Protocol Independent Multicast-Sparse Mode (PIM-SM): Protocol Specification (RFC2117)
Original Publication Date: 1997-Jun-01
Included in the Prior Art Database: 2019-Feb-15
Internet Society Requests For Comment (RFCs)
D. Estrin: AUTHOR [+9]
This document describes a protocol for efficiently routing to multicast groups that may span wide-area (and inter-domain) internets. This memo defines an Experimental Protocol for the Internet community.
Network Working Group D. Estrin Request for Comments: 2117 USC Category: Experimental D. Farinacci CISCO A. Helmy USC D. Thaler UMICH S. Deering XEROX M. Handley UCL V. Jacobson LBL C. Liu USC P. Sharma USC L. Wei CISCO June 1997
Protocol Independent Multicast-Sparse Mode (PIM-SM): Protocol Specification
Status of This Memo
This memo defines an Experimental Protocol for the Internet community. This memo does not specify an Internet standard of any kind. Discussion and suggestions for improvement are requested. Distribution of this memo is unlimited.
The author list has been reordered to reflect the involvement in detailed editorial work on this specification document. The first four authors are the primary editors and are listed alphabetically. The rest of the authors, also listed alphabetically, participated in all aspects of the architectural and detailed design but managed to get away without hacking the latex!
Estrin, et. al. Experimental [Page 1]
RFC 2117 PIM-SM June 1997
This document describes a protocol for efficiently routing to multicast groups that may span wide-area (and inter-domain) internets. We refer to the approach as Protocol Independent Multicast--Sparse Mode (PIM-SM) because it is not dependent on any particular unicast routing protocol, and because it is designed to support sparse groups as defined in . This document describes the protocol details. For the motivation behind the design and a description of the architecture, see . Section 2 summarizes PIM-SM operation. It describes the protocol from a network perspective, in particular, how the participating routers interact to create and maintain the multicast distribution tree. Section 3 describes PIM-SM operations from the perspective of a single router implementing the protocol; this section constitutes the main body of the protocol specification. It is organized according to PIM-SM message type; for each message type we describe its contents, its generation, and its processing.
Sections 3.8 and 3.9 summarize the timers and flags referred to throughout this document. Section 4 provides packet format details.
The most significant functional changes since the January ’95 version involve the Rendezvous Point-related mechanisms, several resulting simplifications to the protocol, and removal of the PIM-DM protocol details to a separate document  (for clarity).
2 PIM-SM Protocol Overview
In this section we provide an overview of the architectural components of PIM-SM.
A router receives explicit Join/Prune messages from those neighboring routers that have downstream group members. The router then forwards data packets addressed to a multicast group, G, only onto those interfaces on which explicit joins have been received. Note that all routers mentioned in this document are assumed to be PIM-SM capable, unless otherwise specified.
A Designated Router (DR) sends periodic Join/Prune messages toward a group-specific Rendezvous Point...