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                                                          Juniper
Juniper

Expires: August 2, November 10, 2016                                 February 2,                                  May 10, 2016

                   E-TREE Support in EVPN & PBB-EVPN
                     draft-ietf-bess-evpn-etree-04
                     draft-ietf-bess-evpn-etree-05

Abstract

   The Metro Ethernet Forum (MEF) has defined a rooted-multipoint
   Ethernet service known as Ethernet Tree (E-Tree).  [ETREE-FMWK]
   proposes a A solution
   framework for supporting this service in MPLS
   networks. networks is proposed in
   and RFC called "A Framework for E-Tree Service over MPLS Network".
   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

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

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

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

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

Copyright and License Notice

   Copyright (c) 2013 2016 IETF Trust and the persons identified as the
   document authors. All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document. Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document. Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1  Terminology . . . . . . . . . . . . . . . . . . . . . . . .  4
   2  E-Tree Scenarios and EVPN / PBB-EVPN Support  . . . . . . . . .  4
     2.1 Scenario 1: Leaf OR Root site(s) per PE  . . . . . . . . . .  4
     2.2 Scenario 2: Leaf OR Root site(s) per AC  . . . . . . . . . .  5
     2.3 Scenario 3: Leaf OR Root site(s) per MAC . . . . . . . . . .  6
   3 Operation for EVPN . . . . . . . . . . . . . . . . . . . . . . .  7
     3.1 Known Unicast Traffic  . . . . . . . . . . . . . . . . . . .  7
     3.2 BUM Traffic  . . . . . . . . . . . . . . . . . . . . . . . .  8
       3.2.1 BUM traffic originated from a single-homed site on a
             leaf AC  . . . . . . . . . . . . . . . . . . . . . . . .  9
       3.2.2 BUM traffic originated from a single-homed site on a
             root AC  . . . . . . . . . . . . . . . . . . . . . . . .  9
       3.2.3 BUM traffic originated from a multi-homed site on a
             leaf AC  . . . . . . . . . . . . . . . . . . . . . . . .  9
       3.2.4 BUM traffic originated from a multi-homed site on a
             root AC  . . . . . . . . . . . . . . . . . . . . . . . .  9
     3.3 E-TREE Traffic Flows for EVPN  . . . . . . . . . . . . . . . 10
       3.3.1 E-Tree with MAC Learning . . . . . . . . . . . . . . . . 10
       3.3.2 E-Tree without MAC Learning  . . . . . . . . . . . . . . 11
   4 Operation for PBB-EVPN . . . . . . . . . . . . . . . . . . . . . 11
     4.1 Known Unicast Traffic  . . . . . . . . . . . . . . . . . . . 12
     4.2 BUM Traffic  . . . . . . . . . . . . . . . . . . . . . . . . 12
     4.3 E-Tree without MAC Learning  . . . . . . . . . . . . . . . . 13
   5 BGP Encoding . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     5.1 E-TREE Extended Community  . . . . . . . . . . . . . . . . . 13
     5.2 PMSI Tunnel Attribute  . . . . . . . . . . . . . . . . . . . 14
   6  Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . 14 15
   7  Security Considerations . . . . . . . . . . . . . . . . . . . . 14 15
   8  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 14 15
   9  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 15
     9.1  Normative References  . . . . . . . . . . . . . . . . . . . 15
     9.2  Informative References  . . . . . . . . . . . . . . . . . . 15
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15 16

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]

   [RFC7387] 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]

   [RFC7432] 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]
   [RFC7623] 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 OR Root site(s) per AC

   - Leaf OR Root site(s) per MAC

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

   In this scenario, a PE may receive traffic from either Root sites OR
   Leaf sites for a given MAC-VRF/bridge table, but not both
   concurrently. In other words, a given EVI on a PE is either
   associated with a root or leaf. The PE may have both Root and Leaf
   sites albeit for different EVIs.

                   +---------+            +---------+
                   |   PE1   |            |   PE2   |
    +---+          |  +---+  |  +------+  |  +---+  |            +---+
    |CE1+---ES1----+--+   |  |  | MPLS |  |  |   +--+----ES2-----+CE2|
    +---+  (Root)  |  |MAC|  |  |  /IP |  |  |MAC|  |   (Leaf)   +---+
                   |  |VRF|  |  |      |  |  |VRF|  |
                   |  |   |  |  |      |  |  |   |  |            +---+
                   |  |   |  |  |      |  |  |   +--+----ES3-----+CE3|
                   |  +---+  |  +------+  |  +---+  |   (Leaf)   +---+
                   +---------+            +---------+

   Figure 1: Scenario 1

   In such scenario, an EVPN PE implementation MAY provide E-TREE
   service using topology constraint among the PEs belonging to the same
   EVI. The purpose of this topology constraint is to avoid having PEs
   with only  Leaf sites importing and processing BGP MAC routes from
   each other. 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 the number of EVIs is very large
   (e.g., more than 64K), then RT type 0 as defined in [RFC4360] SHOULD
   be used; otherwise, RT type 2 is sufficient [RFC7153].

2.2 Scenario 2: Leaf OR Root site(s) per AC

   In this scenario, a PE receives traffic from either Root OR Leaf
   sites (but not both) on a given Attachment Circuit (AC) of an EVI. In
   other words, an AC (ES or ES/VLAN) is either associated with a Root
   or Leaf (but not both).

                     +---------+            +---------+
                     |   PE1   |            |   PE2   |
    +---+            |  +---+  |  +------+  |  +---+  |            +---+
    |CE1+-----ES1----+--+   |  |  |      |  |  |   +--+---ES2/AC1--+CE2|
    +---+    (Leaf)  |  |MAC|  |  | MPLS |  |  |MAC|  |   (Leaf)   +---+
                     |  |VRF|  |  |  /IP |  |  |VRF|  |
                     |  |   |  |  |      |  |  |   |  |            +---+
                     |  |   |  |  |      |  |  |   +--+---ES2/AC2--+CE3|
                     |  +---+  |  +------+  |  +---+  |   (Root)   +---+
                     +---------+            +---------+

   Figure 2: Scenario 2

   In this scenario, if there are PEs with only root (or leaf) sites per
   EVI, then the RT constrain procedures described in section 2.1 can
   also be used here. However, when a Root site is added to a Leaf PE,
   then that PE needs to process MAC routes from all other Leaf PEs and
   add them to its forwarding table. For this scenario, if for a given
   EVI, the majority of PEs will 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.

2.3 Scenario 3: Leaf OR Root site(s) per MAC

   In this scenario, a PE may receive traffic from both Root AND Leaf
   sites on a given Attachment Circuit (AC) of an EVI. Since an
   Attachment Circuit (ES or ES/VLAN) carries traffic from both Root and
   Leaf sites, the granularity at which Root or Leaf sites are
   identifies is on a per MAC address. This scenario is considered in
   this draft for EVPN service with only known unicast traffic - i.e.,
   there is no BUM traffic.

                     +---------+            +---------+
                     |   PE1   |            |   PE2   |
    +---+            |  +---+  |  +------+  |  +---+  |            +---+
    |CE1+-----ES1----+--+   |  |  |      |  |  |   +--+---ES2/AC1--+CE2|
    +---+    (Root)  |  | E |  |  | MPLS |  |  | E |  | (Leaf/Root)+---+
                     |  | V |  |  |  /IP |  |  | V |  |
                     |  | I |  |  |      |  |  | I |  |            +---+
                     |  |   |  |  |      |  |  |   +--+---ES2/AC2--+CE3|
                     |  +---+  |  +------+  |  +---+  |   (Leaf)   +---+
                     +---------+            +---------+

   Figure 3: Scenario 3

3 Operation for EVPN

   [EVPN]

   [RFC7432] defines the notion of ESI MPLS label used for split-horizon
   filtering of BUM traffic at the egress PE. Such egress filtering
   capabilities can be leveraged in provision of E-TREE services as seen
   shortly. In other words, [EVPN] [RFC7432] has inherent capability to support E-
   TREE
   E-TREE services without defining any new BGP routes but by just
   defining a new BGP Extended Community for leaf indication as shown
   later in this document.

3.1 Known Unicast Traffic

   Since in EVPN, MAC learning is performed in control plane via
   advertisement of BGP routes, the filtering needed by E-TREE service
   for known unicast traffic can be performed at the ingress PE, thus
   providing very efficient filtering and avoiding sending known unicast
   traffic over MPLS/IP core to be filtered at the egress PE as done in
   traditional E-TREE solutions (e.g., E-TREE for VPLS).

   To provide such ingress filtering for known unicast traffic, a PE
   MUST indicate to other PEs what kind of sites (root or leaf) its MAC
   addresses are associated with by advertising a leaf indication flag
   (via an Extended Community) along with each of its MAC/IP
   Advertisement route. The lack of such flag indicates that the MAC
   address is associated with a root site. This scheme applies to all
   scenarios described in section 2.

   Furthermore, for multi-homing scenario of section 2.2, where an AC is
   either root or leaf (but not both), the PE MAY advertise leaf
   indication along with the Ethernet A-D per EVI route. This
   advertisement is used for sanity checking in control-plane to ensure
   that there is no discrepancy in configuration among different PEs of
   the same redundancy group. For example, if a leaf site is multi-homed
   to PE1 an PE2, and PE1 advertises the Ethernet A-D per EVI
   corresponding to this leaf site with the leaf-indication flag but PE2
   does not, then the receiving PE notifies the operator of such
   discrepancy and ignore the leaf-indication flag on PE1. In other
   words, in case of discrepancy, the multi-homing for that pair of PEs
   is assumed to be in default "root" mode for that <ESI, EVI> or <ESI,
   EVI/VLAN>. The leaf indication flag on Ethernet A-D per EVI route
   tells the receiving PEs that all MAC addresses associated with this
   <ESI, EVI> or <ESI, EVI/VLAN> are from a leaf site. Therefore, if a
   PE receives a leaf indication for an AC via the Ethernet A-D per EVI
   route but doesn't receive a leaf indication in the corresponding MAC
   route, then it notify the operator and ignore the leaf indication on
   the Ethernet A-D per EVI route.

   Tagging MAC addresses with a leaf indication 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 Leafs, then the packet is not forwarded.

   To support the above ingress filtering functionality, a new E-TREE
   Extended Community with a Leaf indication flag is introduced [section
   5.2]. This new Extended Community MUST be advertised with MAC/IP
   Advertisement route and MAY be advertised with an Ethernet A-D per
   EVI route as described above.

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 Leaf AC or a
   root AC, the MPLS-encapsulated frames MUST be tagged with an
   indication when they originated from a Leaf AC. In other words, leaf
   indication for BUM traffic is done at the granularity of AC. This can
   be achieved in EVPN through the use of a MPLS label where it can be
   used to either identify the Ethernet segment of origin per [RFC 7432] [RFC7432]
   (i.e., ESI label) or it can be used to indicate that the packet is
   originated from a leaf site (Leaf label).

   BUM traffic sent over a P2MP LSP or ingress replication, may need to
   carry an upstream assigned or downstream assigned MPLS label
   (respectively) for the purpose of egress filtering to indicate to the
   egress PEs whether this packet is originated from a leaf AC.

   The main difference between downstream and upstream assigned MPLS
   label is that in case of downstream assigned not all egress PE
   devices need to receive the label just like ingress replication
   procedures defined in [RFC7432].

   There are four scenarios to consider as follow. In all these
   scenarios, the imposition PE imposes the right MPLS label associated
   with the originated Ethernet Segment (ES) depending on whether the
   Ethernet frame originated from a Root or a Leaf site on that Ethernet
   Segment (ESI or Leaf label). The mechanism by which the PE identifies
   whether a given frame originated from a Root or a Leaf site on the
   segment is based on the Ethernet Tag associated with the frame (e.g.,
   whether the frame received on a leaf or a root AC). Other mechanisms
   for identifying whether an ingress AC is a root or leaf is beyond the
   scope of this document.

3.2.1 BUM traffic originated from a single-homed site on a leaf AC

   In this scenario, the ingress PE adds a special MPLS label indicating
   a Leaf site. This special Leaf MPLS label, used for single-homing
   scenarios, is not on a per ES basis but rather on a per PE basis -
   i.e., a single Leaf MPLS label is used for all single-homed ES's on
   that PE. This Leaf label is advertised to other PE devices, using a
   new EVPN Extended Community called E-TREE Extended Community (section
   5.1) along with an Ethernet A-D per ES route with ESI of zero and a
   set of Route Targets (RTs) corresponding to all EVIs on the PE with
   at least one leaf site per EVI. The set of Ethernet A-D per ES routes
   may be needed if the number of Route Targets (RTs) that need to be
   sent exceed the limit on a single route per [RFC 7432]. [RFC7432]. The ESI for
   the Ethernet A-D per ES route is set to zero to indicate single-homed
   sites.

   When a PE receives this special Leaf label in the data path, it
   blocks the packet if the destination AC is of type Leaf; otherwise,
   it forwards the packet.

3.2.2 BUM traffic originated from a single-homed site on a root AC

   In this scenario, the ingress PE does not add any ESI or Leaf label
   and it operates per [RFC7432] procedures.

3.2.3 BUM traffic originated from a multi-homed site on a leaf AC

   In this scenario, it is assumed that While different ACs (VLANs) on
   the same ES could have different root/leaf designation (some being
   roots and some being leaves), the same VLAN does have the same
   root/leaf designation on all PEs on the same ES. Furthermore, it is
   assumed that there is no forwarding among subnets - ie, the service
   is EVPN L2 and not EVPN IRB. IRB use case is outside the scope of
   this document.

   In such scenarios,  If a multicast packet is originated from a leaf
   AC, then it only needs to carry Leaf label described in section
   3.2.1. This label is sufficient in providing the necessary egress
   filtering of BUM traffic from getting sent to leaf ACs including the
   leaf AC on the same Ethernet Segment.

3.2.4 BUM traffic originated from a multi-homed site on a root AC

   In this scenario, both the ingress and egress PE devices follows the
   procedure defined in [RFC 7432] [RFC7432] for adding and/or processing an ESI
   MPLS label.

3.3 E-TREE Traffic Flows for EVPN

   Per [ETREE-FMWK], [RFC7387], 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 among Root and Leaf 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 all PEs
   for that EVI (i.e., PEs that have Leaf sites as well as PEs that have
   Root sites). 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. For the scenario
   described in section 2.1 (or possibly section 2.2), these routes are
   imported only by PEs with at least one Root site in the EVI - i.e., 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 per
   [RFC 7432].
   [RFC7432].

   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 [RFC7432].

   To support multicast/broadcast from Leaf to Root sites, ingress
   replication should be sufficient for most scenarios where there are
   only a few Roots (typically two). Therefore, in a typical scenario, a
   root PE needs to support both a P2MP tunnel in transmit direction
   from itself to leaf PEs and at the same time it needs to support
   ingress-replication tunnels in receive direction from leaf PEs to
   itself. In order to signal this efficiently from the root PE, a new
   composite tunnel type is defined per section 5.3.  This new composite
   tunnel type is advertised by the root PE to simultaneously indicate a
   P2MP tunnel in transmit direction and an ingress-replication tunnel
   in the receive direction for the BUM traffic.

   If the number of Roots is large, P2MP tunnels originated at the PEs
   with Leaf sites may be used and thus there will be no need to use the
   modified PMSI tunnel attribute in section 5.2 for composite tunnel
   type.

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 only multicast
   or broadcast. In this case, the PEs do not exchange EVPN MAC
   Advertisement routes. Instead, the Inclusive Multicast Ethernet Tag
   (IMET) routes are used to support BUM traffic.

   The fields of the IMET route are populated per the procedures defined
   in [RFC7432], and the multicast tunnel setup criteria are as
   described in the previous section.

   Just as in the previous section, if the number of PEs with root sites
   are only a few and thus ingress replication is desired from leaf PEs
   to these root PEs, then the modified PMSI attribute as defined in
   section 5.3 should be used.

4 Operation for PBB-EVPN

   In PBB-EVPN, the PE must advertise advertises a Root/Leaf indication along with each
   B-MAC Advertisement route, to indicate whether the associated B-
   MAC B-MAC
   address corresponds to a Root or a Leaf site. Similar to Just like the EVPN
   case, this flag will be added to the new E-TREE Extended Community defined in section [5.2], and [5.1] is
   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 is per ES as specified in [RFC7623] and implicitly denoting Root
   Root, and the other B-MAC address is per PE and 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. community where "Leaf-indication" flag
   is set. In such multi-homing scenarios where and Ethernet Segment has
   both Root and Leaf ACs, it is assumed that While different ACs
   (VLANs) on the same ES could have different root/leaf designation
   (some being roots and some being leaves), the same VLAN does have the
   same root/leaf designation on all PEs on the same ES. Furthermore, it
   is assumed that there is no forwarding among subnets - ie, the
   service is L2 and not IRB. IRB use case is outside the scope of this
   document.

   The ingress PE uses the right B-MAC source address depending on
   whether the Ethernet frame originated from the Root or Leaf site AC 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 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 the Leaf one as such in the
   MAC Advertisement route. These B-MAC addresses are used as source
   addresses for traffic originating from single-homed segments. The B-
   MAC address used for indicating Leaf sites can be the same for both
   single-homed and multi-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.

4.2 BUM Traffic

   For BUM traffic, the PEs must perform egress filtering. When a PE
   receives a MAC advertisement route, route (which will be used as a source B-
   MAC), it updates its Ethernet Segment egress filtering function
   (based on the B-MAC source B-MAC 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] [RFC7623] and
   does not require any additional flags in the data-plane.

   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.

4.3 E-Tree without MAC Learning

   In scenarios where the traffic of interest is only Multicast and/or
   broadcast, the PEs implementing an E-Tree service do not need to do
   any MAC learning. In such scenarios the filtering must be performed
   on egress PEs. For PBB-EVPN, the handling of such traffic is per
   section 4.2 without C-MAC learning part of it at both ingress and
   egress PEs.

5 BGP Encoding

   This document defines two new BGP Extended Community for EVPN.

5.1 E-TREE Extended Community

   This Extended Community is a new transitive Extended Community having
   a Type field value of 0x06 (EVPN) and the Sub-Type 0x04. 0x05. It is used
   for leaf indication of known unicast and BUM traffic. For BUM
   traffic, the Leaf Label field is set to a valid MPLS label and this
   EC is advertised along with Ethernet A-D per ES route with an ESI of
   zero to enable egress filtering on disposition PEs per section 3.2.1
   and 3.2.3. There is no need to send ESI Label Extended Community when
   sending Ethernet A-D per ES route with an ESI of zero. For known
   unicast traffic, the Leaf flag bit is set to one and this EC is
   advertised along with MAC/IP Advertisement route per section 3.1.

   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 Sub-Type=0x05 | Flags(1 Octet)|  Reserved=0   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |  Reserved=0   |           Leaf Label                          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The low-order bit of the Flags octet is defined as the "Leaf-
   Indication" bit. A value of one indicates a Leaf AC/Site.

   When this EC is advertised along with MAC/IP Advertisement route, route (for
   known unicast traffic), the Leaf-Indication flag MUST be set to one
   and Leaf Label is set to zero. The received PE should ignore Leaf
   Label and only processes Leaf-Indication flag. A value of zero for
   Leaf-Indication flag is invalid when sent along with MAC/IP
   advertisement route and an error should be logged.

   When this EC is advertised along with Ethernet A-D per ES route (with
   ESI of zero), zero) for BUM traffic, the Leaf Label MUST be set to a valid
   MPLS label and the Leaf-Indication flag should be set to zero. The
   received PE should ignore the Leaf-Indication flag. A non-valid MPLS
   label when sent along with the Ethernet A-D per ES route, should be
   logged as an error.

5.2 PMSI Tunnel Attribute

   [RFC 6514]

   [RFC6514] defines PMSI Tunnel attribute which is an optional
   transitive attribute with the following format:

         +---------------------------------+
         |  Flags (1 octet)                |
         +---------------------------------+
         |  Tunnel Type (1 octets)         |
         +---------------------------------+
         |  MPLS Label (3 octets)          |
         +---------------------------------+
         |  Tunnel Identifier (variable)   |
         +---------------------------------+

   This draft uses all the fields per existing definition except for the
   following modifications to the Tunnel Type and Tunnel Identifier:

   When receiver ingress-replication label is needed, the high-order bit
   of the tunnel type field (C bit - Composite tunnel bit) is set while
   the remaining low-order seven bits indicate the tunnel type as
   before. When this C bit is set, the "tunnel identifier" field would
   begin with a three-octet label, followed by the actual tunnel
   identifier for the transmit tunnel.  PEs that don't understand the
   new meaning of the high-order bit would treat the tunnel type as an
   invalid tunnel type. For the PEs that do understand the new meaning
   of the high-order, if ingress replication is desired when sending BUM
   traffic, the PE will use the the label in the Tunnel Identifier field
   when sending its BUM traffic.

6  Acknowledgement

   We would like to thank Dennis Cai, Antoni Przygienda, and Jeffrey
   Zhang for their valueable valuable comments.

7  Security Considerations

   Same

   Since this draft uses the EVPN constructs of [RFC7432] and [RFC7623],
   the same security considerations in these drafts are also applicable
   here. Furthermore, this draft provides additional security check by
   allowing sites (or ACs) of an EVPN instance to be designated as [RFC7432].
   "Root" or "Leaf" and preventing any traffic exchange among "Leaf"
   sites of that VPN through ingress filtering for known unicast traffic
   and egress filtering for BUM traffic.

8  IANA Considerations

   This document requests the allocation of value 4 5 in the "EVPN
   Extended Community Sub-Types" registry defined in [RFC7153] and
   modification of the registry as follow:

         SUB-TYPE VALUE     NAME                        Reference

         0x04

         0x05               E-TREE Extended Community   This document
         6-255              Unassigned

9  References

9.1  Normative References

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

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

   [RFC7623] Sajassi et al., "Provider Backbone Bridging Combined with
              Ethernet VPN (PBB-EVPN)", September, 2015.

9.2  Informative References

   [ETREE-FMWK]

   [RFC7387] Key et al., "A Framework for E-Tree Service over MPLS
   Network", draft-ietf-l2vpn-etree-frwk-03, work in progress, September
   2013.

   [PBB-EVPN] Sajassi et al., "PBB-EVPN", draft-ietf-l2vpn-pbb-evpn-
   05.txt, work in progress, October, 2013. October 2014.

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

   [RFC7153] Rosen et al., "IANA Registries for BGP Extended
   Communities",  March, 2014.

   [RFC6514] Aggarwal et al., "BGP Encodings and Procedures for
   Multicast in MPLS/BGP IP VPNs",  February, 2012.

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 aisaac@juniper.net

   Sami Boutros
   Cisco
   Email: sboutros@cisco.com boutros.sami@gmail.com

   John Drake
   Juniper
   Email: jdrake@juniper.net

   Wen Lin
   Juniper
   Email: wlin@juniper.net