PIM Designated Router Load Balancing
RFC 8775

Document Type RFC - Proposed Standard (April 2020; No errata)
Authors Yiqun Cai  , Heidi Ou  , Sri Vallepalli  , Mankamana Mishra  , Stig Venaas  , Andy Green 
Last updated 2020-04-22
Replaces draft-hou-pim-drlb
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Document shepherd Mike McBride
Shepherd write-up Show (last changed 2019-01-14)
IESG IESG state RFC 8775 (Proposed Standard)
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Internet Engineering Task Force (IETF)                            Y. Cai
Request for Comments: 8775                                         H. Ou
Category: Standards Track                                  Alibaba Group
ISSN: 2070-1721                                            S. Vallepalli
                                                                        
                                                               M. Mishra
                                                               S. Venaas
                                                     Cisco Systems, Inc.
                                                                A. Green
                                                         British Telecom
                                                              April 2020

                  PIM Designated Router Load Balancing

Abstract

   On a multi-access network, one of the PIM-SM (PIM Sparse Mode)
   routers is elected as a Designated Router.  One of the
   responsibilities of the Designated Router is to track local multicast
   listeners and forward data to these listeners if the group is
   operating in PIM-SM.  This document specifies a modification to the
   PIM-SM protocol that allows more than one of the PIM-SM routers to
   take on this responsibility so that the forwarding load can be
   distributed among multiple routers.

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
   https://www.rfc-editor.org/info/rfc8775.

Copyright Notice

   Copyright (c) 2020 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
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction
   2.  Terminology
   3.  Applicability
   4.  Functional Overview
     4.1.  GDR Candidates
   5.  Protocol Specification
     5.1.  Hash Mask and Hash Algorithm
     5.2.  Modulo Hash Algorithm
       5.2.1.  Modulo Hash Algorithm Examples
       5.2.2.  Limitations
     5.3.  PIM Hello Options
       5.3.1.  PIM DR Load-Balancing Capability (DRLB-Cap) Hello
               Option
       5.3.2.  PIM DR Load-Balancing List (DRLB-List) Hello Option
     5.4.  PIM DR Operation
     5.5.  PIM GDR Candidate Operation
     5.6.  DRLB-List Hello Option Processing
     5.7.  PIM Assert Modification
     5.8.  Backward Compatibility
   6.  Operational Considerations
   7.  IANA Considerations
     7.1.  Initial Registry
     7.2.  Assignment of New Hash Algorithms
   8.  Security Considerations
   9.  References
     9.1.  Normative References
     9.2.  Informative References
   Acknowledgements
   Authors' Addresses

1.  Introduction

   On a multi-access LAN (such as an Ethernet) with one or more PIM-SM
   (PIM Sparse Mode) [RFC7761] routers, one of the PIM-SM routers is
   elected as a Designated Router (DR).  The PIM DR has two
   responsibilities in the PIM-SM protocol.  For any active sources on a
   LAN, the PIM DR is responsible for registering with the Rendezvous
   Point (RP) if the group is operating in PIM-SM.  Also, the PIM DR is
   responsible for tracking local multicast listeners and forwarding
   data to these listeners if the group is operating in PIM-SM.

   Consider the following LAN in Figure 1:

                             (core networks)
                              |     |     |
                              |     |     |
                             R1    R2     R3
                              |     |     |
                              ----(LAN)----
                                    |
                                    |
                            (many receivers)

                        Figure 1: LAN with Receivers

   Assume R1 is elected as the DR.  According to the PIM-SM protocol, R1
   will be responsible for forwarding traffic to that LAN on behalf of
   all local members.  In addition to keeping track of membership
   reports, R1 is also responsible for initiating the creation of source
   and/or shared trees towards the senders or the RPs.  The membership
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