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: April 10, 2016                                 October 10, 2015


                   E-TREE Support in EVPN & PBB-EVPN
                     draft-ietf-bess-evpn-etree-03


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

   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

   The list of Internet-Draft Shadow Directories can be accessed at



Sajassi et al.           Expires April 10, 2016                 [Page 1]


INTERNET DRAFT     E-TREE Support in EVPN & PBB-EVPN      April 10, 2016


   http://www.ietf.org/shadow.html


Copyright and License Notice

   Copyright (c) 2013 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
   5 BGP Encoding . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     5.1 E-TREE Extended Community  . . . . . . . . . . . . . . . . . 13
     5.2 PMSI Tunnel Attribute  . . . . . . . . . . . . . . . . . . . 14



Sajassi et al.           Expires April 10, 2016                 [Page 2]


INTERNET DRAFT     E-TREE Support in EVPN & PBB-EVPN      April 10, 2016


   6  Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . 14
   7  Security Considerations . . . . . . . . . . . . . . . . . . . . 14
   8  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 14
   9  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     9.1  Normative References  . . . . . . . . . . . . . . . . . . . 15
     9.2  Informative References  . . . . . . . . . . . . . . . . . . 15
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15












































Sajassi et al.           Expires April 10, 2016                 [Page 3]


INTERNET DRAFT     E-TREE Support in EVPN & PBB-EVPN      April 10, 2016


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 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



Sajassi et al.           Expires April 10, 2016                 [Page 4]


INTERNET DRAFT     E-TREE Support in EVPN & PBB-EVPN      April 10, 2016


   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 32K or 64K), then RT type 0 as defined in [RFC4360]
   SHOULD be used; otherwise, RT type 2 is sufficient.

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).














Sajassi et al.           Expires April 10, 2016                 [Page 5]


INTERNET DRAFT     E-TREE Support in EVPN & PBB-EVPN      April 10, 2016


                     +---------+            +---------+
                     |   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



Sajassi et al.           Expires April 10, 2016                 [Page 6]


INTERNET DRAFT     E-TREE Support in EVPN & PBB-EVPN      April 10, 2016


3 Operation for EVPN

   [EVPN] 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] has inherent capability to support 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.




Sajassi et al.           Expires April 10, 2016                 [Page 7]


INTERNET DRAFT     E-TREE Support in EVPN & PBB-EVPN      April 10, 2016


   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 of whether they originated from a Leaf AC or not. In other
   words, leaf/root indication for BUM traffic is done at the
   granularity of AC. This can be achieved in EVPN through the use of
   the ESI MPLS label. Therefore, the ESI MPLS label can be used to
   either identify the Ethernet segment of origin per [RFC 7432] or it
   can be used to indicate that the packet is originated from a leaf
   site.

   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 root AC or a leaf
   AC.

   The main difference between downstream and upstream assigned ESI MPLS
   label is that in case of downstream assigned not all egress PE
   devices need to receive the ESI 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 ESI MPLS label
   depending on whether the Ethernet frame originated from a Root or a
   Leaf site on that Ethernet Segment. 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).



Sajassi et al.           Expires April 10, 2016                 [Page 8]


INTERNET DRAFT     E-TREE Support in EVPN & PBB-EVPN      April 10, 2016


   Other mechanisms for identifying whether an egress 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 MPLS 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 the leaf
   ACs on the PE. 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]. The RT(s) represent EVIs with
   at least a leaf site in them.  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 ESI MPLS 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 MPLS
   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 a multi-homed Ethernet Segment
   (ES) can have a mixed of both leaf and root ACs with each AC
   designating a subnet (e.g., a VLAN). 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 for further study.

   In such scenarios,  If a multicast packet is originated from a leaf
   AC, then it only needs to carry Leaf MPLS 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] for adding and/or processing an ESI
   MPLS label.




Sajassi et al.           Expires April 10, 2016                 [Page 9]


INTERNET DRAFT     E-TREE Support in EVPN & PBB-EVPN      April 10, 2016


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 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 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 per [RFC 7432].

   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



Sajassi et al.           Expires April 10, 2016                [Page 10]


INTERNET DRAFT     E-TREE Support in EVPN & PBB-EVPN      April 10, 2016


   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 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 route import rules are as described in previous
   sections.

   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 a Root/Leaf indication along with
   each B-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 new E-TREE Extended Community
   defined in section [5.2], 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 implicitly denoting Root and the other
   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



Sajassi et al.           Expires April 10, 2016                [Page 11]


INTERNET DRAFT     E-TREE Support in EVPN & PBB-EVPN      April 10, 2016


   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.

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, 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.

   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.




Sajassi et al.           Expires April 10, 2016                [Page 12]


INTERNET DRAFT     E-TREE Support in EVPN & PBB-EVPN      April 10, 2016


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 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. 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 | Flags(1 Octet)|               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |  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, 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), 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.





Sajassi et al.           Expires April 10, 2016                [Page 13]


INTERNET DRAFT     E-TREE Support in EVPN & PBB-EVPN      April 10, 2016


5.2 PMSI Tunnel Attribute

   [RFC 6514] 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 comments.

7  Security Considerations

   Same security considerations as [RFC7432].

8  IANA Considerations

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

9  References




Sajassi et al.           Expires April 10, 2016                [Page 14]


INTERNET DRAFT     E-TREE Support in EVPN & PBB-EVPN      April 10, 2016


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.

   [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.

   [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



Sajassi et al.           Expires April 10, 2016                [Page 15]


INTERNET DRAFT     E-TREE Support in EVPN & PBB-EVPN      April 10, 2016


   Bloomberg Issac
   Email: aisaac71@bloomberg.net


   Sami Boutros
   Cisco
   Email: sboutros@cisco.com












































Sajassi et al.           Expires April 10, 2016                [Page 16]