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Network Working Group                                   B. Haberman, Ed.Request for Comments: 5075                                       JHU APLCategory: Standards Track                                      R. Hinden                                                                   Nokia                                                           November 2007IPv6 Router Advertisement Flags OptionStatus of This Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Abstract   The IPv6 Neighbor Discovery's Router Advertisement message contains   an 8-bit field reserved for single-bit flags.  Several protocols have   reserved flags in this field and others are preparing to reserve a   sufficient number of flags to exhaust the field.  This document   defines an option to the Router Advertisement message that expands   the available number of flag bits available.Table of Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .22.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . .23.  Current Router Advertisement Flags  . . . . . . . . . . . . . .24.  Flags Expansion Option  . . . . . . . . . . . . . . . . . . . .35.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . .46.  Security Considerations . . . . . . . . . . . . . . . . . . . .57.  References  . . . . . . . . . . . . . . . . . . . . . . . . . .57.1.  Normative References  . . . . . . . . . . . . . . . . . . .57.2.  Informative References  . . . . . . . . . . . . . . . . . .6Haberman & Hinden           Standards Track                     [Page 1]

RFC 5075                 IPv6 RA Flags Options             November 20071.  Introduction   The IPv6 Neighbor Discovery Protocol's (NDP) [RFC4861] Router   Advertisement message contains an 8-bit field reserved for single-bit   flags.  Several protocols have reserved flags in this field and   others are preparing to reserve a sufficient number of flags to   exhaust the field.   This document defines an option for the Router Advertisement message   that expands the available number of flag bits by adding an   additional 48 flag bits to NDP messages.2.  Terminology   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this   document are to be interpreted as described in [RFC2119].3.  Current Router Advertisement Flags   Currently, the NDP Router Advertisement message contains the   following one-bit flags defined in published RFCs:    0 1 2 3 4 5 6 7   +-+-+-+-+-+-+-+-+   |M|O|H|Prf|P|R|R|   +-+-+-+-+-+-+-+-+                   Figure 1: Router Advertisement Flags   o  M - Managed Address Configuration Flag [RFC4861]   o  O - Other Configuration Flag [RFC4861]   o  H - Mobile IPv6 Home Agent Flag [RFC3775]   o  Prf - Router Selection Preferences [RFC4191]   o  P - Neighbor Discovery Proxy Flag [RFC4389]   o  R - Reserved   With other protocols in the works (e.g., Detecting Network   Attachment) that want to use flags in the NDP messages, it is   necessary to define an expansion capability to support new features.Haberman & Hinden           Standards Track                     [Page 2]

RFC 5075                 IPv6 RA Flags Options             November 20074.  Flags Expansion Option   The Neighbor Discovery specification [RFC4861] contains the   capability to define NDP options.  The following (Figure 2) is the   definition of the Expanded Flags Option (EFO) for NDP Router   Advertisement messages.    0                   1                   2                   3    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |     Type      |    Length     |         Bit fields available ..   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   ... for assignment                                              |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+           Figure 2: Router Advertisement Expanded Flags Option   o  Type - TBD (to be assigned by IANA)   o  Length - The length MUST be checked when processing the option in      order to allow for future expansion of this option.  An      implementation of this specification MUST set the Length to 1,      MUST ignore any unrecognized data, and MUST be able to recognize      the specific length in order to skip over unrecognized bits.   o  Bits - allocated by IANA   The definition and usage of these bits is to be found in the document   requesting their allocation.   During the construction/transmission, this option:   o  MUST only occur in Router Advertisement messages.   o  MUST occur prior to any additional options associated with any      flags set in this option.   o  MUST only occur once in the Router Advertisement message.   o  MUST NOT be added to a Router Advertisement message if no flags in      the option are set.   o  MUST set all unused flags to zero.Haberman & Hinden           Standards Track                     [Page 3]

RFC 5075                 IPv6 RA Flags Options             November 2007   Upon reception, a receiver processing NDP messages containing this   option:   o  MUST ignore the option if it occurs in a message other than a      Router Advertisement.   o  MUST ignore all instances of the option except the first one      encountered in the Router Advertisement message.   o  MUST ignore the option if the Length is less than 1.   o  MUST ignore any unknown flag bits.   The bit fields within the option are numbered from left to right,   from 8 to 55 (starting as bit offset 16 in the option) and follow the   numbering of the flag bits in the RA option described in Figure 1.   Flag bits 0 to 7 are found in the Router Advertisement message header   defined in [RFC4861].5.  IANA Considerations   IANA has defined a new IPv6 Neighbor Discovery option for the option   defined in this document of the form:             +------+---------------------------+-----------+             | Type | Description               | Reference |             +------+---------------------------+-----------+             | 26   | RA Flags Extension Option | [RFC5075] |             +------+---------------------------+-----------+   The registry for these options can be found at:http://www.iana.org/assignments/icmpv6-parameters   IANA has created a new registry for IPv6 ND Router Advertisement   flags.  This should include the current flags in the RA option and in   the extension option defined in this document.  The new registry has   been added to the icmpv6-parameters as shown above.  The format for   the registry is:Haberman & Hinden           Standards Track                     [Page 4]

RFC 5075                 IPv6 RA Flags Options             November 2007   +---------------+---------------------------------------+-----------+   | RA Option Bit | Description                           | Reference |   +---------------+---------------------------------------+-----------+   | 0             | M - Managed Address Configuration     | [RFC4861] |   |               | Flag                                  |           |   | 1             | O - Other Configuration Flag          | [RFC4861] |   | 2             | H - Mobile IPv6 Home Agent Flag       | [RFC3775] |   | 3             | Prf - Router Selection Preferences    | [RFC4191] |   | 4             | Prf - Router Selection Preferences    | [RFC4191] |   | 5             | P - Neighbor Discovery Proxy Flag     | [RFC4389] |   | 6-53          | R - Reserved; Available for           |           |   |               | assignment                            |           |   | 54-55         | Private Experimentation               |           |   +---------------+---------------------------------------+-----------+   The assignment of new RA flags in the RA option header and the bits   defined in the RA extension option defined in this document require   standards action or IESG approval [RFC2434].6.  Security Considerations   This protocol shares the security issues of NDP that are documented   in the "Security Considerations" section of [RFC4861].   The inclusion of additional optional bit fields provides a potential   covert channel that is useful for passing information.7.  References7.1.  Normative References   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC2434]  Narten, T. and H. Alvestrand, "Guidelines for Writing an              IANA Considerations Section in RFCs",BCP 26,RFC 2434,              October 1998.   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,              "Neighbor Discovery for IP version 6 (IPv6)",RFC 4861,              September 2007.Haberman & Hinden           Standards Track                     [Page 5]

RFC 5075                 IPv6 RA Flags Options             November 20077.2.  Informative References   [RFC3775]  Johnson, D., Perkins, C., and J. Arkko, "Mobility Support              in IPv6",RFC 3775, June 2004.   [RFC4191]  Draves, R. and D. Thaler, "Default Router Preferences and              More-Specific Routes",RFC 4191, November 2005.   [RFC4389]  Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery              Proxies (ND Proxy)",RFC 4389, April 2006.Authors' Addresses   Brian Haberman (editor)   Johns Hopkins University Applied Physics Lab   11100 Johns Hopkins Road   Laurel, MD  20723-6099   USA   Phone: +1 443 778 1319   EMail: brian@innovationslab.net   Robert Hinden   Nokia   313 Fairchild Drive   Mountain View, CA  94043   USA   Phone: +1 650 625 2004   EMail: bob.hinden@nokia.comHaberman & Hinden           Standards Track                     [Page 6]

RFC 5075                 IPv6 RA Flags Options             November 2007Full Copyright Statement   Copyright (C) The IETF Trust (2007).   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, THE IETF TRUST 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.Haberman & Hinden           Standards Track                     [Page 7]