Internet-Draft PIM Type Extension and Reserved Bits May 2023
Venaas & Retana Expires 25 November 2023 [Page]
Workgroup:
PIM
Internet-Draft:
draft-ietf-pim-rfc8736bis-04
Obsoletes:
8736 (if approved)
Updates:
3973, 5015, 5059, 6754, 7761, 8364 (if approved)
Published:
Intended Status:
Standards Track
Expires:
Authors:
S. Venaas
Cisco Systems, Inc.
A. Retana
Futurewei Technologies, Inc.

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 extends the PIM type space.

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 RFC8736.

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/.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on 25 November 2023.

Table of Contents

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 in the Reserved field of 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 updates the "PIM Message Types" registry to indicate 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 originally defined PIM message types were in the range from 0 to 15. Message type 15 had been 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. The type space extension in [RFC6166] was made obsolete by [RFC8736]. This document obsoletes [RFC8736].

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 updated 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: Updated 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 Unassigned [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 unassigned.

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 unassigned.

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 unsassigned.

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 extends types 13, 14, and 15 such that each becomes 16 new types, resulting in 48 types available for future PIM extensions. This extension is achieved by defining a Subtype field (see Figure 3) using the four most significant flag bits (bits 4-7). The notation type.subtype is used to reference the new extended types. The remaining four flag bits (bits 0-3, abbreviated as FB below) are to be defined by each extended type.

Each of the extended types is represented by the eight bits resulting from the concatenation of the Type and Subtype fields. No relationship is expected or implied between extended type messages with a common Type field.

    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, and changes their registration status to Unassigned, as shown in Table 1. The registration policy remains IETF Review [RFC8126]. Assignments to this registry MUST define any non-default usage (see Section 4) of the flag bits in addition to the type.

Extended type 15.15 is Reserved [RFC8126] for future extensions.

Because this document obsoletes RFC 8736, IANA is asked to change all registration information that references [RFC8736] to instead reference [this document].

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

Table 1: Updated PIM Message Types Registry
Type Name Flag Bits Reference
0 Hello 0-7: Unassigned [RFC3973][RFC7761]
1 Register 0-7: Unassigned [RFC7761]
2 Register Stop 0-7: Unassigned [RFC7761]
3 Join/Prune 0-7: Unassigned [RFC3973][RFC7761]
4 Bootstrap 0-6: Unassigned [RFC5059][RFC7761]
7: No-Forward [RFC5059]
5 Assert 0-7: Unassigned [RFC3973][RFC7761]
6 Graft 0-7: Unassigned [RFC3973]
7 Graft-Ack 0-7: Unassigned [RFC3973]
8 Candidate RP Advertisement 0-7: Unassigned [RFC7761]
9 State Refresh 0-7: Unassigned [RFC3973]
10 DF Election 0-3: Unassigned [RFC5015]
4-7: Subtype [RFC5015]
11 ECMP Redirect 0-7: Unassigned [RFC6754]
12 PIM Flooding Mechanism 0-6: Unassigned [RFC8364]
7: No-Forward [RFC8364]
13.0-15.14 Unassigned 0-3: Unassigned [This document]
15.15 Reserved 0-3: Reserved [This document]

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, , <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, , <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, , <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, , <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, , <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, , <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, , <https://www.rfc-editor.org/info/rfc5059>.
[RFC6166]
Venaas, S., "A Registry for PIM Message Types", RFC 6166, DOI 10.17487/RFC6166, , <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, , <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, , <https://www.rfc-editor.org/info/rfc8364>.
[RFC8736]
Venaas, S. and A. Retana, "PIM Message Type Space Extension and Reserved Bits", RFC 8736, DOI 10.17487/RFC8736, , <https://www.rfc-editor.org/info/rfc8736>.

Authors' Addresses

Stig Venaas
Cisco Systems, Inc.
Tasman Drive
San Jose, CA 95134
United States of America
Alvaro Retana
Futurewei Technologies, Inc.
2330 Central Expressway
Santa Clara, CA 95050
United States of America