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Network Working Group                                          D. Thaler
Internet-Draft                                                 M. Talwar
Intended status: Standards Track                             A. Aggarwal
Expires: December 29, 2008                         Microsoft Corporation
                                                             L. Vicisano
                                                           Cisco Systems
                                                             T. Pusateri
                                                                      !j
                                                           June 27, 2008


         Automatic IP Multicast Without Explicit Tunnels (AMT)
                  draft-ietf-mboned-auto-multicast-09

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   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."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on December 29, 2008.













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Abstract

   Automatic Multicast Tunneling (AMT) allows multicast communication
   amongst isolated multicast-enabled sites or hosts, attached to a
   network which has no native multicast support.  It also enables them
   to exchange multicast traffic with the native multicast
   infrastructure and does not require any manual configuration.  AMT
   uses an encapsulation interface so that no changes to a host stack or
   applications are required, all protocols (not just UDP) are handled,
   and there is no additional overhead in core routers.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  5
   2.  Applicability  . . . . . . . . . . . . . . . . . . . . . . . .  6
   3.  Requirements notation  . . . . . . . . . . . . . . . . . . . .  7
   4.  Definitions  . . . . . . . . . . . . . . . . . . . . . . . . .  8
     4.1.  AMT Pseudo-Interface . . . . . . . . . . . . . . . . . . .  8
     4.2.  AMT Gateway  . . . . . . . . . . . . . . . . . . . . . . .  8
     4.3.  AMT Site . . . . . . . . . . . . . . . . . . . . . . . . .  8
     4.4.  AMT Relay Router . . . . . . . . . . . . . . . . . . . . .  8
     4.5.  AMT Relay Anycast Prefix . . . . . . . . . . . . . . . . .  9
     4.6.  AMT Relay Anycast Address  . . . . . . . . . . . . . . . .  9
     4.7.  AMT Subnet Anycast Prefix  . . . . . . . . . . . . . . . .  9
     4.8.  AMT Gateway Anycast Address  . . . . . . . . . . . . . . .  9
   5.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     5.1.  Receiving Multicast in an AMT Site . . . . . . . . . . . . 10
       5.1.1.  Scalability Considerations . . . . . . . . . . . . . . 11
       5.1.2.  Spoofing Considerations  . . . . . . . . . . . . . . . 11
       5.1.3.  Protocol Sequence for a Gateway Joining SSM
               Receivers to a Relay . . . . . . . . . . . . . . . . . 12
     5.2.  Sourcing Multicast from an AMT site  . . . . . . . . . . . 14
       5.2.1.  Supporting Site-MBone Multicast  . . . . . . . . . . . 15
       5.2.2.  Supporting Site-Site Multicast . . . . . . . . . . . . 16
   6.  Message Formats  . . . . . . . . . . . . . . . . . . . . . . . 17
     6.1.  AMT Relay Discovery  . . . . . . . . . . . . . . . . . . . 17
       6.1.1.  Type . . . . . . . . . . . . . . . . . . . . . . . . . 17
       6.1.2.  Reserved . . . . . . . . . . . . . . . . . . . . . . . 17
       6.1.3.  Discovery Nonce  . . . . . . . . . . . . . . . . . . . 17
     6.2.  AMT Relay Advertisement  . . . . . . . . . . . . . . . . . 17
       6.2.1.  Type . . . . . . . . . . . . . . . . . . . . . . . . . 18
       6.2.2.  Reserved . . . . . . . . . . . . . . . . . . . . . . . 18
       6.2.3.  Discovery Nonce  . . . . . . . . . . . . . . . . . . . 18
       6.2.4.  Relay Address  . . . . . . . . . . . . . . . . . . . . 18
     6.3.  AMT Request  . . . . . . . . . . . . . . . . . . . . . . . 18
       6.3.1.  Type . . . . . . . . . . . . . . . . . . . . . . . . . 19
       6.3.2.  Reserved . . . . . . . . . . . . . . . . . . . . . . . 19



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       6.3.3.  Request Nonce  . . . . . . . . . . . . . . . . . . . . 19
     6.4.  AMT Membership Query . . . . . . . . . . . . . . . . . . . 19
       6.4.1.  Type . . . . . . . . . . . . . . . . . . . . . . . . . 20
       6.4.2.  Reserved . . . . . . . . . . . . . . . . . . . . . . . 20
       6.4.3.  Response MAC . . . . . . . . . . . . . . . . . . . . . 20
       6.4.4.  Request Nonce  . . . . . . . . . . . . . . . . . . . . 20
       6.4.5.  IGMP/MLD Query (including IP Header) . . . . . . . . . 20
     6.5.  AMT Membership Update  . . . . . . . . . . . . . . . . . . 21
       6.5.1.  Type . . . . . . . . . . . . . . . . . . . . . . . . . 21
       6.5.2.  Reserved . . . . . . . . . . . . . . . . . . . . . . . 22
       6.5.3.  Response MAC . . . . . . . . . . . . . . . . . . . . . 22
       6.5.4.  Request Nonce  . . . . . . . . . . . . . . . . . . . . 22
       6.5.5.  IGMP/MLD Message (including IP Header) . . . . . . . . 22
     6.6.  AMT IP Multicast Data  . . . . . . . . . . . . . . . . . . 22
       6.6.1.  Type . . . . . . . . . . . . . . . . . . . . . . . . . 23
       6.6.2.  Reserved . . . . . . . . . . . . . . . . . . . . . . . 23
       6.6.3.  IP Multicast Data  . . . . . . . . . . . . . . . . . . 23
   7.  AMT Gateway Details  . . . . . . . . . . . . . . . . . . . . . 24
     7.1.  At Startup Time  . . . . . . . . . . . . . . . . . . . . . 24
     7.2.  Gateway Group and Source Addresses . . . . . . . . . . . . 24
       7.2.1.  IPv4 . . . . . . . . . . . . . . . . . . . . . . . . . 25
       7.2.2.  IPv6 . . . . . . . . . . . . . . . . . . . . . . . . . 25
     7.3.  Joining Groups with MBone Sources  . . . . . . . . . . . . 26
     7.4.  Responding to Relay Changes  . . . . . . . . . . . . . . . 26
     7.5.  Joining SSM Groups with AMT Gateway Sources  . . . . . . . 27
     7.6.  Receiving AMT Membership Updates by the Gateway  . . . . . 27
     7.7.  Sending data to SSM groups . . . . . . . . . . . . . . . . 27
   8.  Relay Router Details . . . . . . . . . . . . . . . . . . . . . 28
     8.1.  At Startup time  . . . . . . . . . . . . . . . . . . . . . 28
     8.2.  Receiving Relay Discovery messages sent to the Anycast
           Address  . . . . . . . . . . . . . . . . . . . . . . . . . 28
     8.3.  Receiving Membership Updates from AMT Gateways . . . . . . 28
     8.4.  Receiving (S,G) Joins from the Native Side, for AMT
           Sources  . . . . . . . . . . . . . . . . . . . . . . . . . 29
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 30
     9.1.  IPv4 and IPv6 Anycast Prefix Allocation  . . . . . . . . . 30
       9.1.1.  IPv4 . . . . . . . . . . . . . . . . . . . . . . . . . 30
       9.1.2.  IPv6 . . . . . . . . . . . . . . . . . . . . . . . . . 30
     9.2.  IPv4 and IPv6 AMT Subnet Prefix Allocation . . . . . . . . 30
       9.2.1.  IPv4 . . . . . . . . . . . . . . . . . . . . . . . . . 30
       9.2.2.  IPv6 . . . . . . . . . . . . . . . . . . . . . . . . . 30
     9.3.  UDP Port number  . . . . . . . . . . . . . . . . . . . . . 30
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 31
   11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 32
   12. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 33
   13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 34
     13.1. Normative References . . . . . . . . . . . . . . . . . . . 34
     13.2. Informative References . . . . . . . . . . . . . . . . . . 34



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   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 36
   Intellectual Property and Copyright Statements . . . . . . . . . . 38

















































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1.  Introduction

   The primary goal of this document is to foster the deployment of
   native IP multicast by enabling a potentially large number of nodes
   to connect to the already present multicast infrastructure.
   Therefore, the techniques discussed here should be viewed as an
   interim solution to help in the various stages of the transition to a
   native multicast network.

   To allow fast deployment, the solution presented here only requires
   small and concentrated changes to the network infrastructure, and no
   changes at all to user applications or to the socket API of end-
   nodes' operating systems.  The protocol introduced in this
   specification can be deployed in a few strategically-placed network
   nodes and in user-installable software modules (pseudo device drivers
   and/or user-mode daemons) that reside underneath the socket API of
   end-nodes' operating systems.  This mechanism is very similar to that
   used by "6to4" [RFC3056], [RFC3068] to get automatic IPv6
   connectivity.

   Effectively, AMT treats the unicast-only inter-network as a large
   non-broadcast multi-access (NBMA) link layer, over which we require
   the ability to multicast.  To do this, multicast packets being sent
   to or from a site must be encapsulated in unicast packets.  If the
   group has members in multiple sites, AMT encapsulation of the same
   multicast packet will take place multiple times by necessity.

























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2.  Applicability

   AMT is not a substitute for native multicast or a statically
   configured multicast tunnel for high traffic flow.  Unicast
   replication is required to reach multiple receivers that are not part
   of the native multicast infrastructure.  Unicast replication is also
   required by non-native sources to different parts of the native
   multicast infrastructure.  However, this is no worse than regular
   unicast distribution of streams and in most cases much better.

   The following problems are addressed:

   1.  Allowing isolated sites/hosts to receive the SSM flavor of
       multicast ([RFC4607]).

   2.  Allowing isolated non-NAT sites/hosts to transmit the SSM flavor
       of multicast.

   3.  Allowing isolated sites/hosts to receive general multicast (ASM
       [RFC1112]).

   This document does not address allowing isolated sites/hosts to
   transmit general multicast.  We expect that other solutions (e.g.,
   Tunnel Brokers, a la [RFC3053]) will be used for sites that desire
   this capability.

   Implementers should be aware that site administrators may have
   configured administratively scoped multicast boundaries and a remote
   gateway may provide a means to circumvent administrative boundaries.
   Therefore, implementations should allow for the configuration of such
   boundaries on relays and gateways and perform filtering as needed.




















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3.  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].














































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4.  Definitions

    +---------------+        Internet            +---------------+
    | AMT Site      |                            | Native MCast  |
    |               |                            |               |
    |        +------+----+         AMT      +----+----+ AMT      |
    |        |AMT Gateway|         Anycast  |AMT Relay| Subnet   |
    |        |     +-----+-+       Prefix +-+-----+   | Prefix   |
    |        |     |AMT IF | <------------|AMT IF |   |--------> |
    |        |     +-----+-+              +-+-----+   |          |
    |        +------+----+                  +----+----+          |
    |               |                            |               |
    +---------------+                            +---------------+

4.1.  AMT Pseudo-Interface

   AMT encapsulation of multicast packets inside unicast packets occurs
   at a point that is logically equivalent to an interface, with the
   link layer being the unicast-only network.  This point is referred to
   as a pseudo-interface.  Some implementations may treat it exactly
   like any other interface and others may treat it like a tunnel end-
   point.

4.2.  AMT Gateway

   A host, or a site gateway router, supporting an AMT Pseudo-
   Interface.  It does not have native multicast connectivity to the
   native multicast backbone infrastructure.  It is simply referred to
   in this document as a "gateway".

4.3.  AMT Site

   A multicast-enabled network not connected to the multicast backbone
   served by an AMT Gateway.  It could also be a stand- alone AMT
   Gateway.

4.4.  AMT Relay Router

   A multicast router configured to support transit routing between AMT
   Sites and the native multicast backbone infrastructure.  The relay
   router has one or more interfaces connected to the native multicast
   infrastructure, zero or more interfaces connected to the non-
   multicast capable inter-network, and an AMT pseudo-interface.  It is
   simply referred to in this document as a "relay".

   As with [RFC3056], we assume that normal multicast routers do not
   want to be tunnel endpoints (especially if this results in high fan
   out), and similarly that service providers do not want encapsulation



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   to arbitrary routers.  Instead, we assume that special-purpose
   routers will be deployed that are suitable for serving as relays.

4.5.  AMT Relay Anycast Prefix

   A well-known address prefix used to advertise (into the unicast
   routing infrastructure) a route to an available AMT Relay Router.
   This could also be private (i.e., not well-known) for a private
   relay.

   Prefixes for both IPv4 and IPv6 will be assigned in a future version
   of this draft.

4.6.  AMT Relay Anycast Address

   An anycast address which is used to reach the nearest AMT Relay
   Router.

   This address corresponds to the setting the low-order octet of the
   AMT Relay Anycast Prefix to 1 (for both IPv4 and IPv6).

4.7.  AMT Subnet Anycast Prefix

   A well-known address prefix used to advertise (into the M-RIB of the
   native multicast-enabled infrastructure) a route to AMT Sites.  This
   prefix will be used to enable sourcing SSM traffic from an AMT
   Gateway.

4.8.  AMT Gateway Anycast Address

   An anycast address in the AMT Subnet Anycast Prefix range, which is
   used by an AMT Gateway to enable sourcing SSM traffic from local
   applications.


















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5.  Overview

5.1.  Receiving Multicast in an AMT Site

                               Internet
    +---------------+                            +---------------+
    | AMT Site      |     2. 3-way Membership    | MBone         |
    |               |          Handshake         |               |
    |   1. Join +---+---+ =================> +---+---+           |
    |     +---->|Gateway|                    | Relay |           |
    |     |     +---+---+ <================= +---+---+           |
    |   R-+         |       3. Receive Data      |               |
    +---------------+                            +---------------+

                    Receiving Multicast in an AMT Site

   AMT relays and gateways cooperate to transmit multicast traffic
   sourced within the native multicast infrastructure to AMT sites:
   relays receive the traffic natively and unicast-encapsulate it to
   gateways; gateways decapsulate the traffic and possibly forward it
   into the AMT site.

   Each gateway has an AMT pseudo-interface that serves as a default
   multicast route.  Requests to join a multicast session are sent to
   this interface and encapsulated to a particular relay reachable
   across the unicast-only infrastructure.

   Each relay has an AMT pseudo-interface too.  Multicast traffic sent
   on this interface is encapsulated to zero or more gateways that have
   joined to the relay.  The AMT recipient-list is determined for each
   multicast session.  This requires the relay to keep state for each
   gateway which has joined a particular group or (source, group) pair.
   Multicast packets from the native infrastructure behind the relay
   will be sent to each gateway which has requested them.

   All multicast packets (data and control) are encapsulated in unicast
   packets.  UDP encapsulation is used for all AMT control and data
   packets using the IANA reserved UDP port number for AMT.

   Each relay, plus the set of all gateways using the relay, together
   are thought of as being on a separate logical NBMA link.  This
   implies that the AMT recipient-list is a list of "link layer"
   addresses which are (IP address, UDP port) pairs.

   Since the number of gateways using a relay can be quite large, and we
   expect that most sites will not want to receive most groups, an
   explicit-joining protocol is required for gateways to communicate
   group membership information to a relay.  The two most likely



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   candidates are the IGMP/MLD protocol [RFC3376], [RFC3810], and the
   PIM-Sparse Mode protocol [RFC4601].  Since an AMT gateway may be a
   host, and hosts typically do not implement routing protocols,
   gateways will use IGMP/MLD as described in Section 7 below.  This
   allows a host kernel (or a pseudo device driver) to easily implement
   AMT gateway behavior, and obviates the relay from the need to know
   whether a given gateway is a host or a router.  From the relay's
   perspective, all gateways are indistinguishable from hosts on an NBMA
   leaf network.

5.1.1.  Scalability Considerations

   It is possible that millions of hosts will enable AMT gateway
   functionality and so an important design goal is not to create
   gateway state in each relay until the gateway joins a multicast
   group.  But even the requirement that a relay keep group state per
   gateway that has joined a group introduces potential scalability
   concerns.

   Scalability of AMT can be achieved by adding more relays, and using
   an appropriate relay discovery mechanism for gateways to discover
   relays.  The solution we adopt is to assign addresses in anycast
   fashion to relays [RFC1546], [RFC4291].  However, simply sending
   periodic membership reports to an anycast address can cause
   duplicates.  Specifically, if routing changes such that a different
   relay receives a periodic membership report, both the new and old
   relays will encapsulate data to the AMT site until the old relay's
   state times out.  This is obviously undesirable.  Instead, we use the
   anycast address merely to find the unicast address of a relay to
   which membership reports are sent.

   Since adding another relay has the result of adding another
   independent NBMA link, this allows the gateways to be spread out
   among more relays so as to keep the number of gateways per relay at a
   reasonable level.

5.1.2.  Spoofing Considerations

   An attacker could affect the group state in the relay or gateway by
   spoofing the source address in the join or leave reports.  This can
   be used to launch reflection or denial of service attacks on the
   target.  Such attacks can be mitigated by using a three way handshake
   between the gateway and the relay for each multicast membership
   report or leave.

   When a gateway or relay wants to send a membership report, it first
   sends an AMT Request with a request nonce in it.  The receiving side
   (the respondent) can calculate a message authentication code (MAC)



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   based on (for example) the source IP address of the Request, the
   source UDP port, the request nonce, and a secret key known only to
   the respondent.  The algorithm and the input used to calculate the
   MAC does not have to be standardized since the respondent generates
   and verifies the MAC and the originator simply echoes it.

   An AMT Membership Query is sent back including the request nonce and
   the MAC to the originator of the Request.  The originator then sends
   the IGMP/MLD Membership/Listener Report or Leave/Done (including the
   IP Header) along with the request nonce and the received MAC back to
   the respondent finalizing the 3-way handshake.

   Upon reception, the respondent can recalculate the MAC based on the
   source IP address, the source UDP port, the request nonce, and the
   local secret.  The IGMP/MLD message is only accepted if the received
   MAC matches the calculated MAC.

   The local secret never has to be shared with the other side.  It is
   only used to verify return routability of the originator.

   Since the same Request Nonce and source IP address can be re-used,
   the receiver SHOULD change its secret key at least once per hour.
   However, AMT Membership updates received with the previous secret
   MUST be accepted for up to the IGMP/MLD Query Interval.

5.1.3.  Protocol Sequence for a Gateway Joining SSM Receivers to a Relay

   This description assumes the Gateway can be a host joining as a
   receiver or a network device acting as a Gateway when a directly
   connected host joins as a receiver.

   o  Receiver at AMT site sends IGMPv3/MLDv2 report joining (S1,G1).

   o  Gateway receives report.  If it has no tunnel state with a Relay,
      it originates an AMT Relay Discovery message addressed to the
      Anycast Relay IP address.  The AMT Relay Discovery message can be
      sent on demand if no relay is known at this time or at startup and
      be periodically refreshed.

   o  The closest Relay topologically receives the AMT Relay Discovery
      message and returns the nonce from the Discovery in an AMT Relay
      Advertisement message so the Gateway can learn of the Relay's
      unique IP address.

   o  When the Gateway receives the AMT Relay Advertisement message, it
      now has an address to use for all subsequent (S,G) entries it will
      join on behalf of attached receivers (or itself).




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   o  If the gateway has a valid Response MAC from a previous AMT Query
      message, it can send an AMT Membership Update message as described
      below.  Otherwise, the Gateway sends an AMT Request message to the
      Relay's unique IP address to begin the process of joining the
      (S,G).  The gateway also SHOULD initialize a timer used to send
      periodic Requests to a random value from the interval [0, [Query
      Interval]] before sending the first periodic report, in order to
      prevent startup synchronization.

   o  The Relay responds to the AMT Request message by returning the
      nonce from the Request in a AMT Query message.  The Query message
      contains an IGMP/MLD QUERY indicating how often the Gateway should
      repeat AMT Request messages so the (S,G) state can stay refreshed
      in the Relay.  The Query message also includes an opaque security
      code which is generated locally (with no external coordination).

   o  When the Gateway receives the AMT Query message it responds by
      copying the security code from the AMT Query message into a AMT
      Membership Update message.  The Update message contains (S1,G1) in
      an IGMPv3/MLDv2 formatted packet with an IP header.  The nonce
      from the AMT Request is also included in the AMT Membership Update
      message.

   o  When the Relay receives the AMT Membership Update, it will add the
      tunnel to the Gateway in it's outgoing interface list for it's
      (S1,G1) entry stored in the multicast routing table.  If the
      (S1,G1) entry was created do to this interaction, the multicast
      routing protocol running on the Relay will trigger a Join message
      towards source S1 to build a native multicast tree in the native
      multicast infrastructure.

   o  As packets are sent from the host S1, they will travel natively
      down the multicast tree associated with (S1,G1) in the native
      multicast infrastructure to the Relay.  The Relay will replicate
      to all interfaces in it's outgoing interface list as well as the
      tunnel outgoing interface, which is encapsulated in a unicast AMT
      Multicast Data message.

   o  When the Gateway receives the AMT Multicast Data message, it will
      accept the packet since it was received over the pseudo-interface
      associated with the tunnel to the Relay it had attached to, and
      forward the packet to the outgoing interfaces joined by any
      attached receiver hosts (or deliver the packet to the application
      when the Gateway is the receiver).

   o  If later (S2,G2) is joined by a receiver, a 3-way handshake of
      Request/ Query/Update occurs for this entry.  The Discovery/
      Advertisement exchange is not required.



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   o  To keep the state for (S1,G1) and (S2,G2) alive in the Relay, the
      Gateway will send periodic AMT Membership Updates.  The Membership
      Update can be sent directly if the sender has a valid nonce from a
      previous Request.  If not, an AMT Request messages should be sent
      to solicit a Query Message.  When sending a periodic state
      refresh, all joined state in the Gateway is packed in the fewest
      number of AMT Membership Update messages.

   o  When the Gateway leaves all (S,G) entries, the Relay can free
      resources associated with the tunnel.  It is assumed that when the
      Gateway would want to join an (S,G) again, it would start the
      Discovery/Advertisement tunnel establishment process over again.

   This same procedure would be used for receivers who operate in Any-
   Source Multicast (ASM) mode.

5.2.  Sourcing Multicast from an AMT site

   Two cases are discussed below: multicast traffic sourced in an AMT
   site and received in the MBone, and multicast traffic sourced in an
   AMT site and received in another AMT site.

   In both cases only SSM sources are supported.  Furthermore this
   specification only deals with the source residing directly in the
   gateway.  To enable a generic node in an AMT site to source
   multicast, additional coordination between the gateway and the
   source-node is required.

   The gateway SHOULD allow for filtering link-local and site-local
   traffic.

   The general mechanism used to join towards AMT sources is based on
   the following:

   1.  Applications residing in the gateway use addresses in the AMT
       Subnet Anycast Prefix to send multicast, as a result of sourcing
       traffic on the AMT pseudo-interface.

   2.  The AMT Subnet Anycast Prefix is advertised for RPF reachability
       in the M-RIB by relays and gateways.

   3.  Relays or gateways that receive a join for a source/group pair
       use information encoded in the address pair to rebuild the
       address of the gateway (source) to which to encapsulate the join
       (see Section 7.2 for more details).  The membership reports use
       the same three way handshake as outlined in Section 5.1.2





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5.2.1.  Supporting Site-MBone Multicast

                                Internet
    +---------------+                            +---------------+
    | AMT Site      |     2. 3-way Membership    | MBone         |
    |               |           Handshake        |               |
    |           +---+---+ <================= +---+---+ 1. Join   |
    |           |Gateway|                    | Relay |<-----+    |
    |           +---+---+ =================> +---+---+      |    |
    |               |      3. Receive Data       |          +-R  |
    +---------------+                            +---------------+

                           Site-MBone Multicast

   If a relay receives an explicit join from the native infrastructure,
   for a given (source, group) pair where the source address belongs to
   the AMT Subnet Anycast Prefix, then the relay will periodically
   (using the rules specified in Section 5.1.2) encapsulate membership
   updates for the group to the gateway.  The gateway must keep state
   per relay from which membership reports have been sent, and forward
   multicast traffic from the site to all relays from which membership
   reports have been received.  The choice of whether this state and
   replication is done at the link-layer (i.e., by the tunnel interface)
   or at the network-layer is implementation dependent.

   If there are multiple relays present, this ensures that data from the
   AMT site is received via the closest relay to the receiver.  This is
   necessary when the routers in the native multicast infrastructure
   employ Reverse-Path Forwarding (RPF) checks against the source
   address, such as occurs when PIM Sparse-Mode [RFC4601] is used by the
   multicast infrastructure.

   The solution above will scale to an arbitrary number of relays, as
   long at the number of relays requiring multicast traffic from a given
   AMT site remains reasonable enough to not overly burden the site's
   gateway.

   A source at or behind an AMT gateway requires the gateway to do the
   replication to one or more relays and receiving gateways.  If this
   places too much of a burden on the sourcing gateway, the source
   should join the native multicast infrastructure through a permanent
   tunnel so that replication occurs within the native multicast
   infrastructure.








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5.2.2.  Supporting Site-Site Multicast

                               Internet
    +---------------+                            +---------------+
    | AMT Site      |     2. 3-way Membership    | AMT Site      |
    |               |          Handshake         |               |
    |           +---+---+ <================= +---+---+ 1. Join   |
    |           |Gateway|                    |Gateway|<-----+    |
    |           +---+---+ =================> +---+---+      |    |
    |               |      3. Receive Data       |          +-R  |
    +---------------+                            +---------------+

                            Site-Site Multicast

   Since we require gateways to accept membership reports, as described
   above, it is also possible to support multicast among AMT sites,
   without requiring assistance from any relays.

   When a gateway wants to join a given (source, group) pair, where the
   source address belongs to the AMT Subnet Anycast Prefix, then the
   gateway will periodically unicast encapsulate an IGMPv3/MLDv2 Report
   [RFC3376], [RFC3810] (including IP Header) directly to the site
   gateway for the source.

   We note that this can result in a significant amount of state at a
   site gateway sourcing multicast to a large number of other AMT sites.
   However, it is expected that this is not unreasonable for two
   reasons.  First, the gateway does not have native multicast
   connectivity, and as a result is likely doing unicast replication at
   present.  The amount of state is thus the same as what such a site
   already deals with.  Secondly, any site expecting to source traffic
   to a large number of sites could get a point-to-point tunnel to the
   native multicast infrastructure, and use that instead of AMT.


















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6.  Message Formats

6.1.  AMT Relay Discovery

   The AMT Relay Discovery message is a UDP packet sent from the AMT
   gateway unicast address to the AMT relay anycast address to discover
   the unicast address of an AMT relay.

   The UDP source port is uniquely selected by the local host operating
   system.  The UDP destination port is the IANA reserved AMT port
   number.  The UDP checksum MUST be valid in AMT control messages.

   The payload of the UDP packet contains the following fields.


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type=0x1  |     Reserved                                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Discovery Nonce                                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                            AMT Relay Discovery

6.1.1.  Type

   The type of the message.

6.1.2.  Reserved

   A 24-bit reserved field.  Sent as 0, ignored on receipt.

6.1.3.  Discovery Nonce

   A 32-bit random value generated by the gateway and replayed by the
   relay.

6.2.  AMT Relay Advertisement

   The AMT Relay Advertisement message is a UDP packet sent from the AMT
   relay anycast address to the source of the discovery message.

   The UDP source port is the IANA reserved AMT port number and the UDP
   destination port is the source port received in the Discovery
   message.  The UDP checksum MUST be valid in AMT control messages.




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   The payload of the UDP packet contains the following fields.


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type=0x2  |     Reserved                                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Discovery Nonce                                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Relay Address                                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                          AMT Relay Advertisement

6.2.1.  Type

   The type of the message.

6.2.2.  Reserved

   A 24-bit reserved field.  Sent as 0, ignored on receipt.

6.2.3.  Discovery Nonce

   A 32-bit random value generated by the gateway and replayed by the
   relay.

6.2.4.  Relay Address

   The unicast IPv4 or IPv6 address of the AMT relay.  The family can be
   determined by the length of the Advertisement.

6.3.  AMT Request

   A Request packet is sent to begin a 3-way handshake for sending an
   IGMP/MLD Membership/Listener Report or Leave/Done.  It can be sent
   from a gateway to a relay, from a gateway to another gateway, or from
   a relay to a gateway.

   It is sent from the originator's unique unicast address to the
   respondents' unique unicast address.

   The UDP source port is uniquely selected by the local host operating
   system.  It can be different for each Request and different from the
   source port used in Discovery messages but does not have to be.  The
   UDP destination port is the IANA reserved AMT port number.  The UDP



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   checksum MUST be valid in AMT control messages.


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type=0x3  |     Reserved                                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Request Nonce                                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                          AMT Relay Advertisement

6.3.1.  Type

   The type of the message.

6.3.2.  Reserved

   A 24-bit reserved field.  Sent as 0, ignored on receipt.

6.3.3.  Request Nonce

   A 32-bit identifier used to distinguish this request.

6.4.  AMT Membership Query

   An AMT Membership Query packet is sent from the respondent back to
   the originator to solicit an AMT Membership Update while confirming
   the source of the original request.  It contains a relay Message
   Authentication Code (MAC) that is a cryptographic hash of a private
   secret, the originators address, and the request nonce.

   It is sent from the destination address received in the Request to
   the source address received in the Request which is the same address
   used in the Relay Advertisement.

   The UDP source port is the IANA reserved AMT port number and the UDP
   destination port is the source port received in the Request message.
   The UDP checksum MUST be valid in AMT control messages.










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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type=0x4  |    Reserved   |         Response MAC          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Response MAC (continued)                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Request Nonce                                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            IGMP Membership Query or MLD Listener Query        |
   |            (including IP Header)                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            ...                                                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                           AMT Membership Query

6.4.1.  Type

   The type of the message.

6.4.2.  Reserved

   A 8-bit reserved field.  Sent as 0, ignored on receipt.

6.4.3.  Response MAC

   A 48-bit hash generated by the respondent and sent to the originator
   for inclusion in the AMT Membership Update.  The algorithm used for
   this is chosen by the respondent but an algorithm such as HMAC-MD5-48
   [RFC2104] SHOULD be used at a minimum.

6.4.4.  Request Nonce

   A 32-bit identifier used to distinguish this request echoed back to
   the originator.

6.4.5.  IGMP/MLD Query (including IP Header)

   The message contains either an IGMP Query or an MLD Multicast
   Listener Query.  The IGMP or MLD version sent should default to
   IGMPv3 or MLDv2 unless explicitly configured to use IGMPv2 or MLDv1.
   The IGMP/MLD Query includes a full IP Header.  The IP source address
   of the query would match the anycast address on the pseudo interface.
   The TTL of the outer header should be sufficient to reach the tunnel
   endpoint and not mimic the inner header TTL which is typically 1 for
   IGMP/MLD messages.



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6.5.  AMT Membership Update

   An AMT Membership Update is sent to report a membership after a valid
   Response MAC has been received.  It contains the original IGMP/MLD
   Membership/Listener Report or Leave/Done received over the AMT
   pseudo-interface including the original IP header.  It echoes the
   Response MAC received in the AMT Membership Query so the respondent
   can verify return routability to the originator.

   It is sent from the destination address received in the Query to the
   source address received in the Query which should both be the same as
   the original Request.

   The UDP source and destination port numbers should be the same ones
   sent in the original Request.

   The relay is not required to use the IP source address of the IGMP
   Membership Report for any particular purpose.

   The same Request Nonce and Response MAC can be used across multiple
   AMT Membership Update messages without having to send individual AMT
   Membership Query messages.


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type=0x5  |    Reserved   |         Response MAC          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Response MAC (continued)                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Request Nonce                                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            IGMP or MLD Message (including IP header)          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            ...                                                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                           AMT Membership Update

6.5.1.  Type

   The type of the message.







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6.5.2.  Reserved

   A 8-bit reserved field.  Sent as 0, ignored on receipt.

6.5.3.  Response MAC

   The 48-bit MAC received in the Membership Query and echoed back in
   the Membership Update.

6.5.4.  Request Nonce

   A 32-bit identifier used to distinguish this request.

6.5.5.  IGMP/MLD Message (including IP Header)

   The message contains either an IGMP Membership Report, an IGMP
   Membership Leave, an MLD Multicast Listener Report, or an MLD
   Listener Done.  The IGMP or MLD version sent should be in response
   the version of the query received in the AMT Membership Query.  The
   IGMP/MLD Message includes a full IP Header.

6.6.  AMT IP Multicast Data

   The AMT Data message is a UDP packet encapsulating the IP Multicast
   data requested by the originator based on a previous AMT Membership
   Update message.

   It is sent from the unicast destination address of the Membership
   update to the source address of the Membership Update.

   The UDP source and destination port numbers should be the same ones
   sent in the original Query.  The UDP checksum SHOULD be 0 in the AMT
   IP Multicast Data message.

   The payload of the UDP packet contains the following fields.


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type=0x6  |    Reserved   |     IP Multicast Data ...     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            ...                                                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                           AMT IP Multicast Data




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6.6.1.  Type

   The type of the message.

6.6.2.  Reserved

   An 8-bit reserved field.  Sent as 0, ignored on receipt.

6.6.3.  IP Multicast Data

   The original IP Multicast data packet that is being replicated by the
   relay to the gateways including the original IP header.







































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7.  AMT Gateway Details

   This section details the behavior of an AMT Gateway, which may be a
   router serving an AMT site, or the site may consist of a single host,
   serving as its own gateway.

7.1.  At Startup Time

   At startup time, the AMT gateway will bring up an AMT pseudo-
   interface to be used for encapsulation.  The gateway needs to
   discover an AMT Relay to send Membership Requests.  It can send an
   AMT Relay Discovery at startup time or wait until it has a group
   membership to report.  The AMT Relay Discovery message is sent to the
   AMT Relay Anycast Address.  A unicast address (which is treated as a
   link-layer address to the encapsulation interface) is received in the
   AMT Relay Advertisement message.  The discovery process SHOULD be
   done periodically (e.g., once a day) to re-resolve the unicast
   address of a close relay.  To prevent startup synchronization, the
   timer SHOULD use at least 10 percent jitter.

   If the gateway is serving as a local router, it SHOULD also function
   as an IGMP/MLD Proxy, as described in [RFC4605], with its IGMP/MLD
   host-mode interface being the AMT pseudo-interface.  This enables it
   to translate group memberships on its downstream interfaces into
   IGMP/MLD Reports.  Hosts receiving multicast packets through an AMT
   gateway acting as a proxy should ensure that their M-RIB accepts
   multicast packets from the AMT gateway for the sources it is joining.

7.2.  Gateway Group and Source Addresses

   To support sourcing traffic to SSM groups by a gateway with a global
   unicast address, the AMT Subnet Anycast Prefix is treated as the
   subnet prefix of the AMT pseudo-interface, and an anycast address is
   added on the interface.  This anycast address is formed by
   concatenating the AMT Subnet Anycast Prefix followed by the high bits
   of the gateway's global unicast address.

   The remaining bits of its global unicast address are appended to the
   SSM prefix to create the group address and any spare bits may be
   allocated using local policy.

   If a gateway wants to source multicast traffic, it must select the
   gateway source address and SSM group address in such a way that the
   AMT relay can have enough information to reconstruct the gateway's
   unicast address when it receives an SSM join for the source.

   Note that multiple gateways might end up with the same anycast
   address assigned to their pseudo-interfaces.



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7.2.1.  IPv4

   For example, if IANA assigns the IPv4 prefix x.y/16 as the AMT Subnet
   Anycast Prefix, and the gateway has global unicast address a.b.c.d,
   then the AMT Gateway's Anycast Source Address will be x.y.a.b.  Since
   the IPv4 SSM group range is 232/8, it MUST allocate IPv4 SSM groups
   in the range 232.c.d/24.

           Group:
                 8                  16                 8
           +------------+------------------------+-------------+
           | SSM prefix |     Low 16 bits of     |    Local    |
           |   232/8    |  real source address   |    Policy   |
           +------------+------------------------+-------------+

           Source:
           +-------------------------+-------------------------+
           |16-bit AMT unicast prefix| high 16 bits of real src|
           +-------------------------+-------------------------+

                                IPv4 format

   This allows for 2^8 (256) IPv4 group addresses for use by each AMT
   gateway.

7.2.2.  IPv6

   Similarly for IPv6, this is illustrated in the following figure.

           Group:
                 32                  64                 32
           +------------+------------------------+-------------+
           | SSM prefix |     Low 64 bits of     |    Local    |
           | FF3x::/32  |  real source address   |    Policy   |
           +------------+------------------------+-------------+

           Source:
           +-------------------------+-------------------------+
           |64-bit AMT unicast prefix| high 64 bits of real src|
           +-------------------------+-------------------------+

                                IPv6 format

   This allows for 2^32 (over 4 billion) IPv6 group addresses for use by
   each AMT gateway.






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7.3.  Joining Groups with MBone Sources

   The IGMP/MLD protocol usually operates by having the Querier
   multicast an IGMP/MLD Query message on the link.  This behavior does
   not work on NBMA links which do not support multicast.  Since the set
   of gateways is typically unknown to the relay (and potentially quite
   large), unicasting the queries is also impractical.  The following
   behavior is used instead.

   Applications residing in a gateway should join groups on the AMT
   pseudo-interface, causing IGMP/MLD Membership/Listener Reports to be
   sent over that interface.  When UDP encapsulating the membership
   reports (and in fact any other messages, unless specified otherwise
   in this document), the destination address in the outer IP header is
   the relay's unicast address.  Robustness is provided by the
   underlying IGMP/MLD protocol messages sent on the AMT pseudo-
   interface.  In other words, the gateway does not need to retransmit
   IGMP/MLD Membership/Listener Reports and Leave/Done messages received
   on the pseudo-interface since IGMP/MLD will already do this.  The
   gateway simply needs to encapsulate each IGMP/MLD Membership/Listener
   Report and Leave/Done message it receives.

   However, since periodic IGMP/MLD Membership/Listener Reports are sent
   in response to IGMP/MLD Queries, a mechanism to trigger periodic
   Membership/Listener Reports and Leave/Done messages is necessary.
   The gateway should use a timer to trigger periodic AMT Membership
   Updates.

   If the gateway is behind a firewall device, the firewall may require
   the gateway to periodically refresh the UDP state in the firewall at
   a shorter interval than the standard IGMP/MLD Query interval.  AMT
   Requests can be sent periodically to solicit IGMP/MLD Queries.  The
   interval at which the AMT Requests are sent should be configurable to
   ensure the firewall does not revert to blocking the UDP encapsulated
   IP Multicast data packets.  When the AMT Query is received, it can be
   ignored unless it is time for a periodic AMT Membership Update.

   The relay can use the Querier's Robustness Variable (QRV) defined in
   [RFC3376] and [RFC3810] to adjust the number of Membership/Listener
   Reports that are sent by the host joining the group.

7.4.  Responding to Relay Changes

   When a gateway determines that its current relay is unreachable
   (e.g., upon receipt of an ICMP Unreachable message [RFC0792] for the
   relay's unicast address), it may need to repeat relay address
   discovery.  However, care should be taken not to abandon the current
   relay too quickly due to transient network conditions.



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7.5.  Joining SSM Groups with AMT Gateway Sources

   An IGMPv3/MLDv2 Report for a given (source, group) pair MAY be
   encapsulated directly to the source, when the source address belongs
   to the AMT Subnet Anycast Prefix.

   The "link-layer" address to use as the destination address in the
   outer IP header is obtained as follows.  The source address in the
   inclusion list of the IGMPv3/MLDv2 report will be an AMT Gateway
   Anycast Address with the high bits of the address, and the remaining
   bits will be in the middle of the group address.

   Section 7.2 describes this format to recover the gateway source
   address.

7.6.  Receiving AMT Membership Updates by the Gateway

   When an AMT Request is received by the gateway from another gateway
   or relay, it follows the same 3-way handshake procedure a relay would
   follow if it received the AMT Request.  It generates a MAC and
   responds with an AMT Membership Query.  When the AMT Membership
   Update is received, it verifies the MAC and then processes the IGMP/
   MLD Membership/Listener Report or Leave/Done.

   At the gateway, the IGMP/MLD packet should be an IGMPv3/MLDv2 source
   specific (S,G) join or leave.

   If S is not the AMT Gateway Anycast Address, the packet is silently
   discarded.  If G does not contain the low bits of the global unicast
   address (as described above), the packet is also silently discarded.

   The gateway adds the source address (from the outer IP header) and
   UDP port of the report to a membership list for G. Maintaining this
   membership list may be done in any implementation-dependent manner.
   For example, it might be maintained by the "link-layer" inside the
   AMT pseudo-interface, making it invisible to the normal IGMP/MLD
   module.

7.7.  Sending data to SSM groups

   When multicast packets are sent on the AMT pseudo-interface, they are
   encapsulated as follows.  If the group address is not an SSM group,
   then the packet is silently discarded (this memo does not currently
   provide a way to send to non-SSM groups).

   If the group address is an SSM group, then the packet is unicast
   encapsulated to each remote node from which the gateway has received
   an IGMPv3/MLDv2 report for the packet's (source, group) pair.



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8.  Relay Router Details

8.1.  At Startup time

   At startup time, the relay router will bring up an NBMA-style AMT
   pseudo-interface.  It shall also add the AMT Relay Anycast Address on
   some interface.

   The relay router shall then advertise the AMT Relay Anycast Prefix
   into the unicast-only Internet, as if it were a connection to an
   external network.  When the advertisement is done using BGP, the AS
   path leading to the AMT Relay Anycast Prefix shall include the
   identifier of the local AS.

   The relay router shall also enable IGMPv3/MLDv2 on the AMT pseudo-
   interface, except that it shall not multicast Queries (this might be
   done, for example, by having the AMT pseudo-device drop them, or by
   having the IGMP/MLD module not send them in the first place).

   Finally, to support sourcing SSM traffic from AMT sites, the AMT
   Subnet Anycast Prefix is assigned to the AMT pseudo-interface, and
   the AMT Subnet Anycast Prefix is injected by the AMT Relay into the
   M-RIB of MBGP.

8.2.  Receiving Relay Discovery messages sent to the Anycast Address

   When a relay receives an AMT Relay Discovery message directed to the
   AMT Relay Anycast Address, it should respond with an AMT Relay
   Advertisement containing its unicast address.  The source and
   destination addresses of the advertisement should be the same as the
   destination and source addresses of the discovery message
   respectively.  Further, the nonce in the discovery message MUST be
   copied into the advertisement message.

8.3.  Receiving Membership Updates from AMT Gateways

   The relay operates passively, sending no periodic IGMP/MLD Queries
   but simply tracking membership information according to AMT Request/
   Query/Membership Update tuples received.  In addition, the relay must
   also do explicit membership tracking, as to which gateways on the AMT
   pseudo-interface have joined which groups.  Once an AMT Membership
   Update has been successfully received, it updates the forwarding
   state for the appropriate group and source (if provided).  When data
   arrives for that group, the traffic must be encapsulated to each
   gateway which has joined that group or (S,G).

   The explicit membership tracking and unicast replication may be done
   in any implementation-specific manner.  Some examples are:



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   1.  The AMT pseudo-device driver might track the group information
       and perform the replication at the "link-layer", with no changes
       to a pre-existing IGMP/MLD module.

   2.  The IGMP/MLD module might have native support for explicit
       membership tracking, especially if it supports other NBMA-style
       interfaces.

   If a relay wants to affect the rate at which the AMT Requests are
   originated from a gateway, it can tune the membership timeout by
   adjusting the Querier's Query Interval Code (QQIC) field in the IGMP/
   MLD Query contained within the AMT Membership Query message.  The
   QQIC field is defined in [RFC3376] and [RFC3810].  However, since the
   gateway may need to send AMT Requests frequently enough to prevent
   firewall state from timing out, the relay may be limited in its
   ability to spread out Requests coming from a gateway by adjusting the
   QQIC field.

8.4.  Receiving (S,G) Joins from the Native Side, for AMT Sources

   The relay sends an IGMPv3/MLDv2 report to the AMT source as described
   above in Section 5.1.2





























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9.  IANA Considerations

9.1.  IPv4 and IPv6 Anycast Prefix Allocation

   The IANA should allocate an IPv4 prefix and an IPv6 prefix dedicated
   to the public AMT Relays to advertise to the native multicast
   backbone.  The prefix length should be determined by the IANA; the
   prefix should be large enough to guarantee advertisement in the
   default-free BGP networks.

9.1.1.  IPv4

   A prefix length of 16 will meet this requirement.

9.1.2.  IPv6

   A prefix length of 32 will meet this requirement.  IANA has
   previously set aside the range 2001::/16 for allocating prefixes for
   this purpose.

9.2.  IPv4 and IPv6 AMT Subnet Prefix Allocation

   It should also be noted that this prefix length directly affects the
   number of groups available to be created by the AMT gateway: in the
   IPv4 case, a prefix length of 16 gives 256 groups, and a prefix
   length of 8 gives 65536 groups.

   All allocations are a one time effort and there will be no need for
   any recurring assignment after this stage.

9.2.1.  IPv4

   As described above in Section 7.2.1 an IPv4 prefix with a length of
   16 is requested for this purpose.

9.2.2.  IPv6

   As described above in Section 7.2.2 an IPv6 prefix with a length of
   32 is requested.

9.3.  UDP Port number

   IANA has previously allocated UDP reserved port number 2268 for AMT
   encapsulation.







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10.  Security Considerations

   The anycast technique introduces a risk that a rogue router or a
   rogue AS could introduce a bogus route to the AMT Relay Anycast
   prefix, and thus divert the traffic.  Network managers have to
   guarantee the integrity of their routing to the AMT Relay Anycast
   prefix in much the same way that they guarantee the integrity of all
   other routes.

   Within the native MBGP infrastructure, there is a risk that a rogue
   router or a rogue AS could inject a false route to the AMT Subnet
   Anycast Prefix, and thus divert joins and cause RPF failures of
   multicast traffic.  As the AMT Subnet Anycast Prefix will be
   advertised by multiple entities, guaranteeing the integrity of this
   shared MBGP prefix is much more challenging than verifying the
   correctness of a regular unicast advertisement.  To mitigate this
   threat, routing operators should configure the BGP sessions to filter
   out any more specific advertisements for the AMT Subnet Anycast
   Prefix.

   Gateways and relays will accept and decapsulate multicast traffic
   from any source from which regular unicast traffic is accepted.  If
   this is for any reason felt to be a security risk, then additional
   source address based packet filtering MUST be applied:

   1.  To prevent a rogue sender (that can't do traditional spoofing
       because of e.g. access lists deployed by its ISP) from making use
       of AMT to send packets to an SSM tree, a relay that receives an
       encapsulated multicast packet MUST discard the multicast packet
       if the IP source address in the outer header does not match the
       source address that would be extracted using the rules of
       Section 7.2.

   2.  A gateway MUST discard encapsulated multicast packets if the
       source address in the outer header is not the address to which
       the encapsulated join message was sent.  An AMT Gateway that
       receives an encapsulated IGMPv3/MLDv2 (S,G)-Join MUST discard the
       message if the IP destination address in the outer header does
       not match the source address that would be extracted using the
       rules of Section 7.2.











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11.  Contributors

   The following people provided significant contributions to earlier
   versions of this draft.

     Dirk Ooms
     OneSparrow
     Belegstraat 13; 2018 Antwerp; Belgium
     EMail: dirk@onesparrow.com










































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12.  Acknowledgments

   Most of the mechanisms described in this document are based on
   similar work done by the NGTrans WG for obtaining automatic IPv6
   connectivity without explicit tunnels ("6to4").  Tony Ballardie
   provided helpful discussion that inspired this document.

   In addition, extensive comments were received from Pekka Savola, Greg
   Shepherd, Dino Farinacci, Toerless Eckert, Marshall Eubanks, John
   Zwiebel, and Lenny Giuliano.

   Juniper Networks was instrumental in funding several versions of this
   draft as well as an open source implementation.






































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13.  References

13.1.  Normative References

   [RFC0792]  Postel, J., "Internet Control Message Protocol", STD 5,
              RFC 792, September 1981.

   [RFC3376]  Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
              Thyagarajan, "Internet Group Management Protocol, Version
              3", RFC 3376, October 2002.

   [RFC3810]  Vida, R. and L. Costa, "Multicast Listener Discovery
              Version 2 (MLDv2) for IPv6", RFC 3810, June 2004.

   [RFC4605]  Fenner, B., He, H., Haberman, B., and H. Sandick,
              "Internet Group Management Protocol (IGMP) / Multicast
              Listener Discovery (MLD)-Based Multicast Forwarding
              ("IGMP/MLD Proxying")", RFC 4605, August 2006.

   [RFC4607]  Holbrook, H. and B. Cain, "Source-Specific Multicast for
              IP", RFC 4607, August 2006.

13.2.  Informative References

   [RFC1112]  Deering, S., "Host extensions for IP multicasting", STD 5,
              RFC 1112, August 1989.

   [RFC1546]  Partridge, C., Mendez, T., and W. Milliken, "Host
              Anycasting Service", RFC 1546, November 1993.

   [RFC2104]  Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
              Hashing for Message Authentication", RFC 2104,
              February 1997.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3053]  Durand, A., Fasano, P., Guardini, I., and D. Lento, "IPv6
              Tunnel Broker", RFC 3053, January 2001.

   [RFC3056]  Carpenter, B. and K. Moore, "Connection of IPv6 Domains
              via IPv4 Clouds", RFC 3056, February 2001.

   [RFC3068]  Huitema, C., "An Anycast Prefix for 6to4 Relay Routers",
              RFC 3068, June 2001.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, February 2006.



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   [RFC4601]  Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
              "Protocol Independent Multicast - Sparse Mode (PIM-SM):
              Protocol Specification (Revised)", RFC 4601, August 2006.
















































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Authors' Addresses

   Dave Thaler
   Microsoft Corporation
   One Microsoft Way
   Redmond, WA  98052-6399
   USA

   Phone: +1 425 703 8835
   Email: dthaler@microsoft.com


   Mohit Talwar
   Microsoft Corporation
   One Microsoft Way
   Redmond, WA  98052-6399
   USA

   Phone: +1 425 705 3131
   Email: mohitt@microsoft.com


   Amit Aggarwal
   Microsoft Corporation
   One Microsoft Way
   Redmond, WA  98052-6399
   USA

   Phone: +1 425 706 0593
   Email: amitag@microsoft.com


   Lorenzo Vicisano
   Cisco Systems
   170 West Tasman Dr.
   San Jose, CA  95134
   USA

   Phone: +1 408 525 2530
   Email: lorenzo@cisco.com











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   Tom Pusateri
   !j
   222 E. Jones Ave.
   Wake Forest, NC  27587
   USA

   Email: pusateri@bangj.com












































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Full Copyright Statement

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