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  <!ENTITY RFC7432 SYSTEM "http://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7432.xml"> nbhy   "&#8209;">
  <!ENTITY RFC7524 SYSTEM "http://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7524.xml">
<!ENTITY RFC6513 SYSTEM "http://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6513.xml">
<!ENTITY RFC6514 SYSTEM "http://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6514.xml">
<!ENTITY RFC7988 SYSTEM "http://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7988.xml">
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<rfc category="std" xmlns:xi="http://www.w3.org/2001/XInclude" updates="7432" docName="draft-ietf-bess-evpn-bum-procedure-updates-14" ipr="trust200902"> number="9572" ipr="trust200902" obsoletes="" submissionType="IETF" category="std" consensus="true" xml:lang="en" tocInclude="true" tocDepth="3" symRefs="true" sortRefs="true" version="3">

  <!-- xml2rfc v2v3 conversion 3.12.0 -->
  <front>
    <title abbrev="evpn-bum-procedure-update">Updates on EVPN abbrev="EVPN BUM Procedures: Updates">Updates to EVPN Broadcast, Unknown Unicast, or Multicast (BUM) Procedures</title>
    <seriesInfo name="RFC" value="9572"/>
    <author fullname="Zhaohui Zhang" initials="Z." surname="Zhang">
      <organization>Juniper Networks</organization>
      <address>
        <email>zzhang@juniper.net</email>
      </address>
    </author>
    <author fullname="Wen Lin" initials="W." surname="Lin">
      <organization>Juniper Networks</organization>
      <address>
        <email>wlin@juniper.net</email>
      </address>
    </author>
    <author fullname="Jorge Rabadan" initials="J." surname="Rabadan">
      <organization>Nokia</organization>
      <address>
        <email>jorge.rabadan@nokia.com</email>
      </address>
    </author>
    <author fullname="Keyur Patel" initials="K." surname="Patel">
      <organization>Arrcus</organization>
      <address>
        <email>keyur@arrcus.com</email>
      </address>
    </author>
    <author fullname="Ali Sajassi" initials="A." surname="Sajassi">
      <organization>Cisco Systems</organization>
      <address>
        <email>sajassi@cisco.com</email>
      </address>
    </author>
    <date year="2021"/> year="2024" month="May" />
    <area>rtg</area>
    <workgroup>BESS</workgroup>

<keyword>per-region I-PMSI</keyword>
<keyword>selective multicast forwarding</keyword>
<keyword>tunnel segmentation</keyword>
<keyword>inter-AS segmentation</keyword>
<keyword>inter-region segmentation</keyword>

    <abstract>
      <t>This document specifies updated procedures for handling
         broadcast, unknown unicast, and multicast
         Broadcast, Unknown Unicast, or Multicast (BUM) traffic in
         Ethernet VPNs (EVPN), (EVPNs), including selective multicast, multicast
         and segmentation of provider tunnel segmentation. tunnels. This document updates RFC 7432.
      </t>
    </abstract>

    <note title="Requirements Language">
    <t>
          The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
          NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED",
          "MAY", and "OPTIONAL" in this document are to be interpreted as
          described in BCP 14 <xref target="RFC2119"/> <xref
          target="RFC8174"/> when, and only when, they appear in all
          capitals, as shown here.
    </t>
    </note>
  </front>
  <middle>
    <section title="Terminology">
    <t>It is expected that audience is familiar with MVPN [RFC6513] [RFC6514], VPLS Multicast [RFC7117] and EVPN [RFC7432] concepts and
       terminologies. For convenience, the following terms are briefly
       explained.
    <list style="symbols">
       <t>PMSI [RFC6513]: P-Multicast Service Interface - a conceptual interface for a PE
          to send customer multicast traffic to all or some PEs in the same
          VPN.
       </t>
       <t>I-PMSI: Inclusive PMSI - to all PEs in the same VPN.
       </t>
       <t>S-PMSI: Selective PMSI - to some of the PEs in the same VPN.
       </t>
	   <t>I/S-PMSI A-D Route: Auto-Discovery routes used to announce the tunnels that instantiate an I/S-PMSI.
	   </t>
       <t>Leaf Auto-Discovery (A-D) routes [RFC6513]: For explicit leaf tracking purpose.
       Triggered by I/S-PMSI A-D routes and targeted at triggering
	   route's (re-)advertiser. Its NLRI embeds the entire NLRI of the triggering PMSI A-D route.
       </t>
       <t>IMET A-D route [RFC7432]: Inclusive Multicast Ethernet Tag A-D route.
          The EVPN equivalent of MVPN Intra-AS I-PMSI A-D route
		  used to announce the tunnels that instantiate an I-PMSI.
       </t>
       <t>SMET A-D route <xref target="I-D.ietf-bess-evpn-igmp-mld-proxy"/>:
	      Selective Multicast Ethernet Tag A-D route. The EVPN
          equivalent of MVPN Leaf A-D route but unsolicited and untargeted.
       </t>
       <t>PMSI Tunnel Attribute (PTA): An optional transitive BGP attribute
          that may be attached to PMSI/Leaf A-D routes to provide
          information for a PMSI tunnel.
       </t>
    </list>
    </t>
    </section>
    <section title="Introduction">
    <t>[RFC7117] numbered="true" toc="default">
      <name>Introduction</name>
      <t><xref target="RFC7117" format="default"/> specifies procedures for Multicast multicast in the Virtual Private LAN
       Service (VPLS Multicast) multicast), using both inclusive tunnels and
       selective tunnels with or without inter-as inter-AS segmentation, similar to the
       Multicast VPN (MVPN) procedures specified in [RFC6513] <xref target="RFC6513" format="default"/> and [RFC6514].
       [RFC7524] <xref target="RFC6514" format="default"/>.
       <xref target="RFC7524" format="default"/> specifies inter-area tunnel segmentation procedures for
	   both VPLS Multicast multicast and MVPN. MVPNs.
      </t>
    <t>[RFC7432]
      <t><xref target="RFC7432" format="default"/> specifies BGP MPLS-Based MPLS-based Ethernet VPN (EVPN) procedures,
       including those handling broadcast, unknown unicast, and multicast Broadcast, Unknown Unicast, or Multicast
       (BUM) traffic. A lot of details are referred <xref target="RFC7432"/> refers to [RFC7117], yet
       with quite some <xref target="RFC7117" format="default"/> for details but leaves a few feature gaps like related to selective tunnel and tunnel segmentation (<xref target="segmentation"/>). target="motivation"/>).
      </t>
      <t>This document aims at filling the to fill in those gaps - cover by covering the use of selective
       and segmented tunnels in EVPN. It follows EVPNs.
       In the same editorial choice
       as in RFC7432 and way that <xref target="RFC7432"/> refers to <xref target="RFC7117" format="default"/> for details, this document only specifies differences from relevant procedures provided in [RFC7117] <xref target="RFC7117" format="default"/> and [RFC7524], instead of <xref target="RFC7524" format="default"/>, rather than repeating the text. text from those documents.
       Note that these differences are applicable to EVPN only, EVPNs only
       and are not updates to [RFC7117] <xref target="RFC7117" format="default"/> or [RFC7524]. <xref target="RFC7524" format="default"/>.
      </t>
      <t>MVPN, VPLS VPLS, and EVPN technologies all have the need to discover other PEs Provider Edges (PEs) in the
       same L3/L2 VPN and announce the inclusive tunnels. MVPN technology introduced
       the I-PMSI Inclusive P-Multicast Service Interface (I-PMSI) concept and uses I-PMSI A-D route Auto-Discovery (A-D) routes for that. that purpose.
       EVPN technology uses Inclusive Multicast Ethernet Tag Route (IMET) A-D route routes,
       but VPLS technology just adds an a PMSI Tunnel Attribute (PTA) to the an existing
       VPLS A-D route for that purpose. For selective tunnels, they all
       do use the same term S-PMSI term: Selective PMSI (S-PMSI) A-D routes.
      </t>
	<t>Many places of this
      <t>This document involve often refers to the I-PMSI concept that concept, which is all
       the same for all three technologies. For consistency and convenience,
       an EVPN's IMET A-D route and a VPLS's VPLS A-D route carrying a PTA for BUM traffic
       purpose
       purposes may all each be referred to as an I-PMSI A-D routes route, depending on the
       context.
      </t>
    <!--t>MVPN uses terms I-PMSI and S-PMSI A-D Routes. For
       consistency
<section numbered="true" toc="default">
      <name>Requirements Language</name>
       <t>The key words "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>",
       "<bcp14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>",
       "<bcp14>SHALL NOT</bcp14>", "<bcp14>SHOULD</bcp14>",
       "<bcp14>SHOULD NOT</bcp14>",
       "<bcp14>RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>",
       "<bcp14>MAY</bcp14>", and convenience, "<bcp14>OPTIONAL</bcp14>" in this document will use the same I/S-PMSI
       terms for VPLS
       are to be interpreted as described in BCP&nbsp;14
       <xref target="RFC2119"/> <xref target="RFC8174"/> when, and EVPN. In particular, EVPN's Inclusive Multicast
       Ethernet Tag Route only
       when, they appear in all capitals, as shown here.</t>
</section>
    <section numbered="true" toc="default">
      <name>Terminology</name>
      <t>It is assumed that the reader is familiar with concepts and VPLS's terminologies related to MVPN technology <xref target="RFC6513" format="default"/> <xref target="RFC6514" format="default"/>, VPLS A-D route carrying PTA
       (PMSI Tunnel Attribute) multicast <xref target="RFC7117" format="default"/>, and EVPN technology <xref target="RFC7432" format="default"/>. For convenience, the following terms are briefly
       explained.
      </t>
      <dl spacing="normal">
        <dt>AS:</dt><dd>Autonomous System</dd>
        <dt>PMSI <xref target="RFC6513" format="default"/>:</dt><dd>P-Multicast Service Interface. A conceptual interface for BUM a PE
          to send customer multicast traffic purpose will to all or some PEs in the same
          VPN.</dd>
        <dt>I-PMSI:</dt><dd>Inclusive PMSI. Enables traffic to be referred sent to as all PEs in the same VPN.</dd>
        <dt>S-PMSI:</dt><dd>Selective PMSI. Enables traffic to be sent to some of the PEs in the same VPN.</dd>
        <dt>I/S-PMSI A-D Route:</dt><dd>Auto-Discovery route used to announce the tunnels that instantiate an I/S-PMSI.</dd>
        <dt>Leaf Auto-Discovery (A-D) Route <xref target="RFC6513" format="default"/>:</dt><dd>For explicit leaf-tracking purposes.
       Triggered by I/S-PMSI A-D routes and targeted at the triggering
	   route's (re-)advertiser. Its Network Layer
   Reachability Information (NLRI) embeds the entire NLRI of the triggering PMSI A-D route.</dd>
        <dt>IMET A-D Route <xref target="RFC7432" format="default"/>:</dt><dd>Inclusive Multicast Ethernet Tag A-D route.
          The EVPN equivalent of an MVPN Intra-AS I-PMSI A-D routes. Depending on route
		  used to announce the context, they tunnels that instantiate an I-PMSI.</dd>
        <dt>SMET A-D Route <xref target="RFC9251" format="default"/>:</dt>
	<dd>Selective Multicast Ethernet Tag A-D route. The EVPN
          equivalent of an MVPN Leaf A-D route, but unsolicited and untargeted.</dd>
        <dt>PMSI Tunnel Attribute (PTA):</dt><dd>An optional transitive BGP attribute
          that may be used
       interchangeably.
    </t--> attached to PMSI/Leaf A-D routes to provide
          information for a PMSI tunnel.</dd>
        <dt>IBGP:</dt><dd>Internal BGP (BGP connection between internal peers).</dd>
        <dt>EBGP:</dt><dd>External BGP (BGP connection between external peers).</dd>
        <dt>RT:</dt><dd>Route Target. Controls route importation and propagation.</dd>
      </dl>
    </section>
  </section>
  <section title="Tunnel Segmentation" anchor="segmentation"> anchor="segmentation" numbered="true" toc="default">
        <name>Tunnel Segmentation</name>
        <t>MVPN provider tunnels and EVPN/VPLS BUM provider tunnels, which are
       referred to as MVPN/EVPN/VPLS provider tunnels in this document for
       simplicity, can be segmented for technical or administrative reasons,
       which are summarized in <xref target="motivation"/> target="motivation" format="default"/> of this document.
       [RFC6513]
       <xref target="RFC6513" format="default"/> and [RFC6514] <xref target="RFC6514" format="default"/> cover MVPN inter-as inter-AS segmentation,
       [RFC7117]
       <xref target="RFC7117" format="default"/> covers
       VPLS multicast inter-as inter-AS segmentation, and [RFC7524] (Seamless <xref target="RFC7524" format="default"/> (seamless MPLS
       Multicast)
       multicast) covers inter-area segmentation for both MVPN MVPNs and VPLS. VPLSs.
        </t>
        <t>With tunnel segmentation, different segments of an end-to-end tunnel
	may have different encapsulation overhead. overheads. However, the largest overhead
	of the tunnel caused by an encapsulation method on a particular segment
	is not different from the case of a non-segmented tunnel with that
	encapsulation method. This is similar to the case of a network
	with different link types.
        </t>
        <t>There is a difference between MVPN and VPLS multicast inter-as inter-AS
       segmentation (the VPLS approach is briefly discribed described in <xref target="interaschanges"/>). target="interaschanges" format="default"/>). For simplicity, EVPN EVPNs will use the same procedures as
       in MVPN. those for
       MVPNs. All ASBRs can re-advertise
       their choice of the best route. Each can become the root of its
       intra-AS segment and inject traffic it receives from its upstream,
       while each downstream PE/ASBR will only pick one of the upstream ASBRs
       as its upstream. This is also the behavior even for VPLS in the case of
       inter-area segmentation.
        </t>
        <t>For inter-area segmentation, [RFC7524] <xref target="RFC7524" format="default"/> requires the use of Inter-area
       P2MP the Inter-Area
       Point-to-Multipoint (P2MP) Segmented Next-Hop Extended Community (S-NH-EC), (S-NH-EC) and the setting
       of "Leaf the Leaf Information Required" L Required (L) flag in the PTA in certain situations.
       In the EVPN case, the requirements around the S-NH-EC and the PTA "L" L flag in the PTA
       differ from [RFC7524] <xref target="RFC7524" format="default"/> to make the segmentation procedures transparent to
       ingress and egress PEs.
        </t>
    <t>[RFC7524]
        <t><xref target="RFC7524" format="default"/> assumes that segmentation happens at area borders.
       However, it could be at "regional" borders, where a region could be a
       sub-area, or even an entire AS plus its external links
       (<xref target = "region"/>). That target="region" format="default"/>); this would
       allow for more flexible deployment scenarios (e.g. (e.g., for single-area
       provider networks). This document extends the inter-area segmentation concept
       to inter-region segmentation for EVPN. EVPNs.
        </t>
        <section title="Reasons anchor="motivation" numbered="true" toc="default">
          <name>Reasons for Tunnel Segmentation" anchor="motivation"> Segmentation</name>
          <t>Tunnel segmentation may be required and/or desired because of for
       administrative and/or technical reasons.
          </t>
          <t>For example, an MVPN/VPLS/EVPN network may span multiple providers providers,
       and the end-to-end provider
       tunnels have to be segmented at and stitched by the ASBRs.
       Different providers may use different tunnel technologies (e.g.,
       provider A uses Ingress Replication [RFC7988], ingress replication <xref target="RFC7988" format="default"/>, provider B uses RSVP-TE
       P2MP [RFC4875] while <xref target="RFC4875" format="default"/>, and provider C uses mLDP [RFC6388]). Multipoint LDP (mLDP) <xref target="RFC6388" format="default"/>). Even if they use
       the same tunnel technology like (e.g., RSVP-TE
       P2MP,
       P2MP), it may be impractical to set up the tunnels across provider
       boundaries.
          </t>
          <t>The same situations may apply between the ASes and/or areas of a
       single provider. For example, the backbone area may use RSVP-TE
       P2MP tunnels while non-backbone areas may use mLDP tunnels.
          </t>
          <t>Segmentation can also be used to divide an AS/area into smaller regions,
       so that control plane state and/or forwarding plane state/burden can be
       limited to that of individual regions. For example, instead of Ingress
       Replicating
       ingress-replicating to 100 PEs in the entire AS, with inter-area segmentation
       [RFC7524]
       <xref target="RFC7524" format="default"/>, a PE only needs to replicate to local PEs and ABRs. Area Border Routers (ABRs).
       The ABRs will further replicate to their downstream PEs and ABRs.
       This not only reduces the forwarding plane burden, but also reduces
       the leaf tracking leaf-tracking burden in the control plane.
          </t>
    <t>Smaller regions also have
          <t>In the benefit that, in case of tunnel aggregation, smaller regions provide the benefit of
       making it is easier to find congruence among the segments of
       different constituent (service) tunnels and the resulting aggregation
       (base) tunnel in a region. This leads to better bandwidth efficiency,
       because the more congruent they are, the fewer leaves of the base
       tunnel need to discard traffic when a service tunnel's segment
       does not need to receive the traffic (yet it is receiving the traffic
       due to aggregation).
          </t>
          <t>Another advantage of the smaller region is smaller BIER [RFC8279]
       sub-domains. Bit Index
       Explicit Replication (BIER) subdomains <xref target="RFC8279" format="default"/>.
       With BIER, packets carry a BitString,
       in which the bits correspond to edge routers that needs need to receive
       traffic. Smaller sub-domains subdomains means that smaller BitStrings can be used
       without having to send multiple copies of the same packet.
          </t>
<!--
    <t>Finally, EVPN tunnel segmentation can be used for EVPN DCIs,
       as discussed in <xref target="dci"/>. It follows the same concepts
       discussed above.
    </t>
-->
    </section>
    </section>
      </section>
    <section title="Additional anchor="routes" numbered="true" toc="default">
      <name>Additional Route Types of EVPN NLRI" anchor="routes">
    <t>[RFC7432] NLRI</name>
      <t><xref target="RFC7432" format="default"/> defines the format of EVPN NLRI as the following:
    <figure>
	<artwork> follows:
      </t>
      <artwork name="" type="" align="left" alt=""><![CDATA[
                 +-----------------------------------+
                 |    Route Type (1 octet)           |
                 +-----------------------------------+
                 |     Length (1 octet)              |
                 +-----------------------------------+
                 | Route Type specific (variable)    |
                 +-----------------------------------+
	</artwork>
    </figure>
]]></artwork>
      <t>
        So far far, eight route types have been defined in [RFC7432], <xref target="I-D.ietf-bess-evpn-prefix-advertisement"/>, target="RFC7432" format="default"/>,
        <xref target="RFC9136" format="default"/>, and
        <xref target="I-D.ietf-bess-evpn-igmp-mld-proxy"/>:
    <figure>
	<artwork>
      + 1 - Ethernet Auto-Discovery (A-D) route
      + 2 - MAC/IP Advertisement route
      + 3 - Inclusive target="RFC9251" format="default"/>:
      </t>
<table anchor="tab-0">
  <name>Pre-existing Route Types</name>
  <thead>
    <tr>
      <th>Value</th>
      <th>Description</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>1</td>
      <td>Ethernet Auto-discovery</td>
    </tr>
    <tr>
      <td>2</td>
      <td>MAC/IP Advertisement</td>
    </tr>
    <tr>
      <td>3</td>
      <td>Inclusive Multicast Ethernet Tag route
      + 4 - Ethernet Segment route
      + 5 - IP Prefix Route
      + 6 - Selective Tag</td>
    </tr>
    <tr>
      <td>4</td>
      <td>Ethernet Segment</td>
    </tr>
    <tr>
      <td>5</td>
      <td>IP Prefix</td>
    </tr>
    <tr>
      <td>6</td>
      <td>Selective Multicast Ethernet Tag Route
      + 7 - Multicast Join Route</td>
    </tr>
    <tr>
      <td>7</td>
      <td>Multicast Membership Report Synch Route
      + 8 - Multicast Route</td>
    </tr>
    <tr>
      <td>8</td>
      <td>Multicast Leave Synch Route
	</artwork>
    </figure> Route</td>
    </tr>
  </tbody>
</table>

      <t>
        This document defines three additional route types:
    <figure>
	<artwork>
      + 9  - Per-Region I-PMSI A-D route
      + 10 - S-PMSI A-D route
      + 11 - Leaf A-D route
	</artwork>
    </figure>
      </t>
<table anchor="tab-0a">
  <name>New Route Types</name>
  <thead>
    <tr>
      <th>Value</th>
      <th>Description</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>9</td>
      <td>Per-Region I-PMSI A-D route</td>
    </tr>
    <tr>
      <td>10</td>
      <td>S-PMSI A-D route</td>
    </tr>
    <tr>
      <td>11</td>
      <td>Leaf A-D route</td>
    </tr>
  </tbody>
</table>
      <t>
        The "Route Type specific" field of the type Type 9 and type Type 10 EVPN NLRIs
        starts with a type Type 1 RD, RD (Route Distinguisher), whose Administrator sub-field MUST <bcp14>MUST</bcp14> match
        that of the RD in all current non-Leaf EVPN routes that are not Leaf A-D routes
        (<xref target="leaf"/>)
		EVPN target="leaf" format="default"/>), i.e., non-Leaf A-D routes
        from the same advertising router for a given EVI. EVPN instance (EVI).
      </t>
      <section title="Per-Region anchor="per-region" numbered="true" toc="default">
        <name>Per-Region I-PMSI A-D route" anchor="per-region"> Route</name>
        <t>The Per-region per-region I-PMSI A-D route has the following format. Its usage is
       discussed in <xref target="aggregation"/>.
    <figure>
	<artwork> target="aggregation" format="default"/>.
        </t>
        <artwork name="" type="" align="left" alt=""><![CDATA[
                +-----------------------------------+
                |       RD (8 octets)               |
                +-----------------------------------+
                |  Ethernet Tag ID (4 octets)       |
                +-----------------------------------+
                |  Region ID (8 octets)             |
                +-----------------------------------+
	</artwork>
    </figure>
]]></artwork>
        <t>
        The Region ID identifies the region and is encoded just as how in the same way that an
        Extended Community
        EC is encoded, as detailed in
        <xref target="aggregation"/>. target="aggregation" format="default"/>.
        </t>
      </section>
      <section title="S-PMSI numbered="true" toc="default">
        <name>S-PMSI A-D route"> Route</name>
        <t>The S-PMSI A-D route has the following format:
    <figure>
	<artwork>
        </t>
        <artwork name="" type="" align="left" alt=""><![CDATA[
                +-----------------------------------+
                |       RD (8 octets)               |
                +-----------------------------------+
                |  Ethernet Tag ID (4 octets)       |
                +-----------------------------------+
                | Multicast Source Length (1 octet) |
                +-----------------------------------+
                |  Multicast Source (Variable) (variable)      |
                +-----------------------------------+
                |  Multicast Group Length (1 octet) |
                +-----------------------------------+
                |  Multicast Group   (Variable) (variable)       |
                +-----------------------------------+
                |Originator's Addr Length (1 octet) |
                +-----------------------------------+
                |Originator's Addr (4 or 16 octets) |
                +-----------------------------------+
	</artwork>
    </figure>
]]></artwork>
        <t>
        Other than the addition of the Ethernet Tag ID and Originator's Addr
        Length,
        Length fields, it is identical
        to the S-PMSI A-D route as defined in [RFC7117]. <xref target="RFC7117" format="default"/>. The procedures specified
        in [RFC7117] <xref target="RFC7117" format="default"/> also apply (including wildcard functionality),
        except that the granularity level is per Ethernet Tag.
        </t>
      </section>
      <section title="Leaf anchor="leaf" numbered="true" toc="default">
        <name>Leaf A-D route" anchor="leaf"> Route</name>
        <t>The Route Type specific field of a Leaf A-D route consists of
       the following:
    <figure>
	<artwork>
        </t>
        <artwork name="" type="" align="left" alt=""><![CDATA[
                +-----------------------------------+
                |      Route Key (variable)         |
                +-----------------------------------+
                |Originator's Addr Length (1 octet) |
                +-----------------------------------+
                |Originator's Addr (4 or 16 octets) |
                +-----------------------------------+
	</artwork>
    </figure>
]]></artwork>
        <t>
        A Leaf A-D route is originated in response to a PMSI route,
        which could be an Inclusive Multicast Tag IMET A-D route, a per-region
        I-PMSI A-D route, an S-PMSI A-D route, or some other types of
        routes that may be defined in the future that triggers trigger Leaf A-D
        routes. The Route Key is the NLRI of the
        route for which this Leaf A-D route is generated.
        </t>
        <t>The general procedures of for Leaf A-D route are routes were first specified in
       [RFC6514]
       <xref target="RFC6514" format="default"/> for MVPN. MVPNs. The principles therein apply to VPLS VPLSs and EVPN EVPNs as well.
       [RFC7117] has
       <xref target="RFC7117" format="default"/> provides details for regarding VPLS Multicast, multicast, and this document points
       out some specifics for EVPN, e.g. EVPNs, e.g., in <xref target="inter-as"/>. target="inter-as" format="default"/>.
        </t>
      </section>
    </section>
    <section title="Selective Multicast"> numbered="true" toc="default">
      <name>Selective Multicast</name>
      <t><xref target="I-D.ietf-bess-evpn-igmp-mld-proxy"/> target="RFC9251" format="default"/> specifies
       procedures for EVPN selective forwarding of IP multicast traffic using SMET
       routes. It assumes that selective forwarding is always used with IR ingress replication
       for all flows (though the same signaling can also be used for an
	   ingress PE to find out learn the set of egress PEs for selective
	   forwarding with BIER).
	   An NVE
	   A Network Virtualization Edge (NVE) proxies the IGMP/MLD state ("MLD" stands for "Multicast Listener Discovery") that it learns on its
       ACs
       Attachment Circuits (ACs) to (C-S,C-G) or (C-*,C-G) SMET routes that advertises are advertised to other NVEs,
       and a receiving NVE converts the SMET routes back to IGMP/MLD messages
       and sends them out of its ACs. The receiving NVE also uses the SMET
       routes to identify which NVEs need to receive traffic for a particular
       (C-S,C-G) or (C-*,C-G) to achieve selective forwarding using IR ingress replication or
       BIER.
      </t>
      <t>With the above procedures, selective forwarding is done for all flows flows,
       and the SMET routes are advertised for all flows.
       It is possible that an operator may not want to track all those
       (C-S, C-G) or (C-*,C-G) state states on the NVEs, and the multicast traffic
       pattern allows inclusive forwarding for most flows while selective
       forwarding is needed only for a few high-rate flows. For that, that reason,
       or for tunnel types other than IR/BIER, ingress replication or BIER, S-PMSI/Leaf A-D procedures
       defined for Selective Multicast selective multicast for VPLS in [RFC7117] <xref target="RFC7117" format="default"/> are used. Other
       than the fact that different route types and formats are specified with an EVPN SAFI
       for S-PMSI A-D and Leaf A-D routes (<xref target="routes"/>), target="routes" format="default"/>), all
       procedures specified in [RFC7117] <xref target="RFC7117" format="default"/> with respect to Selective Multicast selective multicast apply to
       EVPN
       EVPNs as well, including wildcard procedures. In a nutshell, a source
       NVE advertises S-PMSI A-D routes to announce the tunnels used for
       certain flows, and receiving NVEs either join the announced PIM/mLDP
       tunnel or respond with Leaf A-D routes if the Leaf Information Required L
       flag is set in the S-PMSI A-D route's PTA (so that the source NVE can
       include them as tunnel leaves).
      </t>
      <t>An optimization to the [RFC7117] procedures provided in <xref target="RFC7117" format="default"/> may be applied.  Even if
   a source NVE sets the L flag to request Leaf A-D routes, an egress
   NVE MAY <bcp14>MAY</bcp14> omit the Leaf A-D route if it has already advertised a
   corresponding SMET route, and the source NVE MUST <bcp14>MUST</bcp14> use that in lieu of
   the Leaf A-D route.
      </t>
      <t>The optional optimizations specified for MVPN MVPNs in
       <xref target="RFC8534"/> target="RFC8534" format="default"/> are also applicable
       to EVPN EVPNs when the procedures for S-PMSI/Leaf A-D routes procedures are used for EVPN
       selective multicast forwarding.
      </t>
    </section>
    <section title="Inter-AS Segmentation" anchor="inter-as"> anchor="inter-as" numbered="true" toc="default">
      <name>Inter-AS Segmentation</name>
      <section title="Differences anchor="interaschanges" numbered="true" toc="default">
        <name>Differences from Section 7.2.2 of [RFC7117] When RFC 7117 when Applied to EVPN" anchor="interaschanges"> EVPNs</name>
        <t>The first paragraph of Section 7.2.2.2 of [RFC7117] <xref target="RFC7117" sectionFormat="of" section="7.2.2.2"/> says:
    <figure>
	<artwork>
   "...
        </t>
<blockquote>
   ... The best route procedures ensure that if multiple
   ASBRs, in an AS, receive the same Inter-AS A-D route from their EBGP
   neighbors, only one of these ASBRs propagates this route in Internal
   BGP (IBGP).  This ASBR becomes the root of the intra-AS segment of
   the inter-AS tree and ensures that this is the only ASBR that accepts
   traffic into this AS from the inter-AS tree."
	</artwork>
    </figure> tree.
</blockquote>
        <t>
       The above VPLS behavior requires complicated VPLS specific VPLS-specific procedures
       for the ASBRs to reach agreement. For EVPN, EVPNs, a different approach
       is used and used; the above quoted text from <xref target="RFC7117"/> is not applicable to EVPN. EVPNs.
        </t>
        <t>With the different approach for EVPN/MVPN, EVPNs/MVPNs, each ASBR will re-advertise
       its received Inter-AS A-D route to its IBGP peers and becomes the root
       of an intra-AS segment of the inter-AS tree. The intra-AS segment
       rooted at one ASBR is disjoint with from another intra-AS segment rooted
       at another ASBR. This is the same as the procedures for S-PMSI routes
       in [RFC7117] <xref target="RFC7117" format="default"/> itself.
        </t>
        <t>The following bullet in Section 7.2.2.2 of [RFC7117] <xref target="RFC7117" sectionFormat="of" section="7.2.2.2"/> does not apply
	to EVPN.
    <figure>
	<artwork>
     + If EVPNs.
        </t>
<blockquote>
       <ul><li>If the ASBR uses ingress replication to instantiate the intra-AS
       segment of the inter-AS tunnel, the re-advertised route MUST NOT <bcp14>MUST NOT</bcp14>
       carry the PMSI Tunnel attribute.
	</artwork>
    </figure>
    </t> attribute.</li></ul>
</blockquote>
        <t>The following bullet in Section 7.2.2.2 of [RFC7117]:
    <figure>
	<artwork>
     + <xref target="RFC7117" sectionFormat="of" section="7.2.2.2"/>:
        </t>
<blockquote><ul><li>
       If the ASBR uses a P-multicast tree to instantiate the intra-AS
       segment of the inter-AS tunnel, the PMSI Tunnel attribute MUST <bcp14>MUST</bcp14>
       contain the identity of the tree that is used to instantiate the
       segment (note that the ASBR could create the identity of the tree
       prior to the actual instantiation of the segment).  If, in order
       to instantiate the segment, the ASBR needs to know the leaves of
       the tree, then the ASBR obtains this information from the A-D
       routes received from other PEs/ASBRs in the ASBR's own AS.
	</artwork>
    </figure>
    </t> AS.</li></ul>
</blockquote>
        <t>is changed to the following when applied to EVPN:
    <figure>
	<artwork>
      "The PMSI Tunnel attribute MUST EVPNs:
        </t>
<blockquote><ul><li>
      The PTA <bcp14>MUST</bcp14> specify the tunnel for the segment.
      If and only if, in order to establish the tunnel, the ASBR needs to
      know the leaves of the tree, then the ASBR MUST <bcp14>MUST</bcp14> set the L flag to
      1 in the PTA to trigger Leaf A-D routes from egress PEs and
      downstream ASBRs. It MUST <bcp14>MUST</bcp14> be (auto-)configured with an import RT,
      which controls acceptance of leaf Leaf A-D routes by the ASBR."
	</artwork>
    </figure>
     </t> ASBR.</li></ul>
</blockquote>
        <t>Accordingly, the following paragraph in Section 7.2.2.4 of [RFC7117]:
    <figure>
	<artwork>
   "If <xref target="RFC7117" sectionFormat="of" section="7.2.2.4"/>:
        </t>
<blockquote>
   If the received Inter-AS A-D route carries the PMSI Tunnel attribute
   with the Tunnel Identifier set to RSVP-TE P2MP LSP, then the ASBR
   that originated the route MUST <bcp14>MUST</bcp14> establish an RSVP-TE P2MP LSP with the
   local PE/ASBR as a leaf.  This LSP MAY <bcp14>MAY</bcp14> have been established before
   the local PE/ASBR receives the route, or it MAY <bcp14>MAY</bcp14> be established after
   the local PE receives the route."
	</artwork>
    </figure> route.
</blockquote>
        <t>
        is changed to the following when applied to EVPN: EVPNs:
        </t>
     <t>
   "If
<blockquote>
 If the received Inter-AS A-D route has the L flag set in its PTA,
 then a receiving PE MUST <bcp14>MUST</bcp14> originate a corresponding Leaf A-D route, while
   a route.
 A receiving ASBR MUST <bcp14>MUST</bcp14> originate a corresponding Leaf A-D
 route if and only if one of the following conditions is met:
 (1) it received and imported one or more corresponding Leaf A-D
 routes from its downstream IBGP or EBGP peers, peers or (2) it has
 non-null downstream forwarding state for the PIM/mLDP tunnel that
 instantiates its downstream intra-AS segment. The targeted ASBR for the Leaf A-D
 route, which (re-)advertised the Inter-AS A-D route, MUST <bcp14>MUST</bcp14> establish a tunnel to the
 leaves discovered by the Leaf A-D routes."
    </t> routes.
</blockquote>
      </section>
      <section title="I-PMSI anchor="leaf-tracking" numbered="true" toc="default">
        <name>I-PMSI Leaf Tracking"
             anchor="leaf-tracking"> Tracking</name>
        <t>An ingress PE does not set the L flag in its Inclusive Multicast
       Ethernet Tag (IMET) IMET A-D route's PTA,
       even with Ingress Replication tunnels or RSVP-TE P2MP tunnels.
       It does not rely on the Leaf A-D routes to discover leaves in
       its AS, and Section 11.2 of [RFC7432] <xref target="RFC7432" sectionFormat="of" section="11.2"/> explicitly states that the L
       flag must be set to zero. 0.
        </t>
        <t>An implementation of [RFC7432] <xref target="RFC7432" format="default"/> might have used the Originating
       Router's IP Address field of the IMET A-D
       routes to determine the leaves, leaves or might have used the Next Hop field
       instead. Within the same AS, both will lead to the same result.
        </t>
        <t>With segmentation, an ingress PE MUST <bcp14>MUST</bcp14> determine the leaves
       in its AS from the BGP next hops in all its received IMET A-D
       routes, so it does not have to set the L flag set to request Leaf A-D
       routes. PEs within the same AS will all have different next hops
       in their IMET A-D routes (hence (and hence will all be considered as leaves),
       and PEs from other ASes will have the next hop in their IMET A-D
       routes set to addresses of ASBRs in this local AS, hence AS; hence, only those
       ASBRs will be considered as leaves (as proxies for those PEs in other
       ASes). Note that in the case of Ingress Replication, ingress replication, when an ASBR
       re-advertises IMET A-D routes to IBGP peers, it MUST <bcp14>MUST</bcp14> advertise the
       same label for all those routes for the same Ethernet Tag ID and the same
       EVI. Otherwise, duplicated copies will be sent by the ingress PE
	   and received by egress PEs in other regions. For the same reason,
	   when an ingress PE builds its flooding list, if multiple routes
	   have the same (nexthop, label) tuple tuple, they MUST <bcp14>MUST</bcp14> only be
	   added as a single branch in the flooding list.
        </t>
      </section>
      <section title="Backward Compatibility" anchor="compatibility"> anchor="compatibility" numbered="true" toc="default">
        <name>Backward Compatibility</name>
        <t>The above procedures assume that all PEs are upgraded to support
       the segmentation procedures:
       <list style="symbols">
          <t>An
        </t>
        <ul spacing="normal">
          <li>An ingress PE uses the Next Hop and not the Originating
             Router's IP Address to determine leaves for the I-PMSI tunnel.
          </t>
          <t>An
          </li>
          <li>An egress PE sends Leaf A-D routes in response to I-PMSI routes,
             if the PTA has the L flag set by the re-advertising ASBR.
          </t>
          <t>In
          </li>
          <li>In the case of Ingress Replication, ingress replication, when an ingress PE builds
   its flooding list, multiple I-PMSI routes may have the same (nexthop, label)
   tuple
   tuple, and only a single branch for those routes will be added in the flooding
   list.
          </t>
       </list>
    </t>
          </li>
        </ul>
        <t>If a deployment has legacy PEs that does do not support the above,
       then a legacy ingress PE would include all PEs (including those
       in remote ASes) as leaves of the inclusive tunnel and try to send
       traffic to them directly (no segmentation), which is either undesired undesirable
       or not possible; impossible; a legacy egress PE would not send Leaf A-D routes
       so the ASBRs would not know to send external traffic to them.
        </t>
        <t>If this backward compatibility backward-compatibility problem needs to be addressed, the
	following procedure MUST <bcp14>MUST</bcp14> be used (see <xref target="aggregation"/> target="aggregation" format="default"/>
	for per-PE/AS/region I-PMSI A-D routes):
       <list style="symbols">
          <t>An
        </t>
        <ul spacing="normal">
          <li>An upgraded PE indicates in its per-PE I-PMSI A-D
             route that it supports the new procedures. This is done
             by setting a flag bit in the EVPN Multicast Flags Extended
             Community.
          </t>
          <t>All
          </li>
          <li>All per-PE I-PMSI A-D routes are restricted to the local AS
             and not propagated to external peers.
          </t>
          <t>The
          </li>
          <li>The ASBRs in an AS originate per-region I-PMSI A-D routes
             and advertise them to their external peers to specify tunnels
             used to carry traffic from the local AS to other ASes.
             Depending on the types of tunnels being used, the L flag
             in the PTA may be set, in which case the downstream ASBRs
             and upgraded PEs will send Leaf A-D routes to pull traffic
             from their upstream ASBRs. In a particular downstream AS,
             one of the ASBRs is elected, based on the per-region
             I-PMSI A-D routes for a particular source AS,
             to send traffic from that source AS to legacy PEs in the
             downstream AS.
             The traffic arrives at the elected ASBR on the tunnel
             announced in the best per-region I-PMSI A-D route for the source
             AS, that as selected by the ASBR has selected of from all those the routes that it received
             over EBGP or IBGP sessions. The election procedure is described in
             <xref target="election"/>.
          </t>
          <t>In target="election" format="default"/>.
          </li>
          <li>In an ingress/upstream AS, if and only if an ASBR has active downstream
             receivers (PEs and ASBRs), which are learned either explicitly
             via Leaf A-D routes or implicitly via PIM join Join or mLDP label
             mapping, the ASBR originates a per-PE I-PMSI A-D route (i.e., a
             regular Inclusive Multicast Ethernet Tag IMET route) into the local
             AS,
             AS and stitches incoming per-PE I-PMSI tunnels into its
             per-region I-PMSI tunnel. With this, Via this process, it gets traffic from
             local PEs and send sends the traffic to other ASes via the tunnel announced in
             its per-region I-PMSI A-D route.
          </t>
       </list>
    </t>
          </li>
        </ul>
        <t>Note that, that even if there is are no backward compatibility issue, backward-compatibility issues, the use of
       per-region I-PMSI has A-D routes provides the benefit of keeping all per-PE I-PMSI A-D routes
       in their local ASes, greatly reducing the flooding of the routes and
       their corresponding Leaf A-D routes (when needed), needed) and reducing the number of
       inter-as
       inter-AS tunnels.
        </t>
        <section title="Designated anchor="election" numbered="true" toc="default">
          <name>Designated ASBR Election" anchor="election"> Election</name>
          <t>When an ASBR re-advertises a per-region I-PMSI A-D route into an AS
       in which a designated ASBR needs to be used to forward traffic
       to the legacy PEs in the AS, it MUST <bcp14>MUST</bcp14> include a DF Designated Forwarder (DF) Election EC.
       The EC and its use is are specified in <xref target="RFC8584"/>. target="RFC8584" format="default"/>.
       The AC-DF bit in the DF Election EC MUST <bcp14>MUST</bcp14> be cleared.
       If it is known that no legacy PEs exist in the AS, the ASBR MUST NOT <bcp14>MUST NOT</bcp14>
       include the EC and MUST <bcp14>MUST</bcp14> remove the DF Election EC if one is carried in
       the per-region I-PMSI A-D routes that it receives. Note that this is done
       for each set of per-region I-PMSI A-D routes with the same NLRI.
          </t>
          <t>Based on the procedures specified in
       <xref target="RFC8584"/>, target="RFC8584" format="default"/>, an election
       algorithm is determined according to the DF Election ECs carried in
       the set of per-region I-PMSI routes of the same NLRI re-adverised re-advertised into the AS.
       The algorithm is then applied to a candidate list, which is the set of
       ASBRs that re-advertised the per-region I-PMSI routes of the same NLRI
       carrying the DF Election EC.
          </t>
        </section>
      </section>
    </section>
    <section title="Inter-Region Segmentation" anchor="inter-region"> anchor="inter-region" numbered="true" toc="default">
      <name>Inter-Region Segmentation</name>
      <section title="Area/AS anchor="region" numbered="true" toc="default">
        <name>Area/AS vs. Region" anchor="region">
    <t>[RFC7524] is for Region</name>
        <t><xref target="RFC7524" format="default"/> addresses MVPN/VPLS inter-area segmentation and does not explicitly cover
       EVPN.
       EVPNs. However, if "area" is replaced by "region" and "ABR" is replaced
       by "RBR" (Regional Border Router) Router), then everything still works, works and
       can be applied to EVPN EVPNs as well.
        </t>
        <t>A region can be a sub-area, or it can be an entire AS AS, including its
       external links. Instead of automatic automatically defining a region definition based on
       IGP areas, a region would be defined as a BGP peer group. In fact,
       even with IGP area based a region definition, definition based on an IGP area, a BGP peer group
       listing the PEs and ABRs in an area is still needed.
        </t>
        <t>Consider the following example diagram for inter-as inter-AS segmentation:
    <figure>
	<artwork>
        </t>
        <artwork name="" type="" align="left" alt=""><![CDATA[
          ---------           ------             ---------
         /         \         /      \           /         \
        /           \       /        \         /           \
       | PE1 o    ASBR1 -- ASBR2    ASBR3 -- ASBR4    o PE2 |
        \           /       \        /         \           /
         \         /         \      /           \         /
          ---------           ------             ---------
          AS 100              AS 200              AS 300
       |-----------|--------|---------|--------|------------|
          segment1  segment2 segment3  segment4  segment5
	</artwork>
    </figure>
]]></artwork>
        <t>
       The inter-as inter-AS segmentation procedures specified so far ([RFC6513] [RFC6514],
       [RFC7117], (<xref target="RFC6513" format="default"/>, <xref target="RFC6514" format="default"/>,
       <xref target="RFC7117" format="default"/>, and <xref target="inter-as"/> target="inter-as" format="default"/> of this document) require all
       ASBRs to be involved, and Ingress Replication ingress replication is used between two ASBRs
       in different ASes.
        </t>
        <t>
       In the above diagram, it's possible that ASBR1/4 does not support
       segmentation, and the provider tunnels in AS 100/300 can actually
       extend across the external link. In this case, the inter-region
       segmentation procedures can be used instead - -- a region is the
       entire (AS100 + AS100 plus the ASBR1-ASBR2 link) link or (AS300 + the entire AS300 plus the
       ASBR3-ASBR4 link). link.
       ASBR2/3 would be the RBRs, and ASBR1/4 will just be a transit core
       router with respect to provider tunnels.
        </t>
        <t>As illustrated in the diagram below, ASBR2/3 will establish a multihop
       EBGP session with session, either with a RR Route Reflector (RR) or directly with PEs in the neighboring
       AS. I/S-PMSI A-D routes from ingress PEs will not be processed by
       ASBR1/4. When ASBR2 re-advertises the routes into AS 200, it changes
       the next hop to its own address and changes its PTA to specify the tunnel
       type/identification in its own AS. When ASBR3 re-advertises
       I/S-PMSI A-D routes into the neighboring AS 300, it changes the
       next hop to its own address and changes its PTA to specify the tunnel
       type/identification in the neighboring region. Now Now, the segment is
       rooted at ASBR3 and extends across the external link to PEs.
    <figure>
	<artwork>
        </t>
        <artwork name="" type="" align="left" alt=""><![CDATA[
          ---------           ------             ---------
         /   RR....\.mh-ebpg /      \    mh-ebgp/....RR   \
        /    :      \    `. /        \ .'      /      :    \
       | PE1 o    ASBR1 -- ASBR2    ASBR3 -- ASBR4    o PE2 |
        \           /       \        /         \           /
         \         /         \      /           \         /
          ---------           ------             ---------
          AS 100              AS 200              AS 300
       |-------------------|----------|---------------------|
          segment 1          segment 2         segment 3
	</artwork>
    </figure>
    </t>
]]></artwork>
      </section>
      <section title="Per-region Aggregation" anchor="aggregation"> anchor="aggregation" numbered="true" toc="default">
        <name>Per-Region Aggregation</name>
        <t>Notice that every I/S-PMSI route from each PE will be propagated
       throughout all the ASes or regions. They may also trigger corresponding
       Leaf A-D routes routes, depending on the types of tunnels used in each region.
       This may become result in too many - routes and corresponding tunnels. To address
       this concern, the I-PMSI routes from all PEs in a an AS/region can be
       aggregated into a single I-PMSI route originated from the RBRs,
       and traffic from all those individual I-PMSI tunnels
       will be switched into the single I-PMSI tunnel. This is like the
       MVPN Inter-AS I-PMSI route originated by ASBRs.
        </t>
        <t>The MVPN Inter-AS I-PMSI A-D route can be better called as per-AS a "per-AS I-PMSI
       A-D route, route", to be compared against the (per-PE) Intra-AS I-PMSI A-D routes
       originated by each PE. In this document document, we will call it as per-region a "per-region
       I-PMSI A-D route, route" in case cases where we want to apply the aggregation at the regional
       level. The per-PE I-PMSI routes will not be propagated to other
       regions. If multiple RBRs are connected to a region, then each
       will advertise such a route, with the same Region ID and Ethernet Tag ID (<xref target=
       "per-region"/>). target="per-region" format="default"/>). Similar to the per-PE I-PMSI A-D
       routes, RBRs/PEs in a downstream region will each select a the best one route
       from all those re-advertised by the upstream RBRs, RBRs and hence will only
       receive traffic injected by one of them.
        </t>
    <t>MVPN does
        <t>MVPNs do not aggregate S-PMSI routes from all PEs in an AS like it
       does they
       do for I-PMSIs I-PMSI routes, because the number of PEs that will advertise
       S-PMSI routes for the same (s,g) (S,G) or (*,g) (*,G) is small. This is also the
       case for EVPN, EVPNs, i.e., there is are no per-region S-PMSI routes.
        </t>
        <t>Notice that per-region I-PMSI routes can also be used to address
       backwards compatibility issue,
       backward-compatibility issues, as discussed in
       <xref target="compatibility"/>. target="compatibility" format="default"/>.
        </t>
        <t>The Region ID in the per-region I-PMSI route's NLRI is encoded like an
       EC. For example, the
       Region ID can encode an AS number or area ID in the following EC format:
       <list style="symbols">
          <t>For
        </t>
        <ul spacing="normal">
          <li>For a two-octet AS number, a Transitive Two-Octet AS-Specific AS-specific
             EC of sub-type 0x09 (Source AS), with the Global Administrator
             sub-field set to the AS number and the Local Administrator
             sub-field set to 0.
          </t>
          <t>For
          </li>
          <li>For a four-octet AS number, a Transitive Four-Octet AS-Specific AS-specific
             EC of sub-type 0x09 (Source AS), with the Global Administrator
             sub-field set to the AS number and the Local Administrator
             sub-field set to 0.
          </t>
          <t>For
          </li>
          <li>For an area ID, a Transitive IPv4-Address-Specific IPv4-Address-specific EC of any
             sub-type, with the Global Administrator
             sub-field set to the area ID and the Local Administrator
             sub-field set to 0.
          </t>
       </list>
       Uses
          </li>
        </ul>
        <t>
       The use of other EC encoding MAY encodings <bcp14>MAY</bcp14> be allowed as long as it they uniquely
       identifies
       identify the region and the RBRs for the same region uses use the
       same Region ID.
        </t>
      </section>
      <section title="Use numbered="true" toc="default">
        <name>Use of S-NH-EC">
    <t>[RFC7524] S-NH-EC</name>
        <t><xref target="RFC7524" format="default"/> specifies the use of the S-NH-EC because it does not allow ABRs
       to change the BGP next hop when they re-advertise I/S-PMSI A-D routes
       to downstream areas. That behavior is only to be consistent with the MVPN
       Inter-AS I-PMSI A-D routes, whose next hop must not be changed
       when they're re-advertised by the segmenting ABRs for reasons specific
       to MVPN. MVPNs. For EVPN, EVPNs,
       it is perfectly fine to change the next hop when RBRs re-advertise
       the I/S-PMSI A-D routes, instead of relying on the S-NH-EC. As a result,
       this document specifies that RBRs change the BGP next hop when they
       re-advertise I/S-PMSI A-D routes and do not use the S-NH-EC.
       The This provides
       the advantage of this is that neither ingress PEs nor egress PEs need to
       understand/use the S-NH-EC, and a consistent procedure (based on BGP next
       hop)
       hops) is used for both inter-as inter-AS and inter-region segmentation.
        </t>
        <t>
	If a downstream PE/RBR needs to originate Leaf A-D routes, it constructs
       an IP-based Route Target Extended Community by
      placing the IP address carried in the Next Hop of the received
      I/S-PMSI A-D route in the Global Administrator field of the
      Community, extended
      community, with the Local Administrator field of this Community extended community
      set to 0 0, and also setting the Extended Communities attribute of the
      Leaf A-D route to that Community. extended community.
        </t>
        <t>Similar to [RFC7524], <xref target="RFC7524" format="default"/>, the upstream RBR MUST <bcp14>MUST</bcp14> (auto-)configure
	a
	an RT with the Global Administrator field set to the Next Hop in
	the re-advertised I/S-PMSI A-D route and with the Local Administrator
	field set to 0. With this, Using this technique, the mechanisms specified in [RFC4684] <xref target="RFC4684" format="default"/>
	for constrained BGP route
   distribution can be used along with this specification to ensure that
   only the needed PE/ABR will have to process a said particular Leaf A-D route.
        </t>
      </section>
      <section title="Ingress numbered="true" toc="default">
        <name>Ingress PE's I-PMSI Leaf Tracking">
    <t>[RFC7524] Tracking</name>
        <t><xref target="RFC7524" format="default"/> specifies that when an ingress PE/ASBR (re-)advertises an a
       VPLS I-PMSI A-D route, it sets the L flag to 1 in the route's PTA.
       Similar to the inter-as inter-AS case, this is actually not really needed
       for EVPN. EVPNs. To be consistent with the inter-as inter-AS case, the ingress PE
       does not set the L flag in its originated I-PMSI A-D routes,
       and it determines the leaves based on the BGP next hops in its received
       I-PMSI A-D routes, as specified in <xref target="leaf-tracking"/>. target="leaf-tracking" format="default"/>.
        </t>
        <t>The same backward compatibility backward-compatibility issue exists, and the same solution
       as in that for the inter-as inter-AS case applies, as specified in <xref target=
       "compatibility"/>. target="compatibility" format="default"/>.
        </t>
      </section>
    </section>
    <section title="Multi-homing Support">
<!--
    <t>EVPN support active-active multi-homing. For BUM traffic, only an
       elected DF PE is allowed to send to a multi-homed Ethernet Segment (ES),
       while a TS may use any of its active-active links to the ES. If the
       link a TS uses is not attached to the DF PE, the receiving non-DF PE
       will deliver the traffic to all PEs in the same EVI, including the DF PE
       for the sourcing ES. To prevent the DF PE from delivering the received
       traffic back to the ES, in case of MPLS encapsulation, a BUM packet
       from a non-DF PE carries an ESI
       label, so that when the DF receives the packet it will know from the ESI
       label that the packet is from a non-DF for an ES and will not send the
       packet back to the ES.
    </t>
--> numbered="true" toc="default">
      <name>Multihoming Support</name>
	<t>To support multi-homing multihoming with segmentation, ESI Ethernet Segment Identifier (ESI) labels SHOULD <bcp14>SHOULD</bcp14> be
	allocated from a "Domain-wide Common Block" (DCB)
	<xref target="I-D.ietf-bess-mvpn-evpn-aggregation-label"/> target="RFC9573" format="default"/> for all
	tunnel types types, including Ingress Replication. Replication tunnels <xref target="RFC7988"/>.
	Via means outside the scope of this document, PEs know that ESI labels
	are from DCB a DCB, and then existing multi-homing multihoming procedures will then work as is "as is"
	(whether a multi-homed multihomed Ethernet Segment spans across segmentation
	regions or not).
      </t>
      <t>Not using DCB-allocated ESI labels is outside the scope of this
	document.<!-- It would require complicated forwarding
	procedures on segmentation points, and, in case of multi-homing across
	segmentation regions, complicated control plane procedures as well.-->
	document.
      </t>
    </section>
    <section anchor="IANA" title="IANA Considerations"> numbered="true" toc="default">
      <name>IANA Considerations</name>
      <t>IANA has temporarily assigned the following new EVPN route types in
	  the EVPN "EVPN Route Types Types" registry:
    <list style="symbols">
    <t>9  - Per-Region I-PMSI A-D route</t>
    <t>10 - S-PMSI A-D route</t>
    <t>11 - Leaf A-D route</t>
    </list>
      </t>
      <t>This document requests IANA to assign

<table anchor="tab-1">
<name>New Route Types</name>
  <thead>
    <tr>
      <th>Value</th>
      <th>Description</th>
      <th>Reference</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>9</td>
      <td>Per-Region I-PMSI A-D route</td>
      <td>RFC 9572</td>
    </tr>
    <tr>
      <td>10</td>
      <td>S-PMSI A-D route</td>
      <td>RFC 9572</td>
    </tr>
    <tr>
      <td>11</td>
      <td>Leaf A-D route</td>
      <td>RFC 9572</td>
    </tr>
  </tbody>
</table>
      <t>IANA has assigned one flag bit from the
         EVPN Multicast
         "Multicast Flags Extended Community Flags Community" registry to be created in
         [draft-ietf-bess-evpn-igmp-mld-proxy]:
    <list style="symbols">
    <t>Bit-S - Segmentation Procedure Support
    </t>
    </list> by
         <xref target="RFC9251"/>:
      </t>
<table anchor="tab-2">
<name>New Multicast Flag</name>
  <thead>
    <tr>
      <th>Bit</th>
      <th>Name</th>
      <th>Reference</th>
      <th>Change Controller</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>8</td>
      <td>Segmentation Support</td>
      <td>RFC 9572</td>
      <td>IETF</td>
    </tr>
  </tbody>
</table>
    </section>
    <section anchor="Security" title="Security Considerations"> numbered="true" toc="default">
      <name>Security Considerations</name>
      <t>
	  The Selective Forwarding procedures specified in this document for selective forwarding via S-PMSI/Leaf A-D routes
	  in this document
	  are based on the same procedures as those used for MVPN [RFC6513] [RFC6514] MVPNs <xref target="RFC6513" format="default"/> <xref target="RFC6514" format="default"/>
	  and VPLS Multicast [RFC7117]. multicast <xref target="RFC7117" format="default"/>. The procedures for tunnel segmentation procedures as specified
	  in this document are based on the similar procedures used for MVPN inter-AS
	  [RFC6514] tunnel segmentation <xref target="RFC6514" format="default"/> and inter-area [RFC7524] tunnel segmentation, and segmentation <xref target="RFC7524" format="default"/>, as well as procedures
	  for VPLS Multicast [RFC7117] inter-as multicast inter-AS tunnel segmentation. segmentation <xref target="RFC7117" format="default"/>.
    When applied to EVPN, EVPNs, they do not introduce new security concerns
    besides what have been
    beyond those discussed in [RFC6513], [RFC6514], [RFC7117], <xref target="RFC6513" format="default"/>, <xref target="RFC6514" format="default"/>, <xref target="RFC7117" format="default"/>,
    and [RFC7524]. <xref target="RFC7524" format="default"/>. They also do not introduce new security concerns
    compared to [RFC7432]. <xref target="RFC7432" format="default"/>.
      </t>
    </section>
  </middle>
  <back>
    <references>
      <name>References</name>
      <references>
        <name>Normative References</name>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.2119.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8174.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7432.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7117.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7524.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8584.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8534.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6513.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6514.xml"/>

<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9251.xml"/>

<!-- draft-ietf-bess-mvpn-evpn-aggregation-label (RFC 9573) -->
<reference anchor='RFC9573' target="https://www.rfc-editor.org/info/rfc9573">
<front>
<title>MVPN/EVPN Tunnel Aggregation with Common Labels</title>
<author initials='Z' surname='Zhang' fullname='Zhaohui Zhang'>
<organization />
</author>
<author initials='E' surname='Rosen' fullname='Eric Rosen'>
<organization />
</author>
<author initials='W' surname='Lin' fullname='Wen Lin'>
<organization />
</author>
<author initials='Z' surname='Li' fullname='Zhenbin Li'>
<organization />
</author>
<author initials='IJ' surname='Wijnands' fullname='IJsbrand Wijnands'>
<organization />
</author>
<date year='2024' month='May' />
</front>
<seriesInfo name="RFC" value="9573"/>
<seriesInfo name="DOI" value="10.17487/RFC9573"/>
</reference>

      </references>
      <references>
        <name>Informative References</name>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8279.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.4875.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.4684.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6388.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7988.xml"/>

        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9136.xml"/>
      </references>
    </references>

    <section anchor="Acknowledgements" title="Acknowledgements"> numbered="false" toc="default">
      <name>Acknowledgements</name>
      <t>The authors thank Eric Rosen, John Drake, and Ron Bonica <contact fullname="Eric Rosen"/>, <contact fullname="John Drake"/>, and <contact fullname="Ron Bonica"/> for their
         comments and suggestions.
      </t>
    </section>
    <section title="Contributors"> numbered="false" toc="default">
      <name>Contributors</name>
      <t>The following people also contributed to this document through their earlier
       work in EVPN selective multicast.
    <figure>
	<artwork>
Junlin Zhang
Huawei Technologies
Huawei
      </t>
<contact fullname="Junlin Zhang">
  <organization>Huawei Technologies</organization>
  <address>
    <postal>
      <street>Huawei Bld., No.156 No. 156 Beiqing Rd.
Beijing  100095
China

Email: jackey.zhang@huawei.com

Zhenbin Li
Huawei Technologies
Huawei Rd.</street>
      <city>Beijing</city>
      <code>100095</code>
      <country>China</country>
    </postal>
    <email>jackey.zhang@huawei.com</email>
  </address>
</contact>

<contact fullname="Zhenbin Li">
  <organization>Huawei Technologies</organization>
  <address>
    <postal>
      <street>Huawei Bld., No.156 No. 156 Beiqing Rd.
Beijing  100095
China

Email: lizhenbin@huawei.com
	</artwork>
    </figure>
    </t> Rd.</street>
      <city>Beijing</city>
      <code>100095</code>
      <country>China</country>
    </postal>
    <email>lizhenbin@huawei.com</email>
  </address>
</contact>
    </section>
  </middle>

  <back>
    <references title="Normative References">
	  &RFC2119;
	  &RFC8174;
      &RFC7432;
      &RFC7117;
      &RFC7524;
      &RFC8584;
      &RFC8534;
      &RFC6513;
      &RFC6514;
      <?rfc include='reference.I-D.ietf-bess-evpn-igmp-mld-proxy'?>
      <?rfc include='reference.I-D.ietf-bess-mvpn-evpn-aggregation-label'?>
    </references>

    <references title="Informative References">
      &RFC8279;
      &RFC4875;
      &RFC4684;
      &RFC6388;
      &RFC7988;
      <?rfc include='reference.I-D.ietf-bess-evpn-prefix-advertisement'?>
    </references>
  </back>
</rfc>