Network Working Group S. Venaas
Internet-Draft Cisco Systems, Inc.
Updates: 3973, 5015, 6754, 7761, 8364 A. Retana
(if approved) Huawei R&D USA
Intended status: Standards Track June 27, 2018
Expires: December 29, 2018

PIM reserved bits and type space extension
draft-venaas-pim-reserved-bits-01

Abstract

The currently defined 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, RFC6754 and RFC8364, by specifying the use of the currently Reserved bits for each PIM message.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on December 29, 2018.

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Table of Contents

1. Introduction

The currently defined PIM version 2 messages share a common message header format defined in the PIM Sparse Mode [RFC7761] and Dense Mode [RFC3973] specifications. The common header definition contains eight reserved bits. The message types defined in these documents all use this common header. However, several messages already make use of one or more bits, including the Bootstrap [RFC5059], DF-Election [RFC5015], and PIM Flooding Mechanism (PFM) [RFC8364] messages. 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] [RFC3973] 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 the per message type usage. For a particular message type, the usage of the flag bits can be defined in the document defining the message type, or a new document that updates that document.

The PIM message types as defined in the PIM Sparse Mode [RFC7761] and Dense Mode [RFC3973] specifications 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. The registration procedure for the extended type space is the same as for the existing type space, and the existing PIM message type registry is updated to include the extended type space.

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            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	

The common PIM header is defined in section 4.9 of [RFC7761] and section 4.7.1 of [RFC3973]. 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. Currently for the message types 0 (Hello), 1 (Register), 2 (Register Stop), 3 (Join/Prune), 5 (Assert), 6 (Graft), 7 (Graft-Ack), 8 (Candidate RP Advertisement), 9 (State Refresh) and 11 (ECMP Redirect), all flag bits are Reserved.

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            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	

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 currently 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 Type 13 (Type Space Extension)

This type and the flag bit usage is defined in Section 5.

4.5. Flag Bits for Type 14 (Type Space Extension)

This type and the flag bit usage is defined in Section 5.

4.6. Flag Bits for Type 15 (Type Space Extension)

This type and the flag bit usage is defined in Section 5.

5. PIM Type Space Extension

The type space defined by the existing PIM specifications is almost exhausted. This document defines types 13, 14 and 15 (Type Space Extension) allowing for 48 additional types by for each of the three types, using the four most significant flag bits (bits 4-7) as a new field to store the extended type. These types are referred to as types 13.0 to 13.15, 14.0 to 14.15 and 15.0 to 15.15 where the last number denotes the value stored in the new field. The remaining four flag bits (bits 0-3) are Reserved to be used by each extended type. The specification of a new PIM extended type MUST indicate whether the bits should be treated differently. The common header for the new types is shown in the diagram below. The "Type" field is set to 13, 14 or 15, and the extended type field "SubType" denotes the value after the dot.

    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            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	

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 and also creates a PIM Message Type Flag Bits registry that shows which flag bits are defined for use by each of the PIM message types.

The following changes should be made to the existing PIM Message Types registry. For types 4 (Bootstrap) and 8 (Candidate RP Advertisement) a reference to RFC5059 should be added. For the currently unassigned types 13 and 14, and the reserved type 15, the name should be changed to "Type Space Extension", and reference this document. In addition, right underneath each of the rows for types 13, 14 and 15, there should be a new row where it says "13.0-13.15 Unassigned", "14.0-14.15 Unassigned" and "15.0-15.15 Unassigned", respectively.

A new registry called "PIM Message Type Flag Bits" should be created in the pim-paremeters section with registration procedure "IETF Review" as defined in [RFC8126] with this document as a reference. The initial content of the registry should be as below.

 Type      bit(s)         Name                   Reference
--------------------------------------------------------------
  0         0-7   Reserved                  [RFC3973][RFC7761]
  1         0-7   Reserved                  [RFC3973][RFC7761]
  2         0-7   Reserved                  [RFC3973][RFC7761]
  3         0-7   Reserved                  [RFC3973][RFC7761]
  4         0-6   Reserved                  [RFC3973][RFC7761]
  4         7     No-Forward                [RFC5059]
  5         0-7   Reserved                  [RFC3973][RFC7761]
  6         0-7   Reserved                  [RFC3973][RFC7761]
  7         0-7   Reserved                  [RFC3973][RFC7761]
  8         0-7   Reserved                  [RFC3973][RFC7761]
  9         0-7   Reserved                  [RFC3973][RFC7761]
 10         0-3   Reserved                  [RFC3973][RFC7761]
 10         4-7   Sub-type                  [RFC5015]
 11         0-7   Reserved                  [RFC6754]
 12         0-6   Reserved                  [RFC3973][RFC7761]
 12         7     No-Forward                [RFC8364]
 13         0-3   N/A (used by 13.0-13.15)  [this document]
 13         4-7   Extended type             [this document]
 13.0-13.15 0-3   Reserved                  [this document]
 14         0-3   N/A (used by 14.0-14.15)  [this document]
 14         4-7   Extended type             [this document]
 14.0-14.15 0-3   Reserved                  [this document]
 15         0-3   N/A (used by 15.0-15.15)  [this document]
 15         4-7   Extended type             [this document]
 15.0-15.15 0-3   Reserved                  [this document]
	

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.
[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.
[RFC5015] Handley, M., Kouvelas, I., Speakman, T. and L. Vicisano, "Bidirectional Protocol Independent Multicast (BIDIR-PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007.
[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.
[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.
[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.
[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.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017.
[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.

8.2. Informative References

[RFC6166] Venaas, S., "A Registry for PIM Message Types", RFC 6166, DOI 10.17487/RFC6166, April 2011.

Authors' Addresses

Stig Venaas Cisco Systems, Inc. Tasman Drive San Jose, CA 95134 USA EMail: stig@cisco.com
Alvaro Retana Huawei R&D USA 2330 Central Expressway Santa Clara, CA 95050 USA EMail: alvaro.retana@huawei.com