[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: (draft-liu-bonica-v6ops-dhcpv6-slaac-problem) 00 01 02 03 04 05 06 07

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


Html markup produced by rfcmarkup 1.129c, available from https://tools.ietf.org/tools/rfcmarkup/