



Internet Engineering Task Force (IETF)                         S. Venaas
Request for Comments: 8736                           Cisco Systems, Inc.
Obsoletes: 6166                                                A. Retana
Updates: 3973, 5015, 5059, 6754, 7761,      Futurewei Technologies, Inc.
         8364                                              February 2020
Category: Standards Track                                               
ISSN: 2070-1721


           PIM Message Type Space Extension and Reserved Bits

Abstract

   The PIM version 2 messages share a common message header format.  The
   common header definition contains eight reserved bits.  This document
   specifies how these bits may be used by individual message types and
   creates a registry containing the per-message-type usage.  This
   document also extends the PIM type space by defining three new
   message types.  For each of the new types, four of the previously
   reserved bits are used to form an extended type range.

   This document updates RFCs 7761 and 3973 by defining the use of the
   currently Reserved field in the PIM common header.  This document
   further updates RFCs 7761 and 3973, along with RFCs 5015, 5059, 6754,
   and 8364, by specifying the use of the currently reserved bits for
   each PIM message.

   This document obsoletes RFC 6166.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8736.

Copyright Notice

   Copyright (c) 2020 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
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction
   2.  Conventions Used in This Document
   3.  PIM Header Common Format
   4.  Flag Bit Definitions
     4.1.  Flag Bits for Type 4 (Bootstrap)
     4.2.  Flag Bits for Type 10 (DF Election)
     4.3.  Flag Bits for Type 12 (PFM)
     4.4.  Flag Bits for Types 13, 14, and 15 (Type Space Extension)
   5.  PIM Type Space Extension
   6.  Security Considerations
   7.  IANA Considerations
   8.  References
     8.1.  Normative References
     8.2.  Informative References
   Authors' Addresses

1.  Introduction

   The PIM version 2 messages share a common message header format
   defined in the PIM Sparse Mode specification [RFC7761].  The common
   header definition contains eight reserved bits.  While all message
   types use this common header, there is no document formally
   specifying that these bits are to be used per message type.

   This document refers to the bits specified as "reserved" in the
   common PIM header [RFC7761] as "PIM message type Flag Bits" or,
   simply, "Flag Bits", and it specifies that they are to be separately
   used on a per-message-type basis.  It creates a registry containing
   the per-message-type usage.

   This document updates [RFC7761] and [RFC3973] by defining the use of
   the currently Reserved field in the PIM common header.  This document
   further updates [RFC7761] and [RFC3973], along with [RFC5015],
   [RFC5059], [RFC6754], and [RFC8364], by specifying the use of the
   currently reserved bits for each PIM message.

   The currently defined PIM message types are in the range from 0 to
   15.  That type space is almost exhausted.  Message type 15 was
   reserved by [RFC6166] for type space extension.  In Section 5, this
   document specifies the use of the Flag Bits for message types 13, 14,
   and 15 in order to extend the PIM type space.  This document
   obsoletes [RFC6166].

2.  Conventions Used in This Document

   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.  PIM Header Common Format

   The common PIM header is defined in Section 4.9 of [RFC7761].  This
   document updates the definition of the Reserved field and refers to
   that field as "PIM message type Flag Bits" or, simply, "Flag Bits".
   The new common header format is as below.

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |PIM Ver| Type  |   Flag Bits   |           Checksum            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Figure 1: New Common Header

   The Flag Bits field is defined in Section 4.  All other fields remain
   unchanged.

4.  Flag Bit Definitions

   Unless otherwise specified, all the flag bits for each PIM type are
   Reserved [RFC8126].  They MUST be set to zero on transmission, and
   they MUST be ignored upon receipt.  The specification of a new PIM
   type MUST indicate whether the bits should be treated differently.

   When defining flag bits, it is helpful to have a well-defined way of
   referring to a particular bit.  The most significant of the flag
   bits, the bit immediately following the Type field, is referred to as
   bit 7.  The least significant, the bit right in front of the Checksum
   field, is referred to as bit 0.  This is shown in the diagram below.

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |PIM Ver| Type  |7 6 5 4 3 2 1 0|           Checksum            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                            Figure 2: Flag Bits

4.1.  Flag Bits for Type 4 (Bootstrap)

   PIM message type 4 (Bootstrap) [RFC5059] defines flag bit 7 as No-
   Forward.  The usage of the bit is defined in that document.  The
   remaining flag bits are reserved.

4.2.  Flag Bits for Type 10 (DF Election)

   PIM message type 10 (DF Election) [RFC5015] specifies that the four
   most significant flag bits (bits 4-7) are to be used as a subtype.
   The usage of those bits is defined in that document.  The remaining
   flag bits are reserved.

4.3.  Flag Bits for Type 12 (PFM)

   PIM message type 12 (PIM Flooding Mechanism) [RFC8364] defines flag
   bit 7 as No-Forward.  The usage of the bit is defined in that
   document.  The remaining flag bits are reserved.

4.4.  Flag Bits for Types 13, 14, and 15 (Type Space Extension)

   These types and the corresponding flag bits are defined in Section 5.

5.  PIM Type Space Extension

   This document defines types 13, 14, and 15, such that each of these
   types has 16 subtypes, providing a total of 48 subtypes available for
   future PIM extensions.  This is achieved by defining a new Subtype
   field (see Figure 3) using the four most significant flag bits (bits
   4-7).  The notation type.subtype is used to reference these new
   extended types.  The remaining four flag bits (bits 0-3) are reserved
   to be used by each extended type (abbreviated as FB below).

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |PIM Ver| Type  |Subtype|  FB   |           Checksum            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                             Figure 3: Subtypes

6.  Security Considerations

   This document clarifies the use of the flag bits in the common PIM
   header, and it extends the PIM type space.  As such, there is no
   impact on security or changes to the considerations in [RFC7761] and
   [RFC3973].

7.  IANA Considerations

   This document updates the "PIM Message Types" registry to indicate
   which flag bits are defined for use by each of the PIM message types.
   The registry now references this document.  The registration policy
   remains IETF Review [RFC8126].  Assignments into this registry MUST
   define any non-default usage (see Section 4) of the flag bits in
   addition to the type.

   The updated "PIM Message Types" registry is shown below.

    +------------+---------------+---------------+--------------------+
    | Type       | Name          | Flag Bits     | Reference          |
    +============+===============+===============+====================+
    | 0          | Hello         | 0-7: Reserved | [RFC3973][RFC7761] |
    +------------+---------------+---------------+--------------------+
    | 1          | Register      | 0-7: Reserved | [RFC7761]          |
    +------------+---------------+---------------+--------------------+
    | 2          | Register Stop | 0-7: Reserved | [RFC7761]          |
    +------------+---------------+---------------+--------------------+
    | 3          | Join/Prune    | 0-7: Reserved | [RFC3973][RFC7761] |
    +------------+---------------+---------------+--------------------+
    | 4          | Bootstrap     | 0-6: Reserved | [RFC5059][RFC7761] |
    |            |               +---------------+--------------------+
    |            |               | 7: No-Forward | [RFC5059]          |
    +------------+---------------+---------------+--------------------+
    | 5          | Assert        | 0-7: Reserved | [RFC3973][RFC7761] |
    +------------+---------------+---------------+--------------------+
    | 6          | Graft         | 0-7: Reserved | [RFC3973]          |
    +------------+---------------+---------------+--------------------+
    | 7          | Graft-Ack     | 0-7: Reserved | [RFC3973]          |
    +------------+---------------+---------------+--------------------+
    | 8          | Candidate RP  | 0-7: Reserved | [RFC7761]          |
    |            | Advertisement |               |                    |
    +------------+---------------+---------------+--------------------+
    | 9          | State Refresh | 0-7: Reserved | [RFC3973]          |
    +------------+---------------+---------------+--------------------+
    | 10         | DF Election   | 0-3: Reserved | [RFC5015]          |
    |            |               +---------------+--------------------+
    |            |               | 4-7: Subtype  | [RFC5015]          |
    +------------+---------------+---------------+--------------------+
    | 11         | ECMP Redirect | 0-7: Reserved | [RFC6754]          |
    +------------+---------------+---------------+--------------------+
    | 12         | PIM Flooding  | 0-6: Reserved | [RFC8364]          |
    |            | Mechanism     +---------------+--------------------+
    |            |               | 7: No-Forward | [RFC8364]          |
    +------------+---------------+---------------+--------------------+
    | 13.0-15.15 | Unassigned    | 0-3:          | RFC 8736           |
    |            |               | Unassigned    |                    |
    +------------+---------------+---------------+--------------------+

                Table 1: Updated PIM Message Types Registry

   The unassigned types above, as explained in Section 5, use the
   extended type notation of type.subtype.  Each extended type only has
   4 flag bits available.  New extended message types should be assigned
   consecutively, starting with 13.0, then 13.1, etc.

8.  References

8.1.  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>.

   [RFC7761]  Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
              Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
              Multicast - Sparse Mode (PIM-SM): Protocol Specification
              (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
              2016, <https://www.rfc-editor.org/info/rfc7761>.

   [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>.

8.2.  Informative References

   [RFC3973]  Adams, A., Nicholas, J., and W. Siadak, "Protocol
              Independent Multicast - Dense Mode (PIM-DM): Protocol
              Specification (Revised)", RFC 3973, DOI 10.17487/RFC3973,
              January 2005, <https://www.rfc-editor.org/info/rfc3973>.

   [RFC5015]  Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano,
              "Bidirectional Protocol Independent Multicast (BIDIR-
              PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007,
              <https://www.rfc-editor.org/info/rfc5015>.

   [RFC5059]  Bhaskar, N., Gall, A., Lingard, J., and S. Venaas,
              "Bootstrap Router (BSR) Mechanism for Protocol Independent
              Multicast (PIM)", RFC 5059, DOI 10.17487/RFC5059, January
              2008, <https://www.rfc-editor.org/info/rfc5059>.

   [RFC6166]  Venaas, S., "A Registry for PIM Message Types", RFC 6166,
              DOI 10.17487/RFC6166, April 2011,
              <https://www.rfc-editor.org/info/rfc6166>.

   [RFC6754]  Cai, Y., Wei, L., Ou, H., Arya, V., and S. Jethwani,
              "Protocol Independent Multicast Equal-Cost Multipath
              (ECMP) Redirect", RFC 6754, DOI 10.17487/RFC6754, October
              2012, <https://www.rfc-editor.org/info/rfc6754>.

   [RFC8364]  Wijnands, IJ., Venaas, S., Brig, M., and A. Jonasson, "PIM
              Flooding Mechanism (PFM) and Source Discovery (SD)",
              RFC 8364, DOI 10.17487/RFC8364, March 2018,
              <https://www.rfc-editor.org/info/rfc8364>.

Authors' Addresses

   Stig Venaas
   Cisco Systems, Inc.
   Tasman Drive
   San Jose, CA 95134
   United States of America

   Email: stig@cisco.com


   Alvaro Retana
   Futurewei Technologies, Inc.
   2330 Central Expressway
   Santa Clara, CA 95050
   United States of America

   Email: alvaro.retana@futurewei.com
