Multicast Path MTU
draft-nandy-singla-utkarsh-pim-mcast-path-mtu-00

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INTERNET-DRAFT                                      Tathagata Nandy
Intended Status: Proposed Standard                  HPE 
                                                    Nitin Singla    
                                                    HPE
                                                    Utkarsh Srivastava
                                                    HPE
Expires: 19 October 2020                            April 19, 2020

                          Multicast Path MTU
        draft-nandy-singla-utkarsh-pim-mcast-path-mtu-00
                
Abstract
   Path MTU discovery (rfc1191) is a standard technique to determine
   the supported MTU between two Internet Protocol (IP) hosts to avoid
   any fragmentation. In a multicast distribution tree, source will
   not know where the receivers are located. So the technique used to
   compute the path MTU for a unicast stream does not work in a
   multicast network.  This document describes a method to discover
   multicast path MTU with the goal to avoid traffic loss. This
   solution also aims to solve the problem of traffic loss in for
   multicast streams because of incorrect MTU setting and no path MTU
   support for multicast networks. 
  
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Internet-Draft            PIM Multicast Path MTU            April 2020


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions used in this document . . . . . . . . . . . . .  3
   3.  Problem Statement . . . . . . . . . . . . . . . . . . . . .  4
   4.  Multicast Data Path . . . . . . . . . . . . . . . . . . . .  5
     4.1. FHR to RP  . . . . . . . . . . . . . . . . . . . . . . .  5
     4.2.  Generic Routing . . . . . . . . . . . . . . . . . . . .  5
     4.3.  LHR to Host . . . . . . . . . . . . . . . . . . . . . .  6
   5.  Security Considerations . . . . . . . . . . . . . . . . . .  6
   6. IANA considerations . . . . . . . . . . . . . . . . . . . .   6
   7. References  . . . . . . . . . . . . . . . . . . . . . . . .   7
     7.1.  Normative References . . . . . . . . . . . . . . . . .   7
     7.2.  Informative References . . . . . . . . . . . . . . . .   7
   8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8    
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . .  8

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1.  Introduction
   When one IP host has a large amount of data to send to another
   host, the data is transmitted as a series of IP datagrams. It is
   usually preferable that these datagrams be of the largest size that
   does not require fragmentation anywhere along the path from the
   source to the destination.  (For the case against fragmentation,
   see [5].) This datagram size is referred to as the Path MTU (PMTU),
   and it is equal to the minimum of the MTUs of each hop in the path.
   A shortcoming of the current Internet protocol suite is the lack of
   a standard mechanism for a host to discover the PMTU of an
   arbitrary path.  Note: The Path MTU is what in [1] is called the
   "Effective MTU for sending" (EMTU_S). A PMTU is associated with a
   path, which is a particular combination of IP source and
   destination address and perhaps a Type-of-service (TOS).  The
   current practice [1] is to use the lesser of 576 and the first-hop
   MTU as the PMTU for any destination that is not connected to the
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