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rfc:rfc5175

Network Working Group B. Haberman, Ed. Request for Comments: 5175 JHU APL Obsoletes: 5075 R. Hinden Category: Standards Track Nokia

                                                            March 2008
               IPv6 Router Advertisement Flags Option

Status 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 number of flag bits available.

Table of Contents

 1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 2
 2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 2
 3.  Current Router Advertisement Flags  . . . . . . . . . . . . . . 2
 4.  Flags Expansion Option  . . . . . . . . . . . . . . . . . . . . 3
 5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
 6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
 7.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 5
   7.1.  Normative References  . . . . . . . . . . . . . . . . . . . 5
   7.2.  Informative References  . . . . . . . . . . . . . . . . . . 6

Haberman & Hinden Standards Track [Page 1] RFC 5175 IPv6 RA Flags Options March 2008

1. 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 5175 IPv6 RA Flags Options March 2008

4. 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 - 26
 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 5175 IPv6 RA Flags Options March 2008

 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 | [RFC5175] |
           +------+---------------------------+-----------+
 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 5175 IPv6 RA Flags Options March 2008

 +---------------+---------------------------------------+-----------+
 | 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. References

7.1. 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 5175 IPv6 RA Flags Options March 2008

7.2. 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.com

Haberman & Hinden Standards Track [Page 6] RFC 5175 IPv6 RA Flags Options March 2008

Full Copyright Statement

 Copyright (C) The IETF Trust (2008).
 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.
 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.

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Haberman & Hinden Standards Track [Page 7]

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