IPv6 Neighbor Discovery Overlay Multilink Network Interface (OMNI) Option
draft-templin-6man-omni-option-09

Document Type Active Internet-Draft (individual)
Authors Fred Templin  , Tony Whyman 
Last updated 2021-02-12
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Network Working Group                                    F. Templin, Ed.
Internet-Draft                                        The Boeing Company
Intended status: Standards Track                               A. Whyman
Expires: August 16, 2021                 MWA Ltd c/o Inmarsat Global Ltd
                                                       February 12, 2021

   IPv6 Neighbor Discovery Overlay Multilink Network Interface (OMNI)
                                 Option
                   draft-templin-6man-omni-option-09

Abstract

   This document defines a new IPv6 Neighbor Discovery (ND) option
   termed the "Overlay Multilink Network Interface (OMNI) Option".  The
   OMNI option may appear in any IPv6 ND message type; it is processed
   by interface types that recognize the option and ignored by all other
   interface types.  The option supports functions such as prefix
   registration and multilink coordination, and is extensible to support
   additional functions in the future.

Status of This Memo

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   to this document.  Code Components extracted from this document must
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  The Overlay Multilink Network Interface (OMNI) IPv6 ND Option   3
     3.1.  Sub-Options . . . . . . . . . . . . . . . . . . . . . . .   4
       3.1.1.  Pad1  . . . . . . . . . . . . . . . . . . . . . . . .   5
       3.1.2.  PadN  . . . . . . . . . . . . . . . . . . . . . . . .   6
       3.1.3.  Interface Attributes (Type 1) . . . . . . . . . . . .   6
       3.1.4.  Sub-Type Extension  . . . . . . . . . . . . . . . . .   8
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   This document defines a new IPv6 Neighbor Discovery (ND) option
   termed the "Overlay Multilink Network Interface (OMNI) Option".  The
   OMNI option may appear in any IPv6 ND message type; it is processed
   by interface types that recognize the option and ignored by all other
   interface types.  The option supports functions such as prefix
   registration and multilink coordination for interface types such as
   the OMNI interface [I-D.templin-6man-omni-interface], and is
   extensible to support additional functions in the future.

   The following sections discuss the OMNI option format and contents.
   Use cases appear in IPv6 over specific link layer documents such as
   [I-D.templin-6man-omni-interface], where the International Civil
   Aviation Organization (ICAO) has expressed interest in the option in
   support of their Document 9896 [ATN][ATN-IPS].  An IPv6 ND option
   Type number assignment is requested in the IANA Considerations
   section.

2.  Terminology

   The terminology in the normative references applies.  The term
   "underlying interface" refers to one of potentially multiple Layer-2
   interfaces over which a Layer-3 (virtual) interface is configured.

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   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119][RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  The Overlay Multilink Network Interface (OMNI) IPv6 ND Option

   An Overlay Multilink Network Interface (OMNI) IPv6 ND option is
   defined.  The option (known as the "OMNI option") is formatted as
   shown in Figure 1:

        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    |    Preflen    | S/T-omIndex   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       ~                          Sub-Options                          ~
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 1: OMNI Option Format

   In this format:

   o  Type is set to TBD1.

   o  Length is set to the number of 8 octet blocks in the option.

   o  Preflen is an 8 bit field that determines the length of prefix
      associated with an IPv6 address of the IPv6 ND message.  Values 0
      through 128 specify a valid prefix length (all other values are
      invalid).  For IPv6 ND messages sent from the source to a target
      node, Preflen applies to the IPv6 source address and provides the
      length that the source is requesting or asserting.  For IPv6 ND
      messages replies from the target to the original source, Preflen
      applies to the IPv6 destination address and indicates the length
      that the target is granting.

   o  S/T-omIndex is a 1-octet field that encodes a value between 0 and
      255 identifying the source or target underlying interface for the
      IPv6 ND message.  For RS and NS messages S/T-omIndex refers to the
      "Source" underlying interface over which the message is sent,
      while for RA and NA messages S/T-omIndex refers to the "Target"
      underlying interface that will receive the message.

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   o  Sub-Options is a Variable-length field, of length such that the
      complete OMNI Option is an integer multiple of 8 octets long.
      Contains one or more Sub-Options, as described in Section 3.1.

   The OMNI option may appear in any IPv6 ND message type; it is
   processed by interfaces that recognize the option and ignored by all
   other interfaces.  If multiple OMNI option instances appear in the
   same IPv6 ND message, the interface processes the Preflen and S/
   T-omIndex fields in the first instance and ignores those fields in
   all other instances.  The interface processes the Sub-Options of all
   OMNI option instances in the same IPv6 ND message in the consecutive
   order in which they occur.

   The OMNI option(s) in each IPv6 ND message may include full or
   partial information for the neighbor.  The union of the information
   in the most recently received OMNI options is therefore retained, and
   the information is aged/removed in conjunction with the corresponding
   neighbor cache entry.

3.1.  Sub-Options

   The OMNI option includes zero or more Sub-Options.  Each consecutive
   Sub-Option is concatenated immediately after its predecessor.  All
   Sub-Options except Pad1 (see below) are in type-length-value (TLV)
   encoded in the following format:

         0                   1                   2
         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
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
        | Sub-Type|     Sub-length      | Sub-Option Data ...
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

                        Figure 2: Sub-Option Format

   o  Sub-Type is a 5-bit field that encodes the Sub-Option type.  Sub-
      Options defined in this document are:

        Option Name               Sub-Type
        Pad1                           0
        PadN                           1
        Interface Attributes (Type 1)  2
        Sub-Type Extension            30

                                 Figure 3

      Sub-Types 3-29 are available for future assignment for major
      protocol functions.  Sub-Type 31 is reserved by IANA.

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   o  Sub-Length is an 11-bit field that encodes the length of the Sub-
      Option Data (i.e., ranging from 0 to 2034 octets).

   o  Sub-Option Data is a block of data with format determined by Sub-
      Type and length determined by Sub-Length.

   During transmission, the OMNI interface codes Sub-Type and Sub-Length
   together in network byte order in 2 consecutive octets, where Sub-
   Option Data may be up to 2034 octets in length.  This allows ample
   space for coding large objects (e.g., ascii character strings,
   protocol messages, security codes, etc.), while a single OMNI option
   is limited to 2040 octets the same as for any IPv6 ND option.  If the
   Sub-Options to be coded would cause an OMNI option to exceed 2040
   octets, the OMNI interface codes any remaining Sub-Options in
   additional OMNI option instances in the intended order of processing
   in the same IPv6 ND message.  Implementations must therefore observe
   size limitations, and must refrain from sending IPv6 ND messages
   larger than the OMNI interface MTU.

   During reception, the OMNI interface processes each OMNI option Sub-
   Option while skipping over and ignoring any unrecognized Sub-Options.
   The OMNI interface processes the Sub-Options of all OMNI option
   instances in the consecutive order in which they appear in the IPv6
   ND message, beginning with the first instance and continuing through
   any additional instances to the end of the message.  If a Sub-Option
   length would cause the running total for that OMNI option to exceed
   the length coded in the option header, the interface accepts any Sub-
   Options already processed and ignores the remainder of that OMNI
   option.  The interface then processes any remaining OMNI options in
   the same fashion to the end of the IPv6 ND message.

   Note: large objects that exceed the Sub-Option Data limit of 2034
   octets are not supported under the current specification; if this
   proves to be limiting in practice, future specifications may define
   support for fragmenting large objects across multiple OMNI options
   within the same IPv6 ND message.

   The following Sub-Option types and formats are defined in this
   document (note that other documents that are active at the time of
   this writing will define additional Sub-Option types in the near
   future):

3.1.1.  Pad1

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         0
         0 1 2 3 4 5 6 7
        +-+-+-+-+-+-+-+-+
        | S-Type=0|x|x|x|
        +-+-+-+-+-+-+-+-+

                              Figure 4: Pad1

   o  Sub-Type is set to 0.  If multiple instances appear in OMNI
      options of the same message all are processed.

   o  Sub-Type is followed by three 'x' bits, set randomly on
      transmission and ignored on receipt.  Pad1 therefore consists of a
      whole single octet with the most significant 5 bits set to 0, and
      with no Sub-Length or Sub-Option Data fields following.

3.1.2.  PadN

         0                   1                   2
         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
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
        | S-Type=1|    Sub-length=N     | N padding octets ...
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

                              Figure 5: PadN

   o  Sub-Type is set to 1.  If multiple instances appear in OMNI
      options of the same message all are processed.

   o  Sub-Length is set to N (from 0 to 2047) being the number of
      padding octets that follow.

   o  Sub-Option Data consists of N padding octets that are typically
      zero-valued (any non-zero values that may appear in the padding
      octets are not to be interpreted in any way other than as simple
      padding).

3.1.3.  Interface Attributes (Type 1)

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        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | S-Type=2|    Sub-length=N     |    omIndex    |    omType     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |  Provider ID  | Link  | Resvd |P00|P01|P02|P03|P04|P05|P06|P07|
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |P08|P09|P10|P11|P12|P13|P14|P15|P16|P17|P18|P19|P20|P21|P22|P23|
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |P24|P25|P26|P27|P28|P29|P30|P31|P32|P33|P34|P35|P36|P37|P38|P39|
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |P40|P41|P42|P43|P44|P45|P46|P47|P48|P49|P50|P51|P52|P53|P54|P55|
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |P56|P57|P58|P59|P60|P61|P62|P63|
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 6: Interface Attributes (Type 1)

   o  Sub-Type is set to 2.  If multiple instances with different
      omIndex values appear in OMNI options of the same message all are
      processed; if multiple instances with the same omIndex value
      appear, the first is processed and all others are ignored.

   o  Sub-Length is set to N (from 1 to 2047) that encodes the number of
      Sub-Option Data octets that follow.

   o  omIndex is a 1-octet field containing a value from 0 to 255
      identifying the underlying interface for which the interface
      attributes apply.

   o  omType is a 1-octet field containing a value from 0 to 255
      corresponding to the underlying interface identified by omIndex.

   o  Provider ID is a 1-octet field containing a value from 0 to 255
      corresponding to the underlying interface identified by omIndex.

   o  Link encodes a 4-bit link metric.  The value '0' means the link is
      DOWN, and the remaining values mean the link is UP with metric
      ranging from '1' ("lowest") to '15' ("highest").

   o  Resvd is reserved for future use.

   o  A 16-octet ""Preferences" field immediately follows 'Resvd', with
      values P[00] through P[63] corresponding to the 64 Differentiated
      Service Code Point (DSCP) values [RFC2474].  Each 2-bit P[*] field
      is set to the value '0' ("disabled"), '1' ("low"), '2' ("medium")
      or '3' ("high") to indicate a QoS preference for underlying
      interface selection purposes.

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3.1.4.  Sub-Type Extension

   Since the Sub-Type field is only 5 bits in length, future
   specifications of major protocol functions may exhaust the remaining
   Sub-Type values available for assignment.  This document therefore
   defines Sub-Type 30 as an "extension", meaning that the actual sub-
   option type is determined by examining a 1 octet "Extension-Type"
   field immediately following the Sub-Length field.  The Sub-Type
   Extension is formatted as shown in Figure 7:

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |S-Type=30|     Sub-length=N    | Extension-Type|               ~
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               ~
       ~                                                               ~
       ~                       Extension-Type Body                     ~
       ~                                                               ~
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 7: Sub-Type Extension

   o  Sub-Type is set to 30.  If multiple instances appear in OMNI
      options of the same message all are processed, where each
      individual extension defines its own policy for processing
      multiple of that type.

   o  Sub-Length is set to N (from 1 to 2034) that encodes the number of
      Sub-Option Data octets that follow.  The Extension-Type field is
      always present; hence, the maximum Extension-Type Body length is
      2033 octets.

   o  Extension-Type contains a 1 octet Sub-Type Extension value between
      0 and 255.

   o  Extension-Type Body contains an N-1 octet block with format
      defined by the given extension specification.

   Extension-Type values 0 through 252 are available for assignment by
   future specifications, which must also define the format of the
   Extension-Type Body and its processing rules.  Extension-Type values
   253 and 254 are reserved for experimentation, as recommended in
   [RFC3692], and value 255 is reserved by IANA.

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4.  IANA Considerations

   The IANA is instructed to allocate a Type number TBD1 from the
   registry "IPv6 Neighbor Discovery Option Formats" for the OMNI option
   (see: Section 13 of [RFC4861]) as a provisional registration in
   accordance with Section 4.13 of [RFC8126].

   The OMNI option defines a 5-bit Sub-Type field, for which IANA is
   instructed to create and maintain a new registry entitled "OMNI
   option Sub-Type values".  Initial values for the OMNI option Sub-Type
   values registry are given below; future assignments are to be made
   through Expert Review [RFC8126].

      Value    Sub-Type name                  Reference
      -----    -------------                  ----------
      0        Pad1                           [RFCXXXX]
      1        PadN                           [RFCXXXX]
      2        Interface Attributes (Type 1)  [RFCXXXX]
      3-29     Unassigned
      30       Sub-Type Extension             [RFCXXXX]
      31       Reserved                       [RFCXXXX]

                   Figure 8: OMNI Option Sub-Type Values

5.  Security Considerations

   Security considerations for IPv6 [RFC8200] and IPv6 Neighbor
   Discovery [RFC4861] apply.

6.  Acknowledgements

   This document is aligned with the International Civil Aviation
   Organization (ICAO) Aeronautical Telecommunications Network (ATN)
   with Internet Protocol Services (ATN/IPS) development program.

   This document is aligned with the IETF 6man (IPv6) working group.

7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

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   [RFC3692]  Narten, T., "Assigning Experimental and Testing Numbers
              Considered Useful", BCP 82, RFC 3692,
              DOI 10.17487/RFC3692, January 2004,
              <https://www.rfc-editor.org/info/rfc3692>.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              DOI 10.17487/RFC4861, September 2007,
              <https://www.rfc-editor.org/info/rfc4861>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,
              <https://www.rfc-editor.org/info/rfc8200>.

7.2.  Informative References

   [ATN]      Maiolla, V., "The OMNI Interface - An IPv6 Air/Ground
              Interface for Civil Aviation, IETF Liaison Statement
              #1676, https://datatracker.ietf.org/liaison/1676/", March
              2020.

   [ATN-IPS]  WG-I, ICAO., "ICAO Document 9896 (Manual on the
              Aeronautical Telecommunication Network (ATN) using
              Internet Protocol Suite (IPS) Standards and Protocol),
              Draft Edition 3 (work-in-progress)", December 2020.

   [I-D.templin-6man-omni-interface]
              Templin, F. and T. Whyman, "Transmission of IP Packets
              over Overlay Multilink Network (OMNI) Interfaces", draft-
              templin-6man-omni-interface-69 (work in progress), January
              2021.

   [RFC2474]  Nichols, K., Blake, S., Baker, F., and D. Black,
              "Definition of the Differentiated Services Field (DS
              Field) in the IPv4 and IPv6 Headers", RFC 2474,
              DOI 10.17487/RFC2474, December 1998,
              <https://www.rfc-editor.org/info/rfc2474>.

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Authors' Addresses

   Fred L. Templin (editor)
   The Boeing Company
   P.O. Box 3707
   Seattle, WA  98124
   USA

   Email: fltemplin@acm.org

   Tony Whyman
   MWA Ltd c/o Inmarsat Global Ltd
   99 City Road
   London  EC1Y 1AX
   England

   Email: tony.whyman@mccallumwhyman.com

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