PIM Message Type Space Extension and Reserved Bits
draft-ietf-pim-reserved-bits-03

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 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.

This document obsoletes RFC6166.

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 https://datatracker.ietf.org/drafts/current/.

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This Internet-Draft will expire on February 16, 2020.

Copyright Notice

Copyright (c) 2019 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 (https://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. 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 [RFC7761] specification. The common header definition contains eight Reserved bits. The message types defined in these documents all 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. Documents defining a new message type MUST define the usage of the corresponding Flag Bits.

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

    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  |   Flags Bits  |           Checksum            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        

FIgure 1: New Common Header

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.

The Flags 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 sub-type. The remaining Flag Bits are Reserved.

4.3. Flag Bits for Type 12 (PFM)

PIM message type 12 (PFM) [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. Documents defining a new extended message type MUST define the usage of the corresponding Flag Bits.

    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| Rsvd  |           Checksum            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        

Figure 3: Sub-Types

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 should now reference this document instead of [RFC6166]. The Registration Policy remains IETF Review [RFC8126].

The updated PIM Message Types registry is shown below.

 Type       Flag Bits              Name                 Reference
---------------------------------------------------------------------
  0           N/A      Hello                       [RFC3973][RFC7761]
  0           0-7      Reserved                    [RFC3973][RFC7761]
  1           N/A      Register                    [RFC7761]
  1           0-7      Reserved                    [RFC7761]
  2           N/A      Register Stop               [RFC7761]
  2           0-7      Reserved                    [RFC7761]
  3           N/A      Join/Prune                  [RFC3973][RFC7761]
  3           0-7      Reserved                    [RFC3973][RFC7761]
  4           N/A      Bootstrap                   [RFC7761]
  4           0-6      Reserved                    [RFC5059][RFC7761]
  4           7        No-Forward                  [RFC5059]
  5           N/A      Assert                      [RFC3973][RFC7761]
  5           0-7      Reserved                    [RFC3973][RFC7761]
  6           N/A      Graft                       [RFC3973]
  6           0-7      Reserved                    [RFC3973]
  7           N/A      Graft-Ack                   [RFC3973] 
  7           0-7      Reserved                    [RFC3973]
  8           N/A      Candidate RP Advertisement  [RFC7761]
  8           0-7      Reserved                    [RFC7761]
  9           N/A      State Refresh               [RFC3973]
  9           0-7      Reserved                    [RFC3973]
 10           N/A      DF Election                 [RFC5015]
 10           0-3      Reserved                    [RFC5015]
 10           4-7      Subtype                     [RFC5015]
 11           N/A      ECMP Redirect               [RFC6754]
 11           0-7      Reserved                    [RFC6754]
 12           N/A      PIM Flooding Mechanism      [RFC8364]
 12           0-6      Reserved                    [RFC8364]
 12           7        No-Forward                  [RFC8364]
 13.0-13.15   N/A      Unassigned                  [this document]
 14.0-14.15   N/A      Unassigned                  [this document]
 15.0-15.15   N/A      Unassigned                  [this document]

Table 1: Updated PIM Message Types Registry

8. References

8.1. Normative References

8.2. Informative References

Authors' Addresses