BESS Workgroup                                           A. Sajassi, Ed.
INTERNET-DRAFT                                                  S. Salam
Intended Status: Standards Track                                   Cisco
Updates: RFC7385                                                J. Drake
                                                                 Juniper
                                                               J. Uttaro
                                                                     ATT
                                                              S. Boutros
                                                                  VMware
                                                              J. Rabadan
                                                                   Nokia

Expires: March 1, June 12, 2017                                  January 12, 2017                                 September 1, 2016

                   E-TREE Support in EVPN & PBB-EVPN
                     draft-ietf-bess-evpn-etree-07
                     draft-ietf-bess-evpn-etree-08

Abstract

   The Metro Ethernet Forum (MEF) has defined a rooted-multipoint
   Ethernet service known as Ethernet Tree (E-Tree). A solution
   framework for supporting this service in MPLS 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. This document makes use of the
   most significant bit of the scope governed by the IANA registry
   created by RFC7385, and hence updates that RFC accordingly.

Status of this Memo

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

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

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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  7
   3 Operation for EVPN . . . . . . . . . . . . . . . . . . . . . . .  7
     3.1 Known Unicast Traffic  . . . . . . . . . . . . . . . . . . .  7  8
     3.2 BUM Traffic  . . . . . . . . . . . . . . . . . . . . . . . .  8  9
       3.2.1 BUM traffic originated from a single-homed site on a
             leaf AC  . . . . . . . . . . . . . . . . . . . . . . . .  9 10
       3.2.2 BUM traffic originated from a single-homed site on a
             root AC  . . . . . . . . . . . . . . . . . . . . . . . .  9 10
       3.2.3 BUM traffic originated from a multi-homed site on a
             leaf AC  . . . . . . . . . . . . . . . . . . . . . . . .  9 10
       3.2.4 BUM traffic originated from a multi-homed site on a
             root AC  . . . . . . . . . . . . . . . . . . . . . . . . 10
     3.3 E-TREE Traffic Flows for EVPN  . . . . . . . . . . . . . . . 10 11
       3.3.1 E-Tree with MAC Learning . . . . . . . . . . . . . . . . 10 11
       3.3.2 E-Tree without MAC Learning  . . . . . . . . . . . . . . 11 12
   4 Operation for PBB-EVPN . . . . . . . . . . . . . . . . . . . . . 11 12
     4.1 Known Unicast Traffic  . . . . . . . . . . . . . . . . . . . 12 13
     4.2 BUM Traffic  . . . . . . . . . . . . . . . . . . . . . . . . 12 13
     4.3 E-Tree without MAC Learning  . . . . . . . . . . . . . . . . 13 14
   5 BGP Encoding . . . . . . . . . . . . . . . . . . . . . . . . . . 13 14
     5.1 E-TREE Extended Community  . . . . . . . . . . . . . . . . . 13 14
     5.2 PMSI Tunnel Attribute  . . . . . . . . . . . . . . . . . . . 14 15
   6  Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . 15 16
   7  Security Considerations . . . . . . . . . . . . . . . . . . . . 15 16
   8  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 15 16
     8.1 Considerations for PMSI Tunnel Types . . . . . . . . . . . . 15 16
   9  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 16 17
     9.1  Normative References  . . . . . . . . . . . . . . . . . . . 16 17
     9.2  Informative References  . . . . . . . . . . . . . . . . . . 16 17
   Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 18
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17 18

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.

   [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.

   [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.
   [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 root(s) or leaf(s). 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, topology constraint, provided by using tailored BGP Route Target (RT) import/export
   policies among the PEs belonging to the same EVI, can be used to
   restrict the communications among Leaf PEs. To restrict the
   communications among Leaf sites connected to the same PE and
   belonging to the same EVI, split-horizon filtering is used to block
   traffic from one Leaf interface to another Leaf interface of a given
   E-TREE 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.

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 Root(s) a Root AC or Leaf(s) a Leaf AC
   (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 just like the previous scenario (in section 2.1),
   two Route Targets (one for Root and another for Leaf) can be used.
   However, the difference is that on a PE with both Root and Leaf ACs,
   all remote MAC routes are PEs imported and thus there needs to be a way
   to differentiate remote MAC routes associated with only root (or leaf) sites per
   EVI, then Leaf ACs versus
   the RT constrain procedures described ones associated with Root ACs in section 2.1 order to apply the proper
   ingress filtering.

   In order to support such ingress filtering on the ingress PE with
   both Leaf and Root ACs, one the following two approaches can
   also be used here. However, when used:

   A) To use two MAC-VRFs (two bridge tables per VLANs if a given VLAN
   exists on the PE for both Leaf and Root site is added ACs of an EVI) - one for Root
   ACs and another for Leaf ACs.

   B) To color MAC addresses with Leaf or Root color before distributing
   them in BGP to other PEs depending on whether they are learned on a
   Leaf PE,
   then AC or a Root AC.

   Maintaining two MAC-VRFs (two bridge tables) per VLAN (when both Leaf
   and Root ACs exists for that PE needs VLAN) would either require two lookups
   be performed per MAC address in each direction in case of a miss, or
   duplicating many MAC addresses between the two bridge tables
   belonging to process the same VLAN (same E-TREE instance). Unless two lookups
   are made, duplication of MAC routes addresses would be needed for both
   locally learned and remotely learned MAC addresses. Locally learned
   MAC addresses from all other Leaf PEs ACs need to be duplicated onto Root bridge
   table and
   add them locally learned MAC addresses from Root ACs need to its forwarding be
   duplicated onto Leaf bridge table. Remotely learned MAC addresses
   from Root ACs need to be copied onto both Root and Leaf bridge
   tables. Because of potential inefficiencies associated with data-
   plane implementation of additional MAC lookup or duplication of MAC
   entries, option (A) is not believed to be implementable without
   dataplane performance inefficiencies in some platforms and thus this
   draft introduces the coloring option (B) as detailed in section 3.1.

   In order to avoid two MAC-VRFs, this draft introduces the coloring
   option (B) as detailed in section 3.1.

   For this scenario, if for a given EVI, the vast 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 MAY be used in
   order to alleviate the configuration and operational overhead. overhead associated with using
   two RTs per EVI at the expense of having unwanted MAC addresses on
   the Leaf-only PEs.

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 single 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
   identified is on a per MAC address. This scenario is considered in
   this draft for EVPN service with only known unicast traffic because
   the DF filtering per [RFC7432] would not be compatible with the
   required egress filtering - i.e., BUM traffic is not supported in
   this scenario and it is dropped . by the ingress PE.

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

   [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, [RFC7432] 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/IP Advertisement route, then it notifies 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.

   In situation where MAC moves are allowed among Leaf and Root sites
   (e.g., non-static MAC), PEs can receive multiple MAC/IP
   advertisements routes for the same MAC address with different
   Leaf/Root indications (and possibly different ESIs for multi-homing
   scenarios). In such situations, MAC mobility procedures take
   precedence to first identify the location of the MAC before
   associating that MAC with a Root or a Leaf site.

   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

   This specification does not provide support for filtering BUM traffic
   on the ingress PE because it is not possible to perform filtering of
   BUM traffic on the ingress PE, as is the case with known unicast
   described above, due to the multi-destination nature of BUM 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 [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].

   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 as known-unicast traffic.

   There are four scenarios to consider as follows. In all these
   scenarios, the ingress 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 label 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 AC identifier for that segment
   (e.g., Ethernet Tag of the frame for 802.1Q frames). Other mechanisms
   for identifying root or leaf (e.g., on a per MAC address basis) 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 [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 label 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 leafs), the same AC (e.g., 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 or broadcast 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 [RFC7432] for adding and/or processing an ESI
   MPLS label.

3.3 E-TREE Traffic Flows for EVPN

   Per [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(s) 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
   [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
   route is used to support BUM traffic.

   The fields of this 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 advertises 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. Just like the EVPN
   case, the new E-TREE Extended Community defined in section [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 advertised: one B-MAC
   address is per ES as specified in [RFC7623] and implicitly denoting
   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 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 leafs), 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 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.

   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 (which will be used as a source B-
   MAC for BUM traffic), it updates its egress filtering (based on the
   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 its B-MAC list used for egress
   filtering.
   filtering - i.e., to block traffic from that B-MAC address.

   - 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 [RFC7623] and
   does not require any additional flags in the data-plane.

   Just as in section 3.2, 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 as known-unicast 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 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=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 (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) 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

   [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.

   Using the Composite flag for Tunnel Types 0x00 'no tunnel information
   present' and 0x06 'Ingress Replication' is invalid, and should be
   treated as an invalid tunnel type on reception.

6  Acknowledgement

   We would like to thank Dennis Cai, Antoni Przygienda, and Jeffrey
   Zhang for their valuable comments. The authors would also like to
   thank Thomas Morin for shepherding this document and providing
   valuable comments.

7  Security Considerations

   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
   "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

   IANA has allocated value 5 in the "EVPN Extended Community Sub-Types"
   registry defined in [RFC7153] as follow:

         SUB-TYPE VALUE     NAME                        Reference

         0x05               E-TREE Extended Community   This document

8.1 Considerations for PMSI Tunnel Types
   The "P-Multicast Service Interface Tunnel (PMSI Tunnel) Tunnel Types"
   registry in the "Border Gateway Protocol (BGP) Parameters" registry
   needs to be updated to reflect the use of the most significant bit to
   advertise the use of "composite tunnels" (section 5.2).

   For this purpose, this document updates RFC7385.

   The registry is to be updated, by removing the entries for 0xFB-0xFE
   and 0x0F, and replacing them by:

   - 0x7B-0x7E Reserved for Experimental Use [this document]- document]
   - 0x7F  Reserved [this document]- document]
   - 0x80-0xFF Not Allocatable, corresponds to Composite tunnel types
     [this document]

   The allocation policy for values 0x00 to 0x7A is IETF Review
   [RFC5226]. The range for experimental use is now 0x7B-0x7E, and value
   in this range are not to be assigned. The status of 0x7F may only be
   changed through Standards Action [RFC5226].

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.

              [RFC7385] Andersson et al., "IANA Registry for P-Multicast
              Service Interface (PMSI) Tunnel Type Code Points",
              October, 2014.

              [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.

9.2  Informative References

   [RFC7387] Key et al., "A Framework for E-Tree Service over MPLS
   Network", October 2014.

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

Contributors

   In addition to the authors listed on the front page, the following
   co-authors have also contributed to this document:

   Wim Henderickx
   Nokia

   Aldrin Isaac
   Wen Lin
   Juniper

Authors' Addresses

   Ali Sajassi
   Cisco
   Email: sajassi@cisco.com

   Samer Salam
   Cisco
   Email: ssalam@cisco.com

   John Drake
   Juniper
   Email: jdrake@juniper.net

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

   Sami Boutros
   VMware
   Email: sboutros@vmware.com
   Jorge Rabadan
   Nokia
   Email: jorge.rabadan@nokia.com