L2VPN Workgroup                                              Ali Sajassi
INTERNET-DRAFT                                               Samer Salam
Intended Status: Standards Track                            Sami Boutros
                                                                   Cisco
Wim Henderickx
Jorge Rabadan                                                 Jim Uttaro
Alcatel-Lucent                                                      AT&T

John Drake                                                  Aldrin Isaac
Wen Lin                                                        Bloomberg
Juniper

Expires: December 10, 18, 2015                                 June 10, 18, 2015

                   E-TREE Support in EVPN & PBB-EVPN
                     draft-ietf-bess-evpn-etree-00
                     draft-ietf-bess-evpn-etree-01

Abstract

   The Metro Ethernet Forum (MEF) has defined a rooted-multipoint
   Ethernet service known as Ethernet Tree (E-Tree).  [ETREE-FMWK]
   proposes a solution framework for supporting this service in MPLS
   networks. This document discusses how those functional requirements
   can be easily met with (PBB-)EVPN and how (PBB-)EVPN offers a more
   efficient implementation of these functions.

Status of this Memo

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Copyright and License Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors. All rights reserved.

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   described in the Simplified BSD License.

Table of Contents

   1  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  3  4
     1.1  Terminology . . . . . . . . . . . . . . . . . . . . . . . .  3  4
   2  E-Tree Scenarios and EVPN / PBB-EVPN Support  . . . . . . . . .  3  4
     2.1 Scenario 1: Leaf OR Root site(s) per PE  . . . . . . . . . .  3  4
     2.2 Scenario 2: Leaf AND Root site(s) per PE . . . . . . . . . .  4  5
     2.3 Scenario 3: Leaf AND Root site(s) per Ethernet Segment . . .  4  5
   3 Operation for EVPN . . . . . . . . . . . . . . . . . . . . . . .  5  6
     3.1 Known Unicast Traffic  . . . . . . . . . . . . . . . . . . .  5  7
     3.2 BUM Traffic  . . . . . . . . . . . . . . . . . . . . . . . .  6  7
       3.2.1 BUM Traffic supported by P2MP Tunnels  . . . . . . . . .  7
       3.2.1 BUM Traffic supported by Ingress Replication . . . . . .  9
     3.3 E-TREE Traffic Flows for EVPN  . . . . . . . . . . . . . . .  8 10
       3.3.1 E-Tree with MAC Learning . . . . . . . . . . . . . . . .  8 11
       3.3.2 E-Tree without MAC Learning  . . . . . . . . . . . . . .  9 11
   4 Operation for PBB-EVPN . . . . . . . . . . . . . . . . . . . . .  9 12
     4.1 Known Unicast Traffic  . . . . . . . . . . . . . . . . . . .  9 12
     4.2 BUM Traffic  . . . . . . . . . . . . . . . . . . . . . . . . 10 13
   5  Acknowledgement BGP Encoding . . . . . . . . . . . . . . . . . . . . . . . . 10 . . 13
     5.1 E-TREE Extended Community  . . . . . . . . . . . . . . . . . 13
   6  Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . 14
   7  Security Considerations . . . . . . . . . . . . . . . . . . . . 10
   7 14
   8  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 10
   8 14
   9  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     8.1 14
     9.1  Normative References  . . . . . . . . . . . . . . . . . . . 10
     8.2 14
     9.2  Informative References  . . . . . . . . . . . . . . . . . . 11 14
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11 15

1  Introduction

   The Metro Ethernet Forum (MEF) has defined a rooted-multipoint
   Ethernet service known as Ethernet Tree (E-Tree). In an E-Tree
   service, endpoints are labeled as either Root or Leaf sites. Root
   sites can communicate with all other sites. Leaf sites can
   communicate with Root sites but not with other Leaf sites.

   [ETREE-FMWK] proposes the solution framework for supporting E-Tree
   service in MPLS networks. The document identifies the functional
   components of the overall solution to emulate E-Tree services in
   addition to Ethernet LAN (E-LAN) services on an existing MPLS
   network.

   [EVPN] is a solution for multipoint L2VPN services, with advanced
   multi-homing capabilities, using BGP for distributing customer/client
   MAC address reach-ability information over the MPLS/IP network. [PBB-
   EVPN] combines the functionality of EVPN with [802.1ah] Provider
   Backbone Bridging for MAC address scalability.

   This document discusses how the functional requirements for E-Tree
   service can be easily met with (PBB-)EVPN and how (PBB-)EVPN offers a
   more efficient implementation of these functions.

1.1  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [KEYWORDS].

2  E-Tree Scenarios and EVPN / PBB-EVPN Support

   In this section, we will categorize support for E-Tree into three
   different scenarios, depending on the nature of the site association
   (Root/Leaf) per PE or per Ethernet Segment:

   - Leaf OR Root site(s) per PE

   - Leaf AND Root site(s) per PE

   - Leaf AND Root site(s) per Ethernet Segment

2.1 Scenario 1: Leaf OR Root site(s) per PE

   In this scenario, a PE may have Root sites OR Leaf sites for a given
   VPN instance, but not both concurrently. The PE may have both Root
   and Leaf sites albeit for different VPNs. Every Ethernet Segment
   connected to the PE is uniquely identified as either a Root or a Leaf
   site.

                     +---------+            +---------+
                     |   PE1   |            |   PE2   |
    +---+            |  +---+  |  +------+  |  +---+  |            +---+
    |CE1+-----ES1----+--+   |  |  | MPLS |  |  |   +--+----ES2-----+CE2|
    +---+    (Root)  |  | E |  |  |  /IP |  |  | E |  |   (Leaf)   +---+
                     |  | V |  |  |      |  |  | V |  |
                     |  | I |  |  |      |  |  | I |  |            +---+
                     |  |   |  |  |      |  |  |   +--+----ES3-----+CE3|
                     |  +---+  |  +------+  |  +---+  |   (Leaf)   +---+
                     +---------+            +---------+

   Figure 1: Scenario 1

2.2 Scenario 2: Leaf AND Root site(s) per PE

   In this scenario, a PE may have a set of one or more Root sites AND a
   set of one or more Leaf sites for a given VPN instance. Every
   Ethernet Segment connected to the PE is uniquely identified as either
   a Root or a Leaf site.

                     +---------+            +---------+
                     |   PE1   |            |   PE2   |
    +---+            |  +---+  |  +------+  |  +---+  |            +---+
    |CE1+-----ES1----+--+   |  |  |      |  |  |   +--+----ES2-----+CE2|
    +---+    (Leaf)  |  | E |  |  | MPLS |  |  | E |  |   (Leaf)   +---+
                     |  | V |  |  |  /IP |  |  | V |  |
                     |  | I |  |  |      |  |  | I |  |            +---+
                     |  |   |  |  |      |  |  |   +--+----ES3-----+CE3|
                     |  +---+  |  +------+  |  +---+  |   (Root)   +---+
                     +---------+            +---------+

   Figure 2: Scenario 2

2.3 Scenario 3: Leaf AND Root site(s) per Ethernet Segment

   In this scenario, a PE may have a set of one or more Root sites AND a
   set of one or more Leaf sites for a given VPN instance. An Ethernet
   Segment connected to the PE may be identified as both a Root and a
   Leaf site concurrently.

                     +---------+            +---------+
                     |   PE1   |            |   PE2   |
    +---+            |  +---+  |  +------+  |  +---+  |            +---+
    |CE1+-----ES1----+--+   |  |  |      |  |  |   +--+----ES2-----+CE2|
    +---+ (Leaf/Root)|  | E |  |  | MPLS |  |  | E |  | (Leaf/Root)+---+
                     |  | V |  |  |  /IP |  |  | V |  |
                     |  | I |  |  |      |  |  | I |  |            +---+
                     |  |   |  |  |      |  |  |   +--+----ES3-----+CE3|
                     |  +---+  |  +------+  |  +---+  |   (Leaf)   +---+
                     +---------+            +---------+

   Figure 3: Scenario 3

3 Operation for EVPN

   [EVPN] defines the notion of an Ethernet Segment which can be readily
   used to identify a Root and/or Leaf site in E-TREE services. In other
   words, [EVPN] has inherent capability to support E-TREE services
   without defining any new BGP routes. It only requires a  minor
   modification to the existing procedures and a new BGP Extended
   Community for leaf indication as shown later in this document.

   The following procedures are used consistently for all the scenarios
   highlighted in the previous section.

3.1 Known Unicast Traffic

   For known unicast traffic,

   In addition to the PE must advertise procedures below (which is a Leaf indication
   along with each MAC Advertisement route, MUST requirement), an
   EVPN PE implementation MAY provide topology constraint among the PEs
   belonging to indicate that the same EVI associated MAC address was learnt from a Leaf Attachment Circuit
   (AC). with an E-TREE service. The lack
   purpose of a this topology constraint is to avoid having PEs with only
   Leaf indication, indicates the sites (e.g., scenario 1 in section 2.1) importing and processing
   BGP MAC address is
   learnt routes from each other, thereby unnecessarily exhausting
   their RIB tables. However, when a root AC.  In other words, Root site is added to a default mode of operation Leaf PE
   (e.g., scenario 2 and 3 in an EVPN is that all ACs are root (can transmit sections 2.2 and 2.3), then that PE needs
   to process MAC routes from all other Leaf PEs and add them to its
   forwarding table. To support such topology constrain in EVPN, two BGP
   Route-Targets (RTs) are used for every EVPN Instance (EVI): one RT is
   associated with the Root sites and the other is associated with the
   Leaf sites. On a per EVI basis, every PE exports the single RT
   associated with its type of site(s). Furthermore, a PE with Root
   site(s) imports both Root and Leaf RTs, whereas a PE with Leaf
   site(s) only imports the Root RT. If for a given EVI, the PEs can
   eventually have both Leaf and Root sites attached, even though they
   may start as  Root-only or Leaf-only PEs, then it is recommended to
   use a single RT per EVI and avoid additional configuration and
   operational overhead. If the number of EVIs is very large (e.g., more
   than 32K or 64K), then RT type 0 as defined in [RFC4360] SHOULD be
   used; otherwise, RT type 2 is sufficient.

   The following procedures are used consistently for all the scenarios
   highlighted in the previous section.

3.1 Known Unicast Traffic

   For known unicast traffic, the PE must advertise a Leaf indication
   along with each MAC Advertisement route, to indicate that the
   associated MAC address was learnt from a Leaf Attachment Circuit
   (AC). The lack of a Leaf indication, indicates the MAC address is
   learnt from a root AC.  In other words, the default mode of operation
   in an EVPN is that all ACs are root (can transmit and receive traffic
   to/from other ACs in an EVI) unless the AC is explicitly identified
   as a leaf.

   Tagging MAC addresses with a leaf indication when they are associated
   with a leaf AC, enables remote PEs to perform ingress filtering for
   known unicast traffic - i.e., on the ingress PE, the MAC destination
   address lookup yields, in addition to the forwarding adjacency, a
   flag which indicates whether the target MAC is associated with a Leaf
   site or not. The ingress PE cross-checks this flag with the status of
   the originating AC, and if both are a Leaf, Leafs, then the packet is not
   forwarded.

   The PE places all Leaf Ethernet Segments (ACs) ACs of a given bridge domain in a single
   split-horizon group in order to prevent intra-PE forwarding among
   Leaf ACs (segments). ACs. This split-horizon function applies to both known unicast
   and BUM traffic as well. traffic.

   To support the above ingress filtering functionality, a new E-TREE
   Extended Community with a Leaf indication flag will be is introduced [section
   xxx].
   5.1]. This new Extended Community will be is advertised with each EVPN MAC/IP
   Advertisement route.

3.2 BUM Traffic

   For BUM traffic, it is not possible to perform filtering on the
   ingress PE, as is the case with known unicast, because of the multi-
   destination nature of the traffic. As such, the solution relies on
   egress filtering. In order to apply the proper egress filtering,
   which varies based on whether a packet is sent from a Root or a Leaf, Leaf
   AC, the MPLS-encapsulated frames MUST be tagged with an indication of
   whether they originated from a Root or a Leaf Ethernet Segment. AC. This can be
   achieved in EVPN through the use of the ESI MPLS label, since
   this label. Therefore,
   the ESI MPLS label not only identifies the Ethernet Segment segment of origin
   for a given
   frame. frame, but also it identifies its type (e.g., Leaf or
   Root).

3.2.1 BUM Traffic supported by P2MP Tunnels

   For multi-homing use cases where BUM traffic uses P2MP LSP, the
   egress
   ingress PE can determine whether or not adds an upstream-assigned ESI MPLS label to forward a particular the frame per

   [RFC7432] procedures and sends it to an Ethernet Segment depending on the split-horizon rule defined in
   [EVPN]:

   - If all the intended ingress PE
   devices. Two ESI Label indicates MPLS labels are used for each multi-homed Ethernet
   segment that has both Root and Leaf sites: one ESI MPLS label that
   only identifies the source Ethernet Segment is a
   Root, then the frame can be forwarded on a segment granted of origin per [RFC7432] and
   another one that it
   passes not only identifies the split-horizon check.

   - Ethernet segment of origin
   but also its type (which is Leaf). If an Ethernet segment has only
   Root sites, then the former ESI Label indicates that the source Ethernet Segment MPLS label is a
   Leaf, used and if an Ethernet
   segment has only Leaf sites, then the frame can latter ESI MPLS label is used.

   It should be forwarded only on noted that the former ESI MPLS label implicitly
   identifies a Root segment, granted Ethernet segment - i.e., an ESI MPLS label that it passes is
   signaled without the split-horizon check. new E-TREE Extended Community (defined in
   section [5.1]), is assumed to be of type Root. When advertising the
   ESI MPLS label for a given an Ethernet Segment, a Segment that has Leaf sites, the PE must
   MUST indicate whether that the corresponding ESI is a Root or a Leaf
   site. of type Leaf. This can be is
   achieved by advertising the Ethernet A-D per ES route with with the
   ESI MPLS label Extended Community along with the new E-TREE Extended
   Community defined in section [xxx] that has a Leaf indication flag.

   In the case where a multi-homed Ethernet Segment has both Root and
   Leaf sites attached, two

   The egress PE can determine whether or not to forward a particular
   frame to the destination Ethernet Segment depending on the following
   rules:

   - If the ESI MPLS labels are allocated and
   advertised: one default label indicates that the source Ethernet Segment is
   the same as destination Ethernet segment, then the frame is blocked
   according to the split-horizon rule in [RFC7432].

   - If the ESI MPLS label indicates that denotes Root the source Ethernet Segment is
   not the same as destination Ethernet segment and another it doesn't have any
   Leaf indication, then the frame is forwarded to the destination AC
   according to the split-horizon rule in [RFC7432].

   - If the ESI MPLS label with Leaf indication indicates that denotes Leaf. the source Ethernet Segment is
   not the same as destination Ethernet segment but it has a Leaf
   indication, then the frame is blocked if the destination AC is of
   type Leaf and it is forwarded if the destination AC is of type Root.

   The ingress PE imposes the right ESI MPLS label depending on whether
   the Ethernet frame originated from the Root or Leaf site on that
   Ethernet Segment. The mechanism by which the PE identifies whether a
   given frame originated from a Root or Leaf site on the segment is
   based on the Ethernet Tag associated with the frame (e.g., whether
   the frame come from a leaf or a root AC). Other mechanisms of
   identification, beyond the Ethernet Tag, are outside the scope of
   this document. It should be noted that support for both Root and Leaf
   sites on a single Ethernet Segment requires that the PE performs the
   Ethernet Segment split-horizon check on a per Ethernet Tag basis. In
   the case where a multi-homed Ethernet Segment has only either Root or
   Leaf sites attached, then a single ESI MPL label is allocated and
   advertised.

   Furthermore, a PE advertises a special per-PE Leaf MPLS label to
   indicate Leaf.

   For traffic originated from single-homed segments,
   this label can be either upstream assigned or downstream assigned
   (depending on whether single-homing use cases where BUM traffic uses P2MP LSP or ingress
   replication). However, for traffic originated from multi-homed
   segments, this label is downstream assigned as LSP, the
   ingress replication is
   assumed to be used for BUM traffic. Furthermore, this label is used
   for traffic originating from PE adds a multi-homed segments that are not part
   of the same redundancy group (same ES) as the advertising PE. This special ESI MPLS label indicates to the egress PE that frame if the BUM traffic frame is
   originated from a Leaf AC. Note that this site. This special ESI MPLS label used for
   single-homing scenarios is advertised not on a per
   PE ES basis (i.e. each PE advertises only but rather on a per
   PE basis - i.e., a single such special label).
   It should be noted that this per-PE Leaf ESI MPLS label is not used for multi-
   homed all single-homed
   segments when P2MP LSP is used for BUM traffic or when ingress
   replication is destined to a PE on that shares PE. If the same multi-homed ES -
   i.e., in such scenarios, frame is originated from a Root site,
   then the color-coded per-ES ingress PE does not add any ESI MPLS label per [RFC7432]
   procedures. The egress PE, when receiving this special ESI MPLS
   label, it blocks the frame if the destination AC is
   used (indicating leaf or root).

   This per-PE of type Leaf and
   it forwards the frame if the destination AC is of type Root.

   When a PE wants to advertise this special ESI label to other PE
   devices, it advertises it using ESI MPLS label is advertised along with the Leaf
   indication flag Extended Community
   with the Ethernet A-D per ES route.

   In addition to egress filtering (which is a MUST requirement), an
   EVPN PE implementation MAY provide topology constraint among The ESI for the PEs
   belonging Ethernet A-D per
   ES route, can be of type 3, 4, or 5.

3.2.1 BUM Traffic supported by Ingress Replication

   The procedures for supporting BUM traffic using ingress replication,
   are similar to the same EVI associated with an E-TREE service. ones in the previous section. The
   purpose of this topology constraint main differences
   are that the ESI label is to avoid having PEs with only
   host Leaf sites importing downstream assigned and processing BGP MAC routes from each
   other, thereby unnecessarily exhausting their RIB tables. However,
   when a Root site is added to a Leaf PE, then that not all egress PE needs
   devices need to process
   MAC routes receive the ESI label just like ingress replication
   procedures defined in [RFC7432].

   For frames received from all other Leaf PEs and a multi-homed Ethernet segment, the ingress
   PE may or may not add them an ESI MPLS label based on the following
   criteria:

   - If the frame is forwarded to its forwarding
   table. To support such topology constrain a PE that participates in EVPN, two BGP Route-
   Targets (RTs) are used for every EVPN Instance (EVI): one RT is
   associated with the Root sites same
   multi-homed Ethernet Segment and the other frame is associated with received on a Root AC,
   then the
   Leaf sites. On ingress PE adds a per-ES downstream-assigned ESI MPLS label
   to the frame per EVI basis, every PE exports [RFC7432].

   - If the single RT
   associated with its type of site(s). Furthermore, frame is forwarded to a PE with Root
   site(s) imports both Root that participates in the same
   multi-homed Ethernet Segment and Leaf RTs, whereas the frame is received on a Leaf AC,
   then the ingress PE with adds the a per-ES downstream-assigned ESI MPLS
   label indicating Leaf
   site(s) only imports to the Root RT. frame.

   - If for the frame is forwarded to a given EVI, PE that does not participate in the PEs can
   eventually have both
   same multi-homed Ethernet Segment and the frame is received on a Leaf
   AC, then the ingress PE adds a per-PE downstream-assigned special ESI
   MPLS label indicating Leaf to the frame. This special ESI MPLS label
   is per PE.

   - If the frame is forwarded to a PE that does not participate in the
   same multi-homed Ethernet Segment and the frame is received on a Root sites attached, even though they
   AC, then the ingress PE does not add any ESI MPLS label to the frame
   per [RFC7432].

   For frames received from a single-homed Ethernet segment, the ingress
   PE may start or may not add an ESI MPLS label based on the following
   criteria:

   - If the frame is received on a Root AC, then the ingress PE does not
   add any ESI MPLS label to the frame.

   - If the frame is received on a Leaf AC, then the ingress PE adds a
   special downstream-assigned ESI MPLS label indicating Leaf to the
   frame.

   Just as  Root-only described in the previous section, the Leaf indication is
   signaled using the new E-TREE extended community defined in section
   [5.1] along with the ESI MPLS label extended community with the
   Ethernet A-D per ES route.

   The egress PE can determine whether or Leaf-only PEs, not to forward a particular
   frame to the desitnation Ethernet Segment depending on the following
   rules:

   - If the ESI MPLS label indicates that the source Ethernet Segment is
   the same as destination Ethernet segment, then the frame is blocked
   according to the split-horizon rule in [RFC7432].

   - If the ESI MPLS label indicates that the source Ethernet Segment is
   not the same as destination Ethernet segment and it doesn't have any
   Leaf indication, then the frame is forwarded to the destination AC
   according to the split-horizon rule in [RFC7432].

   - If the ESI MPLS label indicates that the source Ethernet Segment is
   not the same as destination Ethernet segment but it has a Leaf
   indication, then the frame is blocked if the destination AC is of
   type Leaf and it is forwarded if the destination AC is of type Root.

   - If the ESI label is a special ESI MPLS label, then the frame is
   blocked if the destination AC is of type Leaf and it is recommended to
   use a single RT per EVI and avoid additional configuration and
   operational overhead. If forwarded if
   the number of EVIs destination AC is very large (e.g., more
   than 32K or 64K), then RT type 0 as defined in [RFC4360] SHOULD be
   used; otherwise, RT of type 2 is sufficient. Root.

3.3 E-TREE Traffic Flows for EVPN

   Per [ETREE-FMWK], a generic E-Tree service supports all of the
   following traffic flows:

        - Ethernet Unicast from Root to Roots & Leaf
        - Ethernet Unicast from Leaf to Root
        - Ethernet Broadcast/Multicast from Root to Roots & Leafs
        - Ethernet Broadcast/Multicast from Leaf to Roots

   A particular E-Tree service may need to support all of the above
   types of flows or only a select subset, depending on the target
   application. In the case where unicast flows need not be supported,
   the L2VPN PEs can avoid performing any MAC learning function.

   In the subsections that follow, we will describe the operation of
   EVPN to support E-Tree service with and without MAC learning.

3.3.1 E-Tree with MAC Learning

   The PEs implementing an E-Tree service must perform MAC learning when
   unicast traffic flows must be supported from Root to Leaf or from
   Leaf to Root sites. In this case, the PE with Root sites performs MAC
   learning in the data-path over the Ethernet Segments, and advertises
   reachability in EVPN MAC Advertisement routes. These routes will be
   imported by PEs that have Leaf sites as well as by PEs that have Root
   sites, in a given EVI. Similarly, the PEs with Leaf sites perform MAC
   learning in the data-path over their Ethernet Segments, and advertise
   reachability in EVPN MAC Advertisement routes which are imported only
   by PEs with at least one Root site in the EVI. A PE with only Leaf
   sites will not import these routes. PEs with Root and/or Leaf sites
   may use the Ethernet A-D routes for aliasing (in the case of multi-
   homed segments) and for mass MAC withdrawal.

   To support multicast/broadcast from Root to Leaf sites, either a P2MP
   tree rooted at the PE(s) with the Root site(s) or ingress replication
   can be used. The multicast tunnels are set up through the exchange of
   the EVPN Inclusive Multicast route, as defined in [EVPN]. [RFC7432].

   To support multicast/broadcast from Leaf to Root sites, ingress
   replication should be sufficient for most scenarios where there is a
   single Root or few Roots. If the number of Roots is large, a P2MP
   tree rooted at the PEs with Leaf sites may be used.

3.3.2 E-Tree without MAC Learning

   The PEs implementing an E-Tree service need not perform MAC learning
   when the traffic flows between Root and Leaf sites are multicast or
   broadcast. In this case, the PEs do not exchange EVPN MAC
   Advertisement routes. Instead, the Ethernet A-D routes are used to
   exchange the EVPN labels.

   The fields of the Ethernet A-D route are populated per the procedures
   defined in [EVPN], [RFC7432], and the route import rules are as described in
   previous sections.

4 Operation for PBB-EVPN

   In PBB-EVPN, the PE must advertise a Root/Leaf indication along with
   each MAC Advertisement route, to indicate whether the associated B-
   MAC address corresponds to a Root or a Leaf site. Similar to the EVPN
   case, this flag will be added to the Tunnel Encapsulation Type
   Extended Community [RFC5512], new E-TREE extended community
   defined in section [5.1], and advertised with each MAC Advertisement
   route.

   In the case where a multi-homed Ethernet Segment has both Root and
   Leaf sites attached, two B-MAC addresses are allocated and
   advertised: one B-MAC address denotes implicitly denoting Root and the other denotes
   explicitly denoting Leaf. The former B-MAC address is not advertised
   with the E-TREE extended community but the latter B-MAC denoting Leaf
   is advertised with the new E-TREE extended community.

   The ingress PE uses the right B-MAC source address depending on
   whether the Ethernet frame originated from the Root or Leaf site on
   that Ethernet Segment. The mechanism by which the PE identifies
   whether a given frame originated from a Root or Leaf site on the
   segment is based on the Ethernet Tag associated with the frame. Other
   mechanisms of identification, beyond the Ethernet Tag, are outside
   the scope of this document. It should be noted that support for both
   Root and Leaf sites on a single Ethernet Segment requires that the PE
   performs the Ethernet Segment split-horizon check on a per Ethernet
   Tag basis.

   In the case where a multi-homed Ethernet Segment has
   either only Root or
   Leaf sites attached, then a single B-MAC address is allocated and
   advertised per segment.

   Furthermore, a PE advertises two special global B-MAC addresses: one
   for Root and another for Leaf, and tags them as such in the MAC
   Advertisement routes. These B-MAC addresses are used as source
   addresses for traffic originating from single-homed segments.

4.1 Known Unicast Traffic

   For known unicast traffic, the PEs perform ingress filtering: On the
   ingress PE, the C-MAC destination address lookup yields, in addition
   to the target B-MAC address and forwarding adjacency, a flag which
   indicates whether the target B-MAC is associated with a Root or a
   Leaf site. The ingress PE cross-checks this flag with the status of
   the originating site, and if both are a Leaf, then the packet is not
   forwarded.

   The PE places all Leaf Ethernet Segments of a given bridge domain in
   a single split-horizon group in order to prevent intra-PE forwarding
   among Leaf segments. This split-horizon function applies to BUM
   traffic as well.

4.2 BUM Traffic

   For BUM traffic, the PEs must perform egress filtering. When a PE
   receives a MAC advertisement route, it updates its Ethernet Segment
   egress filtering function (based on the B-MAC source address), as
   follows:

   - If the MAC Advertisement route indicates that the advertised B-MAC
   is a Leaf, and the local Ethernet Segment is a Leaf as well, then the
   source B-MAC address is added to the B-MAC filtering list.

   - Otherwise, the B-MAC filtering list is not updated.

   When the egress PE receives the packet, it examines the B-MAC source
   address to check whether it should filter or forward the frame. Note
   that this uses the same filtering logic as baseline [PBB-EVPN] and
   does not require any additional flags in the data-plane.

5 BGP Encoding

   This document defines one new BGP Extended Community for EVPN.

5.1 E-TREE Extended Community

   A new EVPN BGP Extended Community called E-TREE is introduced here.
   This new extended community is a transitive extended community with
   the Type field of 0x06 (EVPN) and the Sub-Type of 0x04. This extended
   community is used to for leaf indication and it is advertised with an
   EVPN MAC/IP route or an Ethernet A-D per ES route. When advertised
   with an Ethernet A-D per ES route, it is sent along with ESI Label
   Extended Community defined in section 7.5 of [RFC7432].

   The E-TREE Extended Community is encoded as an 8-octet value as
   follows:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Type=0x06     | Sub-Type=0x04 |        E-TREE Flags           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         E-TREE Flags                         L|
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Leaf flag (L): A value of 1 indicates a leaf

6  Acknowledgement

   We would like to thank Sami Boutros and Dennis Cai for their his comments.

6

7  Security Considerations

   Same security considerations as [EVPN].

7 [RFC7432].

8  IANA Considerations

   Allocation of Extended Community Type and Sub-Type for EVPN.

8

9  References

8.1

9.1  Normative References

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

   [RFC4360] S. Sangli et al, ""BGP Extended Communities Attribute",
              February, 2006.

              [RFC5512] Mohapatra, P. and E. Rosen, "The BGP
              Encapsulation Subsequent Address Family Identifier (SAFI)
              and the BGP Tunnel Encapsulation Attribute", RFC 5512,
              April 2009.

8.2

   [RFC7432] Sajassi et al., "BGP MPLS Based Ethernet VPN", February,
              2015.

9.2  Informative References

   [ETREE-FMWK] Key et al., "A Framework for E-Tree Service over MPLS
   Network", draft-ietf-l2vpn-etree-frwk-03, work in progress, September
   2013.

   [EVPN] Sajassi et al., "BGP MPLS Based Ethernet VPN", draft-ietf-
   l2vpn-evpn-04.txt, work in progress, July,
   2013.

   [PBB-EVPN] Sajassi et al., "PBB-EVPN", draft-ietf-l2vpn-pbb-evpn-
   05.txt, work in progress, October, 2013.

Authors' Addresses

   Ali Sajassi
   Cisco
   Email: sajassi@cisco.com

   Samer Salam
   Cisco
   Email: ssalam@cisco.com

   Wim Henderickx
   Alcatel-Lucent
   Email: wim.henderickx@alcatel-lucent.com

   Jim Uttaro
   AT&T
   Email: ju1738@att.com

   Aldrin
   Bloomberg Issac
   Email: aisaac71@bloomberg.net

   Sami Boutros
   Cisco
   Email: sboutros@cisco.com