Multicast Routing In Fat Trees
draft-zzhang-rift-multicast-00

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RIFT                                                            Z. Zhang
Internet-Draft                                          Juniper Networks
Intended status: Standards Track                              P. Thubert
Expires: January 9, 2020                                           Cisco
                                                            July 8, 2019

                     Multicast Routing In Fat Trees
                     draft-zzhang-rift-multicast-00

Abstract

   This document specifies multicast procedures with RIFT.  Multicast in
   RIFT is similar to Bidirectional Protocol Independent Multicast (PIM-
   Bidir), with the Rendezvous Point Link (RP-Link) simulated by a
   spanning tree of some Top of Fabric (ToF) nodes and sub-ToF nodes.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC2119.

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

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   Copyright (c) 2019 IETF Trust and the persons identified as the
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   This document is subject to BCP 78 and the IETF Trust's Legal
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   (https://trustee.ietf.org/license-info) in effect on the date of

Zhang & Thubert          Expires January 9, 2020                [Page 1]
Internet-Draft                    mrift                        July 2019

   publication of this document.  Please review these documents
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Specifications  . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   4.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     5.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     5.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   Because of the simple north-south regular topology in Fat Tree
   networks, the PIM-Bidir [RFC5015] solution is extended for multicast
   in RIFT (referred to as MRIFT in this document).  The following is a
   summary of the changes and adaptations compared to PIM-Bidir.

   With PIM-Bidir, PIM joins are sent towards a Rendezvous Point
   Address, which could be an address not belonging to any router.  The
   RPA does belong to a RP Link (RPL), which could be attached to a
   single router or multiple routers (e.g.  RPL is a LAN).  With MRIFT,
   there is no concept of RPA any more (joins are simply sent
   northbound).  The joins are terminated on some sub-ToF nodes and the
   RPL is simulated by a spanning tree among some ToF and sub-ToF nodes.

   Instead of (*,G) trees in PIM-Bidir, MRIFT uses (*,G-Prefix) trees,
   where the G-Prefix could be *, G, or anything in between (e.g.,
   225.1.1.0/24).  For light flows, they could just follow the (*,*)
   tree.  For heavy flows, individual (*,G) trees could be built.  For
   medium flows, some (*,G-prefix) trees could be shared.  All the First
   Hop Routers (FHRs, connecting to sources) and the Last Hop Routers
   (LHRs, connecting to receivers) of a particular (*,G) flow must agree
   on whether a (*,*) or (*,G) or (*,G-prefix) tree is used for the flow
   so that they all join the same tree.  This is done via out of band
   control outside the scope of this document.

   Because of the rich connections in Fat Trees, a router has to choose
   one of its many north neighbors to send join to.  This is done
   through hashing.  The hashing algorithm should lead to several but
   not too many routers choosing the same north neighbor, so that fewer
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