ambiguous, and hosts might vary the behavior of interpreting the flags because of the ambiguity. In the appendix, we provided test results to identify different host operating systems have taken different approaches. This might cause some operational issues as analyzed in section 3. 2. Host Behavior of DHCPv6/SLAAC Interaction In this section, we analyze A, M, and O flags definition, and briefly point out some important test results of host behavior of interpreting these flags in mainstream operating systems implementations. Please note that, A flag has no direct relationship with DHCPv6, but it is somewhat correlated with M and O flags. 2.1. Relevant RA Flags Defined in Standards 2.1.1. A (Autonomous) Flag In ND Prefix Information Option, when the autonomous address- configuration flag (A flag) is set, it indicates that this prefix can be used for SLAAC. For the host behavior, there is an explicit rule in the SLAAC specification [RFC4862]: "If the Autonomous flag is not set, silently ignore the Prefix Information option." But when A flag is set, the SLAAC protocol didn't provide a prescriptive definition. It is not clear the host "could" do SLAAC or "must" do. 2.1.2. M (Managed) Flag In earlier SLAAC specification [RFC2462], the host behavior of interpreting M flag is as below: "On receipt of a valid Router Advertisement, a host copies the value of the advertisement's M bit into ManagedFlag. If the value of ManagedFlag changes from FALSE to TRUE, and the host is not already Liu, et al. Expires May 30, 2014 [Page 3] Internet-Draft DHCPv6/SLAAC PS November 2013 running the stateful address autoconfiguration protocol, the host should invoke the stateful address auto-configuration protocol, requesting both address information and other information. If the value of the ManagedFlag changes from TRUE to FALSE, the host should continue running the stateful address auto-configuration, i.e., the change in the value of the ManagedFlag has no effect. If the value of the flag stays unchanged, no special action takes place. In particular, a host MUST NOT reinvoke stateful address configuration if it is already participating in the stateful protocol as a result of an earlier advertisement." But in the current SLAAC specification [RFC4862], the relative description was removed, the reason was "considering the maturity of implementations and operational experiences. ManagedFlag and OtherConfigFlag were removed accordingly. (Note that this change does not mean the use of these flags is deprecated.)". 2.1.3. O (Otherconfig) Flag As mentioned above, the situation of O flag is similar with M. In earlier SLAAC [RFC2462], the host behavior is clear: "If the value of OtherConfigFlag changes from FALSE to TRUE, the host should invoke the stateful autoconfiguration protocol, requesting information (excluding addresses if ManagedFlag is set to FALSE). If the value of the OtherConfigFlag changes from TRUE to FALSE, the host should continue running the stateful address autoconfiguration protocol, i.e., the change in the value of OtherConfigFlag has no effect. If the value of the flag stays unchanged, no special action takes place. In particular, a host MUST NOT reinvoke stateful configuration if it is already participating in the stateful protocol as a result of an earlier advertisement." And there's another description of the relationship of M and O flags in [RFC2462]: "In addition, when the value of the ManagedFlag is TRUE, the value of OtherConfigFlag is implicitly TRUE as well. It is not a valid configuration for a host to use stateful address autoconfiguration to request addresses only, without also accepting other configuration information." 2.2. Behavior of Current Implementations We did tests of current mainstream desktop/mobile operating systems' behavior (please refer to the appendix for details). This section only briefly illustrates some important results. Liu, et al. Expires May 30, 2014 [Page 4] Internet-Draft DHCPv6/SLAAC PS November 2013 2.2.1. A flag A flag is a switch to control whether to do SLAAC, and it is independent with M/O flags, in another word, A is independent with DHCPv6. At the non-SLAAC-config state (including DHCPv6-only-configured), all the OSes acted the same with A flag, if A set, they all configured SLAAC, it is obvious and reasonable. But when hosts are SLAAC- configured, and A changed from 1 to 0, the behavior varied, some deprecated SLAAC while some ignored the RA messages. 2.2.2. M flag M is a key flag to correlate ND and DHCPv6, but the host behavior on M flag is quite different. In our test, there was one OS treating the flag as prescriptive, it even released DHCPv6 session when M=0. But the others just treat the flag as advisory, when SLAAC was done, it won't care about M=1, and M=0 won't cause operation for the already configured DHCPv6 addresses. Moreover, the two OSes even would not initiate DHCPv6 session until they receives RA messages with M=1, this behavior has an implication that DHCPv6 somehow depends on ND. 2.2.3. O flag In our tests, when M flag is set, the O flag is implicitly set as well; in another word, the hosts would not initial stateful DHCPv6 and stateless DHCPv6 respectively. This is reasonable behavior. But the O flag could be influented by A flag in some OSes. In our test, there are two OSes that won't initiate stateless DHCPv6 when A flag is not set, that is to say, it is not applicable to have a ''stateless DHCPv6 only'' configuration state for some operating systems; it is also not applicable for these two OSes to switch between stateful DHCPv6 and stateless DHCPv6 (according to O flag changing from 0 to 1 or verse vice). 3. Possible Operational Issues of DHCPv6/SLAAC Interaction According to the abovementioned tests, there are possible operational issues as the following. 3.1. Renumbering During IPv6 renumbering, the SLAAC-configured hosts could reconfigure IP addresses by receiving ND Router Advertisement (RA) messages Liu, et al. Expires May 30, 2014 [Page 5] Internet-Draft DHCPv6/SLAAC PS November 2013 containing new prefix information. The DHCPv6-configured hosts could reconfigure addresses by initialing RENEW sessions when the current addresses' lease time is expired or receiving the reconfiguration messages initiated by the DHCPv6 servers. So renumbering won't be a problem when SLAAC-configured hosts would remain SLAAC configuration as well as DHCPv6-managed hosts remaining DHCPv6. But in some situations, SLAAC-configured hosts might need to switch to DHCPv6-managed, or verse vice. In [RFC6879], it described several renumbering scenarios in enterprise network for this requirement; for example, the network may split, merge, relocate or reorganize. But due to current implementations, this requirement is not applicable and has been identified as a gap in [RFC7010]. 3.2. Cold Start Problems If all nodes, or many nodes, restart at the same time after a power cut, the results might not consistent. 3.3. Strong Management Since the host behavior of address configuration is un-controlled and un-predictable by the network side, it might cause gaps to the networks that need strong management (for example, the enterprise networks and the ISP CPE networks). Examples are: o the administrator wants the hosts to do DHCPv6-only configuration, it is not applicable for some operating systems due to current implementation unless manually configure the hosts to DHCPv6-only model o the hosts have been SLAAC-configured, then the administrator wants the hosts to do DHCPv6 simultaneously (e.g. for multihoming) o the administrator wants the hosts to do statelss DHCPv6-only; for example, the hosts are configured with self-generated addresses (e.g. ULA), and they also need to contact the DHCPv6 server for info- configuration 4. Conclusions o The host behavior of SLAAC/DHCPv6 interaction is ambiguous in standard. o The implementations have been varied on this issue. In [RFC4862] it is said "Removed the text regarding the M and O flags, considering the maturity of implementations and operational experiences." The description seems not true anymore. Liu, et al. Expires May 30, 2014 [Page 6] Internet-Draft DHCPv6/SLAAC PS November 2013 o It is foreseeable that the un-uniformed host behavior can cause operational issues, e.g. in renumbering and strong management. 5. Security Considerations No more security considerations than the Neighbor Discovery protocol [RFC4861]. 6. IANA Considerations This draft does not request any IANA action. 7. Acknowledgements The test was done by our research partner BNRC-BUPT (Broad Network Research Centre in Beijing University of Posts and Telecommunications). Thanks for the hard efficient work of the student Xudong Shi and Longyun Yuan. Valuable comment was received from Brian E Carpenter, Mikael Abrahamsson, Dave Thaler, Lee Howard .etc to improve the draft. This document was produced using the xml2rfc tool [RFC2629]. 8. References 8.1. Normative References [RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629, June 1999. [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. 8.2. Informative References [I-D.liu-6renum-dhcpv6-slaac-switching] Liu, B., Wang, W., and X. Gong, "DHCPv6/SLAAC Address Configuration Switching for Host Renumbering", draft-liu- 6renum-dhcpv6-slaac-switching-02 (work in progress), January 2013. [RFC2462] Thomson, S. and T. Narten, "IPv6 Stateless Address Autoconfiguration", RFC 2462, December 1998. Liu, et al. Expires May 30, 2014 [Page 7] Internet-Draft DHCPv6/SLAAC PS November 2013 [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. [RFC6879] Jiang, S., Liu, B., and B. Carpenter, "IPv6 Enterprise Network Renumbering Scenarios, Considerations, and Methods", RFC 6879, February 2013. [RFC7010] Liu, B., Jiang, S., Carpenter, B., Venaas, S., and W. George, "IPv6 Site Renumbering Gap Analysis", RFC 7010, September 2013. Appendix A. Test Details of Host Behaviors /-----\ +---------+ // \\ | DHCPv6 | | Router | | server | \\ // +----+----+ \--+--/ | | | | | | ----+--+----------+----------+---+----- | | | | | | | | | +----+---+ +----+---+ +----+---+ | | | | | | | Host1 | | Host2 | | Host3 | +--------+ +--------+ +--------+ Figure 1 Test Environment The 5 elements were all created in Vmware in one computer, for ease of operation. 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 A Window 7 Virtual Host o Host B Ubuntu 12.10 Virtual Host o Host C Mac OS X v10.7 Virtual Host Liu, et al. Expires May 30, 2014 [Page 8] Internet-Draft DHCPv6/SLAAC PS November 2013 Another test was done dedicated for the mobile phone operating systems. The environment is similar (not in VMware, all are real PC and mobile phones): o Router quagga 0.99-17 soft router installed on Ubuntu 12.10 o DHCPv6 Server: dibbler-server installed on Ubuntu 12.10 o Host D Android 4.0.4 (kernel: 3.0.16-gfa98030; device: HTC Incredible S) o Host E IOS 6.1.3 (model: iPod Touch 4) (Note: The tested Android version didn't support DHCPv6 well, so the following results don't include Android.)A.1 Host Initialing Behavior Host from non-configured to configured, we tested different A/M/O combinations in each OS platform. The states are enumerated as the following, 3 operation systems respectively: o Window 7/Apple IOS * A=0&M=O&O=0, non-config * A=1&M=0&O=0, SLAAC only * A=1&M=0&O=1, SLAAC + Stateless DHCPv6 * A=1&M=1&O=0, SLAAC + DHCPv6 * A=1&M=1&O=1, SLAAC + DHCPv6 * A=0&M=1&O=0, DHCPv6 only (A=0 or Non-PIO) * A=0&M=1&O=1, DHCPv6 only (A=0 or Non-PIO) * A=0&M=0&O=1, Stateless DHCPv6 only o Linux/MAC OS X * A=0&M=O&O=0, non-config * A=1&M=0&O=0, SLAAC only * A=1&M=0&O=1, SLAAC + Stateless DHCPv6 * A=1&M=1&O=0, SLAAC + DHCPv6 Liu, et al. Expires May 30, 2014 [Page 9] Internet-Draft DHCPv6/SLAAC PS November 2013 * A=1&M=1&O=1, SLAAC + DHCPv6 * A=0&M=1&O=0, DHCPv6 only (A=0 or Non-PIO) * A=0&M=1&O=1, DHCPv6 only (A=0 or Non-PIO) * A=0&M=0&O=1, non-config As showed above, Linux and MAC OSX acted the same way, but differated from Windows 7 and Apple IOS. The only difference is when A=0&M=0&O=1, Windows 7/Apple IOS did stateless DHCPv6 while Linux/MAC OSX did nothing. Result summary: o A is interpreted as prescript in each OS at the initial state o M is interpreted as prescript in each OS at the initial state o O is interpreted as prescript in Windows 7 o A and M are independent in each OS at the initial state o A and O are not totally independent in Linux and Mac, A=1 is required for O=1 triggering DHCPv6 info-request o M and O are not totally independent in each OS. M=1 has the implication O=1 A.1. Host Transition Behavior o SLAAC-only host receiving A=0&M=1 * Window 7 would deprecate SLAAC and initiate DHCPv6 * Linux/MAC/IOS would keep SLAAC and don't initiate DHCPv6 unless SLAAC is expired and no continuous RA o DHCPv6-only host receiving A=1&M=0 * Window 7 would release DHCPv6 and do SLAAC * Linux/MAC/IOS would keep DHCPv6 and do SLAAC When the host has been configured, either by SLAAC or DHCPv6, the operating systems interpreting the M flag quite differently. Windows 7 treats the flag as instruction, it even released DHCPv6 session when M=0. Linux and OS X were likely to treat the flag as advisory, Liu, et al. Expires May 30, 2014 [Page 10] Internet-Draft DHCPv6/SLAAC PS November 2013 when SLAAC was done, it won't care about M=1, and M=0 won't cause operation for the already configured DHCPv6 addresses. Please refer to [I-D.liu-6renum-dhcpv6-slaac-switching] for more details. A.2. Host Stateful/Stateless DHCPv6 Behavior o Stateless DHCPv6-configured host receiving M=1 (while keeping O=1) * Window 7 would initiate stateful DHCPv6, configuring address as well as re-configuring other information * Linux/MAC/IOS no action o Statefull DHCPv6-configured host receiving M=0 (while keeping O=1) * Window 7 would release all DHCPv6 configurations including address and other information, and initiate stateless DHCPv6 * Linux/MAC/IOS no action Liu, et al. Expires May 30, 2014 [Page 11] Internet-Draft DHCPv6/SLAAC PS November 2013 Authors' Addresses Bing Liu Huawei Technologies Co., Ltd Q14, Huawei Campus, No.156 Beiqing Road Hai-Dian District, Beijing, 100095 P.R. China Email: leo.liubing@huawei.com Ron Bonica Juniper Networks Sterling, Virginia 20164 USA Email: rbonica@juniper.net Sheng Jiang Huawei Technologies Co., Ltd 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 May 30, 2014 [Page 12] Internet-Draft DHCPv6/SLAAC PS November 2013 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