Cisco Systems, Inc.

Tasman Drive San Jose CA 95134 United States of America stig@cisco.com

Futurewei Technologies, Inc.

2330 Central Expressway Santa Clara CA 95050 United States of America alvaro.retana@futurewei.com

Routing Multicast 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 .

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Table of Contents

• .  Introduction
• .  Conventions Used in This Document
• .  PIM Header Common Format
• .  Flag Bit Definitions
  • .  Flag Bits for Type 4 (Bootstrap)
  • .  Flag Bits for Type 10 (DF Election)
  • .  Flag Bits for Type 12 (PFM)
  • .  Flag Bits for Types 13, 14, and 15 (Type Space Extension)
• .  PIM Type Space Extension
• .  Security Considerations
• .  IANA Considerations
• .  References
  • .  Normative References
  • .  Informative References
• Authors' Addresses

Introduction The PIM version 2 messages share a common message header format defined in the PIM Sparse Mode specification . 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 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 and by defining the use of the currently Reserved field in the PIM common header. This document further updates and , along with , , , and , 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 for type space extension. In , 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 .

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 when, and only when, they appear in all capitals, as shown here.

PIM Header Common Format The common PIM header is defined in . 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.

New Common Header 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

Flag Bit Definitions Unless otherwise specified, all the flag bits for each PIM type are Reserved . 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.

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

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

Flag Bits for Type 10 (DF Election) PIM message type 10 (DF Election) 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.

Flag Bits for Type 12 (PFM) PIM message type 12 (PIM Flooding Mechanism) defines flag bit 7 as No-Forward. The usage of the bit is defined in that document. The remaining flag bits are reserved.

Flag Bits for Types 13, 14, and 15 (Type Space Extension) These types and the corresponding flag bits are defined in .

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).

Subtypes 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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 and .

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 . Assignments into this registry MUST define any non-default usage (see ) of the flag bits in addition to the type. The updated "PIM Message Types" registry is shown below. Updated PIM Message Types Registry

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

The unassigned types above, as explained in , 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.

References Normative References In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. This document specifies Protocol Independent Multicast - Sparse Mode (PIM-SM). PIM-SM is a multicast routing protocol that can use the underlying unicast routing information base or a separate multicast-capable routing information base. It builds unidirectional shared trees rooted at a Rendezvous Point (RP) per group, and it optionally creates shortest-path trees per source. This document obsoletes RFC 4601 by replacing it, addresses the errata filed against it, removes the optional (*,*,RP), PIM Multicast Border Router features and authentication using IPsec that lack sufficient deployment experience (see Appendix A), and moves the PIM specification to Internet Standard. Many protocols make use of points of extensibility that use constants to identify various protocol parameters. To ensure that the values in these fields do not have conflicting uses and to promote interoperability, their allocations are often coordinated by a central record keeper. For IETF protocols, that role is filled by the Internet Assigned Numbers Authority (IANA). To make assignments in a given registry prudently, guidance describing the conditions under which new values should be assigned, as well as when and how modifications to existing values can be made, is needed. This document defines a framework for the documentation of these guidelines by specification authors, in order to assure that the provided guidance for the IANA Considerations is clear and addresses the various issues that are likely in the operation of a registry. This is the third edition of this document; it obsoletes RFC 5226. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. Informative References This document specifies Protocol Independent Multicast - Dense Mode (PIM-DM). PIM-DM is a multicast routing protocol that uses the underlying unicast routing information base to flood multicast datagrams to all multicast routers. Prune messages are used to prevent future messages from propagating to routers without group membership information. This memo defines an Experimental Protocol for the Internet community. This document discusses Bidirectional PIM (BIDIR-PIM), a variant of PIM Sparse-Mode that builds bidirectional shared trees connecting multicast sources and receivers. Bidirectional trees are built using a fail-safe Designated Forwarder (DF) election mechanism operating on each link of a multicast topology. With the assistance of the DF, multicast data is natively forwarded from sources to the Rendezvous-Point (RP) and hence along the shared tree to receivers without requiring source-specific state. The DF election takes place at RP discovery time and provides the route to the RP, thus eliminating the requirement for data-driven protocol events. [STANDARDS-TRACK] This document specifies the Bootstrap Router (BSR) mechanism for the class of multicast routing protocols in the PIM (Protocol Independent Multicast) family that use the concept of a Rendezvous Point as a means for receivers to discover the sources that send to a particular multicast group. BSR is one way that a multicast router can learn the set of group-to-RP mappings required in order to function. The mechanism is dynamic, largely self-configuring, and robust to router failure. [STANDARDS-TRACK] This document provides instructions to IANA for the creation of a registry for PIM message types. It specifies the initial content of the registry, based on existing RFCs specifying PIM message types. It also specifies a procedure for registering new types. In addition to this, one message type is reserved, and may be used for a future extension of the message type space. [STANDARDS-TRACK] A Protocol Independent Multicast (PIM) router uses the Reverse Path Forwarding (RPF) procedure to select an upstream interface and router in order to build forwarding state. When there are equal cost multipaths (ECMPs), existing implementations often use hash algorithms to select a path. Such algorithms do not allow the spread of traffic among the ECMPs according to administrative metrics. This usually leads to inefficient or ineffective use of network resources. This document introduces the ECMP Redirect, a mechanism to improve the RPF procedure over ECMPs. It allows ECMP selection to be based on administratively selected metrics, such as data transmission delays, path preferences, and routing metrics. [STANDARDS-TRACK] Protocol Independent Multicast - Sparse Mode (PIM-SM) uses a Rendezvous Point (RP) and shared trees to forward multicast packets from new sources. Once Last-Hop Routers (LHRs) receive packets from a new source, they may join the Shortest Path Tree (SPT) for the source for optimal forwarding. This document defines a new mechanism that provides a way to support PIM-SM without the need for PIM registers, RPs, or shared trees. Multicast source information is flooded throughout the multicast domain using a new generic PIM Flooding Mechanism (PFM). This allows LHRs to learn about new sources without receiving initial data packets.

Authors' Addresses Cisco Systems, Inc.

Tasman Drive San Jose CA 95134 United States of America stig@cisco.com

Futurewei Technologies, Inc.

2330 Central Expressway Santa Clara CA 95050 United States of America alvaro.retana@futurewei.com