PIM                                                        S. E. Deering
Internet-Draft                                                   Retired
Obsoletes: 1112 (if approved)                             T. Eckert, Ed.
Updates: 791 (if approved)                    Futurewei Technologies USA
Intended status: Standards Track                         30 January 2025
Expires: 3 August 2025


Host Extensions for IP Multicasting and "Any Source Multicasting" (ASM)
                               IP service
                      draft-ietf-pim-rfc1112bis-03

Abstract

   This memo specifies the extensions required of a host implementation
   of the Internet Protocol (IP) to support IP multicast with the IP
   service interface "Any Source Multicast" (ASM).  This specification
   applies to both versions 4 and 6 of the Internet Protocol.
   Distribution of this memo is unlimited.

   This document replaces RFC1112 for everything but its specification
   of the IGMP version 1 protocol.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 3 August 2025.

Copyright Notice

   Copyright (c) 2025 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
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.



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   Please review these documents carefully, as they describe your rights
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   extracted from this document must include Revised BSD License text as
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   This document may contain material from IETF Documents or IETF
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   it for publication as an RFC or to translate it into languages other
   than English.

Table of Contents

   1.  STATUS OF THIS MEMO . . . . . . . . . . . . . . . . . . . . .   4
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
   2.  INTRODUCTION  . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Summary . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  LEVELS OF CONFORMANCE . . . . . . . . . . . . . . . . . . . .   6
     3.1.  Level 0: no support for IP multicasting.  . . . . . . . .   6
     3.2.  Level 1: support for sending but not receiving multicast IP
           datagrams.  . . . . . . . . . . . . . . . . . . . . . . .   7
     3.3.  Level 2: full support for IP multicasting.  . . . . . . .   7
   4.  HOST GROUP ADDRESSES  . . . . . . . . . . . . . . . . . . . .   7
   5.  MODEL OF A HOST IP IMPLEMENTATION . . . . . . . . . . . . . .   8
   6.  SENDING MULTICAST IP DATAGRAMS  . . . . . . . . . . . . . . .   9
     6.1.  Extensions to the IP Service Interface  . . . . . . . . .   9
     6.2.  Extensions to the IP Module . . . . . . . . . . . . . . .  10
     6.3.  Extensions to the Local Network Service Interface . . . .  11
     6.4.  Extensions to an Ethernet Local Network Module  . . . . .  11
     6.5.  Extensions to Local Network Modules other than
           Ethernet  . . . . . . . . . . . . . . . . . . . . . . . .  12
   7.  RECEIVING MULTICAST IP DATAGRAMS  . . . . . . . . . . . . . .  12
     7.1.  Extensions to the IP Service Interface  . . . . . . . . .  12
     7.2.  Extensions to the IP Module . . . . . . . . . . . . . . .  13
     7.3.  Extensions to the Local Network Service Interface . . . .  14
     7.4.  Extensions to an Ethernet Local Network Module  . . . . .  15
     7.5.  Extensions to Local Network Modules other than
           Ethernet  . . . . . . . . . . . . . . . . . . . . . . . .  15
   8.  ROUTING MULTICAST IP DATAGRAMS  . . . . . . . . . . . . . . .  15
   9.  Status changes  . . . . . . . . . . . . . . . . . . . . . . .  16



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     9.1.  Moving RFC1112 and IGMPv1 to historic status  . . . . . .  16
     9.2.  Backward compatibility with IGMPv1  . . . . . . . . . . .  16
     9.3.  Update to RFC 791 . . . . . . . . . . . . . . . . . . . .  16
     9.4.  Update to STD 5 . . . . . . . . . . . . . . . . . . . . .  17
   10. Changes from RFC1112  . . . . . . . . . . . . . . . . . . . .  17
     10.1.  Normative language . . . . . . . . . . . . . . . . . . .  17
     10.2.  References to IGMPv1 . . . . . . . . . . . . . . . . . .  17
     10.3.  New summary  . . . . . . . . . . . . . . . . . . . . . .  17
     10.4.  Any-Source Multicast (ASM) . . . . . . . . . . . . . . .  17
     10.5.  SSM  . . . . . . . . . . . . . . . . . . . . . . . . . .  17
     10.6.  Applicability to both IPv4 and IPv6  . . . . . . . . . .  18
     10.7.  IPv4 Local Network Control Block . . . . . . . . . . . .  18
     10.8.  Special treatment of 224.0.0.1 and FF02::1 . . . . . . .  19
     10.9.  IGMP/MLD messages for Link-Local IPv4 host group
             addresses . . . . . . . . . . . . . . . . . . . . . . .  19
     10.10. Standard for IP multicasting in controlled networks  . .  20
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  20
     11.1.  Protocol Numbers registry  . . . . . . . . . . . . . . .  20
     11.2.  Internet Group Management Protocol (IGMP) Type Numbers
            Registry . . . . . . . . . . . . . . . . . . . . . . . .  20
     11.3.  Multicast 48-bit MAC Addresses registry  . . . . . . . .  21
     11.4.  IPv4 Address range registries  . . . . . . . . . . . . .  21
     11.5.  IPv4 Multicast Address Space registry  . . . . . . . . .  21
     11.6.  IP Flow Information Export registry  . . . . . . . . . .  21
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  21
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  21
     12.2.  Informative References . . . . . . . . . . . . . . . . .  23
   Appendix A.  HOST GROUP ADDRESS ISSUES  . . . . . . . . . . . . .  25
     A.1.  Group Address Binding . . . . . . . . . . . . . . . . . .  25
     A.2.  Allocation of Transient Host Group Addresses  . . . . . .  26
     A.3.  Link-local IP multicast and IGMP/MLD  . . . . . . . . . .  26
   Appendix B.  Discussion and Explanations (TO BE REMOVED)  . . . .  28
     B.1.  RFC-Editor notes  . . . . . . . . . . . . . . . . . . . .  28
     B.2.  Goals and evolution of this document  . . . . . . . . . .  28
     B.3.  Update to RFC791  . . . . . . . . . . . . . . . . . . . .  29
     B.4.  Changelog . . . . . . . . . . . . . . . . . . . . . . . .  30
       B.4.1.  draft-ietf-pim-rfc1112bis-03  . . . . . . . . . . . .  30
       B.4.2.  draft-ietf-pim-rfc1112bis-02  . . . . . . . . . . . .  31
       B.4.3.  draft-ietf-pim-rfc1112bis-01  . . . . . . . . . . . .  31
       B.4.4.  draft-eckert-pim-rfc1112bis-02  . . . . . . . . . . .  32
       B.4.5.  draft-ietf-pim-rfc1112bis-00  . . . . . . . . . . . .  32
       B.4.6.  draft-eckert-pim-rfc1112bis-01  . . . . . . . . . . .  32
       B.4.7.  draft-eckert-pim-rfc1112bis-00  . . . . . . . . . . .  33
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  33







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1.  STATUS OF THIS MEMO

   This memo specifies the extensions required of a host implementation
   of the Internet Protocol (IP) to support IP multicast with the IP
   service interface "Any Source Multicast" (ASM).  This specification
   applies to both versions 4 and 6 of the Internet Protocol.
   Distribution of this memo is unlimited.

   This document replaces RFC1112 for everything except for its
   specification of the IGMP version 1 protocol.

1.1.  Requirements Language

   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 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  INTRODUCTION

2.1.  Summary

   This memo specifies the extensions required of a host implementation
   of the Internet Protocol (IP) to support IP multicast.  It replaces
   [RFC791] for everything except for the specification of the protocol
   IGMP version 1 in Appendix I. of RFC1112.  This document declares
   RFC1112 including IGMP version 1 historic.

   RFC1112 specified IP multicast for version 4 of the IP protocol
   (IPv4, [RFC791]), and refers to that version as IP.  This document
   applies both to version 4 of the IP protocol and version 6 of the IP
   protocol (IPv6, [RFC8200]).  The term IP is used in this document to
   refer to both versions.  Where specifications in support of IP
   multicast for version 6 of the IP protocol where already provided by
   other RFCs, this document provides references to those pre-existing
   specifications, so that this document can serve as a complete single
   point of reference for the host extensions for IP multicast with
   either versions of IP.

   "Source Specific Multicast", (SSM, [SSM]) introduced a complementary
   extension to the IP service from the one specified here.  It is
   relying on components specified here, such as {#ethernet}, and
   extending or superseding others.  The service specified here is
   called "Any Source Multicast" (ASM) to distinguish it explicitly from
   SSM.  This document also describes, where SSM changes specifications
   from RFC1112.




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   Due to the existence of both ASM and SSM, the term "IP multicast"
   best refers to the complete set of IP host extensions in support of
   either service options: this specification for ASM plus [SSM]).  When
   the term IP multicast is used to refer to the IP multicast service
   without further qualification, then ASM is to be implied.

   This specification aims to maintain all the original text of RFC1112
   where technically appropriate.  This incurs the use of some historic
   language, such as "(internet) gateway" to refer to IP routers, and
   capitalization of chapter headings.

   See Section 9 and Section 10 for a detailed list of changes from
   RFC1112.

2.2.  Overview

   IP multicasting is the transmission of an IP datagram to a "host
   group", a set of zero or more hosts identified by a single IP
   destination address.  A multicast datagram is delivered to all
   members of its destination host group with the same "best-efforts"
   reliability as regular unicast IP datagrams, i.e., the datagram is
   not guaranteed to arrive intact at all members of the destination
   group or in the same order relative to other datagrams.

   The membership of a host group is dynamic; that is, hosts may join
   and leave groups at any time.  There is no restriction on the
   location or number of members in a host group.  A host may be a
   member of more than one group at a time.  A host need not be a member
   of a group to send datagrams to it.

   A host group may be permanent or transient.  A permanent group has a
   well-known, administratively assigned IP address.  It is the address,
   not the membership of the group, that is permanent; at any time a
   permanent group may have any number of members, even zero.  Those IP
   multicast addresses that are not reserved for permanent groups are
   available for dynamic assignment to transient groups which exist only
   as long as they have members.














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   Internetwork forwarding of IP multicast datagrams is handled by
   "multicast routers" which may be co-resident with, or separate from,
   internet gateways.  A host transmits an IP multicast datagram as a
   local network multicast which reaches all immediately-neighboring
   members of the destination host group.  If the datagram has an IPv4
   time-to-live or IPv6 hop limit greater than 1, the multicast
   router(s) attached to the local network take responsibility for
   forwarding it towards all other networks that have members of the
   destination group.  On those other member networks that are reachable
   within the IPv4 time-to-live or IPv6 hop limit, an attached multicast
   router completes delivery by transmitting the datagram as a local
   multicast.

   This memo specifies the extensions required of a host IP
   implementation to support IP multicasting, where a "host" is any
   internet host or gateway other than those acting as multicast
   routers.  The algorithms and protocols used within and between
   multicast routers are transparent to hosts and will be specified in
   separate documents.  This memo also does not specify how local
   network multicasting is accomplished for all types of network,
   although it does specify the required service interface to an
   arbitrary local network and gives an Ethernet specification as an
   example.  Specifications for other types of network will be the
   subject of future memos.

3.  LEVELS OF CONFORMANCE

   There are three levels of conformance to this specification:

3.1.  Level 0: no support for IP multicasting.

   There is, at this time, no requirement that all IP implementations
   support IP multicasting.  Level 0 hosts will, in general, be
   unaffected by multicast activity.  The only exception arises on some
   types of local network, where the presence of level 1 or 2 hosts may
   cause misdelivery of multicast IP datagrams to level 0 hosts.  Such
   datagrams can easily be identified by the presence of a class D IP
   address in their destination address field; they SHOULD be quietly
   discarded by hosts that do not support IP multicasting.  Class D
   addresses in support of multicasting with IPv4 are described in
   section 4 of this memo, IPv6 addresses for IP multicasting are
   described in [RFC4291] and [RFC7371].









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3.2.  Level 1: support for sending but not receiving multicast IP
      datagrams.

   Level 1 allows a host to partake of some multicast-based services,
   such as resource location or status reporting, but it does not allow
   a host to join any host groups.  An IP implementation may be upgraded
   from level 0 to level 1 very easily and with little new code.  Only
   sections 4, 5, and 6 of this memo are applicable to level 1
   implementations.

3.3.  Level 2: full support for IP multicasting.

   Level 2 allows a host to join and leave host groups, as well as send
   IP datagrams to host groups.  Most IPv6 hosts require Level 2 support
   because IPv6 Neighbor Discovery ([RFC4861], as used on most link
   types), depends on multicast and requires that nodes join Solicited
   Node multicast addresses.

   Level 2 requires implementation of the Internet Group Management
   Protocol (IGMP) for IPv4 and the equivalent Multicast Listener
   Discovery Protocol (MLD) for IPv6 and extension of the IP and local
   network service interfaces within the host.

   The current protocol versions for full Level 2 support of IP
   multicasting are [IGMPv3] and [MLDv2] or lightweight versions of
   either protocol [IGMPv3lite].

   All of the following sections of this memo are applicable to level 2
   implementations.

4.  HOST GROUP ADDRESSES

   IPv4 Host groups are identified by class D IPv4 addresses, i.e.,
   those with "1110" as their high-order four bits.  Class E IPv4
   addresses, i.e., those with "1111" as their high-order four bits, are
   reserved for future addressing modes.















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   In Internet standard "dotted decimal" notation, IPv4 host group
   addresses range from 224.0.0.0 to 239.255.255.255.  IPv4 host group
   addresses in the "Local Network Control Block", 224.0.0.0 -
   224.0.0.255 are called Link-Local IPv4 host group addresses.  IP
   datagrams with a Link-Local destination address are called Link-Local
   multicast packets.  The IPv4 Link-Local addresses 224.0.0.0 is
   guaranteed not to be assigned to any group, and 224.0.0.1 is assigned
   to the permanent group of all IPv4 hosts (including gateways).  This
   is used to address all IP multicast hosts on the directly connected
   network.  There is no multicast address (or any other IP address) for
   all hosts on the total Internet.  Allocation guidelines for Link-
   Local addresses are specified in [RFC5771].

   The addresses of well-known, permanent groups are to be published in
   "Assigned Numbers", see [RFC3232], currently through the IANA "IPv4
   Multicast Address Space Registry".  [RFC5771] and [RFC6034] refine
   more detailed allocation and uses of different sub-blocks of
   224.0.0.0/4.

   The IPv6 all-hosts group address is FF02::1, IPv6 Host groups are
   identified by IPv6 addresses as defined in [RFC4291] section 2.7 and
   updated by [RFC7346], [RFC7371].  The addresses of other groups are
   currently published via the IANA "IPv6 Multicast Address Space
   Registry".

   IP addresses as specified in [SSM] are not used for ASM IP multicast
   and are not considered IP host groups by [SSM].  They are instead
   only the destination address part G of Source Specific Multicast
   (SSM) IP multicast (S,G) channels.

   Appendix I contains some background discussion of several issues
   related to host group addresses.

5.  MODEL OF A HOST IP IMPLEMENTATION

   The multicast extensions to a host IP implementation are specified in
   terms of the layered model illustrated below in Figure 1.  In this
   model, ICMP/ICMPv6 and (for level 2 hosts) IGMP/MLD are considered to
   be implemented within the IP module, and the mapping of IP addresses
   to local network addresses is considered to be the responsibility of
   local network modules.  This model is for expository purposes only,
   and should not be construed as constraining an actual implementation.









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      |                                                          |
      |              Upper-Layer Protocol Modules                |
      |__________________________________________________________|

   --------------------- IP Service Interface -----------------------
       __________________________________________________________
      |                            |              |              |
      |                            | IPv4:        | IPv6:        |
      |                            | ICMP+IGMP    | ICMPv6+MLD   |
      |    IP [IPv4 and/or IPv6]   |______________|______________|
      |           Module(s)                                      |
      |                                                          |
      |__________________________________________________________|

   ---------------- Local Network Service Interface -----------------
       __________________________________________________________
      |                            |                             |
      |           Local            | IP-to-local address mapping |
      |          Network           |         (e.g., ARP/ND)      |
      |          Modules           |_____________________________|
      |      (e.g., Ethernet)                                    |
      |                                                          |

         Figure 1: multicast extensions to a host IP implementation

   To provide level 1 multicasting, a host IP implementation MUST
   support the transmission of multicast IP datagrams.  To provide level
   2 multicasting, a host MUST also support the reception of multicast
   IP datagrams.  Each of these two new services is described in a
   separate section, below.  For each service, extensions are specified
   for the IP service interface, the IP module, the local network
   service interface, and an Ethernet local network module.  Extensions
   to local network modules other than Ethernet are mentioned briefly,
   but are not specified in detail.

6.  SENDING MULTICAST IP DATAGRAMS

6.1.  Extensions to the IP Service Interface

   Multicast IP datagrams are sent using the same "Send IP" operation
   used to send unicast IP datagrams; an upper-layer protocol module
   merely specifies an IP host group address, rather than an individual
   IP address, as the destination.  However, a number of extensions may
   be necessary or desirable.

   First, the service interface SHOULD provide a way for the upper-layer
   protocol to specify the IPv4 time-to-live or IPv6 hop limit of an
   outgoing multicast datagram, if such a capability does not already



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   exist.  If the upper-layer protocol chooses not to specify a time-to-
   live/hop limit, it SHOULD default to 1 for all multicast IP
   datagrams, so that an explicit choice is required to multicast beyond
   a single network.

   Second, for hosts that may be attached to more than one network, the
   service interface SHOULD provide a way for the upper-layer protocol
   to identify which network interface is be used for the multicast
   transmission.  Only one interface is used for the initial
   transmission; multicast routers are responsible for forwarding to any
   other networks, if necessary.  If the upper-layer protocol chooses
   not to identify an outgoing interface, a default interface SHOULD be
   used, preferably under the control of system management.

   Third (level 2 implementations only), for the case in which the host
   is itself a member of a group to which a datagram is being sent, the
   service interface SHOULD provide a way for the upper-layer protocol
   to inhibit local delivery of the datagram; by default, a copy of the
   datagram is looped back.  This is a performance optimization for
   upper-layer protocols that restrict the membership of a group to one
   process per host (such as a routing protocol), or that handle
   loopback of group communication at a higher layer (such as a
   multicast transport protocol).

   IPv6 socket extensions supporting these functions are defined in
   [RFC3493], section 5.2.

6.2.  Extensions to the IP Module

   To support the sending of multicast IP datagrams, the IP module MUST
   be extended to recognize IP host group addresses when routing
   outgoing datagrams.  Most IP implementations include the following
   logic:

       if IP-destination is on the same local network,
          send datagram locally to IP-destination
       else
          send datagram locally to GatewayTo( IP-destination )

   To allow multicast transmissions, the routing logic MUST be changed
   to:

       if IP-destination is on the same local network
       or IP-destination is a host group,
          send datagram locally to IP-destination
       else
          send datagram locally to GatewayTo( IP-destination )




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   If the sending host is itself a member of the destination group on
   the outgoing interface, a copy of the outgoing datagram MUST be
   looped-back for local delivery, unless inhibited by the sender.
   (Level 2 implementations only.)

   The IP source address of the outgoing datagram MUST be one of the
   individual addresses corresponding to the outgoing interface.

   A host group address or IP address from an SSM range MUST never be
   placed in the source address field or anywhere in a source route or
   record route option of an outgoing IP datagram.  These packets are
   not IP multicast packets but simply invalid packets.

6.3.  Extensions to the Local Network Service Interface

   No change to the local network service interface is required to
   support the sending of multicast IP datagrams.  The IP module merely
   specifies an IP host group destination, rather than an individual IP
   destination, when it invokes the existing "Send Local" operation.

6.4.  Extensions to an Ethernet Local Network Module

   The Ethernet directly supports the sending of local multicast packets
   by allowing multicast addresses in the destination field of Ethernet
   packets.  All that is needed to support the sending of multicast IP
   datagrams is a procedure for mapping IP host group addresses to
   Ethernet multicast addresses.

   An IPv4 host group address is mapped to an Ethernet multicast address
   by placing the low-order 23-bits of the IPv4 address into the low-
   order 23 bits of the Ethernet multicast address 01-00-5E-00-00-00
   (hex).  Because there are 28 significant bits in an IPv4 host group
   address, more than one host group address may map to the same
   Ethernet multicast address.

   Mapping of IPv6 host group addresses to Ethernet is defined in
   [RFC2464] and [RFC6085].

   The address mappings for IP addresses do apply not only to IP host
   group addresses, but also to destination IP addresses used for SSM.











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6.5.  Extensions to Local Network Modules other than Ethernet

   Other networks that directly support multicasting, such as rings or
   buses conforming to the IEEE 802.2 standard, may be handled the same
   way as Ethernet for the purpose of sending multicast IP datagrams.
   For a network that supports broadcast but not multicast, such as the
   Experimental Ethernet, all IP host group addresses may be mapped to a
   single local broadcast address (at the cost of increased overhead on
   all local hosts).  For a point-to-point link joining two hosts (or a
   host and a multicast router), multicasts SHOULD be transmitted
   exactly like unicasts.  For a store-and-forward network like the
   ARPANET or a public X.25 network, all IP host group addresses might
   be mapped to the well-known local address of an IP multicast router;
   a router on such a network would take responsibility for completing
   multicast delivery within the network as well as among networks.

7.  RECEIVING MULTICAST IP DATAGRAMS

7.1.  Extensions to the IP Service Interface

   Incoming multicast IP datagrams are received by upper-layer protocol
   modules using the same "Receive IP" operation as normal, unicast
   datagrams.  Selection of a destination upper-layer protocol is based
   on the protocol field in the IP header, regardless of the destination
   IP address.  However, before any datagrams destined to a particular
   group can be received, an upper-layer protocol must ask the IP module
   to join that group.  Thus, the IP service interface MUST be extended
   to provide two new operations:

       JoinHostGroup  ( group-address, interface )

       LeaveHostGroup ( group-address, interface )

   The JoinHostGroup operation requests that this host become a member
   of the host group identified by "group-address" on the given network
   interface.  The LeaveGroup operation requests that this host give up
   its membership in the host group identified by "group-address" on the
   given network interface.  The interface argument may be omitted on
   hosts that support only one interface.  For hosts that may be
   attached to more than one network, the upper-layer protocol may
   choose to leave the interface unspecified, in which case the request
   will apply to the default interface for sending multicast datagrams
   (see section 6.1).

   It is permissible to join the same group on more than one interface,
   in which case duplicate multicast datagrams may be received.  It is
   also permissible for more than one upper-layer protocol to request
   membership in the same group.



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   Both operations SHOULD return immediately (i.e., they are non-
   blocking operations), indicating success or failure.  Either
   operation may fail due to an invalid group address or interface
   identifier.  JoinHostGroup may fail due to lack of local resources.
   LeaveHostGroup may fail because the host does not belong to the given
   group on the given interface.  LeaveHostGroup may succeed, but the
   membership persist, if more than one upper-layer protocol has
   requested membership in the same group.

   IPv6 socket extensions supporting these functions are defined in
   [RFC3493], section 5.2.  [RFC3678] specifies socket options for these
   functions for ASM and also includes socket options in support of SSM.
   Note that these are UDP socket extensions but not IP socket
   extensions due to the absence of widely adopted/required IP level
   socket APIs.

7.2.  Extensions to the IP Module

   To support the reception of multicast IP datagrams, the IP module
   MUST be extended to maintain a list of host group memberships
   associated with each network interface.  An incoming datagram
   destined to one of those groups is processed exactly the same way as
   datagrams destined to one of the host's individual addresses.

   Incoming datagrams destined to groups to which the host does not
   belong are discarded without generating any error report or log
   entry.  On hosts with more than one network interface, if a datagram
   arrives via one interface, destined for a group to which the host
   belongs only on a different interface, the datagram MUST be quietly
   discarded.  (These cases should occur only as a result of inadequate
   multicast address filtering in a local network module.)

   An incoming datagram is not rejected for having an IPv4 time-to-live
   of 1 or IPv6 Hop Limit of 1.  This field MUST not automatically be
   decremented on arriving datagrams that are not being forwarded.  An
   incoming datagram with an IP host group address in its source address
   field is quietly discarded.  An ICMP/ICMPv6 error message
   (Destination Unreachable, Time Exceeded, Parameter Problem, Source
   Quench, or Redirect) is never generated in response to a datagram
   destined to an IP host group or SSM range destination IP address.











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   The list of host group memberships is updated in response to
   JoinHostGroup and LeaveHostGroup requests from upper-layer protocols.
   Each membership should have an associated reference count or similar
   mechanism to handle multiple requests to join and leave the same
   group.  On the first request to join and the last request to leave a
   group on a given interface, the local network module for that
   interface is notified, so that it may update its multicast reception
   filter (see section 7.3).

   When supporting Level 2, the IP module MUST also be extended to
   implement the IGMP protocol for IPv4 and the MLD protocol for IPv6
   depending on the version(s) of IP to be supported.  IGMP/MLD are used
   to keep neighboring multicast routers informed of the host group
   memberships present on a particular local network.  See Section 10.8
   for potentially special treatment of the all-hosts groups in IGMP/
   MLD.

   Hosts and gateways MAY omit the sending of IGMP messages to report
   membership for Link-Local IPv4 host group addresses, especially on
   networks known not to (be able to) use any form of IGMP snooping.
   This does also apply for the IPv6 Link-Local host group all-hosts
   FF02::1, but not to other Link-Local IPv6 host groups.  See
   Appendix A.3.

7.3.  Extensions to the Local Network Service Interface

   Incoming local network multicast packets are delivered to the IP
   module using the same "Receive Local" operation as local network
   unicast packets.  To allow the IP module to tell the local network
   module which multicast packets to accept, the local network service
   interface is extended to provide two new operations:

       JoinLocalGroup  ( group-address )

       LeaveLocalGroup ( group-address )

   where "group-address" is an IP host group address.  The
   JoinLocalGroup operation requests the local network module to accept
   and deliver up subsequently arriving packets destined to the given IP
   host group address.  The LeaveLocalGroup operation requests the local
   network module to stop delivering up packets destined to the given IP
   host group address.  The local network module is expected to map the
   IP host group addresses to local network addresses as required to
   update its multicast reception filter.  Any local network module is
   free to ignore LeaveLocalGroup requests, and may deliver up packets
   destined to more addresses than just those specified in
   JoinLocalGroup requests, if it is unable to filter incoming packets
   adequately.



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   The local network module MUST NOT deliver up any multicast packets
   that were transmitted from that module; loopback of multicasts is
   handled at the IP layer or higher.

7.4.  Extensions to an Ethernet Local Network Module

   To support the reception of multicast IP datagrams, an Ethernet
   module MUST be able to receive packets addressed to the Ethernet
   multicast addresses that correspond to the host's IP host group
   addresses.  It is highly desirable to take advantage of any address
   filtering capabilities that the Ethernet hardware interface may have,
   so that the host receives only those packets that are destined to it.

   Unfortunately, many current Ethernet interfaces have a small limit on
   the number of addresses that the hardware can be configured to
   recognize.  Nevertheless, an implementation MUST be capable of
   listening on an arbitrary number of Ethernet multicast addresses,
   which may mean "opening up" the address filter to accept all
   multicast packets during those periods when the number of addresses
   exceeds the limit of the filter.

   For interfaces with inadequate hardware address filtering, it may be
   desirable (for performance reasons) to perform Ethernet address
   filtering within the software of the Ethernet module.  This is not
   mandatory, however, because the IP module performs its own filtering
   based on IP destination addresses.

7.5.  Extensions to Local Network Modules other than Ethernet

   Other multicast networks, such as IEEE 802.2 networks, can be handled
   the same way as Ethernet for the purpose of receiving multicast IP
   datagrams.  For pure broadcast networks, such as the Experimental
   Ethernet, all incoming broadcast packets can be accepted and passed
   to the IP module for IP-level filtering.  On point-to-point or store-
   and-forward networks, multicast IP datagrams will arrive as local
   network unicasts, so no change to the local network module should be
   necessary.

8.  ROUTING MULTICAST IP DATAGRAMS

   IPv4 datagrams with a Link-Local destination address MUST never be
   forwarded to a different link by multicast routers, regardless of
   their time-to-live.  See Section 10.7 for explanations.

   The equivalent requirement are specified for IPv6 in [RFC4291],
   section 2.5.6.





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   Rules for forwarding of non Link-Local IP multicast packets are
   outside the scope of this document.

9.  Status changes

9.1.  Moving RFC1112 and IGMPv1 to historic status

   This document moves RFC1112 to historic status which also moves the
   IGMP version 1 protocol as specified in Appendix 1 of RFC1112 to
   historic status, as it is not included into this document anymore.

   All other aspects of RFC1112 beside IGMPv1 are kept and updated by
   this document and maintain their current Internet Standard
   designation from RFC1112 through the normative status of this
   document.

9.2.  Backward compatibility with IGMPv1

   Current or future versions of IGMP or other protocols/mechanisms
   including but not necessary limited to [IGMPv2], [IGMPv3] or
   [IGMPv3lite] do or may include backward compatibility with IGMPv1,
   such as in [IGMPsnooping], which requires them to refer to the
   RFC1112 specification of IGMPv1.

   This document does not ask for any change to any specifications or
   implementations that includes any form of support for IGMPv1 for
   backward compatibility reasons as long as it also includes
   compatibility with a newer version of IGMP starting with [IGMPv2].

   Any new or updated specification that wants to maintain such backward
   compatibility with IGMPv1 need to continue to reference RFC1112 as
   the specification of IGMPv1.

   Any future reference for new or updated work to any other definition
   from RFC1112 (host extensions for IP multicast and/or Any Source
   Multicast service) need to refer to this document instead of RFC1112.

9.3.  Update to RFC 791

   This document is an update to [RFC791] because none of the core
   procedures to send and receive IP multicast packets described in this
   document match those defined for IP unicast packets in [RFC791].
   Instead, IP multicast is carving out parts of the IP address space to
   trigger completely new forwarding for completely new entities: host
   groups in ASM, channels in SSM).  See Appendix B.3 for further
   discussions.





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9.4.  Update to STD 5

   This document replaces RFC1112 in [STD5] which defines IPv4
   ([RFC791]) including its core extensions.

   Note: As there is no precedent for STD86 (IPv6) to include any
   specifications for extension of IPv6, this document is not asked to
   become part of STD86.

10.  Changes from RFC1112

   Beyond the status changes described in Section 9, this document
   introduces the following changes over RFC1112.

   All requirements changes are intended to make this specification
   aligned with long-term, most widely implemented, deployed and
   standardised RFCs for IP multicast, so that this document does not
   create the need to change existing implementations or deployments, as
   could be the case if RFC1112 (without IGMPv1) was to be implemented
   today.

10.1.  Normative language

   This document introduces the use of normative language through
   capitalization.  RFC1112 preceded [RFC2119] and hence did not include
   this language.

10.2.  References to IGMPv1

   References to IGMPv1 in RFC1112 are replaced with references to
   [IGMPv3] in this text.

10.3.  New summary

   The new Section 2.1 summarizes the scope of this document and the
   core new changes over RFC1112.

10.4.  Any-Source Multicast (ASM)

   This update introduces the term "ASM IP multicast" (ASM) as a new
   term for the IP service interface specified in this document (and
   previously in RFC1112) as explained in Section 2.1.

10.5.  SSM

   Section 2.1 explains the relationship of this document to SSM
   ([SSM]).




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   Section 4 adds the specification that the term host groups specified
   in this document does not apply to destination addresses used for
   SSM.

   No functional changes to the IP multicast service are incurred by
   these changes, except that it acknowledges the existence of SSM which
   reduces the range of host group addresses used for ASM.

10.6.  Applicability to both IPv4 and IPv6

   This document is written to apply to both IPv4 and IPv6 by adding
   detail for IPv6 where RFC1112 only covered IPv4.  This includes
   addressing and protocols in support of the service - Multicast
   Listener Discovery [MLDv2] for IPv6 versus IGMP for IPv4.

   IPv6 documents such as [RFC1883] and all its updates (e.g.:
   [RFC8200]) are defining the necessary wire encoding aspects of IP
   multicast in the assumption of the service of RFC1112 for IPv6, but
   without being able to refer to RFC1112, as it was only defined for
   IPv4.  Future documents can refer to this document as the IP
   multicast / ASM service for both IPv4 and IPv6.

   Additional text provides references for IETF UDP socket API
   specifications that instantiate the abstract APIs defined in this
   document.

   No functional changes to the IP multicast service are incurred by
   these changes.

10.7.  IPv4 Local Network Control Block

   RFC1112 defines the requirement for IPv4 datagrams to the all-hosts
   group 224.0.0.1 to never be forwarded beyond a single network.  In
   later RFCs, this behavior became the BCP for the whole IPv4 Local
   Network Control Block 224.0.0.0 - 224.0.0.255, making it the Link-
   Local host group address block for IPv4 multicast.  [RFC2365] and
   [RFC5771], section 4 are the BCPs covering this requirement.

   This document formalizes this BCP behavior as a standard requirement
   in Section 8, superseding and encompassing the more specific
   requirement for just 224.0.0.1 from RFC1112, and mirroring the same
   standardized behavior for IPv6 Link-Local addresses.  Because this is
   actually a requirement against IP multicast routers and not hosts,
   this is now also accordingly described in a separate section.

   This requirement does not incur changes over how IP multicast is
   implemented or deployed.




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10.8.  Special treatment of 224.0.0.1 and FF02::1

   RFC1112, section 7.2 introduced the requirements for hosts to
   permanently join 224.0.0.1.  Its explains this requirement to be in
   support of IGMP (version 1).

   Likewise, [IGMPv2], section 6. and [IGMPv3], section 5. repeat this
   requirement, and [MLDv1], section 6. and [MLDv2] section 6. also
   define the same requirement for the IPv6 all-hosts address FF02::1.

   Because this requirement is considered part of IGMP/MLD, and because
   this document does not anymore specify any form of IGMP, it does not
   repeat this requirement from RFC1112.  Instead, this requirement now
   solely relies on IGMP/MLD specifications to define it.

   These text changes do therefore not incur any requirements changes
   for implementations of these existing versions of IGMP/MLD, By
   leaving out this requirement from the document, future versions of
   IGMP/MLD are also free to choose whether to carry on this method
   without having to update this document.

   Note that [IGMPv3lite] omits this requirement.

10.9.  IGMP/MLD messages for Link-Local IPv4 host group addresses

   RFC1112, Appendix I.  (IGMPv1), [IGMPv2], [IGMPv3], [MLDv1], [MLDv2]
   require hosts to not send IGMP/MLD messages for the all-hosts group.
   This would be in conflict of the general rules of RFC1112 (outside of
   its IGMPv1 specific definitions) and equally this specification if it
   was not enhanced.  This specification therefore contains new text
   that makes it compatible with existing IGMP/MLD specification, and
   with long tern established and deployed implementation practices.

   New text in Appendix A.3 explains how after RFC1112, it became a
   common place implementation choice to not send IGMP messages for any
   IPv4 Link-Local host group address, and explains how this was done
   with good technical reason at the time.  This behavior is so common,
   that [IGMPsnooping] mandates to explicit support it IGMP snooping
   implementations.

   Referring to that explanation, a new MAY requirement in Section 7.2
   allowing (but not recommending) this behavior makes existing
   specifications and deployments compatible with this documents
   specifications.  It is only a MAY even though it is common in IPv4,
   because the experience with IPv6 shows that it does work (of course)
   equally well if this is not done, and can then support better MLD
   snooping than IGMP snooping.




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10.10.  Standard for IP multicasting in controlled networks

   This document removes the claim in the abstract of RFC1112, that
   these host extensions are "... the recommended standard for IP
   multicasting in the Internet."

   The reason for this is that [RFC8815] deprecated the ASM service
   across the Internet because there is no Internet Standard solution
   for protocols to support interdomain ASM except for [RFC3956], which
   is only applicable to IPv6, and even that solution does not resolve
   the challenges to source access control in interdomain deployments.

   In result, ASM is today "only" a recommended solution for controlled
   networks including controlled federated networks for applications for
   which SSM is not preferable.

   However, these limitations to the applicability of ASM do not impact
   the applicability of any parts of the host stack described in this
   document for other IP multicast service interfaces, specifically
   "Source Specific Multicast", [SSM], which inherits all aspects of ASM
   specified in this document, especially the sending (Section 6,
   Section 6.2) of IP multicast packets as well as the mapping to
   ethernet (Section 6.4).  It only amends the joining of IP multicast
   traffic on IP multicast receivers with additional procedures fitting
   into the host stack described in this document.

11.  IANA Considerations

11.1.  Protocol Numbers registry

   IANA is asked to replace the Reference field for the IGMP protocol in
   the Protocol Numbers registry (https://www.iana.org/assignments/
   protocol-numbers/protocol-numbers.xhtml) from RFC1112 to [THIS-RFC].

   Explanation: This protocol number is used by all versions of IGMP,
   including [IGMPv2] and [IGMPv3] and is unaffected by making IGMP
   version 1 historic.

11.2.  Internet Group Management Protocol (IGMP) Type Numbers Registry

   IANA is asked to replace the Reference to RFC1112 for the 0x11 /
   "IGMP Membership Query" entry in the "Internet Group Management
   Protocol (IGMP) Type Numbers Registry"
   (https://www.iana.org/assignments/igmp-type-numbers/igmp-type-
   numbers.xhtml) with "RFC1112, [RFC2236], [RFC3376]".






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   Explanation: This type code messages where introduced by RFC1112 but
   modified versions thereof where also introduced by [RFC2236] and
   [RFC3376], so that it is clearer if all three RFCs are indicated.
   All other references to RFC1112 in this registry are specifically
   referring to that RFC in it's role of defining IGMP version 1 and
   thus need to continue to refer to RFC1112 and not [THIS-RFC.

11.3.  Multicast 48-bit MAC Addresses registry

   IANA is asked to replace the Reference field for the IPv4 Multicast
   range entry in the "IANA Multicast 48-bit MAC Addresses"
   (https://www.iana.org/assignments/ethernet-numbers) from RFC1112 to
   [THIS-RFC].

11.4.  IPv4 Address range registries

   IANA is asked to replace the Reference field for the 240.0.0.0/4
   entry in the "IANA IPv4 Special-Purpose Address Registry"
   (https://www.iana.org/assignments/iana-ipv4-special-registry/iana-
   ipv4-special-registry.xhtml) from RFC1112 to [THIS-RFC].  The
   Section 4 text stays unchanged.

   IANA is asked to replace the Reference to RFC1112 in the "IANA IPv4
   Address Space Registry" (https://www.iana.org/assignments/ipv4-
   address-space/ipv4-address-space.xhtml) with [THIS-RFC].

11.5.  IPv4 Multicast Address Space registry

   IANA is asked to replace the three references to RFC1112 in the "IPv4
   Multicast Address Space Registry" (https://www.iana.org/assignments/
   multicast-addresses/multicast-addresses.xhtml) with [THIS-RFC].

11.6.  IP Flow Information Export registry

   IANA is asked to replace the two references to RFC1112 in the "IPFIX
   Information Elements" registry
   (https://www.iana.org/assignments/ipfix/ipfix.xhtml) with [THIS-RFC].

12.  References

12.1.  Normative References

   [IGMPv2]   Fenner, W., "Internet Group Management Protocol, Version
              2", RFC 2236, DOI 10.17487/RFC2236, November 1997,
              <https://www.rfc-editor.org/rfc/rfc2236>.






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   [IGMPv3]   Haberman, B., "Internet Group Management Protocol, Version
              3", Work in Progress, Internet-Draft, draft-ietf-pim-
              3376bis-12, 27 August 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-pim-
              3376bis-12>.

   [MLDv2]    Haberman, B., "Multicast Listener Discovery Version 2
              (MLDv2) for IPv6", Work in Progress, Internet-Draft,
              draft-ietf-pim-3810bis-12, 27 August 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-pim-
              3810bis-12>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/rfc/rfc2119>.

   [RFC2464]  Crawford, M., "Transmission of IPv6 Packets over Ethernet
              Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998,
              <https://www.rfc-editor.org/rfc/rfc2464>.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, DOI 10.17487/RFC4291, February
              2006, <https://www.rfc-editor.org/rfc/rfc4291>.

   [RFC791]   Postel, J., "Internet Protocol", STD 5, RFC 791,
              DOI 10.17487/RFC0791, September 1981,
              <https://www.rfc-editor.org/rfc/rfc791>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.

   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,
              <https://www.rfc-editor.org/rfc/rfc8200>.

   [SSM]      Holbrook, H. and B. Cain, "Source-Specific Multicast for
              IP", RFC 4607, DOI 10.17487/RFC4607, August 2006,
              <https://www.rfc-editor.org/rfc/rfc4607>.

   [STD5]     Internet Standard 5,
              <https://www.rfc-editor.org/info/std5>.
              At the time of writing, this STD comprises the following:






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              Postel, J., "Internet Protocol", STD 5, RFC 791,
              DOI 10.17487/RFC0791, September 1981,
              <https://www.rfc-editor.org/info/rfc791>.

              Postel, J., "Internet Control Message Protocol", STD 5,
              RFC 792, DOI 10.17487/RFC0792, September 1981,
              <https://www.rfc-editor.org/info/rfc792>.

              Mogul, J., "Broadcasting Internet Datagrams", STD 5,
              RFC 919, DOI 10.17487/RFC0919, October 1984,
              <https://www.rfc-editor.org/info/rfc919>.

              Mogul, J., "Broadcasting Internet datagrams in the
              presence of subnets", STD 5, RFC 922,
              DOI 10.17487/RFC0922, October 1984,
              <https://www.rfc-editor.org/info/rfc922>.

              Mogul, J. and J. Postel, "Internet Standard Subnetting
              Procedure", STD 5, RFC 950, DOI 10.17487/RFC0950, August
              1985, <https://www.rfc-editor.org/info/rfc950>.

              Deering, S., "Host extensions for IP multicasting", STD 5,
              RFC 1112, DOI 10.17487/RFC1112, August 1989,
              <https://www.rfc-editor.org/info/rfc1112>.

12.2.  Informative References

   [IGMPsnooping]
              Christensen, M., Kimball, K., and F. Solensky,
              "Considerations for Internet Group Management Protocol
              (IGMP) and Multicast Listener Discovery (MLD) Snooping
              Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006,
              <https://www.rfc-editor.org/rfc/rfc4541>.

   [IGMPv3lite]
              Liu, H., Cao, W., and H. Asaeda, "Lightweight Internet
              Group Management Protocol Version 3 (IGMPv3) and Multicast
              Listener Discovery Version 2 (MLDv2) Protocols", RFC 5790,
              DOI 10.17487/RFC5790, February 2010,
              <https://www.rfc-editor.org/rfc/rfc5790>.

   [MLDv1]    Deering, S., Fenner, W., and B. Haberman, "Multicast
              Listener Discovery (MLD) for IPv6", RFC 2710,
              DOI 10.17487/RFC2710, October 1999,
              <https://www.rfc-editor.org/rfc/rfc2710>.






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   [RFC1045]  Cheriton, D., "VMTP: Versatile Message Transaction
              Protocol: Protocol specification", RFC 1045,
              DOI 10.17487/RFC1045, February 1988,
              <https://www.rfc-editor.org/rfc/rfc1045>.

   [RFC1723]  Malkin, G., "RIP Version 2 - Carrying Additional
              Information", RFC 1723, DOI 10.17487/RFC1723, November
              1994, <https://www.rfc-editor.org/rfc/rfc1723>.

   [RFC1883]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 1883, DOI 10.17487/RFC1883,
              December 1995, <https://www.rfc-editor.org/rfc/rfc1883>.

   [RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328,
              DOI 10.17487/RFC2328, April 1998,
              <https://www.rfc-editor.org/rfc/rfc2328>.

   [RFC2365]  Meyer, D., "Administratively Scoped IP Multicast", BCP 23,
              RFC 2365, DOI 10.17487/RFC2365, July 1998,
              <https://www.rfc-editor.org/rfc/rfc2365>.

   [RFC3232]  Reynolds, J., Ed., "Assigned Numbers: RFC 1700 is Replaced
              by an On-line Database", RFC 3232, DOI 10.17487/RFC3232,
              January 2002, <https://www.rfc-editor.org/rfc/rfc3232>.

   [RFC3493]  Gilligan, R., Thomson, S., Bound, J., McCann, J., and W.
              Stevens, "Basic Socket Interface Extensions for IPv6",
              RFC 3493, DOI 10.17487/RFC3493, February 2003,
              <https://www.rfc-editor.org/rfc/rfc3493>.

   [RFC3678]  Thaler, D., Fenner, B., and B. Quinn, "Socket Interface
              Extensions for Multicast Source Filters", RFC 3678,
              DOI 10.17487/RFC3678, January 2004,
              <https://www.rfc-editor.org/rfc/rfc3678>.

   [RFC3956]  Savola, P. and B. Haberman, "Embedding the Rendezvous
              Point (RP) Address in an IPv6 Multicast Address",
              RFC 3956, DOI 10.17487/RFC3956, November 2004,
              <https://www.rfc-editor.org/rfc/rfc3956>.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              DOI 10.17487/RFC4861, September 2007,
              <https://www.rfc-editor.org/rfc/rfc4861>.







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   [RFC5771]  Cotton, M., Vegoda, L., and D. Meyer, "IANA Guidelines for
              IPv4 Multicast Address Assignments", BCP 51, RFC 5771,
              DOI 10.17487/RFC5771, March 2010,
              <https://www.rfc-editor.org/rfc/rfc5771>.

   [RFC6034]  Thaler, D., "Unicast-Prefix-Based IPv4 Multicast
              Addresses", RFC 6034, DOI 10.17487/RFC6034, October 2010,
              <https://www.rfc-editor.org/rfc/rfc6034>.

   [RFC6085]  Gundavelli, S., Townsley, M., Troan, O., and W. Dec,
              "Address Mapping of IPv6 Multicast Packets on Ethernet",
              RFC 6085, DOI 10.17487/RFC6085, January 2011,
              <https://www.rfc-editor.org/rfc/rfc6085>.

   [RFC7346]  Droms, R., "IPv6 Multicast Address Scopes", RFC 7346,
              DOI 10.17487/RFC7346, August 2014,
              <https://www.rfc-editor.org/rfc/rfc7346>.

   [RFC7371]  Boucadair, M. and S. Venaas, "Updates to the IPv6
              Multicast Addressing Architecture", RFC 7371,
              DOI 10.17487/RFC7371, September 2014,
              <https://www.rfc-editor.org/rfc/rfc7371>.

   [RFC8815]  Abrahamsson, M., Chown, T., Giuliano, L., and T. Eckert,
              "Deprecating Any-Source Multicast (ASM) for Interdomain
              Multicast", BCP 229, RFC 8815, DOI 10.17487/RFC8815,
              August 2020, <https://www.rfc-editor.org/rfc/rfc8815>.

Appendix A.  HOST GROUP ADDRESS ISSUES

   This appendix is not part of the IP multicasting specification, but
   provides background discussion of several issues related to IP host
   group addresses.

A.1.  Group Address Binding

   The binding of IP host group addresses to physical hosts may be
   considered a generalization of the binding of IP unicast addresses.
   An IP unicast address is statically bound to a single local network
   interface on a single IP network.  An IP host group address is
   dynamically bound to a set of local network interfaces on a set of IP
   networks.









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   It is important to understand that an IP host group address is NOT
   bound to a set of IP unicast addresses.  The multicast routers do not
   need to maintain a list of individual members of each host group.
   For example, a multicast router attached to an Ethernet need
   associate only a single Ethernet multicast address with each host
   group having local members, rather than a list of the members'
   individual IP or Ethernet addresses.

A.2.  Allocation of Transient Host Group Addresses

   This memo does not specify how transient group address are allocated.
   It is anticipated that different portions of the IP transient host
   group address space will be allocated using different techniques.
   For example, there may be a number of servers that can be contacted
   to acquire a new transient group address.  Some higher-level
   protocols (such as VMTP, specified in [RFC1045]) may generate higher-
   level transient "process group" or "entity group" addresses which are
   then algorithmically mapped to a subset of the IP transient host
   group addresses, similarly to the way that IP host group addresses
   are mapped to Ethernet multicast addresses.  A portion of the IP
   group address space may be set aside for random allocation by
   applications that can tolerate occasional collisions with other
   multicast users, perhaps generating new addresses until a suitably
   "quiet" one is found.

   In general, a host cannot assume that datagrams sent to any host
   group address will reach only the intended hosts, or that datagrams
   received as a member of a transient host group are intended for the
   recipient.  Misdelivery must be detected at a level above IP, using
   higher-level identifiers or authentication tokens.  Information
   transmitted to a host group address should be encrypted or governed
   by administrative routing controls if the sender is concerned about
   unwanted listeners.

A.3.  Link-local IP multicast and IGMP/MLD

   On networks, where IP multicast packets are broadcast, such as (non-
   switched) ethernet, IP multicast packets will reach all level 2 IP
   multicast receivers without the need to use IGMP or MLD.  This
   signaling is only necessary for IP multicast receivers when the
   sender is in a different LAN so that IP multicast routers can forward
   the IP multicast traffic from the sender network to the receiver
   network.

   IP multicast packet to a Link-Local IP multicast destination address
   do therefore technically never need any IGMP or MLD signaling on such
   (non-switched broadcast) networks, because they are never forwarded
   between networks (Section 8).



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   During the early years of IPv4 multicast, this understanding resulted
   in implementations for protocols that receive Link-Local IPv4
   multicast packet without implementing IGMP.  Examples of such
   protocols include RIPv2 ([RFC1723]) or OSPF ([RFC2328]) and several
   other protocols, often running on IPv4 routers which had no IPv4
   multicast routing implementation at the time and no IPv4 multicast
   applications for which they needed to be IPv4 multicast receiver for
   non Link-Local IPv4 multicast addresses.

   When these implementations later received implementations of level 2
   IPv4 multicast support, those implementations excluded Link-Local
   host groups, so that those protocols would continue to run without
   IGMP as they had in before.

   Contributing to these implementation choices was also the fact that
   IGMP in the versions specified so far does not allow to keep track of
   ongoing receiver membership status in the absence of an IGMP router
   side implementation, called an IGMP querier.  With the target (Link-
   Local IPv4 multicast only) protocols being deployed in the absence of
   any such IGMP querier, the use of IGMP could also serve arguably no
   purpose except for compliance with RFC1112.

   This situation changed towards the end of the 1990th with the
   introduction of ethernet switches that snoop IGMP messages to
   constrain forwarding of IPv4 multicast packets for a particular IPv4
   multicast group to only those ports with hosts joined to the group.
   This behavior was later documented in [IGMPsnooping] but was widely
   deployed even earlier due to the co-existence of ports with the
   different speeds 10Mbps, 100Mbps and 1Gbps, and the resulting need to
   protect the slower speed ports from potentially large rates of IPv4
   multicast traffic between faster hosts.

   In result, IGMP snooping switches had to flood traffic to Link-Local
   IPv4 multicast groups due to the common absence of IGMP support for
   them, and this is accordingly also recommended by [IGMPsnooping].

   Due to this long-term practice, this document is thus permitting this
   non-use of IGMP for Link-Local host groups by introducing a MAY for
   it in Section 7.2.

   Note that IP multicast routers do not and can not typically report IP
   multicast groups via IGMP or MLD, because they are not joined to them
   as an IP multicast host, but simply need to receive them as an IP
   multicast router to forward them.  Even when an IP multicast router
   is joined to specific IP multicast group as an IP multicast host,
   reporting them via IGMP may sound futile because as an IP multicast
   router it would still need to receive the IP multicast traffic in the
   absence of such IGMP reporting, because it might need to forward it.



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   However, this logic does not apply to Link-Local groups, because they
   are never forwarded and could thus be filtered by IGMP or MLD
   snooping switches if those switches could trust routers to report
   them correctly.  Which they can not do for IPv4 due to its history.

   In recognition of this situation, [MLDv1] for IPv6 did emphasize the
   need to report also Link-Local IPv6 group memberships to avoid these
   issues.  Therefore this document also has no equivalent MAY statement
   for IPv6.

   Note that IGMP/MLD reporting for non Link-Local IP multicast groups
   from an IP multicast router joining it as a host is also not just a
   superficial specification requirement because of the assumption that
   routers need to receive all non Link-Local IP multicast packets.

   Switches that do support snooping of IP multicast routing protocols
   such as PIM may also be able to determine which traffic needs to be
   forwarded to an IP multicast router but those can may not include the
   groups that the IP multicast router has only joined to only as a host
   and is not reporting via IGMP/MLD.

Appendix B.  Discussion and Explanations (TO BE REMOVED)

   [RFC-editor: Please remove this Appendix after observing the
   following section addressed to you]

   Please refer to Section 10 for the non-process discussion of the
   goals of this document.

B.1.  RFC-Editor notes

   The kramdown tooling did not allow to have references for both STD5
   and RFC1112, those fail because the STD5 reference creates an
   "RFC1112" anchor.  Thus there is no separate reference for RFC1112 in
   this version of the document.  This needs to be fixed in XML by
   adding a full reference to RFC1112 and removing the RFC1112 anchor
   from the STD5 reference.

B.2.  Goals and evolution of this document

   The initial goal of this document was to allow for IETF to declare
   the IGMPv1 protocol historic which today is a Full Internet Standard
   due to it being defined in RFC1112.  This should be achieved without
   changing the Full Internet Standard status of the IP Host Extensions
   for IP Multicast and ASM IP Service interface specified in RFC1112
   because those specification are as fundamental to the definition of
   IP multicast as RFC791 is for IP (unicast).




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   The best way to achieve this seemed to be an update to RFC1112 which
   removes all of IGMPv1, but maintains the rest of the document.  None
   of these removal of IGMPv1 changes changed the applicability or
   requirements to existing IP multicast (plus its protocols)
   implementations or other specifications.

   The next refinement was to rectify the situation that there is no
   specification explaining the same details as RFC1112 for IPv6
   multicast even though RFC8200 (full internet standard) even
   explicitly includes IPv6 multicast, and a range of other RFC define
   necessary code-points (such as for ethernet mapping) for IPv6
   multicast.

   Most of the text of this specification can hence can simply talk
   about "IP" which in this specification implies both IPv4 and IPv6,
   and only in places where IPv6 differs, does the document now include
   new explicit text, most often pointing to pre-existing RFCs
   specifying the necessary details for IPv6.  Again, none of these
   changes impact other specs or deployments.

   The third step of refinement was add the necessary verbiage to
   explain the differences between SSM and the specifications in this
   document.  None of these text enhancements incur any functional
   changes of long-term established practices.  Instead, they are only
   resulting in references to SSM RFCs, introduction of the term ASM
   (which was previously only defined in SSM RFCs), and the limitation
   of applicability of terms in this document (such as host group) to
   their use with ASM.

   The last round of changes added and refined details to be in-line
   with long-term established practices and removing any possible
   contradictions between the original RFC1112 text and newer standards
   track specification such as IGMPv2/MLDv3 or long term established
   implementation practices.  This includes the limitation of scope of
   ASM to controlled networks and the definition of the IPv4 Link-Local
   address range, which so far had only been defined through BCP RFC,
   unlike in IPv6, where it's part of the architecture, as well as
   permitting (but not recommending) non-use of IGMP for them.

   In summary, all changes in the document will make this document a
   replacement of rfc1112 which much more reflects the full internet
   standard nature of the technology than rfc1112 did as of recent.

B.3.  Update to RFC791

   This version of the text proposes that this spec is declared to be an
   update to RFC791.




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   The argument made in Section 9.3 to support this classification may
   not be persuasive enough (because the according rfc791 text may be
   read as a perfectly good extension point specification), in which
   case the update status and related text should be deleted.

   However, If anyone where to come up with a re-use of 224.0.0.0/4 for
   any non-IP multicast purposes, havoc might ensure with devices that
   do assume IP multicast semantics, so it may simply be prudent to
   include this declaration.  It would also make the relationship
   between IPv4 and IPv4 multicast be more aligned with IPv6, where IPv6
   multicast is included in RFC8200.

B.4.  Changelog

   This document is hosted at https://github.com/toerless/rfc1112bis.
   Please submit issues with this text as issues to that github and
   report them on pim@ietf.org.

B.4.1.  draft-ietf-pim-rfc1112bis-03

   1.  Changed document text to make the term "ASM" apply only to the IP
       service interface (extensions) specified by the document (and
       shown and explained in existing text), instead of the whole host
       extensions specified in this document (as it was written up to up
       to -02).  This is the only correct semantic, given how all the
       host exensions specified in this document are shared by SSM, only
       the IP service interface is changed/amended by SSM.

   2.  Subdivided section 2 (INTRODUCTION) into sections 2.1 (Summary),
       which contains new text from this spec, and 2.2 (Overview), which
       is unchanged RFC1112 text.  Newly written section 2.1 to
       summarize the key content of this document.  This was so far only
       explained in the much later changes from rfc1112 section.
       Includes IPv4/IPv6 applicability, ASM/SSM naming and maintaining
       most of RFC1112 text as a goal.

   3.  Introduced text to define and explain link local IPv4 host group
       addresses 224.0.0.0 - 224.0.0.255.  This was triggered by trying
       to fix the rfc1112 text sections that Brian Haberman was
       concerned about, which did cover behavior for 224.0.0.1.

   As it turns out, the behavior for 224.0.0.1 was quickly adopted by
   other protocols getting 224.0.0.0/24 addresses and there has been no
   functional specification to explain the non-forwarding behavior for
   these link-local addresses.  Instead, only IANA allocation guideline
   RFCs where introducing them.  This is now rectified with new
   explanatory text in this spec. and a new MAY requirement to permit
   non-use of IGMP for those groups.  See Section 7.2.



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   1.  Changed references to IGMPv3 and MLDv2 to the -bis drafts
       currently in RFC-editor queue.  Also triggered by Brian Haberman
       mentioning them.

   2.  Improved wording in "(Normative) Status Change" section 9.

   5.1 Removed "Update to rfc791" as an open issue and instead claimed
   it as fact in section 9.3.  Added discussion about this point to the
   discussion appendix that is to be removed by RFC-editor.

   5.1 Also added subsection to declare that this document replaces
   RFC1112 in STD5.

   1.  Enhanced/New text in section 10., "changes from RFC1112"

   Especially explaining the changes in the normative section explained
   above and below, triggered by Brian's review.

   1.  Applying changes proposed by Brian Haberman during WGLC.

   7.1 Changed meaning of IP from "IPv4" to "IPv4 and IPv6", accordingly
   updated all text.  Makes a lot of sense given the goal of showing how
   most of the IP multicast host stack operates the same for IPv4 and
   IPv6.

   7.2 Re-added requirement for routers not to forward link-local
   multicast

   7.3 adding MAY requirement to allow non-signaling of Link-Local scope
   IPv4 multicast and IPv6 all-hosts group, and explanations how this is
   better than the prior definitions from rfc1112.  Also includes new
   (length) Appendix A.3 to justify this for IPv4.

   7.4 text nits (thanks, Brian).

B.4.2.  draft-ietf-pim-rfc1112bis-02

   Removed unused references, fefresh - waiting for more reviews.  Added
   IANA section for updates from RFC1112 to RFC1112bis.  Added
   references to RFC5771 and RFC6034 because they actually are the
   references for the IANA 224.0.0.0/4 registrations, which seems a bit
   undocumented given how RFC1112 did introduce the definition (before
   IANA).

B.4.3.  draft-ietf-pim-rfc1112bis-01

   Fix up reference for IGMPv3.  Refined candidate open issues.  Removed
   author discussion.



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B.4.4.  draft-eckert-pim-rfc1112bis-02

   Changed core references from numbered style to name style .

   Changed copyright clause to pre5378Trust200902, which is the same as
   used for RFC8200 due to the presence of text with similar early
   status.

   To resolve Dino's concerns at IETF116 with -01: Added hopefully
   extensive explanation wrt. to how to treat IGMPv1 based on Dino's
   feedback from IETF117: This document does not ask for any removal of
   IGMPv1 in any IETF specs which include it for backward compatibility
   reasons, it only effectively causes it to become historic once
   RFC1112 would be declared historic.

   To resolve Alvaros concerns at IETF1116 with -01: Added normative
   language (MUST/SHOULD).  Seems as if this is quite easy given how
   "must" was written appropriately in the original text.  The logic of
   applying MUST/MUST-NOT was based on understanding by the author how
   none of the MUST would actually put existing working implementations
   out of compliance.

   Added explicit text to move rfc1112 to historic status.

   Moved explanation of changes from rfc1112 from appendix to main text
   as this seem to the common practice for document updates.

   Added claim for this document to be an update to rfc791.  See open
   issues section though.

B.4.5.  draft-ietf-pim-rfc1112bis-00

   Just changed title, added github pointer.

B.4.6.  draft-eckert-pim-rfc1112bis-01

   Changed all use of IPv4 back to IP.  Seems standard in IETF specs.
   Only IPv6 has in IETF specs the distinction of including the version.

   Changed Steve Deerings address to a pseudo-email address at IETF.
   See prior section.

   Converted document into kramdownrfc2629 format for easier editing.

   Claims that rfc2119 language is not desired/used (to maintain maximum
   original text without changes).





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   Rewrote section for updates to rfc1112 to hopefully better motivate/
   explain the reason for this document and detail what its changes are.

B.4.7.  draft-eckert-pim-rfc1112bis-00

   Initial version based on RFC1112 text version, edited.

Authors' Addresses

   Stephen E. Deering
   Retired
   Vancouver, British Columbia
   Canada
   Email: deering@noreply.ietf.org


   Toerless Eckert (editor)
   Futurewei Technologies USA
   United States of America
   Email: tte@cs.fau.de































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