Internet Engineering Task Force (IETF)                     G. Bumgardner
Request for Comments: 7450                                 February 2015
Category: Standards Track
ISSN: 2070-1721


                     Automatic Multicast Tunneling

Abstract

   This document describes Automatic Multicast Tunneling (AMT), a
   protocol for delivering multicast traffic from sources in a
   multicast-enabled network to receivers that lack multicast
   connectivity to the source network.  The protocol uses UDP
   encapsulation and unicast replication to provide this functionality.

   The AMT protocol is specifically designed to support rapid deployment
   by requiring minimal changes to existing network infrastructure.

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 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7450.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1. Introduction ....................................................3
   2. Applicability ...................................................3
   3. Terminology .....................................................4
      3.1. Requirements Notation ......................................4
      3.2. Definitions ................................................4
      3.3. Abbreviations ..............................................5
   4. Protocol Overview ...............................................6
      4.1. General Architecture .......................................6
           4.1.1. Relationship to IGMP and MLD Protocols ..............6
           4.1.2. Gateways ............................................7
           4.1.3. Relays .............................................10
           4.1.4. Deployment .........................................13
           4.1.5. Discovery ..........................................14
      4.2. General Operation .........................................15
           4.2.1. Message Sequences ..................................15
           4.2.2. Tunneling ..........................................26
   5. Protocol Description ...........................................31
      5.1. Protocol Messages .........................................31
           5.1.1. Relay Discovery ....................................31
           5.1.2. Relay Advertisement ................................32
           5.1.3. Request ............................................34
           5.1.4. Membership Query ...................................35
           5.1.5. Membership Update ..................................39
           5.1.6. Multicast Data .....................................41
           5.1.7. Teardown ...........................................43
      5.2. Gateway Operation .........................................45
           5.2.1. IP/IGMP/MLD Protocol Requirements ..................45
           5.2.2. Pseudo-Interface Configuration .....................47
           5.2.3. Gateway Service ....................................48
      5.3. Relay Operation ...........................................61
           5.3.1. IP/IGMP/MLD Protocol Requirements ..................61
           5.3.2. Startup ............................................61
           5.3.3. Running ............................................62
           5.3.4. Shutdown ...........................................73
           5.3.5. Response MAC Generation ............................73
           5.3.6. Private Secret Generation ..........................74
   6. Security Considerations ........................................74
      6.1. Relays ....................................................74
      6.2. Gateways ..................................................76
      6.3. Encapsulated IP Packets ...................................76
   7. IANA Considerations ............................................77
      7.1. IPv4 and IPv6 Anycast Prefix Allocation ...................77
           7.1.1. IPv4 ...............................................77
           7.1.2. IPv6 ...............................................78
      7.2. UDP Port Number ...........................................78

   8. References .....................................................78
      8.1. Normative References ......................................78
      8.2. Informative References ....................................79
   Acknowledgments ...................................................81
   Contributors ......................................................82
   Author's Address ..................................................82

1.  Introduction

   The advantages and benefits provided by multicast technologies are
   well known.  There are a number of application areas that are ideal
   candidates for the use of multicast, including media broadcasting,
   video conferencing, collaboration, real-time data feeds, data
   replication, and software updates.  Unfortunately, many of these
   applications lack multicast connectivity to networks that carry
   traffic generated by multicast sources.  The reasons for the lack of
   connectivity vary but are primarily the result of service provider
   policies and network limitations.

   Automatic Multicast Tunneling (AMT) is a protocol that uses UDP-based
   encapsulation to overcome the aforementioned lack of multicast
   connectivity.  AMT enables sites, hosts, or applications that do not
   have native multicast access to a network with multicast connectivity
   to a source, to request and receive Source-Specific Multicast (SSM)
   [RFC4607] and Any-Source Multicast (ASM) [RFC1112] traffic from a
   network that does provide multicast connectivity to that source.

2.  Applicability

   This document describes a protocol that may be used to deliver
   multicast traffic from a multicast-enabled network to sites that lack
   multicast connectivity to the source network.  This document does not
   describe any methods for sourcing multicast traffic from isolated
   sites, as this topic is out of scope.

   AMT is not intended to be used as a substitute for native multicast,
   especially in conditions or environments requiring high traffic flow.
   AMT uses unicast replication to reach multiple receivers, and the
   bandwidth cost for this replication will be higher than that required
   if the receivers were reachable via native multicast.

   AMT is designed to be deployed at the border of networks possessing
   native multicast capabilities where access and provisioning can be
   managed by the AMT service provider.

3.  Terminology

3.1.  Requirements Notation

   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].

3.2.  Definitions

   This document adopts the following definitions for use in describing
   the protocol:

   Downstream:
      A downstream interface or connection that faces away from the
      multicast distribution root or towards multicast receivers.

   Upstream:
      An upstream interface or connection that faces a multicast
      distribution root or source.

   Non-Broadcast Multi-Access (NBMA):
      An NBMA network or interface is one to which multiple network
      nodes (hosts or routers) are attached, but where packets are
      transmitted directly from one node to another node over a virtual
      circuit or physical link.  NBMA networks do not support multicast
      or broadcast traffic -- a node that sources multicast traffic must
      replicate the multicast packets for separate transmission to each
      node that has requested the multicast traffic.

   Multicast Receiver:
      An entity that requests and receives multicast traffic.  A
      receiver may be a router, host, application, or application
      component.  The method by which a receiver transmits group
      membership requests and receives multicast traffic varies
      according to receiver type.

   Group Membership Database:
      A group membership database describes the current multicast
      subscription state (also referred to as "reception state") for an
      interface or system.  See Section 3 of [RFC3376] for a detailed
      definition.

   Reception State:
      The multicast subscription state of a pseudo-interface, virtual
      interface, or physical network interface.  Often synonymous with
      group membership database.

   Subscription:
      A group or state entry in a group membership database or reception
      state table.  The presence of a subscription entry indicates
      membership in an IP multicast group.

   Group Membership Protocol:
      The term "group membership protocol" is used as a generic
      reference to the Internet Group Management Protocol (IGMP)
      [RFC1112] [RFC2236] [RFC3376] or the Multicast Listener Discovery
      protocol [RFC2710] [RFC3810].

   Multicast Protocol:
      The term "multicast protocol" is used as a generic reference to
      multicast routing protocols used to join or leave multicast
      distribution trees, such as Protocol Independent Multicast -
      Sparse Mode (PIM-SM) [RFC4601].

   Network Address Translation (NAT):
      Network Address Translation is the process of modifying the source
      IP address and port numbers carried by an IP packet while
      transiting a network node (see [RFC2663]).  Intervening NAT
      devices may change the source address and port carried by messages
      sent from an AMT gateway to an AMT relay, possibly producing
      changes in protocol state and behavior.

   Anycast:
      A network addressing and routing method in which packets from a
      single sender are routed to the topologically nearest node in a
      group of potential receivers all identified by the same
      destination address.  See [RFC4786].

3.3.  Abbreviations

      AMT - Automatic Multicast Tunneling protocol.

      ASM - Any-Source Multicast.

      DoS - Denial-of-Service (attack) and DDoS for distributed DoS.

      IGMP - Internet Group Management Protocol (v1, v2, and v3).

      IP - Internet Protocol (v4 and v6).

      MAC - Message Authentication Code (or Cookie).

      MLD - Multicast Listener Discovery protocol (v1 and v2).

      NAT - Network Address Translation (or translation node).

      NBMA - Non-Broadcast Multi-Access (network, interface, or mode).

      PIM - Protocol Independent Multicast.

      SSM - Source-Specific Multicast.