auth48-rfc8313-reply.xml

<?xml version='1.0' encoding='US-ASCII'?>

<!DOCTYPE rfc SYSTEM "rfc2629.dtd">

<rfc submissionType="IETF" number="8313" category="bcp" seriesNo="213"
     consensus="yes" ipr="trust200902">

<?rfc toc="yes"?>
<?rfc compact="yes"?>
<?rfc subcompact="no"?>
<?rfc sortrefs="no"?>
<?rfc symrefs="yes"?>
<?rfc strict="yes"?>

        <front>
        <title abbrev="Multicast for Inter-domain Peering Points">Use of Multicast across Inter-domain Peering Points</title>

        <author role="editor" fullname="Percy S. Tarapore" initials="P.S." surname="Tarapore">
        <organization>AT&amp;T</organization>
        <address><phone>1-732-420-4172</phone><email>tarapore@att.com</email>
        </address>
        </author>

        <author fullname="Robert Sayko" initials="R." surname="Sayko">
        <organization>AT&amp;T</organization>
        <address><phone>1-732-420-3292</phone><email>rs1983@att.com</email>
        </address>
        </author>

        <author fullname="Greg Shepherd" initials="G." surname="Shepherd">
        <organization>Cisco</organization>
        <address><email>shep@cisco.com</email>
        </address>
        </author>

        <author role="editor" fullname="Toerless Eckert" initials="T."
           surname="Eckert">
        <organization abbrev="Huawei">Huawei USA - Futurewei Technologies Inc.</organization>
        <address><email>tte+ietf@cs.fau.de</email>
        </address>
        </author>

        <author fullname="Ram Krishnan" initials="R." surname="Krishnan">
        <organization>SupportVectors</organization>
        <address><email>ramkri123@gmail.com</email>
        </address>
        </author>

      <date month="December" year="2017"/>

      <keyword>multicast security</keyword>
      <keyword>multicast troubleshooting</keyword>
      <keyword>multicast routing</keyword>
      <keyword>multicast tunneling</keyword>
      <keyword>PIM</keyword>
      <keyword>PIM-SSM</keyword>
      <keyword>SSM</keyword>
      <keyword>Source Specific Multicast</keyword>
      <keyword>AMT</keyword>
      <keyword>GRE</keyword>
      <keyword>Automatic Multicast Tunneling</keyword>
      <keyword>BGP</keyword>
      <keyword>MBGP</keyword>
      <keyword>M-BGP</keyword>
      <keyword>MP-BGP</keyword>
      <keyword>exchange</keyword>
      <keyword>exchange point</keyword>
      <keyword>NNI</keyword>
      <keyword>content distribution</keyword>
      <keyword>video streaming</keyword>
      <keyword>anycast</keyword>

      <abstract><t>
   This document examines the use of Source-Specific Multicast (SSM)
   across inter-domain peering points for a specified set of deployment
   scenarios. The objectives are to (1) describe the setup process for
   multicast-based delivery across administrative domains for these
   scenarios and (2) document supporting functionality to enable this
   process.</t>

      </abstract>
      </front>

      <middle>
      <section title="Introduction" anchor="section-1"><t>

   Content and data from several types of applications (e.g., live
   video streaming, software downloads) are well suited for delivery
   via multicast means. The use of multicast for delivering such
   content or other data offers significant savings in terms of utilization of
   resources in any given administrative domain. End User (EU) demand for such
   content or other data is growing. Often, this requires transporting the
   content or other data across administrative domains via inter&nbhy;domain
   peering points.</t>

<t>The objectives of this document are twofold:

<list style="symbols">

<t>Describe the technical process and establish guidelines for
   setting up multicast-based delivery of application content or other data
   across inter&nbhy;domain peering points via a set of use&nbsp;cases
   (where "Use Case&nbsp;3.1" corresponds to <xref target="section-3.1"/>,
   "Use&nbsp;Case&nbsp;3.2" corresponds to <xref target="section-3.2"/>,
   etc.).</t>

<t>Catalog all required exchanges of information between the
   administrative domains to support multicast-based delivery.
   This enables operators to initiate necessary processes to
   support inter&nbhy;domain peering with multicast.</t>

</list></t>

<t>The scope and assumptions for this document are as follows:
<list style="symbols">

<t>Administrative Domain 1 (AD-1) sources content to one or more EUs in one or
more Administrative Domain 2 (AD&nbhy;2) entities. AD&nbhy;1 and AD&nbhy;2
want to use IP multicast to allow support for large and growing EU populations,
with a minimum amount of duplicated traffic to send across network links.

<list style="symbols">

    <t>This document does not detail the case where EUs are originating
    content. To support that additional service, it is recommended that
    some method (outside the scope of this document) be used by which the
    content from EUs is transmitted to the application in AD&nbhy;1 and
    AD&nbhy;1 can send out the traffic as IP multicast. From that point on,
    the descriptions in this document apply, except that they are not complete
    because they do not cover the transport or operational aspects of the leg
    from the EU to AD&nbhy;1.</t>

   <t>This document does not detail the case where AD-1 and AD&nbhy;2 are
   not directly connected to each other and are instead connected via
   one or more other ADs (as opposed to a peering point) that serve as
   transit providers. The cases described in this document where
   tunnels are used between AD&nbhy;1 and AD&nbhy;2 can be applied to such
   scenarios, but SLA ("Service Level Agreement") control, for example, would
   be different. Additional issues will likely exist as well in such
   scenarios. This topic is left for further study.</t>

</list></t>

      <t>For the purposes of this document, the term "peering point"
      refers to a network connection ("link") between two administrative
      network domains over which traffic is exchanged between them. This is
      also referred to as a Network-to-Network Interface (NNI). Unless
      otherwise noted, it is assumed that the peering point is a
      private peering point, where the network connection is a physically or
      virtually isolated network connection solely between AD&nbhy;1 and
      AD&nbhy;2. The other case is that of a broadcast peering point,
      which is a common option in public Internet Exchange Points (IXPs).
      See <xref target="section-4.2.4"/> for more details.</t>

      <t>AD-1 is enabled with native multicast. A peering point exists between
      AD&nbhy;1 and AD&nbhy;2.</t>

      <t>It is understood that several protocols are available for this
      purpose, including Protocol-Independent Multicast - Sparse Mode
      (PIM&nbhy;SM) and Protocol-Independent Multicast -
      Source&nbhy;Specific Multicast (PIM-SSM) <xref target="RFC7761"/>,
      the Internet Group Management Protocol (IGMP) <xref target="RFC3376"/>,
      and Multicast Listener Discovery (MLD) <xref target="RFC3810"/>.</t>

      <t>As described in <xref target="section-2"/>, the source IP address of
      the (so&nbhy;called "(S,G)") multicast stream in the originating AD
      (AD&nbhy;1) is known. Under this condition, using PIM-SSM is beneficial,
      as it allows the receiver's upstream router to send a join message
      directly to the source without the need to invoke an intermediate
      Rendezvous Point (RP). The use of SSM also presents an improved threat
      mitigation profile against attack, as described in <xref
      target="RFC4609"/>. Hence, in the case of inter&nbhy;domain peering, it
      is recommended that only SSM protocols be used; the setup of
      inter&nbhy;domain peering for ASM (Any&nbhy;Source Multicast) is
      out of scope for this document.</t>

      <t>The rest of this document assumes that PIM-SSM and BGP are used
      across the peering point, plus Automatic Multicast Tunneling (AMT) <xref
      target="RFC7450"/> and/or Generic Routing Encapsulation (GRE),
      according to the scenario in question. The use of other protocols is
      beyond the scope of this document.</t>

      <t>AMT is set up at the peering point if either the peering point or
      AD&nbhy;2 is not multicast enabled. It is assumed that an AMT relay will
      be available to a client for multicast delivery. The selection of an
      optimal AMT relay by a client is out of scope for this document. Note
      that using AMT is necessary only when native multicast is unavailable
      in the peering point (Use Case&nbsp;3.3) or in the downstream
      administrative domain (Use Cases&nbsp;3.4 and 3.5).</t>

      <t>It is assumed that the collection of billing data is done at the
       application level and is not considered to be a networking
       issue. The settlements process for EU billing and/or
       inter&nbhy;provider billing is out of scope for this document.</t>

      <t>Inter-domain network connectivity troubleshooting is only
       considered within the context of a cooperative process between
       the two domains.</t>

</list>
</t>


<t>
   This document also attempts to identify ways by which the peering
   process can be improved. Development of new methods for improvement
   is beyond the scope of this document.</t>

      </section>

      <section title="Overview of Inter-domain Multicast Application Transport" anchor="section-2">

      <t>A multicast-based application delivery scenario is as follows:

      <list style="symbols">
      <t>Two independent administrative domains are interconnected via a
      peering point.</t>

      <t>The peering point is either multicast enabled (end-to-end native
      multicast across the two domains) or connected by one of two possible
      tunnel types:

      <list style="symbols">
          <t>A GRE tunnel <xref target="RFC2784"/> allowing multicast
          tunneling across the peering point, or</t>
  
          <t>AMT <xref target="RFC7450"/>.</t>
      </list>
      </t>

      <t>A service provider controls one or more application sources in
      AD&nbhy;1 that will send multicast IP packets via one or more
      (S,G)s (multicast traffic flows; see <xref target="section-4.2.1"/> if
      you are unfamiliar with IP multicast). It is assumed that the service
      being provided is suitable for delivery via multicast (e.g., live video
      streaming of popular events, software downloads to many devices) and
      that the packet streams will be carried by a suitable multicast
      transport protocol.</t>

      <t>An EU controls a device connected to AD-2, which runs an application
      client compatible with the service provider's application source.</t>

      <t>The application client joins appropriate (S,G)s in order to
      receive the data necessary to provide the service to the EU.
      The mechanisms by which the application client learns the
      appropriate (S,G)s are an implementation detail of the
      application and are out of scope for this document.</t>

      </list>
      </t>

      <t>
   The assumption here is that AD-1 has ultimate responsibility for
   delivering the multicast-based service on behalf of the content
   source(s). All relevant interactions between the two domains
   described in this document are based on this assumption.</t>

   <t>
   Note that AD-2 may be an independent network domain (e.g., a Tier&nbsp;1
   network operator domain). Alternately, AD&nbhy;2 could also be an
   enterprise network domain operated by a single customer of AD&nbhy;1. The
   peering point architecture and requirements may have some unique aspects
   associated with enterprise networks; see <xref target="section-3"/>.</t>

   <t>
   The use cases describing various architectural configurations for
   multicast distribution, along with associated requirements, are
   described in <xref target="section-3"/>. <xref target="section-4"/>
   contains a comprehensive list of pertinent information that needs to
   be exchanged between the two domains in order to support functions
   to enable application transport.</t>

   </section>

      <section title="Inter-domain Peering Point Requirements for Multicast" anchor="section-3">
<t>
   The transport of applications using multicast requires that the
   inter&nbhy;domain peering point be enabled to support such a process.
   This section presents five use cases for consideration.</t>

<section title="Native Multicast" anchor="section-3.1">

      <t>
   This use case involves end-to-end native multicast between the two
   administrative domains, and the peering point is also native multicast
   enabled. See <xref target="native-pic"/>.</t>

<figure anchor="native-pic" title="Content Distribution via End-to-End Native Multicast">
<artwork><![CDATA[
   -------------------               -------------------
  /       AD-1        \             /        AD-2       \
 / (Multicast Enabled) \           / (Multicast Enabled) \
/                       \         /                       \
| +----+                |         |                       |
| |    |       +------+ |         |  +------+             |   +----+
| | AS |------>|  BR  |-|---------|->|  BR  |-------------|-->| EU |
| |    |       +------+ |   I1    |  +------+             |I2 +----+
\ +----+                /         \                       /
 \                     /           \                     /
  \                   /             \                   /
   -------------------               -------------------

AD = Administrative Domain (independent autonomous system)
AS = multicast (e.g., content) Application Source
BR = Border Router
I1 = AD-1 and AD-2 multicast interconnection (e.g., MP-BGP)
I2 = AD-2 and EU multicast connection
]]></artwork>
</figure>

      <t>Advantages of this configuration:
      <list style="symbols">
      <t>Most efficient use of bandwidth in both domains.</t>

      <t>Fewer devices in the path traversed by the multicast stream when
      compared to an AMT-enabled peering point.</t>

      </list>
      </t>

      <t>
   From the perspective of AD-1, the one disadvantage associated with
   native multicast to AD&nbhy;2 instead of individual unicast to every EU
   in AD&nbhy;2 is that it does not have the ability to count the number of
   EUs as well as the transmitted bytes delivered to them. This
   information is relevant from the perspective of customer billing and
   operational logs. It is assumed that such data will be collected by
   the application layer. The application-layer mechanisms for
   generating this information need to be robust enough so that all
   pertinent requirements for the source provider and the AD operator
   are satisfactorily met. The specifics of these methods are beyond
   the scope of this document.</t>

      <t>Architectural guidelines for this configuration are as follows:

      <list style="letters">
      <t>Dual homing for peering points between domains is recommended as a
      way to ensure reliability with full BGP table visibility.</t>
      <t>If the peering point between AD-1 and AD-2 is a controlled
      network environment, then bandwidth can be allocated accordingly by the
      two domains to permit the transit of non&nbhy;rate-adaptive multicast
      traffic. If this is not the case, then the multicast traffic must
      support congestion control via any of the mechanisms described in
      Section&nbsp;4.1 of <xref target="BCP145"/>.</t>
      <t>The sending and receiving of multicast traffic between two
      domains is typically determined by local policies associated
      with each domain. For example, if AD&nbhy;1 is a service provider
      and AD&nbhy;2 is an enterprise, then AD&nbhy;1 may support local policies
      for traffic delivery to, but not traffic reception from, AD&nbhy;2.
      Another example is the use of a policy by which AD&nbhy;1 delivers
      specified content to AD&nbhy;2 only if such delivery has been
      accepted by contract.</t>
      <t>It is assumed that relevant information on multicast streams
      delivered to EUs in AD&nbhy;2 is collected by available
      capabilities in the application layer. The precise nature and
      formats of the collected information will be determined by
      directives from the source owner and the domain operators.</t>
      </list>
      </t>

</section>

<section title="Peering Point Enabled with GRE Tunnel" anchor="section-3.2">

<t>
   The peering point is not native multicast enabled in this use case.
   There is a GRE tunnel provisioned over the peering point. See
   <xref target="gre-pic"/>.</t>

<figure anchor="gre-pic" title="Content Distribution via GRE Tunnel">
<artwork><![CDATA[
    -------------------              -------------------
   /       AD-1        \            /        AD-2       \
  / (Multicast Enabled) \          / (Multicast Enabled) \
 /                       \        /                       \
 | +----+          +---+ |  (I1)  | +---+                 |
 | |    |   +--+   |uBR|-|--------|-|uBR|   +--+          |   +----+
 | | AS |-->|BR|   +---+-|        | +---+   |BR| -------->|-->| EU |
 | |    |   +--+<........|........|........>+--+          |I2 +----+
 \ +----+                /   I1   \                       /
  \                     /   GRE    \                     /
   \                   /   Tunnel   \                   /
    -------------------              -------------------

AD = Administrative Domain (independent autonomous system)
AS = multicast (e.g., content) Application Source
uBR = unicast Border Router - not necessarily multicast enabled;
      may be the same router as BR
BR = Border Router - for multicast
I1 = AD-1 and AD-2 multicast interconnection (e.g., MP-BGP)
I2 = AD-2 and EU multicast connection
]]></artwork>
</figure>

<t>In this case, interconnection I1 between AD-1 and AD&nbhy;2 in
   <xref target="gre-pic"/> is multicast enabled via a GRE tunnel
   <xref target="RFC2784"/> between the two BRs and encapsulating
   the multicast protocols across it.</t>

<t>Normally, this approach is chosen if the uBR physically connected to the
   peering link cannot or should not be enabled for IP multicast. This
   approach may also be beneficial if the BR and uBR are the same device but
   the peering link is a broadcast domain (IXP); see
   <xref target="section-4.2.4"/>.</t>

<t>The routing configuration is basically unchanged: instead of 
running BGP (SAFI&nbhy;2) ("SAFI" stands for "Subsequent Address Family
Identifier") across the native IP multicast link between AD&nbhy;1 and
AD&nbhy;2, BGP (SAFI&nbhy;2) is now run across the GRE tunnel.</t>

<t>Advantages of this configuration:
<list style="symbols">

    <t>Highly efficient use of bandwidth in both domains, although not
    as efficient as the fully native multicast use case
    (<xref target="section-3.1"/>).</t>
    
    <t>Fewer devices in the path traversed by the multicast stream
    when compared to an AMT-enabled peering point.</t>
    
    <t>Ability to support partial and/or incremental IP multicast deployments
    in AD&nbhy;1 and/or AD&nbhy;2: only the path or paths between the
    AS&wj;/BR (AD&nbhy;1) and the BR/EU (AD&nbhy;2) need to be multicast
    enabled. The uBRs may not support IP multicast or enabling it could be
    seen as operationally risky on that important edge node, whereas dedicated
    BR nodes for IP multicast may (at least initially) be more acceptable. The
    BR can also be located such that only parts of the domain may need to
    support native IP multicast (e.g., only the core in AD&nbhy;1 but not
    edge networks towards the uBR).</t>
    
    <t>GRE is an existing technology and is relatively simple to implement.</t>

</list>
</t>

      <t>Disadvantages of this configuration:
      <list style="symbols">
      <t>Per Use Case&nbsp;3.1, current router technology cannot count the
      number of EUs or the number of bytes transmitted.</t>

      <t>The GRE tunnel requires manual configuration.</t>

      <t>The GRE tunnel must be established prior to starting the stream.</t>

      <t>The GRE tunnel is often left pinned up.</t>

      </list>
      </t>

      <t>
   Architectural guidelines for this configuration include the
   following:</t>

      <t>
   Guidelines (a) through (d) are the same as those described in
   Use&nbsp;Case&nbsp;3.1. Two additional guidelines are as follows:</t>

   <t><list hangIndent="4" style="hanging">
      <t hangText="e.">
      GRE tunnels are typically configured manually between peering
      points to support multicast delivery between domains.</t>


      <t hangText="f.">
      It is recommended that the GRE tunnel (tunnel server) configuration in
      the source network be such that it only advertises the routes to the
      application sources and not to the entire network. This practice will
      prevent unauthorized delivery of applications through the tunnel (for
      example, if the application (e.g., content) is not part of an
      agreed&nbhy;upon inter&nbhy;domain partnership).</t>

      </list>
      </t>

</section>
<section title="Peering Point Enabled with AMT - Both Domains Multicast Enabled" anchor="section-3.3">

      <t>
   It is assumed that both administrative domains in this use case are
   native multicast enabled here; however, the peering point is not.</t>

      <t>
   The peering point is enabled with AMT. The basic configuration is
   depicted in <xref target="ref-amt-interconnection-between-ad-1-and-ad-2"/>.
   </t>

<figure title="AMT Interconnection between AD-1 and AD-2"
anchor="ref-amt-interconnection-between-ad-1-and-ad-2">
<artwork><![CDATA[
    -------------------              -------------------
   /       AD-1        \            /        AD-2       \
  / (Multicast Enabled) \          / (Multicast Enabled) \
 /                       \        /                       \
 | +----+          +---+ |   I1   | +---+                 |
 | |    |   +--+   |uBR|-|--------|-|uBR|   +--+          |   +----+
 | | AS |-->|AR|   +---+-|        | +---+   |AG| -------->|-->| EU |
 | |    |   +--+<........|........|........>+--+          |I2 +----+
 \ +----+                /  AMT   \                       /
  \                     /  Tunnel  \                     /
   \                   /            \                   /
    -------------------              -------------------

AD = Administrative Domain (independent autonomous system)
AS = multicast (e.g., content) Application Source
AR = AMT Relay
AG = AMT Gateway
uBR = unicast Border Router - not multicast enabled;
      also, either AR = uBR (AD-1) or uBR = AG (AD-2)
I1 = AMT interconnection between AD-1 and AD-2
I2 = AD-2 and EU multicast connection
]]></artwork>
</figure>

<t>Advantages of this configuration:
<list style="symbols">
    <t>Highly efficient use of bandwidth in AD-1.</t>

    <t>AMT is an existing technology and is relatively simple to
       implement. Attractive properties of AMT include the following:

    <list style="symbols">
      <t>Dynamic interconnection between the gateway-relay pair across the
      peering point.</t>

      <t>Ability to serve clients and servers with differing policies.</t>

    </list></t>
</list>
</t>

<t>Disadvantages of this configuration:
<list style="symbols">
    <t>Per Use Case&nbsp;3.1 (AD-2 is native multicast), current router
    technology cannot count the number of EUs or the number of bytes
    transmitted to all EUs.</t>

    <t>Additional devices (AMT gateway and relay pairs) may be
    introduced into the path if these services are not incorporated
    into the existing routing nodes.</t>

    <t>Currently undefined mechanisms for the AG to automatically
    select the optimal AR.</t>

</list>
</t>

     <t>Architectural guidelines for this configuration are as follows:</t>

     <t>
   Guidelines (a) through (d) are the same as those described in
   Use&nbsp;Case&nbsp;3.1. In addition,</t>

   <t><list hangIndent="4" style="hanging">
      <t hangText="e.">
     It is recommended that AMT relay and gateway pairs be configured at the
     peering points to support multicast delivery between domains. AMT tunnels
     will then configure dynamically across the peering points once the
     gateway in AD&nbhy;2 receives the (S,G) information from the EU.</t>

      </list>
      </t>

</section>
<section title="Peering Point Enabled with AMT - AD-2 Not Multicast Enabled" anchor="section-3.4">

      <t>
   In this AMT use case, AD-2 is not multicast enabled. Hence, the
   interconnection between AD&nbhy;2 and the EU is also not multicast
   enabled. This use case is depicted in <xref target="amt-pic"/>.</t>

<figure anchor="amt-pic" title="AMT Tunnel Connecting AD-1 AMT Relay and EU Gateway">
<artwork><![CDATA[
   -------------------               -------------------
   /       AD-1        \            /        AD-2       \
  / (Multicast Enabled) \          / (Not Multicast      \
 /                       \        /              Enabled) \ N(large)
 | +----+          +---+ |        | +---+                 |  # EUs
 | |    |   +--+   |uBR|-|--------|-|uBR|                 |   +----+
 | | AS |-->|AR|   +---+-|        | +---+    ................>|EU/G|
 | |    |   +--+<........|........|...........            |I2 +----+
 \ +----+                / N x AMT\                       /
  \                     /  Tunnel  \                     /
   \                   /            \                   /
    -------------------              -------------------

AS = multicast (e.g., content) Application Source
uBR = unicast Border Router - not multicast enabled;
      otherwise, AR = uBR (in AD-1)
AR = AMT Relay
EU/G = Gateway client embedded in EU device
I2 = AMT tunnel connecting EU/G to AR in AD-1 through
     non-multicast-enabled AD-2
]]></artwork>
</figure>

<t>This use case is equivalent to having unicast distribution of the
   application through AD&nbhy;2. The total number of AMT tunnels would be
   equal to the total number of EUs requesting the application.
   The peering point thus needs to accommodate the total number of AMT
   tunnels between the two domains. Each AMT tunnel can provide the
   data usage associated with each EU.</t>

<t>Advantages of this configuration:
<list style="symbols">
    <t>Efficient use of bandwidth in AD-1 (the closer the AR is to the uBR,
    the more efficient).</t>

    <t>Ability of AD-1 to introduce content delivery based on IP multicast,
    without any support by network devices in AD&nbhy;2: only the application
    side in the EU device needs to perform AMT gateway library functionality
    to receive traffic from the AMT relay.</t>

    <t>Allows AD-2 to "upgrade" to Use Case&nbsp;3.5 (see
    <xref target="section-3.5"/>) at a later time, without any change in
    AD&nbhy;1 at that time.</t>

    <t>AMT is an existing technology and is relatively simple to
    implement. Attractive properties of AMT include the following:
    <list style="symbols">
      <t>Dynamic interconnection between the AMT gateway-relay pair across
      the peering point.</t>
      <t>Ability to serve clients and servers with differing policies.</t>
    </list> </t>

    <t>Each AMT tunnel serves as a count for each EU and is also able to
    track data usage (bytes) delivered to the EU.</t>

</list>
</t>

<t>Disadvantages of this configuration:
<list style="symbols">
    <t>Additional devices (AMT gateway and relay pairs) are introduced into
    the transport path.</t>
    <t>Assuming multiple peering points between the domains, the EU gateway
    needs to be able to find the "correct" AMT relay in AD&nbhy;1.</t>
</list>
</t>

<t>Architectural guidelines for this configuration are as follows:</t>

      <t>
   Guidelines (a) through (c) are the same as those described in
   Use&nbsp;Case&nbsp;3.1. In addition,</t>
 
   <t><list hangIndent="4" style="hanging">
      <t hangText="d.">
     It is necessary that proper procedures be implemented such that
     the AMT gateway at the EU device is able to find the correct AMT relay
     for each (S,G) content stream. Standard mechanisms for that selection
     are still subject to ongoing work. This includes the use of anycast
     gateway addresses, anycast DNS names, or explicit configuration that
     maps (S,G) to a relay address; or letting the application in the
     EU/G provide the relay address to the embedded AMT gateway function.</t>

      <t hangText="e.">
     The AMT tunnel's capabilities are expected to be sufficient for
     the purpose of collecting relevant information on the multicast
     streams delivered to EUs in AD&nbhy;2.</t>

      </list>
      </t>

</section>
<section title="AD-2 Not Multicast Enabled - Multiple AMT Tunnels through AD-2" anchor="section-3.5">

      <t><xref target="amt-pic2"/> illustrates a variation of
      Use Case&nbsp;3.4:</t>

<figure anchor="amt-pic2" title="AMT Tunnel Connecting AMT Gateways and Relays">
<artwork><![CDATA[
   -------------------               -------------------
   /       AD-1        \            /        AD-2       \
  / (Multicast Enabled) \          / (Not Multicast      \
 /                 +---+ \  (I1)  / +---+        Enabled) \
 | +----+          |uBR|-|--------|-|uBR|                 |
 | |    |   +--+   +---+ |        | +---+           +---+ |   +----+
 | | AS |-->|AR|<........|....    | +---+           |AG/|....>|EU/G|
 | |    |   +--+         |  ......|.|AG/|..........>|AR2| |I3 +----+
 \ +----+                /   I1   \ |AR1|   I2      +---+ /
  \                     /  Single  \+---+                /
   \                   / AMT Tunnel \                   /
    -------------------              -------------------

uBR = unicast Border Router - not multicast enabled;
      also, either AR = uBR (AD-1) or uBR = AGAR1 (AD-2)
AS = multicast (e.g., content) Application Source
AR = AMT Relay in AD-1
AGAR1 = AMT Gateway/Relay node in AD-2 across peering point
I1 = AMT tunnel connecting AR in AD-1 to gateway in AGAR1 in AD-2
AGAR2 = AMT Gateway/Relay node at AD-2 network edge
I2 = AMT tunnel connecting relay in AGAR1 to gateway in AGAR2
EU/G = Gateway client embedded in EU device
I3 = AMT tunnel connecting EU/G to AR in AGAR2
]]></artwork>
</figure>

      <t>
   Use Case&nbsp;3.4 results in several long AMT tunnels crossing the entire
   network of AD&nbhy;2 linking the EU device and the AMT relay in AD&nbhy;1
   through the peering point. Depending on the number of EUs, there is a
   likelihood of an unacceptably high amount of traffic due to the large
   number of AMT tunnels -- and unicast streams -- through the peering
   point. This situation can be alleviated as follows:</t>

<t><list style="symbols">

    <t>Provisioning of strategically located AMT nodes in AD-2. An
    AMT&nbsp;node comprises co-location of an AMT gateway and an AMT relay. No
    change is required by AD&nbhy;1, as compared to
    Use&nbsp;Case&nbsp;3.4. This can be done whenever AD&nbhy;2 sees fit
    (e.g., too much traffic across the peering point).</t>

    <t>One such node is on the AD-2 side of the peering point
    (AMT node AGAR1 in <xref target="amt-pic2"/>).</t>

    <t>A single AMT tunnel established across the peering point linking
       the AMT relay in AD&nbhy;1 to the AMT gateway in AMT node AGAR1
       in&nbsp;AD&nbhy;2.</t>

    <t>AMT tunnels linking AMT node AGAR1 at the peering point in AD&nbhy;2
       to other AMT nodes located at the edges of AD&nbhy;2: e.g., AMT
       tunnel&nbsp;I2 linking the AMT relay in AGAR1 to the AMT gateway in
       AMT node&nbsp;AGAR2 (<xref target="amt-pic2"/>).</t>

    <t>AMT tunnels linking an EU device (via a gateway client embedded in
       the device) and an AMT relay in an appropriate AMT node at the edge
       of AD&nbhy;2: e.g., I3 linking the EU gateway in the device to
       the AMT relay in AMT node AGAR2.</t>

    <t>In the simplest option (not shown), AD-2 only deploys a single
       AGAR1 node and lets the EU/G build AMT tunnels directly to it. This 
       setup already solves the problem of replicated traffic across
       the peering point. As soon as there is a need to support more
       AMT tunnels to the EU/G, then additional AGAR2 nodes can be deployed
       by AD&nbhy;2.</t>

</list>
</t>

      <t>
   The advantage of such a chained set of AMT tunnels is that the total
   number of unicast streams across AD&nbhy;2 is significantly reduced, thus
   freeing up bandwidth. Additionally, there will be a single unicast stream
   across the peering point instead of, possibly, an unacceptably large
   number of such streams per Use&nbsp;Case&nbsp;3.4. However, this implies
   that several AMT tunnels will need to be dynamically configured by the
   various AMT gateways, based solely on the (S,G) information received from
   the application client at the EU device. A suitable mechanism for such
   dynamic configurations is therefore critical.</t>

   <t>Architectural guidelines for this configuration are as follows:</t>

      <t>
   Guidelines (a) through (c) are the same as those described in
   Use&nbsp;Case&nbsp;3.1. In addition,</t>

   <t><list hangIndent="4" style="hanging">
      <t hangText="d.">
     It is necessary that proper procedures be implemented such that
     the various AMT gateways (at the EU devices and the AMT nodes in
     AD&nbhy;2) are able to find the correct AMT relay in other AMT nodes
     as appropriate. Standard mechanisms for that selection are still
     subject to ongoing work. This includes the use of anycast gateway
     addresses, anycast DNS names, or explicit configuration that maps
     (S,G) to a relay address. On the EU/G, this mapping information
     may come from the application.</t>

      <t hangText="e.">
     The AMT tunnel's capabilities are expected to be sufficient for
     the purpose of collecting relevant information on the multicast
     streams delivered to EUs in AD&nbhy;2.</t>

      </list>
      </t>

  </section>
</section>

<section title="Functional Guidelines" anchor="section-4">

<t>Supporting functions and related interfaces over the peering point
   that enable the multicast transport of the application are listed in
   this section. Critical information parameters that need to be
   exchanged in support of these functions are enumerated, along with
   guidelines as appropriate. Specific interface functions for
   consideration are as follows.</t>

<section title="Network Interconnection Transport Guidelines" anchor="section-4.1">

   <t>
   The term "network interconnection transport" refers to the
   interconnection points between the two administrative domains. The
   following is a representative set of attributes that the two
   administrative domains will need to agree on to support multicast
   delivery.</t>

      <t><list style="symbols">
       <t>Number of peering points.</t>

       <t>Peering point addresses and locations.</t>

       <t>Connection type - Dedicated for multicast delivery or shared
       with other services.</t>

       <t>Connection mode - Direct connectivity between the two ADs or
       via another ISP.</t>

       <t>Peering point protocol support - Multicast protocols that will
       be used for multicast delivery will need to be supported at
       these points. Examples of such protocols include
       External BGP (EBGP) <xref target="RFC4760"/> peering via
       MP&nbhy;BGP (Multiprotocol BGP) SAFI&nbhy;2
       <xref target="RFC4760"/>.</t>
  
       <t>Bandwidth allocation - If shared with other services, then
       there needs to be a determination of the share of bandwidth
       reserved for multicast delivery. See
       <xref target="section-4.1.1"/> below for more details.</t>
  
       <t>QoS requirements - Delay and/or latency specifications that need to
       be specified in an SLA.</t>
  
       <t>AD roles and responsibilities - The role played by each AD for
       provisioning and maintaining the set of peering points to support
       multicast delivery.</t>
      </list>
      </t>

  <section title="Bandwidth Management" anchor="section-4.1.1">

      <t>Like IP unicast traffic, IP multicast traffic carried across
      non&nbhy;controlled networks must comply with congestion control
      principles as described in <xref target="BCP41"/> and as explained
      in detail for UDP IP multicast in <xref target="BCP145"/>.</t>
      
      <t>Non-controlled networks (such as the Internet) are networks where
      there is no policy for managing bandwidth other than best effort with a
      fair share of bandwidth under congestion. As a simplified rule of thumb,
      complying with congestion control principles means reducing bandwidth
      under congestion in a way that is fair to competing (typically TCP)
      flows ("rate adaptive").</t>
      
      <t>In many instances, multicast content delivery evolves from
      intra&nbhy;domain deployments where it is handled as a controlled
      network service and does not comply with congestion control
      principles. It was given a reserved amount of bandwidth and admitted to
      the network so that congestion never occurs. Therefore, the congestion
      control issue should be given specific attention when evolving to an
      inter&nbhy;domain peering deployment.</t>

      <t>In the case where end-to-end IP multicast traffic passes across the
      network of two ADs (and their subsidiaries/customers), both ADs must
      agree on a consistent traffic-management policy. If, for example,
      AD&nbhy;1 sources non&nbhy;congestion&nbhy;aware IP multicast traffic
      and AD&nbhy;2 carries it as best&nbhy;effort traffic across links shared
      with other Internet traffic (subject to congestion), this will not
      work: under congestion, some amount of that traffic will be dropped,
      often rendering the remaining packets as undecodable garbage clogging
      up the network in AD&nbhy;2; because this traffic is not
      congestion aware, the loss does not reduce this rate.  Competing
      traffic will not get their fair share under congestion, and EUs will be
      frustrated by the extremely bad quality of both their IP multicast
      traffic and other (e.g., TCP) traffic. Note that this is not an IP
      multicast technology issue but is solely a
      transport&nbhy;layer&nbsp;/ application&nbhy;layer issue: the problem
      would just as likely happen if AD&nbhy;1 were to send
      non&nbhy;rate-adaptive unicast traffic -- for example, legacy IPTV
      video&nbhy;on&nbhy;demand traffic, which is typically also
      non&nbhy;congestion aware.  Note that because rate&nbsp;adaptation in IP
      unicast video is commonplace today due to the availability of ABR
      (Adaptive Bitrate) video, it is very unlikely that this will happen in
      reality with IP unicast.</t>
      <t>While the rules for traffic management apply whether IP multicast
      is tunneled or not, the one feature that can make AMT tunnels more
      difficult is the unpredictability of bandwidth requirements across
      underlying links because of the way they can be used: with native IP
      multicast or GRE tunnels, the amount of bandwidth depends on the amount
      of content -- not the number of EUs -- and is therefore easier to plan
      for. AMT tunnels terminating in the EU/G, on the other hand, scale with
      the number of EUs. In the vicinity of the AMT relay, they can introduce
      a very large amount of replicated traffic, and it is not always feasible
      to provision enough bandwidth for all possible EUs to get the highest
      quality for all their content during peak utilization in such setups --
      unless the AMT relays are very close to the EU edge. Therefore, it is
      also recommended that IP multicast rate adaptation be used, even inside
      controlled networks, when using AMT tunnels directly to the EU/G.</t>

      <t>Note that rate-adaptive IP multicast traffic in general does not mean
      that the sender is reducing the bitrate but rather that the EUs that
      experience congestion are joining to a lower-bitrate (S,G) stream of the
      content, similar to ABR streaming over TCP. Therefore, migration from a
      non&nbhy;rate&nbhy;adaptive bitrate to a rate&nbhy;adaptive bitrate in
      IP multicast will also change the dynamic (S,G) join behavior in the
      network, resulting in potentially higher performance requirements for IP
      multicast protocols (IGMP/PIM), especially on the last hops where
      dynamic changes occur (including AMT gateways/relays): in
      non&nbhy;rate-adaptive IP multicast, only "channel change" causes state
      change, but in rate-adaptive multicast, congestion also causes state
      change.</t>

      <t>Even though not fully specified in this document, peerings that rely
      on GRE/AMT tunnels may be across one or more transit ADs instead of an
      exclusive (non&nbhy;shared, L1/L2) path. Unless those transit ADs are
      explicitly contracted to provide other than "best effort" transit
      for the tunneled traffic, the tunneled IP multicast traffic must be
      rate&nbsp;adaptive in order to not violate BCP&nbsp;41 across those
      transit&nbsp;ADs.</t>

  </section>

</section>

<section title="Routing Aspects and Related Guidelines" anchor="section-4.2">

      <t>
   The main objective for multicast delivery routing is to ensure that
   the EU receives the multicast stream from the "most optimal"
   source <xref target="INF_ATIS_10"/>, which typically:</t>

      <t><list style="symbols">
      <t>Maximizes the multicast portion of the
      transport and minimizes any unicast portion of the delivery, and</t>

      <t>Minimizes the overall combined route distance of the network(s).</t>

      </list>
      </t>

      <t>
   This routing objective applies to both native multicast and AMT; the
   actual methodology of the solution will be different for each. Regardless,
   the routing solution is expected to:</t>

      <t><list style="symbols"><t>Be scalable,</t>

      <t>Avoid or minimize new protocol development or modifications,
       and</t>

      <t>Be robust enough to achieve high reliability and to
      automatically adjust to changes and problems in the multicast
      infrastructure.</t>
      </list>
      </t>

      <t>
   For both native and AMT environments, having a source as close as
   possible to the EU network is most desirable; therefore, in some
   cases, an AD may prefer to have multiple sources near different
   peering points. However, that is entirely an implementation issue.</t>

<section title="Native Multicast Routing Aspects" anchor="section-4.2.1">

      <t>
   Native multicast simply requires that the administrative domains
   coordinate and advertise the correct source address(es) at their
   network interconnection peering points (i.e., BRs). An example of
   multicast delivery via a native multicast process across
   two administrative domains is as follows, assuming that the
   interconnecting peering points are also multicast enabled:</t>

      <t><list style="symbols">
      <t>Appropriate information is obtained by
      the EU client, who is a subscriber to AD&nbhy;2 (see
      Use&nbsp;Case&nbsp;3.1). This information is in the form of metadata,
      and it contains instructions directing the EU client to launch an
      appropriate application if necessary, as well as additional information
      for the application about the source location and the group (or stream)
      ID in the form of (S,G) data. The "S" portion provides the name or IP
      address of the source of the multicast stream. The metadata may also
      contain alternate delivery information, such as specifying the unicast
      address of the stream.</t>

      <t>The client uses the join message with (S,G) to join the multicast
      stream <xref target="RFC4604"/>. To facilitate this process, the two
      ADs need to do the following:

      <list style="symbols">
      <t>Advertise the source ID(s) over the peering points.</t>

      <t>Exchange such relevant peering point information as capacity
      and utilization.</t>

      <t>Implement compatible multicast protocols to ensure proper
      multicast delivery across the peering points.</t>

      </list>
      </t>

      </list>
      </t>

</section>
<section title="GRE Tunnel over Interconnecting Peering Point" anchor="section-4.2.2">

      <t>
   If the interconnecting peering point is not multicast enabled and
   both ADs are multicast enabled, then a simple solution is to
   provision a GRE tunnel between the two ADs; see Use Case&nbsp;3.2
   (<xref target="section-3.2"/>). The termination points of the tunnel will
   usually be a network engineering decision but generally will be between the
   BRs or even between the AD&nbhy;2 BR and the AD&nbhy;1 source (or source
   access router). The GRE tunnel would allow end&nbhy;to&nbhy;end native
   multicast or AMT multicast to traverse the interface. Coordination and
   advertisement of the source IP are still required.</t>

      <t>
   The two ADs need to follow the same process as the process described
   in <xref target="section-4.2.1"/> to facilitate multicast delivery across
   the peering points.</t>

</section>
<section title="Routing Aspects with AMT Tunnels" anchor="section-4.2.3">

      <t>
   Unlike native multicast (with or without GRE), an AMT multicast
   environment is more complex. It presents a two-layered problem
   in&nbsp;that there are two criteria that should be simultaneously met:</t>

<t><list style="symbols">
<t>Find the closest AMT relay to the EU that also has
   multicast connectivity to the content source, and</t>

<t>Minimize the AMT unicast tunnel distance.</t>
</list></t>

<t>There are essentially two components in the AMT specification:</t>

<t><list style="hanging">
<t hangText="AMT relays:">These serve the purpose of tunneling UDP multicast
      traffic to the receivers (i.e., endpoints). The AMT relay will
      receive the traffic natively from the multicast media source and
      will replicate the stream on behalf of the downstream AMT gateways,
      encapsulating the multicast packets into unicast packets and sending
      them over the tunnel toward the AMT gateways. In addition, the AMT relay
      may collect various usage and activity statistics. This results in
      moving the replication point closer to the EU and cuts down on traffic
      across the network. Thus, the linear costs of adding unicast subscribers
      can be avoided. However, unicast replication is still required for each
      requesting endpoint within the unicast&nbhy;only network.</t>

<t hangText="AMT gateway:"> The gateway will reside on an endpoint; this
      could be any type of IP host, such as a Personal Computer (PC), mobile
      phone, Set-Top Box (STB), or appliances.  The AMT gateway receives join
      and leave requests from the application via an Application Programming
      Interface (API). In this manner, the gateway allows the endpoint to
      conduct itself as a true multicast endpoint. The AMT gateway will
      encapsulate AMT messages into UDP packets and send them through a
      tunnel (across the unicast-only infrastructure) to the AMT relay.</t>

</list>
</t>

      <t>
   The simplest AMT use case (<xref target="section-3.3"/>) involves peering
   points that are not multicast enabled between two multicast-enabled ADs. An
   AMT&nbsp;tunnel is deployed between an AMT relay on the AD&nbhy;1 side of
   the peering point and an AMT gateway on the AD&nbhy;2 side of the peering
   point. One advantage of this arrangement is that the tunnel is established
   on an as&nbhy;needed basis and need not be a provisioned element. The two
   ADs can coordinate and advertise special AMT relay anycast addresses with,
   and to, each other. Alternately, they may decide to simply provision relay
   addresses, though this would not be an optimal solution in terms of
   scalability.</t>

      <t>
   Use Cases&nbsp;3.4 and 3.5 describe AMT situations that are more
   complicated, as AD&nbhy;2 is not multicast enabled in these two cases. For
   these cases, the EU device needs to be able to set up an AMT tunnel in the
   most optimal manner. There are many methods by which relay selection can be
   done, including the use of DNS-based queries and static lookup tables <xref
   target="RFC7450"/>. The choice of the method is implementation dependent
   and is up to the network operators. Comparison of various methods is out of
   scope for this document and is left for further study.</t>

      <t>
   An illustrative example of a relay selection based on DNS queries
   as part of an anycast IP address process is described here for
   Use Cases&nbsp;3.4 and 3.5
   (Sections&nbsp;<xref target="section-3.4" format="counter"/> and
   <xref target="section-3.5" format="counter"/>). Using an anycast
   IP&nbsp;address for AMT relays allows all AMT gateways to find the
   "closest" AMT relay -- the nearest edge of the multicast topology of the
   source. Note that this is strictly illustrative; the choice of the method
   is up to the network operators. The basic process is as follows:</t>

     <t><list style="symbols">
     <t>Appropriate metadata is obtained by the EU
     client application. The metadata contains instructions directing the EU
     client to an ordered list of particular destinations to seek the
     requested stream and, for multicast, specifies the source location and
     the group (or stream) ID in the form of (S,G) data. The "S" portion
     provides the URI (name or IP address) of the source of the multicast
     stream, and the "G" identifies the particular stream originated by
     that source. The metadata may also contain alternate delivery information
     such as the address of the unicast form of the content to be used --
     for example, if the multicast stream becomes unavailable.</t>

      <t>Using the information from the metadata and, possibly, information
     provisioned directly in the EU client, a DNS query is initiated in
     order to connect the EU client / AMT gateway to an AMT relay.</t>

      <t>Query results are obtained and may return an anycast address or a
     specific unicast address of a relay. Multiple relays will typically
     exist. The anycast address is a routable "pseudo&nbhy;address" shared
     among the relays that can gain multicast access to the source.</t>

     <t>If a specific IP address unique to a relay was not obtained, the
     AMT gateway then sends a message (e.g., the discovery message) to
     the anycast address such that the network is making the routing
     choice of a particular relay, e.g., the relay that is closest to the EU.
     Details are outside the scope of this document. See <xref
     target="RFC4786"/>.</t>

      <t>The contacted AMT relay then returns its specific unicast IP
     address (after which the anycast address is no longer required).
     Variations may exist as well.</t>

      <t>The AMT gateway uses that unicast IP address to initiate a
     three&nbhy;way handshake with the AMT relay.</t>

      <t>The AMT gateway provides the (S,G) information to the AMT relay
      (embedded in AMT protocol messages).</t>

      <t>The AMT relay receives the (S,G) information and uses it to join
      the appropriate multicast stream, if it has not already subscribed
      to that stream.</t>

      <t>The AMT relay encapsulates the multicast stream into the tunnel
      between the relay and the gateway, providing the requested content
      to the EU.</t>

      </list>
      </t>

</section>

<section title="Public Peering Routing Aspects" anchor="section-4.2.4">

<t><xref target="broadcast-peering"/> shows an example of a broadcast
peering point.</t>

<figure anchor="broadcast-peering" title="Broadcast Peering Point">
<artwork><![CDATA[
           AD-1a            AD-1b
           BR                BR
            |                 |
          --+-+---------------+-+-- broadcast peering point LAN
              |                 |
              BR               BR
             AD-2a            AD-2b
]]></artwork>
</figure>

<t>A broadcast peering point is an L2 subnet connecting three or more ADs.
It is common in IXPs and usually consists of Ethernet switch(es) operated by
the IXP connecting to BRs operated by the ADs.</t>

<t>In an example setup domain, AD-2a peers with AD-1a and wants to
receive IP multicast from it. Likewise, AD&nbhy;2b peers with
AD&nbhy;1b and wants to receive IP multicast from it.</t>

<t>Assume that one or more IP multicast (S,G) traffic streams can be served
by both AD&nbhy;1a and AD&nbhy;1b -- for example, because both AD&nbhy;1a
and AD&nbhy;1b contact this content from the same content source.</t>

<t>In this case, AD-2a and AD-2b can no longer control which upstream
domain -- AD&nbhy;1a or AD&nbhy;1b -- will forward this (S,G) into the
LAN. The AD&nbhy;2a BR requests the (S,G) from the AD&nbhy;1a BR,
and the AD&nbhy;2b BR requests the same (S,G) from the AD&nbhy;1b BR.
To avoid duplicate packets, an (S,G) can be forwarded by only one router
onto the LAN; PIM-SM&nbsp;/&nbsp;PIM-SSM detects requests for duplicate
transmissions and resolves them via the so&nbhy;called "assert" protocol
operation, which results in only one BR forwarding the traffic. Assume that
this is the AD&nbhy;1a BR. AD&nbhy;2b will then receive unexpected multicast
traffic from a provider with whom it does not have a mutual agreement
for that traffic. Quality issues in EUs behind AD&nbhy;2b caused by
AD&nbhy;1a will cause a lot of issues related to responsibility and
troubleshooting.</t>

<t>In light of these technical issues, we describe, via the following
options, how IP multicast can be carried across broadcast peering point
LANs:</t>

<t><list style="numbers">

<t>IP multicast is tunneled across the LAN. Any of the GRE/AMT tunneling
solutions mentioned in this document are applicable. This is the one case
where a GRE tunnel between the upstream BR (e.g., AD&nbhy;1a) and downstream
BR (e.g., AD&nbhy;2a) is specifically recommended, as opposed to tunneling
across uBRs (which are not the actual BRs).</t>

<t>The LAN has only one upstream AD that is sourcing IP multicast, and native
IP multicast is used. This is an efficient way to distribute the same IP
multicast content to multiple downstream ADs. Misbehaving downstream BRs can
still disrupt the delivery of IP multicast from the upstream BR to other
downstream BRs; therefore, strict rules must be followed to prohibit such a
case. The downstream BRs must ensure that they will always consider only the
upstream BR as a source for multicast traffic: e.g., no BGP SAFI&nbhy;2
peerings between the downstream ADs across the peering point LAN, so that the
upstream BR is the only possible next&nbsp;hop reachable across this LAN.
Also, routing policies can be configured to avoid falling back to using
SAFI&nbhy;1 (unicast) routes for IP multicast if unicast BGP peering is not
limited in the same way.</t>

<t>The LAN has multiple upstream ADs, but they are federated and agree on a
consistent policy for IP multicast traffic across the LAN. One policy is that
each possible source is only announced by one upstream BR. Another policy is
that sources are redundantly announced (the problematic case mentioned in the
example in <xref target="broadcast-peering"/> above), but the upstream domains
also provide mutual operational insight to help with troubleshooting (outside
the scope of this document).</t>

</list></t>

</section>
</section>
<section title="Back-Office Functions - Provisioning and Logging Guidelines" anchor="section-4.3">

      <t>
   "Back office" refers to the following:</t>

      <t><list style="symbols">
      <t>Servers and content-management systems that support the delivery
      of applications via multicast and interactions between ADs.</t>

      <t>Functionality associated with logging, reporting, ordering,
      provisioning, maintenance, service assurance, settlement, etc.</t>

      </list>
      </t>

<section title="Provisioning Guidelines" anchor="section-4.3.1">

      <t>
   Resources for basic connectivity between ADs' providers need to be
   provisioned as follows:</t>

      <t><list style="symbols">
      <t>Sufficient capacity must be provisioned to support multicast-based
      delivery across ADs.</t>

      <t>Sufficient capacity must be provisioned for connectivity between
      all supporting back&nbsp;offices of the ADs as appropriate. This
      includes activating proper security treatment for these
      back&nbhy;office connections (gateways, firewalls, etc.) as
      appropriate.</t>

      </list>
      </t>

      <t>
   Provisioning aspects related to multicast-based inter-domain
   delivery are as follows.</t>

      <t>
   The ability to receive a requested application via multicast is
   triggered via receipt of the necessary metadata. Hence, this
   metadata must be provided to the EU regarding the multicast URL --
   and unicast fallback if applicable. AD&nbhy;2 must enable the delivery
   of this metadata to the EU and provision appropriate resources for this
   purpose.</t>

      <t>
   It is assumed that native multicast functionality is available across
   many ISP backbones, peering points, and access networks. If, however,
   native multicast is not an option (Use&nbsp;Cases&nbsp;3.4 and 3.5),
   then:</t>

      <t><list style="symbols">
      <t>The EU must have a multicast client to use AMT multicast obtained
      from either (1)&nbsp;the application source (per agreement with
      AD&nbhy;1) or (2)&nbsp;AD&nbhy;1 or AD&nbhy;2 (if delegated by the
      application source).</t>

      <t>If provided by AD-1 or AD-2, then the EU could be redirected to a
      client download site. (Note: This could be an application source
      site.) If provided by the application source, then this source
      would have to coordinate with AD&nbhy;1 to ensure that the proper
      client is provided (assuming multiple possible clients).</t>

      <t>Where AMT gateways support different application sets, all AD&nbhy;2
      AMT relays need to be provisioned with all source and group
      addresses for streams it is allowed to join.</t>

      <t>DNS across each AD must be provisioned to enable a client gateway
      to locate the optimal AMT relay (i.e., longest multicast path and
      shortest unicast tunnel) with connectivity to the content's
      multicast source.</t>

      </list>
      </t>

      <t>
   Provisioning aspects related to operations and customer care are as
   follows.</t>

      <t>
   It is assumed that each AD provider will provision operations and
   customer care access to their own systems.</t>

      <t>
   AD-1's operations and customer care functions must be able to see
   enough of what is happening in AD&nbhy;2's network or in the service
   provided by AD&nbhy;2 to verify their mutual goals and operations, e.g.,
   to know how the EUs are being served. This can be done in two ways:</t>

      <t><list style="symbols">
      <t>Automated interfaces are built between AD-1 and AD-2 such that
      operations and customer care continue using their own systems.
      This requires coordination between the two ADs, with appropriate
      provisioning of necessary resources.</t>

      <t>AD-1's operations and customer care personnel are provided direct
      access to AD&nbhy;2's systems. In this scenario, additional
      provisioning in these systems will be needed to provide necessary
      access. The two ADs must agree on additional provisioning to support
      this option.</t>

      </list>
      </t>

</section>

<section title="Inter-domain Authentication Guidelines" anchor="section-4.3.2">

      <t>
   All interactions between pairs of ADs can be discovered and/or associated
   with the account(s) utilized for delivered applications. Supporting
   guidelines are as follows:</t>

      <t><list style="symbols">
      <t>A unique identifier is recommended to designate each master
      account.</t>

      <t>AD-2 is expected to set up "accounts" (a logical facility generally
      protected by credentials such as login passwords) for use by
      AD&nbhy;1. Multiple accounts, and multiple types or partitions of
      accounts, can apply, e.g., customer accounts, security accounts.</t>

      </list>
      </t>

<t>The reason to specifically mention the need for AD-1 to initiate
interactions with AD&nbhy;2 (and use some account for that), as opposed
to the opposite, is based on the recommended workflow initiated by customers
(see <xref target="section-4.4"/>): the customer contacts the content source,
which is part of AD&nbhy;1. Consequently, if AD&nbhy;1 sees the need to
escalate the issue to AD&nbhy;2, it will interact with AD&nbhy;2 using the
aforementioned guidelines.
</t>

</section>
<section title="Log-Management Guidelines" anchor="section-4.3.3">

<t> Successful delivery (in terms of user experience) of applications or
content via multicast between pairs of interconnecting ADs can be improved
through the ability to exchange appropriate logs for various workflows --
troubleshooting, accounting and billing, optimization of traffic and content
transmission, optimization of content and application development, and
so on.</t>

<t>Specifically, AD&nbhy;1 take over primary responsibility for customer
experience on behalf of the content source, with support from AD&nbhy;2
as needed. The application/content owner is the only participant who has, and
needs, full insight into the application level and can map the customer
application experience to the network traffic flows -- which, with the help of
AD&nbhy;2 or logs from AD&nbhy;2, it can then analyze and interpret.</t>

<t>The main difference between unicast delivery and multicast delivery is that
   the content source can infer a lot more about downstream network problems
   from a unicast stream than from a multicast stream: the multicast
   stream is not per EU, except after the last replication, which is in most
   cases not in AD&nbhy;1. Logs from the application, including the receiver
   side at the EU, can provide insight but cannot help to fully isolate
   network problems because of the IP multicast per&nbhy;application
   operational state built across AD&nbhy;1 and AD&nbhy;2 (aka the (S,G) state
   and any other operational-state features, such as Diffserv QoS).</t>

<t>See <xref target="privacy"/> for more discussion regarding the privacy
considerations of the model described here.</t>

<t>Different types of logs are known to help support operations in AD-1 when
provided by AD&nbhy;2. This could be done as part of AD&nbhy;1/AD&nbhy;2
contracts. Note that except for implied multicast-specific elements, the
options listed here are not unique or novel for IP multicast, but they are
more important for services novel to the operators than for operationally
well&nbhy;established services (such as unicast). We therefore detail them
as follows:</t>

      <t><list style="symbols">
      <t>Usage information logs at an aggregate level.</t>

      <t>Usage failure instances at an aggregate level.</t>

      <t>Grouped or sequenced application access: performance, behavior, and
      failure at an aggregate level to support potential
      application-provider-driven strategies. Examples of aggregate levels
      include grouped video clips, web pages, and software-download sets.</t>

      <t>Security logs, aggregated or summarized according to agreement
      (with additional detail potentially provided during security
      events, by agreement).</t>

      <t>Access logs (EU), when needed for troubleshooting.</t>

      <t>Application logs ("What is the application doing?"), when needed
      for shared troubleshooting.</t>

      <t>Syslogs (network management), when needed for shared
      troubleshooting.</t>

      </list>
      </t>

      <t>
   The two ADs may supply additional security logs to each other, as
   agreed upon in contract(s). Examples include the following:</t>

      <t><list style="symbols">
      <t>Information related to general security-relevant activity, which
      may be of use from a protection or response perspective: types and
      counts of attacks detected, related source information, related target
      information, etc.</t>

      <t>Aggregated or summarized logs according to agreement (with
      additional detail potentially provided during security events, by
      agreement).</t>

      </list>
      </t>

</section>
</section>
<section title="Operations - Service Performance and Monitoring Guidelines" anchor="section-4.4">

      <t>
   "Service performance" refers to monitoring metrics related to
   multicast delivery via probes. The focus is on the service provided
   by AD&nbhy;2 to AD&nbhy;1 on behalf of all multicast application sources
   (metrics may be specified for SLA use or otherwise). Associated
   guidelines are as follows:</t>

<t><list style="symbols">
    <t>Both ADs are expected to monitor, collect, and analyze service
    performance metrics for multicast applications. AD&nbhy;2 provides
    relevant performance information to AD&nbhy;1; this enables AD&nbhy;1 to
    create an end-to-end performance view on behalf of the multicast
    application source.</t>

    <t>Both ADs are expected to agree on the types of probes to be
    used to monitor multicast delivery performance. For example,
    AD&nbhy;2 may permit AD&nbhy;1's probes to be utilized in the AD&nbhy;2
    multicast service footprint. Alternately, AD&nbhy;2 may deploy its
    own probes and relay performance information back to AD&nbhy;1.</t>

</list>
</t>

      <t>
   "Service monitoring" generally refers to a service (as a whole)
   provided on behalf of a particular multicast application source
   provider. It thus involves complaints from EUs when service
   problems occur. EUs direct their complaints to the source provider;
   the source provider in turn submits these complaints to AD&nbhy;1. The
   responsibility for service delivery lies with AD&nbhy;1; as such,
   AD&nbhy;1 will need to determine where the service problem is occurring --
   in its own network or in AD&nbhy;2. It is expected that each AD will have
   tools to monitor multicast service status in its own network.</t>

      <t><list style="symbols">
      <t>Both ADs will determine how best to deploy
      multicast service monitoring tools. Typically, each AD will deploy its
      own set of monitoring tools, in which case both ADs are expected to
      inform each other when multicast delivery problems are
      detected.</t>

      <t>AD-2 may experience some problems in its network. For example,
      for the AMT use cases
      (Sections&nbsp;<xref target="section-3.3" format="counter"/>,
      <xref target="section-3.4" format="counter"/>, and
      <xref target="section-3.5" format="counter"/>), one or more
      AMT relays may be experiencing difficulties. AD&nbhy;2 may be able to
      fix the problem by rerouting the multicast streams via alternate AMT
      relays. If the fix is not successful and multicast service delivery
      degrades, then AD&nbhy;2 needs to report the issue to AD&nbhy;1.</t>

      <t>When a problem notification is received from a multicast
      application source, AD&nbhy;1 determines whether the cause of the
      problem is within its own network or within AD&nbhy;2. If the cause is
      within AD&nbhy;2, then AD&nbhy;1 supplies all necessary information to
      AD&nbhy;2. Examples of supporting information include the following:
      <list style="symbols">
       <t>Kind(s) of problem(s).</t>

       <t>Starting point and duration of problem(s).</t>

       <t>Conditions in which one or more problems occur.</t>

       <t>IP address blocks of affected users.</t>

       <t>ISPs of affected users.</t>

       <t>Type of access, e.g., mobile versus desktop.</t>

       <t>Network locations of affected EUs.</t>

      </list>
      </t>

      <t>Both ADs conduct some form of root-cause analysis for
      multicast service delivery problems. Examples of various
      factors for consideration include:
      <list style="symbols">
       <t>Verification that the service configuration matches the
       product features.</t>

      <t>Correlation and consolidation of the various customer
       problems and resource troubles into a single root-service
       problem.</t>

      <t>Prioritization of currently open service problems, giving
       consideration to problem impacts, SLAs, etc.</t>

      <t>Conducting service tests, including tests performed once or a
       series of tests over a period of time.</t>

      <t>Analysis of test results.</t>

      <t>Analysis of relevant network fault or performance data.</t>

      <t>Analysis of the problem information provided by the customer.</t>

      </list>
      </t>

      <t>Once the cause of the problem has been determined and the
      problem has been fixed, both ADs need to work jointly to
      verify and validate the success of the fix.</t>

      </list>
      </t>

</section>
<section title="Client Reliability Models / Service Assurance Guidelines" anchor="section-4.5">

      <t>
   There are multiple options for instituting reliability architectures.
   Most are at the application level. Both ADs should work these options out
   per their contract or agreement and also with the multicast application
   source providers.</t>

      <t>
   Network reliability can also be enhanced by the two ADs if they
   provision alternate delivery mechanisms via unicast means.</t>

      </section>

<section title="Application Accounting Guidelines" anchor="section-4.6">

<t>Application-level accounting needs to be handled differently in the
application than in IP unicast, because the source side does not directly
deliver packets to individual receivers. Instead, this needs to be signaled
back by the receiver to the source.</t>

<t>
For network transport diagnostics, AD-1 and AD-2 should have mechanisms in
place to ensure proper accounting for the volume of bytes delivered through
the peering point and, separately, the number of bytes delivered to EUs.</t>

      </section>

      </section>

      <section title="Troubleshooting and Diagnostics" anchor="section-5"><t>
   Any service provider supporting multicast delivery of content should be
   able to collect diagnostics as part of multicast troubleshooting practices
   and resolve network issues accordingly. Issues may become apparent or
   identifiable through either (1)&nbsp;network monitoring functions or 
   (2)&nbsp;problems reported by customers, as described in <xref
   target="section-4.4"/>.</t>

      <t>
   It is recommended that multicast diagnostics be performed, leveraging
   established operational practices such as those documented in
   <xref target="MDH-05"/>. However, given that inter&nbhy;domain multicast
   creates a significant interdependence of proper networking functionality
   between providers, there exists a need for providers to be able to
   signal (or otherwise alert) each other if there are any issues noted by
   either one.</t>

      <t>
   For troubleshooting purposes, service providers may also wish to allow
   limited read-only administrative access to their routers to their AD peers.
   Access to active troubleshooting tools -- especially
   <xref target="Traceroute"/> and the tools discussed in <xref 
   target="Mtrace-v2"/> -- is of specific interest.</t>

   <t>Another option is to include this functionality in the IP multicast
   receiver application on the EU device and allow these diagnostics to be
   remotely used by support operations. Note, though, that AMT does not allow
   the passing of traceroute or mtrace requests; therefore, troubleshooting in
   the presence of AMT does not work as well end to end as it can with native
   (or even GRE-encapsulated) IP multicast, especially with regard to
   traceroute and mtrace.

   Instead, troubleshooting directly on the actual network devices is then
   more likely necessary.</t>

      <t>
   The specifics of notifications and alerts are beyond the scope of
   this document, but general guidelines are similar to those described
   in <xref target="section-4.4"/>. Some general communications issues are
   as follows.</t> 

      <t><list style="symbols">
      <t>Appropriate communications channels will be
      established between the customer service and operations groups from both
      ADs to facilitate information-sharing related to diagnostic
      troubleshooting.</t>

      <t>A default resolution period may be considered to resolve open
      issues. Alternately, mutually acceptable resolution periods
      could be established, depending on the severity of the
      identified trouble.</t>

      </list>
      </t>

      </section>

     
      <section title="Security Considerations" anchor="section-6">

<section title="DoS Attacks (against State and Bandwidth)" anchor="section-6.1">

<t>Reliable IP multicast operations require some basic protection against
DoS (Denial of Service) attacks.</t>

<t>SSM IP multicast is self-protecting against attacks from illicit sources;
such traffic will not be forwarded beyond the first&nbhy;hop router, because
that would require (S,G) membership reports from the receiver. Only valid
traffic from sources will be forwarded, because RPF ("Reverse Path
Forwarding") is part of the protocols. One can say that protection against
spoofed source traffic performed in the style of <xref target="BCP38"/> is therefore built into PIM-SM / PIM-SSM.</t>

<t>Receivers can attack SSM IP multicast by originating such (S,G)
membership reports. This can result in a DoS attack against state through the
creation of a large number of (S,G) states that create high control-plane load
or even inhibit the later creation of a valid (S,G). In conjunction with
collaborating illicit sources, it can also result in the forwarding of traffic
from illicit sources.</t>

<t>Today, these types of attacks are usually mitigated by explicitly defining
the set of permissible (S,G) on, for example, the last&nbhy;hop routers in
replicating IP multicast to EUs (e.g., via (S,G) access control lists applied
to IGMP/MLD membership state creation). Each AD (say, "ADi") is expected to
know what sources located in ADi are permitted to send and what their
valid (S,G)s are. ADi can therefore also filter invalid (S,G)s for any
"S" located inside ADi, but not sources located in another AD.

</t>

<t>In the peering case, without further information, AD&nbhy;2 is not aware of
the set of valid (S,G) from AD&nbhy;1, so this set needs to be communicated via
operational procedures from AD&nbhy;1 to AD&nbhy;2 to provide protection
against this type of DoS attack. Future work could signal this information in
an automated way: BGP extensions, DNS resource records, or backend automation
between AD&nbhy;1 and AD&nbhy;2. Backend automation is, in the short term,
the most viable solution: unlike BGP extensions or DNS resource records,
backend automation does not require router software extensions. Observation
of traffic flowing via (S,G) state could also be used to automate the
recognition of invalid (S,G) state created by receivers in the absence of
explicit information from AD&nbhy;1.</t>

<t>The second type of DoS attack through (S,G) membership reports exists when
the attacking receiver creates too much valid (S,G) state and the traffic
carried by these (S,G)s congests bandwidth on links shared with other EUs.
Consider the uplink to a last&nbhy;hop router connecting to 100 EUs. If one EU
joins to more multicast content than what fits into this link, then this would
also impact the quality of the same content for the other 99 EUs. If traffic
is not rate adaptive, the effects are even worse.</t>

<t>The mitigation technique is the same as what is often employed for unicast:
policing of the per&nbhy;EU total amount of traffic. Unlike unicast, though,
this cannot be done anywhere along the path (e.g., on an arbitrary bottleneck
link); it has to happen at the point of last replication to the different
EU. Simple solutions such as limiting the maximum number of joined (S,G)s
per EU are readily available; solutions that take consumed bandwidth
into account are available as vendor-specific features in routers. Note that
this is primarily a non&nbhy;peering issue in AD&nbhy;2; it only becomes a
peering issue if the peering&nbsp;link itself is not big enough to carry all
possible content from AD&nbhy;1 or, as in Use Case&nbsp;3.4, when the AMT
relay in AD&nbhy;1 is that last replication point.
</t>

<t>Limiting the amount of (S,G) state per EU is also a good first measure to
prohibit too much undesired "empty" state from being built (state not carrying
traffic), but it would not suffice in the case of DDoS attacks, e.g., viruses
that impact a large number of EU devices.</t>

</section>

<section  title="Content Security" anchor="section-6.2">

<t>Content confidentiality, DRM (Digital Rights Management),
authentication, and authorization are optional, based on the content
delivered. For content that is "FTA" (Free To Air), the following
considerations can be ignored, and content can be sent unencrypted and
without EU authentication and authorization. Note, though, that the
mechanisms described here may also be desirable for the application source 
to better track users even if the content itself would not require it.</t>

<t>For inter&nbhy;domain content, there are at least two models for content
confidentiality, including (1)&nbsp;DRM authentication and authorization and
(2)&nbsp;EU authentication and authorization:</t>

<t><list style="symbols">
<t>In the classical (IP)TV model, responsibility is per&nbsp;domain, and
content is and can be passed on unencrypted. AD&nbhy;1 delivers content to
AD&nbhy;2; AD&nbhy;2 can further process the content, including features like 
ad&nbsp;insertion, and AD&nbhy;2 is the sole point of contact regarding the
contact for its EUs. In this document, we do not consider this case because
it typically involves service aspects operated by AD&nbhy;2 that are higher
than the network layer; this document focuses on the network-layer
AD&nbhy;1/AD&nbhy;2 peering case but not the application-layer peering
case. Nevertheless, this model can be derived through additional work beyond
what is described here.</t>

<t>The other model is the one in which content confidentiality, DRM,
EU authentication, and EU authorization are end to end: responsibilities of
the multicast application source provider and receiver application.  This is
the model assumed here. It is also the model used in Internet "Over the Top"
(OTT) video delivery. Below, we discuss the threats incurred in this model due
to the use of IP multicast in AD&nbhy;1 or AD&nbhy;2 and across the peering
point.</t>
</list></t>

<t>End-to-end encryption enables end-to-end EU authentication and
authorization: the EU may be able to join (via IGMP/MLD) and receive the
content, but it can only decrypt it when it receives the decryption key from
the content source in AD&nbhy;1. The key is the authorization. Keeping that
key to itself and prohibiting playout of the decrypted content to
non&nbhy;copy-protected interfaces are typical DRM features in that receiver
application or EU device operating system.</t>

<t>End-to-end encryption is continuously attacked. Keys may be subject
to brute-force attacks so that content can potentially be decrypted later,
or keys are extracted from the EU application/device and shared with other
unauthenticated receivers. One important class of content is where the value
is in live consumption, such as sports or other event (e.g., concert)
streaming. Extraction of keying material from compromised authenticated EUs
and sharing with unauthenticated EUs are not sufficient. It is also necessary
for those unauthenticated EUs to get a streaming copy of the content
itself. In unicast streaming, they cannot get such a copy from the content
source (because they cannot authenticate), and, because of asymmetric
bandwidths, it is often impossible to get the content from compromised EUs to
a large number of unauthenticated EUs. EUs behind classical "16&nbsp;Mbps
down, 1&nbsp;Mbps up" ADSL links are the best example.  With increasing
broadband access speeds, unicast peer-to-peer copying of content becomes
easier, but it likely will always be easily detectable by the ADs because of
its traffic patterns and volume.</t>

<t>When IP multicast is being used without additional security, AD&nbhy;2
is not aware of which EU is authenticated for which content. Any
unauthenticated EU in AD&nbhy;2 could therefore get a copy of the encrypted
content without triggering suspicion on the part of AD&nbhy;2 or AD&nbhy;1
and then either (1)&nbsp;live&nbhy;decode it, in the presence of the
compromised authenticated EU and key-sharing or (2)&nbsp;decrypt it later, in
the presence of federated brute-force key-cracking.</t>

<t>To mitigate this issue, the last replication point that is creating (S,G)
copies to EUs would need to permit those copies only after authentication
of the EUs. This would establish the same authenticated "EU only"
copy that is used in unicast.</t>

<t>Schemes for per-EU IP multicast authentication/authorization (and,
as a result, non&nbhy;delivery or copying of per&nbhy;content IP multicast
traffic) have been built in the past and are deployed in service providers for
intra&nbhy;domain IPTV services, but no standards exist for this. For example,
there is no standardized RADIUS attribute for authenticating the IGMP/MLD
filter set, but such implementations exist. The authors of this document
are specifically also not aware of schemes where the same authentication
credentials used to get the encryption key from the content source could also
be used to authenticate and authorize the network-layer IP multicast
replication for the content. Such schemes are technically not difficult to
build and would avoid creating and maintaining a separate network
traffic&nbhy;forwarding authentication/authorization scheme decoupled from the
end&nbhy;to&nbhy;end authentication/authorization system of the
application.</t>

<t>If delivery of such high-value content in conjunction with the
peering described here is desired, the short-term recommendations are
for sources to clearly isolate the source and group addresses used
for different content bundles, communicate those (S,G) patterns from
AD&nbhy;1 to AD&nbhy;2, and let AD&nbhy;2 leverage existing per&nbhy;EU
authentication/authorization mechanisms in network devices to establish
filters for (S,G) sets to each EU.</t>

</section>

<section  title="Peering Encryption" anchor="section-6.3">

<t>Encryption at peering points for multicast delivery may be used per
agreement between AD&nbhy;1 and AD&nbhy;2.</t>

<t>In the case of a private peering link, IP multicast does not have attack
 vectors on a peering link different from those of IP unicast, but the content
 owner may have defined strict constraints against unauthenticated copying of
 even the end-to-end encrypted content; in this case, AD&nbhy;1 and AD&nbhy;2
 can agree on additional transport encryption across that peering link.
 In the case of a broadcast peering connection (e.g., IXP), transport
 encryption is again the easiest way to prohibit unauthenticated copies by
 other ADs on the same peering point.</t>

<t>If peering is across a tunnel that spans intermittent transit ADs
(not discussed in detail in this document), then encryption of that tunnel
traffic is recommended. It not only prohibits possible "leakage" of content
but also protects the information regarding what content is being consumed in
AD&nbhy;2 (aggregated privacy protection).</t>

<t>See <xref target="section-6.4"/> for reasons why the peering point may
also need to be encrypted for operational reasons.</t>

</section>

<section  title="Operational Aspects" anchor="section-6.4">

<t><xref target="section-4.3.3"/> discusses the exchange of log information,
and <xref target="privacy"/> discusses the exchange of program information.
All these operational pieces of data should by default be exchanged via
authenticated and encrypted peer-to-peer communication protocols between
AD&nbhy;1 and AD&nbhy;2 so that only the intended recipients in the peers' AD
have access to it. Even exposure of the least sensitive information to third
parties opens up attack vectors. Putting valid (S,G) information, for example,
into DNS (as opposed to passing it via secured channels from AD&nbhy;1 to
AD&nbhy;2) to allow easier filtering of invalid (S,G) information would also
allow attackers to more easily identify valid (S,G) information and change
their attack vector.</t>

<t>From the perspective of the ADs, security is most critical for log
information, as it provides operational insight into the originating AD
but also contains sensitive user data.</t>

<t>Sensitive user data exported from AD-2 to AD-1 as part of logs could be as
much as the equivalent of 5-tuple unicast traffic flow accounting (but not
more, e.g., no application-level information). As mentioned in <xref
target="privacy"/>, in unicast, AD&nbhy;1 could capture these traffic
statistics itself because this is all about traffic flows (originated by
AD&nbhy;1) to EU receivers in AD&nbhy;2, and operationally passing it from
AD&nbhy;2 to AD&nbhy;1 may be necessary when IP multicast is used because of
the replication taking place in AD&nbhy;2.</t>

<t>Nevertheless, passing such traffic statistics inside AD-1 from a capturing
router to a backend system is likely less subject to third&nbhy;party attacks
than passing it "inter&nbhy;domain" from AD&nbhy;2 to AD&nbhy;1, so more
diligence needs to be applied to secure it.</t>

<t>If any protocols used for the operational exchange of information are not
easily secured at the transport layer or higher (because of the use of legacy
products or protocols in the network), then AD&nbhy;1 and AD&nbhy;2 can also
consider ensuring that all operational data exchanges go across the same
peering point as the traffic and use network&nbhy;layer encryption of the
peering point (as discussed previously) to protect&nbsp;it.</t>

<t>
End-to-end authentication and authorization of EUs may involve some kind of
token authentication and are done at the application layer, independently of
the two ADs. If there are problems related to the failure of token
authentication when EUs are supported by AD&nbhy;2, then some means of
validating proper operation of the token authentication process (e.g.,
validating that backend servers querying the multicast application source
provider's token authentication server are communicating properly) should be
considered. Implementation details are beyond the scope of this document.</t>

<t>In the event of a security breach, the two ADs are expected to have a
mitigation plan for shutting down the peering point and directing multicast
traffic over alternative peering points. It is also expected that appropriate
information will be shared for the purpose of securing the identified
breach.</t>

</section>
</section>

<section title="Privacy Considerations" anchor="privacy">

<t>The described flow of information about content and EUs as described in
this document aims to maintain privacy:</t>

<t>AD-1 is operating on behalf of (or owns) the content source and is
therefore part of the content-consumption relationship with the EU. The
privacy considerations between the EU and AD&nbhy;1 are therefore generally
the same (with one exception; see below) as they would be if no IP multicast
was used, especially because end-to-end encryption can and should be used for
any privacy-conscious content.</t>

<t>Information related to inter-domain multicast transport service is provided
to AD&nbhy;1 by the AD&nbhy;2 operators. AD&nbhy;2 is not required to gain
additional insight into the user's behavior through this process other than
what it would already have without service collaboration with AD&nbhy;1,
unless AD&nbhy;1 and AD&nbhy;2 agree on it and get approval from the&nbsp;EU.
</t>

<t>For example, if it is deemed beneficial for the EU to get support directly
from AD&nbhy;2, then it would generally be necessary for AD&nbhy;2 to be aware
of the mapping between content and network (S,G) state so that AD&nbhy;2 knows
which (S,G) to troubleshoot when the EU complains about problems with 
specific content. The degree to which this dissemination is done by AD&nbhy;1
explicitly to meet privacy expectations of EUs is typically easy to assess by
AD&nbhy;1. Two simple examples are as follows:</t>

<t><list style="symbols">
<t>For a sports content bundle, every EU will happily click on the
"I&nbsp;approve that the content program information is shared with your
service provider" button, to ensure best service reliability, because
service-conscious AD&nbhy;2 would likely also try to ensure that high-value
content, such as the (S,G) for the Super&nbsp;Bowl, would be the first to
receive care in the case of network issues.</t>

<t>If the content in question was content for which the EU expected more
privacy, the EU should prefer a content bundle that included this content in a
large variety of other content, have all content end&nbhy;to&nbhy;end
encrypted, and not share programming information with AD&nbhy;2, to maximize
privacy. Nevertheless, the privacy of the EU against AD&nbhy;2 observing
traffic would still be lower than in the equivalent setup using unicast,
because in unicast, AD&nbhy;2 could not correlate which EUs are watching the
same content and use that to deduce the content. Note that even the setup in
<xref target="section-3.4"/>, where AD&nbhy;2 is not involved in IP multicast
at all, does not provide privacy against this level of analysis by AD&nbhy;2,
because there is no transport-layer encryption in AMT; therefore, AD&nbhy;2
can correlate by on&nbhy;path traffic analysis who is consuming the same
content from an AMT relay from both the (S,G) join messages in AMT and the
identical content segments (that were replicated at the AMT relay).</t>
</list></t>

<t>In summary, because only content to be consumed by multiple EUs is carried
via IP multicast here and all of that content can be
end&nbhy;to&nbhy;end encrypted, the only privacy consideration specific to IP
multicast is for AD&nbhy;2 to know or reconstruct what content an EU is
consuming. For content for which this is undesirable, some form of protections
as explained above are possible, but ideally, the model described in <xref
target="section-3.4"/> could be used in conjunction with future work, e.g.,
adding Datagram Transport Layer Security (DTLS) encryption <xref
target="RFC6347"/> between the AMT relay and the EU.</t>

<t>Note that IP multicast by nature would permit the EU's privacy against the
content source operator because, unlike unicast, the content source does not
natively know which EU is consuming which content: in all cases where
AD&nbhy;2 provides replication, only AD&nbhy;2 knows this directly. This
document does not attempt to describe a model that maintains such a level of
privacy against the content source; rather, we describe a model that only
protects against exposure to intermediate parties -- in this case, AD&nbhy;2.
</t>

</section>

      <section title="IANA Considerations" anchor="iana-cons">
      <t>
      This document does not require any IANA actions.
      </t>

      </section>

      </middle>

      <back>
      <references title="Normative References">

      <?rfc include='reference.RFC.2784'?>
      <?rfc include='reference.RFC.3376'?>
      <?rfc include='reference.RFC.3810'?>
      <?rfc include='reference.RFC.4760'?>
      <?rfc include='reference.RFC.4604'?>
      <?rfc include='reference.RFC.4609'?>
      <?rfc include='reference.RFC.7450'?>
      <?rfc include='reference.RFC.7761'?>

<reference  anchor='BCP38' target='https://www.rfc-editor.org/info/rfc2827'>
<front>
<title>Network Ingress Filtering: Defeating Denial of Service Attacks which employ IP Source Address Spoofing</title>
<author initials='P.' surname='Ferguson' fullname='P. Ferguson'><organization /></author>
<author initials='D.' surname='Senie' fullname='D. Senie'><organization /></author>
<date year='2000' month='May' />
</front>
<seriesInfo name='BCP' value='38'/>
<seriesInfo name='RFC' value='2827'/>
</reference>

<reference  anchor='BCP41' target='https://www.rfc-editor.org/info/rfc2914'>
<front>
<title>Congestion Control Principles</title>
<author initials='S.' surname='Floyd' fullname='S. Floyd'><organization /></author>
<date year='2000' month='September' />
</front>
<seriesInfo name='BCP' value='41'/>
<seriesInfo name='RFC' value='2914'/>
</reference>

<reference  anchor='BCP145' target='https://www.rfc-editor.org/info/rfc8085'>
<front>
<title>UDP Usage Guidelines</title>
<author initials='L.' surname='Eggert' fullname='L. Eggert'><organization /></author>
<author initials='G.' surname='Fairhurst' fullname='G. Fairhurst'><organization /></author>
<author initials='G.' surname='Shepherd' fullname='G. Shepherd'><organization /></author>
<date year='2017' month='March' />
</front>
<seriesInfo name='BCP' value='145'/>
<seriesInfo name='RFC' value='8085'/>
</reference>

      </references>

      <references title="Informative References">

      <?rfc include='reference.RFC.4786'?>
      <?rfc include='reference.RFC.6347'?>

      <reference anchor="INF_ATIS_10"><front>
      <title>CDN Interconnection Use Cases and Requirements in a Multi-Party Federation Environment</title>
      <author>
      </author>
      <date month="December" year="2012"/>
      </front>
      <seriesInfo name="ATIS" value="Standard A-0200010"/>
      </reference>

<!-- draft-ietf-mboned-mdh (Expired) -->
      <reference anchor="MDH-05"><front>
      <title>Multicast Debugging Handbook</title>
      <author fullname="D. Thaler" initials="D." surname="Thaler">
      </author>
      <author fullname="Bernard Aboba" initials="B" surname="Aboba">
      </author>
      <date month="November" year="2000"/>
      </front>
      <seriesInfo name="Work in Progress," value="draft-ietf-mboned-mdh-05"/>
      </reference>

      <reference anchor="Traceroute" target="http://traceroute.org/#source%20code"><front>
      <title>traceroute.org</title>
      <author><organization></organization></author>
      <date/>
      </front>
      </reference>

<!-- draft-ietf-mboned-mtrace-v2 (Waiting for AD Go-Ahead) -->
<reference anchor='Mtrace-v2'>
<front>
<title>Mtrace Version 2: Traceroute Facility for IP Multicast</title>
<author initials='H' surname='Asaeda' fullname='Hitoshi Asaeda'>
    <organization />
</author>
<author initials='K' surname='Meyer' fullname='Kerry Meyer'>
    <organization />
</author>
<author initials='W' surname='Lee' fullname='Weesan Lee' role="editor">
    <organization />
</author>
<date month='November' year='2017'/>
</front>
<seriesInfo name='Work in Progress,' value='draft-ietf-mboned-mtrace-v2-21'/>
</reference>

      </references>

   <section title="Acknowledgments" anchor="acknowledgments" numbered="no">
   <t>
   The authors would like to thank the following individuals for their
   suggestions, comments, and corrections:

<?rfc subcompact="yes"?>
<list style="empty">
   <t>Mikael Abrahamsson</t>
   <t>Hitoshi Asaeda</t>
   <t>Dale Carder</t>
   <t>Tim Chown</t>
   <t>Leonard Giuliano</t>
   <t>Jake Holland</t>
   <t>Joel Jaeggli</t>
   <t>Henrik Levkowetz</t>
   <t>Albert Manfredi</t>
   <t>Stig Venaas</t>

<?rfc subcompact="no"?>
</list></t>
   </section>

  </back>

 </rfc>