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Versions: (draft-key-l2vpn-etree-frwk) 00 01 02 03 04 05 06

Network Working Group                       Raymond Key (editor), Huawei
Internet Draft                                     Simon Delord, Telstra
Category: Informational                       Frederic Jounay, Orange CH
Expires: August 2013                                   Lucy Yong, Huawei
                                                        Lizhong Jin, ZTE
                                         Yuji Kamite, NTT Communications
                                          Wim Henderickx, Alcatel-Lucent


                                                       February 22, 2013


            A Framework for E-Tree Service over MPLS Network
                     draft-ietf-l2vpn-etree-frwk-02


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/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on August 22, 2013.


Abstract

   This document proposes a solution framework for supporting Metro
   Ethernet Forum (MEF) Ethernet Tree (E-Tree) services over a
   Multiprotocol Label Switching (MPLS) network. The objective is to
   provide a simple and effective approach to emulate E-Tree services
   in addition to Ethernet LAN (E-LAN) services on an existing MPLS
   network.






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Table of Contents

   1. Introduction....................................................3
   1.1. Objective and Scope...........................................3
   1.2. Traditional Ethernet Network..................................3
   1.3. MEF Multipoint Ethernet Services..............................3
   1.3.1. Similarity between E-LAN and E-Tree.........................4
   1.3.2. Difference between E-LAN and E-Tree.........................4
   1.4. IETF Multipoint L2VPN Services................................5
   1.4.1. Virtual Private LAN Service (VPLS)..........................5
   1.4.2. Virtual Private Multicast Service (VPMS)....................5
   1.4.3. Ethernet VPN (E-VPN)........................................6
   1.5. Terminology...................................................6
   2. Reference Model.................................................6
   3. Use Cases.......................................................8
   4. Challenges......................................................9
   4.1. Generic E-Tree Service Definition.............................9
   4.1.1. Mandatory Leaf-to-Leaf Communication Restriction............9
   4.2. Use Case Desirable Requirements..............................10
   4.2.1. Ethernet Broadcast/Multicast Optimisation..................10
   4.2.2. IP Multicast Optimisation..................................11
   4.2.3. MAC-based Forwarding Unnecessary...........................11
   4.2.4. MAC-based Forwarding Security Concern......................12
   5. A Solution Framework for MAC-based Forwarding E-Tree...........12
   5.1. VPLS Solution................................................12
   5.1.1. MAC-based Forwarding Any-to-Any Ethernet VPN...............12
   5.1.2. Leaf-to-Leaf Communication Restriction.....................13
   5.1.3. Optional Enhancement - Point-to-Multipoint PW..............13
   5.1.4. Optional Enhancement - IP Multicast in VPLS........ .......14
   5.2. E-VPN Solution...............................................14
   6. Non-MAC-based Forwarding E-Tree................................14
   6.1. Single Root, Broadcast Only - VPMS...........................14
   6.2. Multiple Roots, Broadcast and Unicast........................14
   6.3. E-VPN Solution...............................................15
   7. Security Consideration.........................................15
   8. IANA Considerations............................................15
   9. Acknowledgements...............................................15
   10. References....................................................15
   10.1. Normative References........................................15
   10.2. Informative References......................................16
   Appendix A. Some Possible Ways for Leaf-to-Leaf Communication
               Restriction...........................................18
   Authors' Addresses................................................28
   Intellectual Property and Copyright Statements....................29


Conventions used in this document

   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 [RFC2119].



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1. Introduction

1.1. Objective and Scope

   This document proposes a solution framework for supporting Metro
   Ethernet Forum (MEF) Ethernet Tree (E-Tree) services over a MPLS
   network. The objective is to provide a simple and effective approach
   to emulate E-Tree services in addition to Ethernet LAN (E-LAN)
   services on an existing MPLS network.

   This solution framework makes use of existing IETF specified
   mechanisms unless there are technical reasons why the existing
   mechanisms are insufficient or unnecessary.

   This document does not intend to provide a full specification of the
   solution, but rather to identify the functional components of the
   overall solution, and for each component, whether it is REQUIRED or
   OPTIONAL, whether existing mechanism is sufficient, or whether
   relevant mechanism is already under development.

   In this document, "current standard" refers to [RFC4385], [RFC4447],
   [RFC4448], [RFC4761] and [RFC4762].

1.2. Traditional Ethernet Network

   In this document, traditional Ethernet network refers to the Ethernet
   bridge/switch network, not the Ethernet repeater/hub network.

   Data frame is Ethernet frame.

   Data forwarding is MAC-based forwarding, which includes MAC address
   learning and aging.

   It is important to note that in traditional Ethernet network unicast
   unknown, multicast and broadcast frames are forwarded in exactly the
   same way to every port except the ingress port.

   An Ethernet host receiving a frame checks the destination address in
   the frame to decide whether it is the intended destination.

1.3. MEF Multipoint Ethernet Services

   MEF defines two multipoint Ethernet Service types:
     - E-LAN (Ethernet LAN), multipoint-to-multipoint service
     - E-Tree (Ethernet Tree), rooted-multipoint service

   According to MEF's technical specification, a generic E-LAN/E-Tree
   service is always bidirectional in the sense that ingress frames can
   originate at any endpoint in the service. However, some application
   scenarios of E-Tree may have unidirectional traffic only. Section 3
   will discuss about different use cases.



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   For full specification, please refer to MEF's "Ethernet Services
   Definitions - Phase 2" [MEF6.1] and "Ethernet Services Attributes
   Phase 2" [MEF10.2].

1.3.1. Similarity between E-LAN and E-Tree

   Data frame is Ethernet frame.

   Data forwarding can be MAC-based forwarding or something else, to be
   specified by service provider in the particular service definition.

   Extract from [MEF6.1] Table 7 and Table 9:
   +---------------+---------------------------------------------------+
   | EVC Service   | E-LAN/E-Tree Service Type Requirement             |
   | Attribute     |                                                   |
   +---------------+---------------------------------------------------+
   | Unicast       | Deliver Unconditionally or Deliver Conditionally. |
   | Service Frame | If Delivered Conditionally, MUST specify the      |
   | Delivery      | delivery criteria.                                |
   +---------------+---------------------------------------------------+
   | Multicast     | Deliver Unconditionally or Deliver Conditionally. |
   | Service Frame | If Delivered Conditionally, MUST specify the      |
   | Delivery      | delivery criteria.                                |
   +---------------+---------------------------------------------------+
   | Broadcast     | Deliver Unconditionally or Deliver Conditionally. |
   | Service Frame | If Delivered Conditionally, MUST specify the      |
   | Delivery      | delivery criteria.                                |
   +---------------+---------------------------------------------------+

   It is important to note that it is not a must for a MEF multipoint
   Ethernet service (E-LAN or E-Tree) to use MAC-based forwarding. This
   document presents a solution framework for MAC-based forwarding
   E-Tree in section 5, and also discusses non-MAC-based forwarding
   E-Tree in section 6.

1.3.2. Difference between E-LAN and E-Tree

   Within the context of a multipoint Ethernet service, each endpoint is
   designated as either a Root or a Leaf. A Root can communicate with
   all other endpoints in the same multipoint Ethernet service, however
   a Leaf can only communicate with Roots but not Leafs.

   The only difference between E-LAN and E-Tree is:
     - E-LAN has Root endpoints only, which implies there is no
       communication restriction between endpoints
     - E-Tree has both Root and Leaf endpoints, which implies there is a
       need to enforce communication restriction between Leaf endpoints

   Extract from [MEF10.2] Section 6.3:
   The UNI Type MUST have the value either "Root" or "Leaf." If the type
   of EVC is Point-to-Point or Multipoint-to-Multipoint, then the UNI
   Type MUST equal "Root."


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   Extract from [MEF10.2] Section 6.1.2.2:
   An ingress Service Frame mapped to the EVC at a Leaf UNI MUST NOT
   result in an egress Service Frame at another Leaf UNI but MAY result
   in an egress Service Frame at some or all of the Root UNIs.

   It is important to note that one E-Tree service may have single or
   multiple Root UNIs.

   Extract from [MEF6.1] Section 6.3:
   In its simplest form, an E-Tree Service type can provide a single
   Root for multiple Leaf UNIs. Each Leaf UNI can exchange data with
   only the Root UNI. ... In more sophisticated forms, an E-Tree Service
   type may support two or more Root UNIs. In this scenario, each Leaf
   UNI can exchange data only with the Root UNIs. As well, the Roots can
   communicate with each other. In such a service, redundant access to
   the Root can also be provided, effectively allowing for enhanced
   service reliability and flexibility.

1.4. IETF Multipoint L2VPN Services

1.4.1. Virtual Private LAN Service (VPLS)

   VPLS is a L2VPN service that provides multipoint-to-multipoint
   connectivity for Ethernet across an IP or MPLS-enabled IP Packet
   Switched Network. VPLS emulates the Ethernet VLAN functionality of
   traditional Ethernet network.

   VPLS is a current IETF standard, please refer to [RFC4761] [RFC4762].

   Data frame is Ethernet frame.

   Data forwarding is MAC-based forwarding, which includes MAC address
   learning and aging.

   It is important to note that the current standard VPLS treats
   Ethernet multicast frame in exactly the same way as Ethernet
   broadcast frame and does not restrict transmission of Ethernet
   multicast frame to a smaller set of receivers. An Ethernet host
   receiving a frame checks the destination address in the frame to
   determine whether it is the intended destination.

   VPLS can be used to emulate E-LAN service over MPLS network provided
   that the E-LAN service uses MAC-based forwarding as service frame
   delivery attribute. Considerable number of service providers have
   adopted this approach to provide E-LAN services to customers.

1.4.2. Virtual Private Multicast Service (VPMS)

   VPMS is a L2VPN service that provides point-to-multipoint
   connectivity across a variety of link layers, including Frame Relay,
   ATM, Ethernet, PPP, etc., across an IP or MPLS-enabled IP Packet
   Switched Network.


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   In the Ethernet use case, VPMS provides single coverage of receiver
   membership, i.e. there is no distinct differentiation for multiple
   multicast groups in one VPN. Destination address in Ethernet frame is
   not used in data forwarding.

   VPMS MUST support unidirectional point-to-multipoint traffic from a
   sender to multiple receivers and MAY support reverse traffic in a
   point-to-point manner.

   VPMS is currently under development. Please refer to [Draft VPMS
   Frmwk].

1.4.3. Ethernet VPN (E-VPN)

   E-VPN is an enhanced Layer-2 service that emulates an Ethernet (V)LAN
   across a PSN, primarily targeted to support large-scale L2VPNs with
   resiliency requirements not satisfied by other L2VPN solutions.

   E-VPN is currently under development. Please refer to [Draft EVPN
   Req] [Draft BGP EVPN].

1.5. Terminology

   E-Tree

   An Ethernet VPN in which each Root AC can communicate with every
   other AC, whereas Leaf ACs can only communicate with Root ACs. Each
   AC on an E-Tree construct is designated as either a Root AC or a Leaf
   AC. There can be multiple Root ACs and Leaf ACs per E-Tree construct.

   Root AC

   An ingress frame at a Root AC can be delivered to one or more of
   any of the other ACs in the E-Tree. Please note that this AC is
   bidirectional.

   Leaf AC

   Ingress frame at a Leaf AC can only be delivered to one or more Root
   ACs in the E-Tree. Ingress frame at a Leaf AC MUST NOT be delivered
   to any Leaf ACs in the E-Tree. Please note that this AC is
   bidirectional.

2. Reference Model

   Figure 1 below describes a generic reference model where PE1, PE2 and
   PE3 need to establish an E-Tree construct between different Ethernet
   endpoints. Each PE has 2 Root ACs and 2 Leaf ACs connected to a VSI.
   These VSIs are then linked together via Ethernet PWs.

   In most use cases, an E-Tree construct has only a few Root ACs but
   many Leaf ACs. There may be only Root ACs or only Leaf ACs on a PE.


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                     <------------E-Tree------------>
                    +---------+            +---------+
                    |   PE1   |            |   PE2   |
   +----+           |  +---+  |            |  +---+  |           +----+
   |CE01+----AC1----+--+   |  |            |  |   +--+----AC5----+CE05|
   +----+ (Root AC) |  | V |  |            |  | V |  | (Root AC) +----+
   +----+           |  |   |  |            |  |   |  |           +----+
   |CE02+----AC2----+--+   |  |  Ethernet  |  |   +--+----AC6----+CE06|
   +----+ (Root AC) |  | S +--+-----PW-----+--+ S |  | (Root AC) +----+
   +----+           |  |   |  |            |  |   |  |           +----+
   |CE03+----AC3----+--+   |  |            |  |   +--+----AC7----+CE07|
   +----+ (Leaf AC) |  | I |  |            |  | I |  | (Leaf AC) +----+
   +----+           |  |   |  |            |  |   |  |           +----+
   |CE04+----AC4----+--+   |  |            |  |   +--+----AC8----+CE08|
   +----+ (Leaf AC) |  +-+-+  |            |  +-+-+  | (Leaf AC) +----+
                    |    |    |            |    |    |
                    +----+----+            +----+----+
                         |                      |
                         |Ethernet              |Ethernet
                         |PW                    |PW
                         |                      |
                         |                 +----+----+
                         |                 |    |    |
                         |                 |  +-+-+  |           +----+
                         |                 |  |   +--+----AC9----+CE09|
                         |                 |  | V |  | (Root AC) +----+
                         |                 |  |   |  |           +----+
                         |                 |  |   +--+----AC10---+CE10|
                         +-----------------+--+ S |  | (Root AC) +----+
                                           |  |   |  |           +----+
                                           |  |   +--+----AC11---+CE11|
                                           |  | I |  | (Leaf AC) +----+
                                           |  |   |  |           +----+
                                           |  |   +--+----AC12---+CE12|
                                           |  +---+  | (Leaf AC) +----+
                                           |   PE3   |
                                           +---------+
                     <------------E-Tree------------>

                     Figure 1: E-Tree Reference Model

   With an E-Tree construct:
     - A Root AC can receive from and transmit to any other ACs.
     - A Leaf AC can receive from and transmit to any Root ACs.
     - A Leaf AC cannot receive from and transmit to any other Leaf ACs.

   This applies to all traffic, including Unicast Known, Unicast
   Unknown, Broadcast and Multicast.

   When an Ethernet Frame is received on PE1 via AC1, the frame can be
   transmitted to any other local ACs on PE1 and via Ethernet PWs to any
   remote ACs on PE2 and PE3.


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   However when an Ethernet frame is received on PE1 via AC3, the frame
   can be transmitted to any other local Root ACs on PE1 and via
   Ethernet PWs to any remote Root ACs on PE2 and PE3, but the frame
   cannot be transmitted to any local Leaf ACs on PE1 nor any remote
   Leaf ACs on PE2 and PE3.

3. Use Cases

   Table 1 below presents some major use cases.

       +---------------------------+--------------+------------+
       | Use Case                  | Root         | Leaf       |
   +---+---------------------------+--------------+------------+
   | 1 | Hub & Spoke VPN           | Hub Site     | Spoke Site |
   +---+---------------------------+--------------+------------+
   | 2 | Wholesale Access          | Customer's   | Customer's |
   |   |                           | Interconnect | Subscriber |
   +---+---------------------------+--------------+------------+
   | 3 | Mobile Backhaul           | RAN NC       | RAN BS     |
   +---+---------------------------+--------------+------------+
   | 4 | IEEE 1588 PTPv2           | PTP Server   | PTP Client |
   |   | Clock Synchronisation     |              |            |
   +---+---------------------------+--------------+------------+
   | 5 | Internet Access           | BNG Router   | Subscriber |
   |   | Reference: [TR-101]       |              |            |
   +---+---------------------------+--------------+------------+
   | 6 | Broadcast Video           | Video Source | Subscriber |
   |   | (unidirectional only)     |              |            |
   +---+---------------------------+--------------+------------+
   | 7 | Broadcast/Multicast Video | Video Source | Subscriber |
   |   | plus Control Channel      |              |            |
   +---+---------------------------+--------------+------------+
   | 8 | Device Management         | Management   | Managed    |
   |   |                           | System       | Device     |
   +---+---------------------------+--------------+------------+

                     Table 1: E-Tree Use cases

   Common to all use cases, direct Layer 2 Leaf-to-Leaf communication is
   not required. For Mobile backhaul, this may not be valid for LTE X2
   interfaces in the future.

   If direct Layer 2 Leaf-to-Leaf communication is not allowed due to
   security concern, then E-Tree should be used to prohibit
   communication between Leaf endpoints, otherwise E-LAN is also a
   feasible option.

   Also common to the use cases mentioned above, there may be single or
   multiple Root endpoints in one E-Tree service. The need for multiple
   Root endpoints is usually driven by redundancy requirement. Whether
   a particular E-Tree service needs to support single or multiple Root
   endpoints depends on the target application.


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   A generic E-Tree service supports all the following traffic flows:
     - Ethernet Unicast from Root to Leaf
     - Ethernet Unicast from Leaf to Root
     - Ethernet Unicast from Root 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 the above or only
   a subset depending on the target application.

   Among the use cases mentioned above, broadcast video draws most
   attention. Actually, broadcast video is a representing example for
   content delivery in general, such as news feed, financial data
   feed, etc.

4. Challenges

4.1. Generic E-Tree Service Definition

   This section highlights why the current standard VPLS is insufficient
   for emulating E-Tree service over MPLS network.

4.1.1. Mandatory Leaf-to-Leaf Communication Restriction

   Current standard VPLS treats all ACs equal (i.e. not classified into
   Root or Leaf) and provides any-to-any connectivity among all ACs. The
   current standard VPLS does not include any mechanism of communication
   restriction between specific ACs, therefore is insufficient for
   emulating generic E-Tree service over MPLS network.

   A problem occurs when there are two or more PEs with both Root AC and
   Leaf AC.

   Let's look at the scenario illustrated in Figure 2 below. VPLS is
   used to emulate an E-Tree service over a MPLS network.

   Note: Figure 2 is a hypothetical case solely for explaining the
   problem, and not meant to represent a typical E-Tree service.

                     <------------E-Tree------------>
                    +---------+            +---------+
                    |   PE1   |            |   PE2   |
   +---+            |  +---+  |            |  +---+  |            +---+
   |CE1+-----AC1----+--+   |  |            |  |   +--+----AC3-----+CE3|
   +---+  (Root AC) |  | V |  |  Ethernet  |  | V |  | (Root AC)  +---+
                    |  | S +--+-----PW-----+--+ S |  |
   +---+            |  | I |  |            |  | I |  |            +---+
   |CE2+-----AC2----+--+   |  |            |  |   +--+----AC4-----+CE4|
   +---+  (Leaf AC) |  +---+  |            |  +---+  | (Leaf AC)  +---+
                    +---------+            +---------+

   Figure 2: Problem Scenario for Leaf-to-Leaf Communication Restriction



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   When PE2 receives a frame from PE1 via the Ethernet PW,
     - PE2 does not know which AC on PE1 is the ingress AC
     - PE2 does not know whether the ingress AC is a Leaf AC or not
     - PE2 does not have sufficient information to enforce the
       Leaf-to-Leaf communication restriction

   Examples:
     - CE2 sends a Broadcast/Multicast frame to PE1 via AC2
     - CE2 sends a Unicast frame to PE1 via AC2, destination address in
       Ethernet header equal to CE4's MAC address

   In order to fulfil the generic E-Tree service definition, extension
   to the current VPLS standard will be required. Extension to related
   PWE3 standard may also be required, depending on solution approach.
   Such extensions should have minimal impact on the emulated E-LAN
   services already in operation.

   There are some possible ways to get around this problem that do not
   require extension to the current VPLS standard but they all come with
   significant design complexity or deployment constraints. Appendix A
   highlights the major ones and the related concerns.

4.2. Use Case Desirable Requirements

   There are quite a variety of use cases for E-Tree. For some use
   cases, the generic MEF E-Tree service definition is good enough. For
   some other use cases, there are desirable requirements beyond that.

   The challenges discussed in this section are not related to the
   generic MEF E-Tree service definition but the desirable requirements
   of specific use cases. They may be critical to the success in some
   E-Tree services while totally irrelevant in some others.

4.2.1. Ethernet Broadcast/Multicast Optimisation

   According to MAC-based forwarding, an Ethernet broadcast/multicast/
   unicast unknown frame is forwarded to all ACs other than the ingress
   AC, which implies point-to-multipoint traffic from the ingress PE to
   all other PEs in the VPLS instance.

   The current standard VPLS uses only point-to-point PW between PEs.
   When the Ethernet destination address is broadcast, multicast or
   unicast unknown, the ingress PE replicates the frame on every PW
   towards remote PE belonging to the same VPLS instance. Depending on
   the mapping between the logical topology of the E-Tree service and
   the physical topology of the network, multiple PWs may transverse
   same physical link, result in multiple copies of the same payload
   Ethernet frame on the physical link. Such approach is inefficient in
   terms of bandwidth usage.





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   For some use cases, for example broadcast/multicast video, due to
   nature of the application, there is significant volume of point-to-
   multipoint traffic. Bandwidth optimisation for such traffic within
   the network becomes a concern from the service provider perspective.

   [RFC5501] provides an in-depth discussion on broadcast/multicast
   related requirements for VPLS, see issue B (Replication of PWs on
   shared physical path) in section 3.2.

4.2.2. IP Multicast Optimisation

   The current standard VPLS is a L2VPN service agnostic to customer's
   Layer 3 traffic, hence does not maintain any information about IP
   multicast group membership. Although a Layer 3 IP multicast packet is
   encapsulated in a Layer 2 Ethernet multicast frame, the current
   standard VPLS treats Ethernet multicast frame in exactly the same way
   as Ethernet broadcast frame. Therefore, such payload IP multicast
   packet will be forwarded to every other AC of the same VPLS instance.

   A payload IP multicast packet will be forwarded to all ACs, including
   those with no member of the specific IP multicast group attached.
   Unnecessary traffic consumes bandwidth on access link and may become
   a concern from the customer perspective. In some cases, it may also
   be a security concern as the multicast frame may be forwarded to an
   endpoint other than the intended destinations.

   A payload IP multicast packet will be forwarded to a remote PE with
   no member of the specific IP multicast group attached. Unnecessary
   traffic consumes bandwidth in the network and may become a concern
   from the service provider perspective.

   For some use cases, for example multicast video, due to nature of the
   application, there is significant volume of IP multicast traffic and
   different IP multicast groups are required in one E-Tree service. The
   above may become a real concern from both the customer and service
   provider perspectives.

   [RFC5501] provides an in-depth discussion on broadcast/multicast
   related requirements for VPLS, see both issue A (Replication to non-
   member site) and issue B (Replication of PWs on shared physical path)
   in section 3.2.

4.2.3. MAC-based Forwarding Unnecessary

   For some use cases, for example broadcast video, due to nature of the
   application, there is only broadcast unidirectional traffic from Root
   to all other endpoints. It is unnecessary to use destination address
   for data forwarding. Deliver unconditionally for ingress frame at
   Root endpoint may be a simpler approach than MAC-based forwarding.





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4.2.4. MAC-based Forwarding Security Concern

   MAC-based forwarding will make an unicast frame from a Root destined
   for a specific Leaf being forwarded to other endpoints in addition to
   the intended destination when the frame is classified as unicast
   unknown, may be due to MAC address aged out or MAC address table
   overflow.

   MAC address spoofing may cause an unicast frame from a Root destined
   for a specific Leaf being forwarded to an endpoint different from the
   intended destination.

   If such unicast frame carries sensitive information strictly for the
   intended destination only, then the MAC-based forwarding may cause a
   security concern from the customer perspective.

   For some use cases where mutually un-trusted subscribers are
   connected to leaf endpoints in the same E-Tree service, such as
   Internet access and wholesale access, this is a valid concern.

   There are some possible mitigations:
     - For every Leaf endpoint of the particular E-Tree service, deploy
       a service provider controlled router between the Leaf endpoint
       and the customer network
     - Customer to deploy encryption for sensitive information, for
       example IPsec, SSL, SSH, HTTPS

   Whether the MAC-based forwarding really becomes a security concern
   depends on the particular application and the deployment scenario.
   This is unlikely to be a critical concern in most cases.

5. A Solution Framework for MAC-based Forwarding E-Tree

   As mentioned in section 1.3.1. E-Tree can use MAC-based forwarding or
   something else for data forwarding. This section presents a solution
   framework for MAC-based forwarding E-Tree. Section 6 will discuss
   other variants.

5.1. VPLS Solution

   This is a VPLS based solution. Functional components of the solution
   are identified and discussed in the subsections.

5.1.1. MAC-based Forwarding Any-to-Any Ethernet VPN

   This is a REQUIRED component.

   This component is the current standard VPLS and PWE3 as specified in
   [RFC4385] [RFC4447] [RFC4448] [RFC4761] [RFC4762], which provides
   any-to-any connectivity among all ACs in one VPLS instance.

   This is the base component. All other REQUIRED/OPTIONAL components
   are to be added on top of this component.

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5.1.2. Leaf-to-Leaf Communication Restriction

   This is in response to the challenge in section 4.1.1. Mandatory
   Leaf-to-Leaf Communication Restriction.

   This is a REQUIRED component.

   This component is a minimal extension to the current VPLS and PWE3
   standards, with the objective to provide a simple and effective way
   to support generic E-Tree services in addition to E-LAN services
   using VPLS on a MPLS network.

   [Draft VPLS ETree Req] is a work in progress requirement draft.

   Different solutions have been proposed:
     - Control Word L-bit solution, [Draft CW L-bit] [Draft VPLS ETree]
     - Dual VLAN solution, [Draft VPLS PE ETree] [Draft VPLS ETree BGP]
     - Multiple PW solution, [Draft VPLS ETree Multi PW]

5.1.3. Optional Enhancement - Point-to-Multipoint PW

   This is in response to the challenge in section 4.2.1. Ethernet
   Broadcast/Multicast Optimisation.

   This is an OPTIONAL component, applicable only when there is
   significant volume of Ethernet broadcast/multicast traffic.

   Point-to-Multipoint pseudowire (P2MP PW) is a PW attached to a source
   used to distribute Layer 1 or Layer 2 format traffic to a set of
   receivers. P2MP PW is unidirectional but optionally bidirectional.

   By using P2MP PW, the ingress PE is not responsible for replicating
   the payload frame on each P2P PW towards egress PE, instead the
   network elements along the physical path participate in replication.
   The replication is done by the underlying point-to-multipoint label
   switched path (P2MP LSP).

   Extension to current VPLS standard will be required to specify how
   P2MP PW and P2P PW should be used and how MAC learning works on P2MP
   PW. Please refer to [Draft LDP-VPLS Bcast].

   P2MP PW is currently under development. Please refer to [Draft P2MP
   PW Req] [Draft P2MP PW Sig].

   It is important to note that this component will align with the
   recommendation in [RFC4665],
   "With the exception of IPLS, an L2VPN service SHOULD be agnostic to
   customer's Layer 3 traffic (e.g., IP, IPX, Appletalk) encapsulated
   within Layer 2 frames."





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5.1.4. Optional Enhancement - IP Multicast in VPLS

   This is in response to the challenge in section 4.2.2. IP Multicast
   Optimisation.

   This is an OPTIONAL component, applicable only when there is
   significant volume of IP multicast traffic and different IP multicast
   groups are required in one E-Tree service.

   Multicast in VPLS is currently under development, with the objective
   to provide efficient ways to support IP multicast services over VPLS.
   It covers IP multicast group membership control and also bandwidth
   optimisation. Please refer to [Draft Mcast VPLS].

   It is important to note that this component will make use of Layer 3
   IP multicast information in payload frames to improve transport
   efficiency, hence will not align with the recommendation in [RFC4665]
   that an L2VPN service SHOULD be agnostic to customer's Layer 3
   traffic.

5.2. E-VPN Solution

   A E-VPN based solution has been proposed. Please refer to [Draft EVPN
   ETree].

6. Non-MAC-based Forwarding E-Tree

   This section presents some variants of E-Tree services which do not
   use MAC-based forwarding as the service frame delivery attribute.

6.1. Single Root, Broadcast Only - VPMS

   This is in response to the challenge in section 4.2.3. MAC-based
   Forwarding Unnecessary.

   VPMS provides single coverage of receiver membership. Destination
   address in Ethernet frame is not used in data forwarding.

   For E-Tree service of single Root and only unidirectional broadcast
   traffic from the Root, for example certain broadcast video or similar
   content delivery applications, VPMS will be a much more simple and
   effective solution than VPLS.

   VPMS is currently under development. Please refer to [Draft VPMS
   Frmwk].

6.2. Multiple Roots, Broadcast and Unicast

   This is in response to the challenge in section 4.2.4. MAC-based
   Forwarding Security Concern.

   This will be added in later version of this document.


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6.3. E-VPN Solution

   A E-VPN based solution has been proposed. Please refer to [Draft EVPN
   ETree].

7. Security Considerations

   This will be added in later version of this document.

8. IANA Considerations

   This will be added in later version of this document.

9. Acknowledgements

   This will be added in later version of this document.

10. References

10.1. Normative References

   [MEF6.1]     Metro Ethernet Forum, Ethernet Services Definitions -
                Phase 2, April 2008

   [MEF10.2]    Metro Ethernet Forum, Ethernet Services Attributes
                Phase 2, October 2009

   [RFC2119]    Bradner, S., Key words for use in RFCs to Indicate
                Requirement Levels, BCP 14, RFC 2119, March 1997

   [RFC4385]    Bryant,S., Swallow, G., and Al, Pseudowire Emulation
                Edge-to-Edge (PWE3) Control Word for Use over an MPLS
                PSN, February 2006.

   [RFC4447]    Martini, L., and al, Pseudowire Setup and Maintenance
                Using the Label Distribution Protocol (LDP), April 2006

   [RFC4448]    Martini, L., and al, Encapsulation Methods for
                Transport of Ethernet over MPLS Networks, April 2006

   [RFC4665]    Augustyn & Serbest, Service Requirements for Layer 2
                Provider-Provisioned Virtual Private Networks,
                September 2006

   [RFC4761]    Kompella & Rekhter, Virtual Private LAN Service (VPLS)
                Using BGP for Auto-Discovery and Signaling, January 2007

   [RFC4762]    Lasserre & Kompella, Virtual Private LAN Service (VPLS)
                Using Label Distribution Protocol (LDP) Signaling,
                January 2007

   [RFC5501]    Kamite, et al., Requirements for Multicast Support in
                Virtual Private LAN Services, March 2009

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10.2. Informative References

   [TR-101]     Broadband Forum, Migration to Ethernet-Based Broadband
                Aggregation Issue 2, July 2011

   [Draft VPLS ETree Req]
                Key, et al., Requirements for MEF E-Tree Support in
                VPLS, draft-ietf-l2vpn-etree-reqt-03 (work in progress),
                October 2012

   [Draft CW L-bit]
                Delord, et al., Control Word Reserved bit for use in
                E-Tree, draft-delord-pwe3-cw-bit-etree-07 (work in
                progress), April 2012

   [Draft VPLS ETree]
                Key, et al., Extension to VPLS for E-Tree,
                draft-key-l2vpn-vpls-etree-07 (work in progress),
                April 2012

   [Draft VPLS PE ETree]
                Jiang, et al., VPLS PE Model for E-Tree Support,
                draft-ietf-l2vpn-vpls-pe-etree-01 (work in progress),
                February 2013

   [Draft VPLS ETree BGP]
                Jiang, et al., E-Tree Support in VPLS with BGP
                Signaling, draft-jiang-l2vpn-etree-bgp-00
                (work in progress), February 2012

   [Draft VPLS ETree Multi PW]
                Ram, et al., Extension to VPLS for E-Tree Using Multiple
                PWs, draft-ram-l2vpn-etree-multiple-pw-01 (work in
                progress), March 2012

   [Draft P2MP PW Req]
                Jounay, et al., Requirements for Point-to-Multipoint
                Pseudowire, draft-ietf-pwe3-p2mp-pw-requirements-05
                (work in progress), September 2011

   [Draft P2MP PW Sig]
                Sivabalan, et al., Signaling Root-Initiated Point-to-
                Multipoint Pseudowires using LDP,
                draft-ietf-pwe3-p2mp-pw-04 (work in progress),
                March 2012

   [Draft LDP-VPLS Bcast]
                Delord, et al., Extension to LDP-VPLS for Ethernet
                Broadcast and Multicast,
                draft-ietf-l2vpn-ldp-vpls-broadcast-exten-05 (work in
                progress), February 2013



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   [Draft Mcast VPLS]
                Raggarwa, Kamite & Fang, Multicast in VPLS,
                draft-ietf-l2vpn-vpls-mcast-13 (work in progress),
                January 2013

   [Draft VPMS Frmwk]
                Kamite, et al., Framework and Requirements for Virtual
                Private Multicast Service (VPMS),
                draft-ietf-l2vpn-vpms-frmwk-requirements-05 (work in
                progress), October 2012

   [Draft EVPN Req]
                Sajassi, Aggarwal, et al., Requirements for Ethernet VPN
                (E-VPN), draft-ietf-l2vpn-evpn-req-01 (work in
                progress), October 2012

   [Draft BGP EVPN]
                Sajassi, Aggarwal, et al., BGP MPLS Based Ethernet VPN,
                draft-ietf-l2vpn-evpn-02 (work in progress),
                October 2012

   [Draft EVPN ETree]
                Sajassi, et al., E-TREE Support in E-VPN,
                draft-sajassi-l2vpn-evpn-etree-01 (work in progress),
                October 2012





























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Appendix A. Some Possible Ways for Leaf-to-Leaf Communication
            Restriction

   This appendix briefly describes the following approaches:
   - Single Root Only (A.1)
   - Only one PE has Roots (A.2)
   - Only one PE with both Root & Leaf
     - Backhaul Root (A.3)
     - Backhaul Leaf (A.4)
     - H-VPLS Root (A.5)
     - H-VPLS Leaf (A.6)
   - Separate PEs for Root and Leaf (A.7)
   - Separate VSI for Root and Leaf
     - Internal Connection (A.8)
     - External Connection (A.9)
   - Separate PWs for "From Root" traffic and "From Leaf" traffic (A.10)
   - "From Root" or "From Leaf" derived from source MAC address (A.11)
   - Static MAC address configuration for Root AC (A.12)

   Reference Model for Leaf-to-Leaf Communication Restriction

                     <------------E-Tree------------>
                    +---------+            +---------+
                    |   PE1   |            |   PE2   |
   +----+           |  +---+  |            |  +---+  |           +----+
   |CE01+----AC1----+--+   |  |            |  |   +--+----AC5----+CE05|
   +----+ (Root AC) |  | V |  |            |  | V |  | (Root AC) +----+
   +----+           |  |   |  |            |  |   |  |           +----+
   |CE02+----AC2----+--+   |  |  Ethernet  |  |   +--+----AC6----+CE06|
   +----+ (Root AC) |  | S +--+-----PW-----+--+ S |  | (Root AC) +----+
   +----+           |  |   |  |            |  |   |  |           +----+
   |CE03+----AC3----+--+   |  |            |  |   +--+----AC7----+CE07|
   +----+ (Leaf AC) |  | I |  |            |  | I |  | (Leaf AC) +----+
   +----+           |  |   |  |            |  |   |  |           +----+
   |CE04+----AC4----+--+   |  |            |  |   +--+----AC8----+CE08|
   +----+ (Leaf AC) |  +---+  |            |  +---+  | (Leaf AC) +----+
                    |         |            |         |
                    +---------+            +---------+

   For the diagrams in this appendix, "L" indicates the particular AC or
   PW belonging to the PE local split horizon group specifically for
   Leaf-to-Leaf Communication Restriction. No communication is allowed
   between any two members of a split horizon group.











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A.1. Single Root Only

                     <------------E-Tree------------>
                    +---------+            +---------+
                    |   PE1   |            |   PE2   |
   +----+           |  +---+  |            |  +---+  |
   |CE01+----AC1----+--+   |  |            |  |   |  |
   +----+ (Root AC) |  | V |  |            |  | V |  |
                    |  |   |  |            |  |   |  |
                    |  |   |  |  Ethernet  |  |   |  |
                    |  | S +L-+-----PW-----+--+ S |  |
   +----+           |  |   |  |            |  |   |  |           +----+
   |CE03+----AC3----+-L+   |  |            |  |   +L-+----AC7----+CE07|
   +----+ (Leaf AC) |  | I |  |            |  | I |  | (Leaf AC) +----+
   +----+           |  |   |  |            |  |   |  |           +----+
   |CE04+----AC4----+-L+   |  |            |  |   +L-+----AC8----+CE08|
   +----+ (Leaf AC) |  +---+  |            |  +---+  | (Leaf AC) +----+
                    |         |            |         |
                    +---------+            +---------+

   Concerns:
   - Not fulfil multi-Root requirement of generic MEF E-Tree service
     definition


A.2. Only one PE has Roots

                     <------------E-Tree------------>
                    +---------+            +---------+
                    |   PE1   |            |   PE2   |
   +----+           |  +---+  |            |  +---+  |
   |CE01+----AC1----+--+   |  |            |  |   |  |
   +----+ (Root AC) |  | V |  |            |  | V |  |
   +----+           |  |   |  |            |  |   |  |
   |CE02+----AC2----+--+   |  |  Ethernet  |  |   |  |
   +----+ (Root AC) |  | S +L-+-----PW-----+--+ S |  |
   +----+           |  |   |  |            |  |   |  |           +----+
   |CE03+----AC3----+-L+   |  |            |  |   +L-+----AC7----+CE07|
   +----+ (Leaf AC) |  | I |  |            |  | I |  | (Leaf AC) +----+
   +----+           |  |   |  |            |  |   |  |           +----+
   |CE04+----AC4----+-L+   |  |            |  |   +L-+----AC8----+CE08|
   +----+ (Leaf AC) |  +---+  |            |  +---+  | (Leaf AC) +----+
                    |         |            |         |
                    +---------+            +---------+

   Concerns:
   - Deployment constraint







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A.3. Only one PE with both Root & Leaf - Backhaul Root

                        +---AC5(Root AC)---------------------------+
                        |                                          |
                        | +-AC6(Root AC)----------------------+    |
                        | |                                   |    |
                        | |                                   |    |
                        | |                                   |    |
                    +---+-+---+            +---------+        |    |
                    |   | |   |            |         |        |    |
   +----+           |  ++-++  |            |  +---+  |        |  +-+--+
   |CE01+----AC1----+--+   |  |            |  |   |  |        |  |CE05|
   +----+ (Root AC) |  | V |  |            |  | V |  |        |  +----+
   +----+           |  |   |  |            |  |   |  |        |  +----+
   |CE02+----AC2----+--+   |  |  Ethernet  |  |   |  |        +--+CE06|
   +----+ (Root AC) |  | S +L-+-----PW-----+--+ S |  |           +----+
   +----+           |  |   |  |            |  |   |  |           +----+
   |CE03+----AC3----+-L+   |  |            |  |   +L-+----AC7----+CE07|
   +----+ (Leaf AC) |  | I |  |            |  | I |  | (Leaf AC) +----+
   +----+           |  |   |  |            |  |   |  |           +----+
   |CE04+----AC4----+-L+   |  |            |  |   +L-+----AC8----+CE08|
   +----+ (Leaf AC) |  +---+  |            |  +---+  | (Leaf AC) +----+
                    |   PE1   |            |   PE2   |
                    +---------+            +---------+
                     <------------E-Tree------------>

   Concerns:
   - Deployment constraint
   - Long fibre path

























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A.4. Only one PE with both Root & Leaf - Backhaul Leaf

                     <------------E-Tree------------>
                    +---------+            +---------+
                    |   PE1   |            |   PE2   |
   +----+           |  +---+  |            |  +---+  |           +----+
   |CE01+----AC1----+--+   |  |            |  |   +--+----AC5----+CE05|
   +----+ (Root AC) |  | V |  |            |  | V |  | (Root AC) +----+
   +----+           |  |   |  |            |  |   |  |           +----+
   |CE02+----AC2----+--+   |  |  Ethernet  |  |   +--+----AC6----+CE06|
   +----+ (Root AC) |  | S +--+-----PW-----+--+ S |  | (Root AC) +----+
   +----+           |  |   |  |            |  |   |  |           +----+
   |CE03+----AC3----+-L+   |  |            |  |   |  |        +--+CE07|
   +----+ (Leaf AC) |  | I |  |            |  | I |  |        |  +----+
   +----+           |  |   |  |            |  |   |  |        |  +----+
   |CE04+----AC4----+-L+   |  |            |  |   |  |        |  |CE08|
   +----+ (Leaf AC) |  ++-++  |            |  +---+  |        |  +-+--+
                    |   L L   |            |         |        |    |
                    +---+-+---+            +---------+        |    |
                        | |                                   |    |
                        | |                                   |    |
                        | |                                   |    |
                        | +-AC7(Leaf AC)----------------------+    |
                        |                                          |
                        +---AC8(Leaf AC)---------------------------+

   Concerns:
   - Deployment constraint
   - Long fibre path

























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A.5. Only one PE with both Root & Leaf - H-VPLS Root

                     <------------E-Tree------------>
                    +---------+            +---------+
                    |   PE1   |            |   PE2   |
   +----+           |  +---+  |  Ethernet  |         |           +----+
   |CE01+----AC1----+--+   +--+-----PW-----+---------+----AC5----+CE05|
   +----+ (Root AC) |  | V |  |            |         | (Root AC) +----+
   +----+           |  |   |  |  Ethernet  |         |           +----+
   |CE02+----AC2----+--+   +--+-----PW-----+---------+----AC6----+CE06|
   +----+ (Root AC) |  | S |  |            |  +---+  | (Root AC) +----+
   +----+           |  |   |  |            |  |   |  |           +----+
   |CE03+----AC3----+-L+   |  |  Ethernet  |  | V +L-+----AC7----+CE07|
   +----+ (Leaf AC) |  | I +L-+-----PW-----+--+ S |  | (Leaf AC) +----+
   +----+           |  |   |  |            |  | I |  |           +----+
   |CE04+----AC4----+-L+   |  |            |  |   +L-+----AC8----+CE08|
   +----+ (Leaf AC) |  +---+  |            |  +---+  | (Leaf AC) +----+
                    |         |            |         |
                    +---------+            +---------+

   Concerns:
   - Design complexity
   - More PW
   - Hair pinning (e.g. CE05 to CE06/07/08) impact bandwidth and delay


A.6. Only one PE with both Root & Leaf - H-VPLS Leaf

                     <------------E-Tree------------>
                    +---------+            +---------+
                    |   PE1   |            |   PE2   |
   +----+           |  +---+  |            |  +---+  |           +----+
   |CE01+----AC1----+--+   |  |            |  |   +--+----AC5----+CE05|
   +----+ (Root AC) |  | V |  |  Ethernet  |  | V |  | (Root AC) +----+
   +----+           |  |   +--+-----PW-----+--+ S |  |           +----+
   |CE02+----AC2----+--+   |  |            |  | I +--+----AC6----+CE06|
   +----+ (Root AC) |  | S |  |            |  |   |  | (Root AC) +----+
   +----+           |  |   |  |  Ethernet  |  +---+  |           +----+
   |CE03+----AC3----+-L+   +L-+-----PW-----+---------+----AC7----+CE07|
   +----+ (Leaf AC) |  | I |  |            |         | (Leaf AC) +----+
   +----+           |  |   |  |  Ethernet  |         |           +----+
   |CE04+----AC4----+-L+   +L-+-----PW-----+---------+----AC8----+CE08|
   +----+ (Leaf AC) |  +---+  |            |         | (Leaf AC) +----+
                    |         |            |         |
                    +---------+            +---------+

   Concerns:
   - Design complexity
   - More PW
   - Hair pinning (e.g. CE08 to CE05/06) impact bandwidth and delay




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A.7. Separate PEs for Root and Leaf
     (PE2 split to PE2R & PE2L)

                     <------------E-Tree------------>
                    +---------+            +---------+
                    |   PE1   |            |   PE2R  |
   +----+           |  +---+  |            |  +---+  |           +----+
   |CE01+----AC1----+--+   |  |  Ethernet  |  | V +--+----AC5----+CE05|
   +----+ (Root AC) |  | V +--+-----PW-----+--+ S |  | (Root AC) +----+
   +----+           |  |   |  |            |  | I |  |           +----+
   |CE02+----AC2----+--+   |  |            |  |   +--+----AC6----+CE06|
   +----+ (Root AC) |  | S |  |            |  +-+-+  | (Root AC) +----+
   +----+           |  |   |  |            |    L    |
   |CE03+----AC3----+-L+   |  |            +----+----+
   +----+ (Leaf AC) |  | I |  |                 |
   +----+           |  |   |  |                 |Ethernet
   |CE04+----AC4----+-L+   |  |                 |PW
   +----+ (Leaf AC) |  +-+-+  |                 |
                    |    L    |            +----+----+
                    +----+----+            |    |    |
                         |                 |  +-+-+  |           +----+
                         |       Ethernet  |  | V +L-+----AC7----+CE07|
                         +----------PW-----+--+ S |  | (Leaf AC) +----+
                                           |  | I |  |           +----+
                                           |  |   +L-+----AC8----+CE08|
                                           |  +---+  | (Leaf AC) +----+
                                           |   PE2L  |
                                           +---------+
                     <------------E-Tree------------>

   Concerns:
   - Require two PEs in one POP
   - More PW





















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A.8. Separate VSI for Root and Leaf - Internal Connection
     (VSI on PE split to VSIR & VSIL)

                     <------------E-Tree------------>
                    +---------+            +---------+
                    |   PE1   |            |   PE2   |
   +----+           |  +---+  |            |  +---+  |           +----+
   |CE01+----AC1----+--+ V |  |            |  | V +--+----AC5----+CE05|
   +----+ (Root AC) |  | S +--+------------+--+ S |  | (Root AC) +----+
   +----+           |  | I |  |            |  | I |  |           +----+
   |CE02+----AC2----+--+ R +L-+--+      +--+-L+ R +--+----AC6----+CE06|
   +----+ (Root AC) |  +-+-+  |  |      |  |  +-+-+  | (Root AC) +----+
                    |    L    |  |      |  |    L    |
                    |    |    |  \      /  |    |    |
                    |    |    |   \    /   |    |    |
                    |    |    |    \  /    |    |    |
                 Internal|    |     \/     |    |Internal
               Connection|    |     /\     |    |Connection
                    |    |    |    /  \    |    |    |
                    |    |    |   /    \   |    |    |
                    |    |    |  /      \  |    |    |
   +----+           |  +-+-+  |  |      |  |  +-+-+  |           +----+
   |CE03+----AC3----+-L+ V |  |  |      |  |  | V +L-+----AC7----+CE07|
   +----+ (Leaf AC) |  | S +--+--+      +--+--+ S |  | (Leaf AC) +----+
   +----+           |  | I |  |            |  | I |  |           +----+
   |CE04+----AC4----+-L+ L |  |   Three    |  | L +L-+----AC8----+CE08|
   +----+ (Leaf AC) |  +-+-+  |  Ethernet  |  +---+  | (Leaf AC) +----+
                    |         |    PWs     |         |
                    +---------+            +---------+

   Concerns:
   - Design complexity
   - More VSI
   - More PW
   - Some vendor implementation may require additional hardware module
     to support internal connection between two VSIs
   - Some vendor implementation may have bandwidth limitation on
     internal connection between two VSIs
   - Some vendor implementation of service-aware management system may
     assume only one VSI per VPLS on one PE














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A.9. Separate VSI for Root and Leaf - External Connection
     (VSI on PE split to VSIR & VSIL)

                     <------------E-Tree------------>
                    +---------+            +---------+
                    |   PE1   |            |   PE2   |
   +----+           |  +---+  |            |  +---+  |           +----+
   |CE01+----AC1----+--+ V |  |            |  | V +--+----AC5----+CE05|
   +----+ (Root AC) |  | S +--+------------+--+ S |  | (Root AC) +----+
   +----+           |  | I |  |            |  | I |  |           +----+
   |CE02+----AC2----+--+ R +L-+--+      +--+-L+ R +--+----AC6----+CE06|
   +----+ (Root AC) |  |   |  |  |      |  |  |   |  | (Root AC) +----+
                    |  |   |  |  |      |  |  |   |  |
     +------AC-X1---+-L+   |  |  \      /  |  |   +L-+----AC-X2-----+
     |    (Leaf AC) |  +---+  |   \    /   |  +---+  | (Leaf AC)    |
     |              |         |    \  /    |         |              |
     |External      |         |     \/     |         |      External|
     |Connection    |         |     /\     |         |    Connection|
     |              |  +---+  |    /  \    |  +---+  |              |
     +------AC-Y1---+--+   |  |   /    \   |  |   +--+----AC-Y2-----+
          (Root AC) |  |   |  |  /      \  |  |   |  | (Root AC)
   +----+           |  |   |  |  |      |  |  |   |  |           +----+
   |CE03+----AC3----+-L+ V |  |  |      |  |  | V +L-+----AC7----+CE07|
   +----+ (Leaf AC) |  | S +--+--+      +--+--+ S |  | (Leaf AC) +----+
   +----+           |  | I |  |            |  | I |  |           +----+
   |CE04+----AC4----+-L+ L |  |   Three    |  | L +L-+----AC8----+CE08|
   +----+ (Leaf AC) |  +-+-+  |  Ethernet  |  +---+  | (Leaf AC) +----+
                    |         |    PWs     |         |
                    +---------+            +---------+

   Concerns:
   - Design complexity
   - More VSI
   - More PW
   - More AC (for external connection between two VSIs)
   - Require additional two high speed physical ports on PE to support
     such external connections
   - Some vendor implementation of service-aware management system may
     assume only one VSI per VPLS on one PE















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A.10. Separate PWs for "From Root" traffic and "From Leaf" traffic

                     <------------E-Tree------------>
                    +---------+            +---------+
                    |   PE1   |            |   PE2   |
   +----+           |  +---+  |            |  +---+  |           +----+
   |CE01+----AC1----+--+   |  |  Ethernet  |  |   +--+----AC5----+CE05|
   +----+ (Root AC) |  | V +--+---PW for---+--+ V |  | (Root AC) +----+
   +----+           |  |   |  |"From Root" |  |   |  |           +----+
   |CE02+----AC2----+--+   |  |  Traffic   |  |   +--+----AC6----+CE06|
   +----+ (Root AC) |  | S |  |            |  | S |  | (Root AC) +----+
   +----+           |  |   |  |            |  |   |  |           +----+
   |CE03+----AC3----+--+   |  |            |  |   +--+----AC7----+CE07|
   +----+ (Leaf AC) |  | I |  |  Ethernet  |  | I |  | (Leaf AC) +----+
   +----+           |  |   +--+---PW for---+--+   |  |           +----+
   |CE04+----AC4----+--+   |  |"From Leaf" |  |   +--+----AC8----+CE08|
   +----+ (Leaf AC) |  +---+  |  Traffic   |  +---+  | (Leaf AC) +----+
                    |         |            |         |
                    +---------+            +---------+

   Concerns:
   - More PW
   - Most, if not all, vendor implementation support only one PW
     between two VSIs on different PEs
   - Most, if not all, vendor implementation of service-aware management
     system assume only one PW between two VSIs on different PEs
   - Asymmetric path for bidirectional traffic between Root and Leaf on
     different PEs (e.g. CE01-->CE07 use the "From Root" PW, CE07-->CE01
     use the "From Leaf" PW)
   - Require extension to current standard VPLS
     - support two PWs between two VSIs on different PEs (both active
       but no loop)
     - share MAC learning between the "From Root" PW and "From Leaf" PW
       (bidirectional traffic may be on asymmetric path)
     - in addition to standard MAC-based forwarding, select which PW to
       use based on whether ingress AC is Root or Leaf
     - filter Leaf-to-Leaf traffic (split horizon group at PW/AC level
       is not good enough because of asymmetric path)
















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A.11. "From Root" or "From Leaf" derived from source MAC address

   Based on the current standard VPLS, a PE has no information about ACs
   on another PE.

   This approach will need additional information exchange between
   ingress PE and egress PE, via OSS or peer to peer.

   Concerns:
   - Require system development or additional signaling between PEs
   - Not an ideal solution from security perspective because of the
     dynamic nature of MAC address to AC mapping


A.12. Static MAC address configuration for Root AC

   This approach requires additional configuration on PEs
   - Disable MAC address learning for Root ACs
   - Static configuration of MAC addresses per Root AC
   - Add filtering for each Root AC
     - Drop ingress frame if source MAC address not equal to any of the
       static MAC addresses configured for the particular Root AC
   - Add filtering for each Leaf AC
     - Drop ingress frame if source MAC address equal to any of the
       static MAC addresses configured for any Root ACs of the VPLS
       instance
     - Drop egress frame if source MAC address not equal to any of the
       static MAC addresses configured for any Root ACs of the VPLS
       instance

   Concerns:
   - No MAC address learning capability for Root ACs
   - Need resources for maintaining the static MAC address configuration
     per Root AC




















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Authors' Addresses

   Raymond Key (editor)
   Huawei
   Email: raymond.key@ieee.org

   Simon Delord
   Telstra
   Email: simon.delord@gmail.com

   Frederic Jounay
   Orange CH
   4 rue caudray 1020 Renens
   Switzerland
   Email: frederic.jounay@orange.ch

   Lucy Yong
   Huawei USA
   1700 Alma Dr. Suite 500
   Plano, TX  75075, USA
   Email: lucy.yong@huawei.com

   Lizhong Jin
   ZTE Corporation
   889, Bibo Road
   Shanghai, 201203, China
   Email: lizhong.jin@zte.com.cn

   Yuji Kamite
   NTT Communications Corporation
   Granpark Tower
   3-4-1 Shibaura, Minato-ku
   Tokyo 108-8118, Japan
   Email: y.kamite@ntt.com

   Wim Henderickx
   Alcatel-Lucent
   Copernicuslaan 50
   2018 Antwerp, Belgium
   Email: wim.henderickx@alcatel-lucent.com














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