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Network Working Group                                          D. Thaler
Internet-Draft                                                 M. Talwar
Intended status: Standards Track                             A. Aggarwal
Expires: January 12, 2012                          Microsoft Corporation
                                                             L. Vicisano
                                                           Qualcomm Inc.
                                                             T. Pusateri
                                                                      !j
                                                                T. Morin
                                                 France Telecom - Orange
                                                           July 11, 2011


                    Automatic IP Multicast Tunneling
                  draft-ietf-mboned-auto-multicast-11

Abstract

   Automatic IP Multicast Tunneling (AMT) allows multicast reception by
   isolated multicast-enabled sites or hosts, attached to a network
   which has no native multicast support.  It enables them to receive
   multicast traffic from the native multicast infrastructure without
   requiring 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.

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 http://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 January 12, 2012.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.



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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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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.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.






























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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  . . . . . . . . . . . . . . . . . . . . . . . .  8
     4.5.  AMT Relay Anycast Prefix . . . . . . . . . . . . . . . . .  9
     4.6.  AMT Relay Anycast Address  . . . . . . . . . . . . . . . .  9
   5.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     5.1.  Scalability Considerations . . . . . . . . . . . . . . . . 11
     5.2.  Spoofing Considerations  . . . . . . . . . . . . . . . . . 11
     5.3.  Protocol Sequence  . . . . . . . . . . . . . . . . . . . . 12
   6.  Message Formats  . . . . . . . . . . . . . . . . . . . . . . . 15
     6.1.  Use of UDP . . . . . . . . . . . . . . . . . . . . . . . . 15
     6.2.  AMT Relay Discovery  . . . . . . . . . . . . . . . . . . . 15
       6.2.1.  Type . . . . . . . . . . . . . . . . . . . . . . . . . 15
       6.2.2.  Reserved . . . . . . . . . . . . . . . . . . . . . . . 15
       6.2.3.  Discovery Nonce  . . . . . . . . . . . . . . . . . . . 15
     6.3.  AMT Relay Advertisement  . . . . . . . . . . . . . . . . . 16
       6.3.1.  Type . . . . . . . . . . . . . . . . . . . . . . . . . 16
       6.3.2.  Reserved . . . . . . . . . . . . . . . . . . . . . . . 16
       6.3.3.  Discovery Nonce  . . . . . . . . . . . . . . . . . . . 16
       6.3.4.  Relay Address  . . . . . . . . . . . . . . . . . . . . 16
     6.4.  AMT Request  . . . . . . . . . . . . . . . . . . . . . . . 16
       6.4.1.  Type . . . . . . . . . . . . . . . . . . . . . . . . . 17
       6.4.2.  Reserved . . . . . . . . . . . . . . . . . . . . . . . 17
       6.4.3.  Request Nonce  . . . . . . . . . . . . . . . . . . . . 17
     6.5.  AMT Membership Query . . . . . . . . . . . . . . . . . . . 17
       6.5.1.  Type . . . . . . . . . . . . . . . . . . . . . . . . . 18
       6.5.2.  Flags  . . . . . . . . . . . . . . . . . . . . . . . . 18
       6.5.3.  Response MAC . . . . . . . . . . . . . . . . . . . . . 19
       6.5.4.  Request Nonce  . . . . . . . . . . . . . . . . . . . . 19
       6.5.5.  IGMP/MLD Query (including IP Header) . . . . . . . . . 19
       6.5.6.  Gateway information fields . . . . . . . . . . . . . . 19
     6.6.  AMT Membership Update  . . . . . . . . . . . . . . . . . . 19
       6.6.1.  Type . . . . . . . . . . . . . . . . . . . . . . . . . 20
       6.6.2.  Reserved . . . . . . . . . . . . . . . . . . . . . . . 20
       6.6.3.  Response MAC . . . . . . . . . . . . . . . . . . . . . 20
       6.6.4.  Request Nonce  . . . . . . . . . . . . . . . . . . . . 21
       6.6.5.  IGMP/MLD Message (including IP Header) . . . . . . . . 21
     6.7.  AMT IP Multicast Data  . . . . . . . . . . . . . . . . . . 21
       6.7.1.  Type . . . . . . . . . . . . . . . . . . . . . . . . . 22
       6.7.2.  Reserved . . . . . . . . . . . . . . . . . . . . . . . 22
       6.7.3.  IP Multicast Data  . . . . . . . . . . . . . . . . . . 22



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     6.8.  AMT Teardown . . . . . . . . . . . . . . . . . . . . . . . 22
       6.8.1.  Type . . . . . . . . . . . . . . . . . . . . . . . . . 23
       6.8.2.  Reserved . . . . . . . . . . . . . . . . . . . . . . . 23
       6.8.3.  Original Response MAC  . . . . . . . . . . . . . . . . 23
       6.8.4.  Original Request Nonce . . . . . . . . . . . . . . . . 23
       6.8.5.  Original Source Port . . . . . . . . . . . . . . . . . 23
       6.8.6.  Original Source Address  . . . . . . . . . . . . . . . 23
   7.  AMT Gateway Details  . . . . . . . . . . . . . . . . . . . . . 25
     7.1.  At Startup Time  . . . . . . . . . . . . . . . . . . . . . 25
     7.2.  Gateway identification . . . . . . . . . . . . . . . . . . 25
     7.3.  Joining Multicast Groups . . . . . . . . . . . . . . . . . 26
     7.4.  Responding to Relay Changes  . . . . . . . . . . . . . . . 26
   8.  AMT Relay Details  . . . . . . . . . . . . . . . . . . . . . . 27
     8.1.  At Startup time  . . . . . . . . . . . . . . . . . . . . . 27
     8.2.  Receiving Relay Discovery messages sent to the Anycast
           Address  . . . . . . . . . . . . . . . . . . . . . . . . . 27
     8.3.  Receiving Membership Updates from AMT Gateways . . . . . . 27
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 29
     9.1.  IPv4 and IPv6 Anycast Prefix Allocation  . . . . . . . . . 29
       9.1.1.  IPv4 . . . . . . . . . . . . . . . . . . . . . . . . . 29
       9.1.2.  IPv6 . . . . . . . . . . . . . . . . . . . . . . . . . 29
     9.2.  UDP Port number  . . . . . . . . . . . . . . . . . . . . . 29
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 30
   11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 31
   12. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 32
   13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 33
     13.1. Normative References . . . . . . . . . . . . . . . . . . . 33
     13.2. Informative References . . . . . . . . . . . . . . . . . . 33
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 35






















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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 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.

   A previous of this solution was previously "Automatic IP Multicast
   without explicit Tunnels", to highlight the fact that the tunneling
   used is lightweight and does not require statically configured
   tunnels used as point to point interfaces.




















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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.  However, this is no worse
   than regular unicast distribution of streams and in most cases much
   better.

   This document specifies procedures allowing isolated sites to receive
   both general Any Source Multicast (ASM, [RFC1112]), and Specific
   Source Multicast (SSM, [RFC4607]).

   Earlier versions of this document were describing how to use AMT to
   allow isolated non-NAT sites/hosts to transmit SSM multicast ; the
   specifications for these functionalities have been left off the
   current document for the following reasons: the drawback that these
   specifications required a source site Gateway to replicate traffic to
   many Relays in the multicast-enabled part of the network, lack of
   contributors to document alternative proposals based on AMT,
   existence of ways to offer similar functionality using Tunnel Broker
   approaches [RFC3053], or at the application layer.

   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 Gateway|         Anycast  |AMT Relay|          |
    |        |     +-----+-+       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

   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).  Instead, we assume that special-purpose routers will be



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   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).
































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5.  Overview

                               Internet
    +---------------+                            +---------------+
    | AMT Site      |     2. 3-way Membership    | Native MCast  |
    |               |          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
   candidates are the IGMP/MLD protocol [RFC3376], [RFC3810], and the
   PIM-Sparse Mode protocol [RFC4601].  Since an AMT gateway may be a



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   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.  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.

   This approach allows the gateways to be spread out among more relays
   so as to keep the number of gateways per relay at a reasonable level.

5.2.  Spoofing Considerations

   An attacker could affect the group state in the relay by spoofing the
   source address in AMT Update messages containing join or leave
   reports.  This can be used to launch reflection or denial of service
   attacks on the target Relay.  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 wants to send a membership report, it first sends an
   AMT Request with a request nonce in it.  The Relay can calculate a
   message authentication code (MAC) 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 Relay.  The algorithm does not have to
   be standardized since the Relay generates and verifies the MAC and
   the Gateway simply echoes it back, but an algorithm such as



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   HMAC-MD5-48 [RFC2104] SHOULD be used at a minimum.

   An AMT Membership Query is sent back to the gateway having originated
   the Request, including the request nonce and the MAC.  The gateway
   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 relay, finalizing the 3-way handshake.

   Upon reception, the relay 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.

   A relay MUST NOT create state for a gateway before successful
   validation of a MAC of an AMT Update from this gateway; a relay
   SHOULD delete all states for a gateway after a small timer after it
   stops having any AMT forwarding state for a Gateway (i.e. the Gateway
   left all multicast groups it had joined).

   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 relay 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.

   The condition might occur where the gateway that initially sent the
   AMT Request dynamically changes its IP address.  This might occur due
   to a change in wireless networks, a DHCP assignment, or another
   network failure.  When this occurs, it is no longer possible to
   verify the MAC using the source address and source port.  Though, in
   order to reduce state, it is desirable to tear down the state that
   was created with the old source address.  A Teardown message with
   special considerations for calculating the MAC is described below to
   perform this function.

5.3.  Protocol Sequence

   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.

   Protocol sequence for a multicast SSM channel (S1,G1):

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





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   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).

   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



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      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.

   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.




















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6.  Message Formats

6.1.  Use of UDP

   All AMT messages are UDP packets.

   Messages sent to the Relay are sent to the IANA reserved AMT port
   number (Section 9), from a source port uniquely selected by the host
   operating system of the Gateway.  Messages sent by the Relay are sent
   from the IANA reserved AMT port number.

   The UDP checksum MUST be valid in all AMT control messages (Relay
   Discovery, Relay Advertisement, Membership Request, Membership Query,
   Membership Update).  Section 6.7 specifies the behavior with
   reference to the UDP checksums of AMT IP Multicast Data messages.

6.2.  AMT Relay Discovery

   The AMT Relay Discovery message is sent from the AMT gateway unicast
   address to the AMT Relay Anycast address to discover the unicast
   address of an AMT relay.

   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

6.2.1.  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.





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6.3.  AMT Relay Advertisement

   The AMT Relay Advertisement message 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 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

6.3.1.  Type

   The type of the message.

6.3.2.  Reserved

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

6.3.3.  Discovery Nonce

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

6.3.4.  Relay Address

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

6.4.  AMT Request

   A Request packet is sent by a Gateway to a Relay to begin a 3-way
   handshake for sending an IGMP/MLD Membership/Listener Report or
   Leave/Done.

   It is sent from the Gateway address to the Relay's unique unicast



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   address.

   The UDP source port is uniquely selected by the local host operating
   system.  It can be different from the source port used in Discovery
   messages but does not have to be.  The UDP source port must be
   consistent across Request and Update messages (see also Section 7.2).

   The UDP destination port is the IANA reserved AMT port number.

    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 Request

6.4.1.  Type

   The type of the message.

6.4.2.  Reserved

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

6.4.3.  Request Nonce

   A 32-bit identifier used to distinguish this request.

6.5.  AMT Membership Query

   An AMT Membership Query packet is sent from the Relay back to the
   Gateway 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 of the Request, i.e. the Relay Address advertised
   in the Relay Advertisement message.

   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.






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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  |    Flags      |         Response MAC          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Response MAC (continued)                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Request Nonce                                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            IGMP Membership Query or MLD Listener Query        |
   |            (including IP Header)                              |
   |            ...                                                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Gateway Port Number       |       Gateway Address ...     | ?
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ?
   |                    ... Gateway Address (ctd) ...              | ?
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ?
   |                    ... Gateway Address (ctd) ...              | ?
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ?
   |                    ... Gateway Address (ctd) ...              | ?
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ?
   |   ... Gateway Address (ctd)   |                                 ?
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                           AMT Membership Query

6.5.1.  Type

   The type of the message.

6.5.2.  Flags

   An 8-bit flags field having the following format:
                    0 1 2 3 4 5 6 7
                   +-+-+-+-+-+-+-+-+
                   |   Reserved  |G|
                   +-+-+-+-+-+-+-+-+

   The "G" flag is set to 1 if Gateway information fields are present in
   the Query message (see below Section 6.5.6), and to zero if they are
   not.

   Other flags are currently unused and reserved: they are sent as zero
   and their value is ignored on receipt.







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6.5.3.  Response MAC

   A 48-bit hash generated by the Relay and sent to the Gateway for
   inclusion in the AMT Membership Update (see Section 5.2).

6.5.4.  Request Nonce

   A 32-bit identifier echoed back to the originator to used to identify
   the corresponding request (see Section 5.2).

6.5.5.  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 IP header should be sufficient to reach the
   tunnel endpoint and not mimic the inner IP header TTL which is
   typically 1 for IGMP/MLD messages.

6.5.6.  Gateway information fields

   The "Gateway Port Number" and "Gateway Address" fields are present in
   the Query message if, and only if, the "G" flag is set in the Flags
   field.

6.5.6.1.  Gateway Port Number

   A 16-bit field containing a UDP port value.

   The Relay sets this field to the value of the UDP source port of the
   Request message that triggered the Query message.

6.5.6.2.  Gateway Address

   A 16-byte field containing the IP source address of the Request
   message that triggered this Query message.  The field contains an
   IPv4-compatible IPv6 address ([RFC4291], section 2.5.5.1) if the
   address is an IPv4 address (i.e. the IPv4 address prefixed with 96
   bits set to zero), or an IPv6 address.

6.6.  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



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   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 UDP destination port is the IANA reserved AMT port number and the
   UDP source port is the source port used for the Request message.

   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

6.6.1.  Type

   The type of the message.

6.6.2.  Reserved

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

6.6.3.  Response MAC

   The 48-bit MAC received in the Membership Query and echoed back in
   the Membership Update (see Section 5.2).



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6.6.4.  Request Nonce

   A 32-bit identifier matching the nonce in the AMT Request (see
   Section 5.2).

6.6.5.  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 function of
   the version of the query received in the AMT Membership Query.  The
   IGMP/MLD Message includes a full IP Header.

6.7.  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 Relay's unique unicast address (destination
   address of the Membership update) to the Gateway's unicast address
   (source address of the Membership Update).

   The UDP source port is the IANA reserved AMT port number and the
   destination port should be the same as the source port of the
   Membership Update that resulted in the creation of forwarding state
   for the encapsulated IP packet.

   The UDP checksum SHOULD be zero for AMT IP Multicast Data messages
   carried over IPv4, and MAY be zero for AMT IP Multicast Data messages
   carried over IPv6 [I-D.ietf-6man-udpchecksums].

   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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6.7.1.  Type

   The type of the message.

6.7.2.  Reserved

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

6.7.3.  IP Multicast Data

   The original IP Multicast data packet that is being replicated by the
   Relay to the Gateway, including the original IP header.

6.8.  AMT Teardown

   An AMT Teardown is sent by a Gateway after a valid Response MAC has
   been received and after the source address that was used to generate
   the Response MAC is no longer available for sending packets.

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

   The UDP destination port number should be the same one sent in the
   original Request.

   An AMT Teardown from the original source address and source port is
   NOT valid and should be discarded if received.  Use an AMT Membership
   Update instead.

   In order for the Relay to verify the Teardown message, this message
   must contain the original source address and source port in addition
   to the Original Request Nonce and Original Response MAC.  In
   situations where NAT is used, this information can be known by the
   Gateway thanks to the optional Gateway information fields in the
   Query message (Section 6.5.6).  Hence, a Relay supporting the
   Teardown mechanism SHOULD include the Gateway information fields in
   the Query messages it sends.

   On reception of a valid Teardown message, a Relay should remove all
   state corresponding to the gateway identified by the (original source
   address, original source port) tuple, and stop forwarding all traffic
   to this destination.









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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=0x7  |    Reserved   |    Original Response MAC      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Original Response MAC (continued)                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Original Request Nonce                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Original Source Port      |  Original Source Address ...  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Original Source Address (ctd) ...            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             ...  Original Source Address (ctd) ...            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             ...  Original Source Address (ctd) ...            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | ... Original Src Addr. (ctd)  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                          AMT Membership Teardown

6.8.1.  Type

   The type of the message.

6.8.2.  Reserved

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

6.8.3.  Original Response MAC

   The 48-bit MAC received in the Membership Query.

6.8.4.  Original Request Nonce

   A 32-bit identifier corresponding to the original Request.

6.8.5.  Original Source Port

   The 16-bit port number used in the original AMT Request message that
   was used to generate the Original Response MAC.

6.8.6.  Original Source Address

   A 16-byte field containing the IP source address used in the original
   AMT Request message that was used to generate the Original Response
   MAC of the Request message that triggered this Query message.  The



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   field contains an IPv4-compatible IPv6 address ([RFC4291], section
   2.5.5.1) if the address is an IPv4 address (i.e. the IPv4 address
   prefixed with 96 bits set to zero), or an IPv6 address.
















































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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 identification

   From the point of view of a Relay, a Gateway is identified by the (IP
   source address, UDP source port) tuple in Membership Update messages.
   If an implementation of Gateway procedure was to use a different UDP
   source port and/or IP source address to join or leave different
   multicast groups, it would appear to the Relay as distinct Gateways.

   For instance, a Relay having forwarding state resulting in the
   forwarding of (S,G) to a said gateway identified by a (IP source
   address, UDP source port) tuple, will not remove this state if it
   receives an AMT Membership Update message from a different (IP source
   address, UDP source port) tuple.

   It results that a Gateway has to use the same UDP source port for AMT
   Request and AMT Update messages related to a same (S,G).  A said
   Gateway instance is typically expected to use the same UDP source
   port and IP source address for all Request and Updates messages for
   all multicast groups.




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7.3.  Joining Multicast Groups

   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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8.  AMT Relay 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).

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.  As noted in Section 7.2,
   the Relay tracks Gateways based on the (IP source address, UDP source
   port) tuple.  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, once to each (address,
   port) of 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.


































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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.  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.

   Gateways 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: a gateway MUST
   discard encapsulated multicast packets if the source address in the
   outer header is not the address of the Relay to which the
   encapsulated join message was sent.  AMT Gateways MUST also drop non-
   multicast traffic incoming on an AMT pseudo-interface.

   AMT Relays MUST NOT process AMT Data messages.

   AMT Relays and Gateways MUST drop IP messages encapsulated in AMT
   Query and Update messages that are not IGMP/MLD messages.

   Even though a Relay does not need to maintain any state before
   completion of the three-way handshake (Section 5.2), if no mitigation
   is in place, it is still possible for one host to instantiate a large
   amount of Gateways instances that would each join one or more
   multicast groups to a Relay, thus resulting in a large amount of
   resources being used on the Relay.  Thus, AMT Relays MUST be
   implemented so as to allow the mitigation of risks of denial of
   service attacks on their resources.  A Relay SHOULD NOT allow the
   instantiation of an unbounded number of AMT pseudo-interfaces for a
   said gateway IP address.  For instance, an implementation may provide
   a way to set a configurable limit on the maximum number of pseudo-
   interfaces to a same gateway IP address, with a default value for
   this limit being low enough to provide protection, and high enough to
   cope with the possibility of an address being shared by multiple
   devices.

   In the case where a Relay is reaching the situation where it would
   stop accepting to instantiate new pseudo-interfaces, it MAY stop
   advertising the AMT Relay Anycast address; thanks to the AMT
   discovery procedures, this will allow legitimate AMT Gateways to fall
   back on another Relay.







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11.  Contributors

   The following people provided significant contributions to earlier
   versions of these specifications:

     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, Lenny Giuliano and Greg Bumgardner.

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

   Greg Shepherd suggested the inclusion of the AMT Membership Teardown
   message based on field experience.

   Contributors from AT&T provided useful inputs and ideas that were
   integrated into these specifications: Mark Altom, Andy Huang, Tom
   Imburgia, Patricia McCrink, Han Nguyen, Doug Nortz and Robert Sayko.































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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.

   [I-D.ietf-6man-udpchecksums]
              Eubanks, M., "UDP Checksums for Tunneled Packets",
              draft-ietf-6man-udpchecksums-00 (work in progress),
              March 2011.

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




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   [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.

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

   [RFC4760]  Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
              "Multiprotocol Extensions for BGP-4", RFC 4760,
              January 2007.






































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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
   Qualcomm Inc.
   3165 Kifer Road
   Santa Clara, CA  95051
   USA

   Email: vicisano@qualcomm.com












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   Tom Pusateri
   !j
   2109 Mountain High Rd.
   Wake Forest, NC  27587
   USA

   Email: pusateri@bangj.com


   Thomas Morin
   France Telecom - Orange
   2, avenue Pierre Marzin
   Lannion  22300
   France

   Phone: +33 2 96 05 3734
   Email: thomas.morin@orange-ftgroup.com


































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