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Versions: 00 01 02 03 04 05 RFC 7152

Network Working Group                       Raymond Key (editor), Huawei
Internet Draft                                     Simon Delord, Telstra
Category: Informational                       Frederic Jounay, Orange CH
Expires: January 2014                             Lu Huang, China Mobile
                                               Zhihua Liu, China Telecom
                                           Manuel Paul, Deutsche Telekom


                                                           July 29, 2013


              Requirements for Metro Ethernet Forum (MEF)
                Ethernet-Tree (E-Tree) Support in L2VPN
                    draft-ietf-l2vpn-etree-reqt-05


Abstract

   This document provides functional requirements for Metro Ethernet
   Forum (MEF) Ethernet Tree (E-Tree) support in multipoint L2VPN
   solutions (referred to as simply L2VPN). It is intended that
   potential solutions will use these requirements as guidelines.


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 January 29, 2014.







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Table of Contents

   1. Introduction....................................................3
   2. IETF Multipoint Ethernet L2VPN Services.........................3
   2.1. VPLS..........................................................3
   2.2. E-VPN.........................................................3
   3. MEF Multipoint Ethernet Services................................3
   3.1. Similarity between E-LAN and E-Tree...........................4
   3.2. Difference between E-LAN and E-Tree...........................4
   3.3. E-Tree Use Cases..............................................5
   3.4. Generic E-Tree Service........................................6
   4. Problem Statement...............................................6
   4.1. Motivation....................................................6
   4.2. Leaf-to-Leaf Communication Restriction........................6
   5. Requirements....................................................7
   5.1. Functional Requirements.......................................7
   5.2. Applicability.................................................7
   5.3. Backward Compatibility........................................8
   5.4. External Network Network Interface............................8
   6. Security Consideration..........................................8
   7. IANA Considerations.............................................8
   8. Contributors....................................................8
   9. Acknowledgements................................................8
   10. References.....................................................8
   10.1. Normative References.........................................8
   10.2. Informative References.......................................9
   Appendix
   A. Frequently Asked Questions.....................................10
   A.1. Are E-Tree requirements addressed in the Virtual
        Private Multicast Service (VPMS) requirements?...............10
   Authors' Addresses................................................11
   Contributors' Addresses...........................................12
   Intellectual Property and Copyright Statements....................12


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

   This document provides functional requirements for Metro Ethernet
   Forum (MEF) Ethernet Tree (E-Tree) support in multipoint L2VPN
   solutions (referred to as simply L2VPN). It is intended that
   potential solutions will use these requirements as guidelines.

   Considerable number of service providers have adopted Virtual Private
   LAN Service (VPLS) to provide MEF Ethernet LAN (E-LAN) services to
   customers. Service Providers currently need a simple and effective
   solution to emulate E-Tree services in addition to E-LAN services on
   their MPLS networks.

   Service providers also expect E-Tree support in any newly developed
   L2VPN technologies.

2. IETF Multipoint Ethernet L2VPN Services

2.1. VPLS

   VPLS [RFC4761] [RFC4762] is a L2VPN service that provides multipoint-
   to-multipoint connectivity for Ethernet across an IP or MPLS-enabled
   IP Packet Switched Network (IP/MPLS PSN). VPLS emulates the Ethernet
   Virtual Local Area Network (VLAN) functionality of traditional
   Ethernet networks. Thus, in VPLS, the customer Ethernet frame is
   transported over the IP/MPLS PSN from the ingress Provider Edge (PE)
   to the egress PE where the destination is connected based on the
   Ethernet frame destination MAC address in the context of the virtual
   switching instance (VSI) to which it belongs.

2.2. Ethernet Virtual Private Network (E-VPN)

   E-VPN is an enhanced Layer-2 service that emulates an Ethernet VLAN
   across an IP/MPLS 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].

3. MEF Multipoint Ethernet Services

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

   For full specification, please refer to [MEF6.1] [MEF10.2].






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3.1. Similarities between E-LAN and E-Tree

   Following are the similarities between E-LAN and E-Tree services.
     - Data frame is an Ethernet frame.
     - Data forwarding is MAC-based forwarding.
     - A generic E-LAN/E-Tree service is always bidirectional in the
       sense that ingress frames can originate at any endpoint in the
       service.

3.2. Differences 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 Leaves.

   The only differences between E-LAN and E-Tree are:
     - 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.
































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3.3. E-Tree Use Cases

   Table 1 below presents some major E-Tree 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           | Radio Area   | RAN Base   |
   |   |                           | Network (RAN)| Station    |
   |   |                           | Network      |            |
   |   |                           | Controller   |            |
   +---+---------------------------+--------------+------------+
   | 4 | IEEE 1588 PTPv2           | Precision    | PTP Client |
   |   | Clock Synchronisation     | time Protocol|            |
   |   |                           | (PTP) Server |            |
   +---+---------------------------+--------------+------------+
   | 5 | Internet Access           | Broadband    | Subscriber |
   |   | [TR-101]                  | Network      |            |
   |   |                           | Gateway      |            |
   +---+---------------------------+--------------+------------+
   | 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 or must be inhibited.

   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.









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3.4. Generic E-Tree Service

   A generic E-Tree service supports multiple Root endpoints. The need
   for multiple Root endpoints is usually driven by redundancy
   requirement. Whether a particular E-Tree service needs to support
   single or multiple Roots depends on the target application.

   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 other Roots & Leaves
     - 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.

4. Problem Statement

4.1. Motivation

   L2VPN can be used to emulate MEF E-LAN service over an IP/MPLS PSN.

   Service providers also require E-Tree support in L2VPN.

4.2. Leaf-to-Leaf Communication Restriction

   In this section, VPLS is used to illustrate the problem. But the same
   principle applies to other L2VPN technologies.

   VPLS treats all attachment circuits (ACs) equally (essentially as
   Roots, although they not classified into Root or Leaf) and provides
   any-to-any connectivity among all ACs. VPLS does not include any
   mechanism for communication restriction between specific ACs.
   Therefore it is insufficient for emulating generic E-Tree service
   over an IP/MPLS PSN.

   As an example of the problems not addressed in VPLS solutions,
   consider the scenario in Figure 1 where there are two PEs, each with
   a Root AC and a Leaf AC and where VPLS is used to emulate an E-Tree
   service interconnecting these ACs over an IP/MPLS PSN.













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                     <------------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 1: Problem Scenario for Leaf-to-Leaf Communication Restriction

   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 where the problems arise:
     - CE2 sends a Broadcast/Multicast Ethernet frame to PE1 via AC2
     - CE2 sends a Unicast Ethernet frame to PE1 via AC2 with a
       destination MAC address corresponding to CE4's MAC address

   Note: Figure 1 is a hypothetical case solely used for explaining the
   problem, and not meant to represent a typical E-Tree service.

   There are some possible ways to get around this problem that do not
   require extensions to existing VPLS solutions but they all come with
   significant design complexity or deployment constraints, please refer
   to [Draft ETree Frwk] Appendix A.

5. Requirements

5.1. Functional Requirements

   Following are the E-Tree L2VPN functional requirements:

   (1) A solution MUST prohibit communication between any two Leaf ACs
       in a L2VPN instance.

   (2) A solution MUST allow multiple Root ACs in a L2VPN instance.

   (3) A solution MUST allow Root AC and Leaf AC of a L2VPN instance to
       co-exist on any PE.

5.2. Applicability

   A solution MUST identify the L2VPN technology ([RFC4761], [RFC4762],
   E-VPN) the solution is applicable to.


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5.3. Backward Compatibility

   A solution SHOULD minimise the impact on VPLS and E-VPN L2VPN
   solutions, especially for the MEF E-LAN services already in
   operation.

   A solution SHOULD be backward compatible with the VPLS and E-VPN
   L2VPN solutions. It SHOULD allow a case where a common L2VPN instance
   is composed of both PEs supporting the solution and PEs not
   supporting it, and the Leaf-to-Leaf communication restriction is
   enforced within the scope of the compliant PEs.

5.4. External Network Network Interface (ENNI)

   A solution SHOULD support Root Operator Virtual Connection (OVC) End
   Point, Leaf OVC End Point and Trunk OVC End Point specified in
   [MEF26.1].

6. Security Considerations

   This document introduces a requirement of prohibiting communication
   between any two Leaf ACs in a L2VPN instance. In some use cases, such
   requirement is imposed because of security reasons. Other than that,
   there are no additional security considerations beyond those already
   described in [RFC4761] [RFC4762] [Draft EVPN Req].

7. IANA Considerations

   This document has no actions for IANA.

8. Contributors

   Ruediger Kunze, Deutsche Telekom
   Nick Del Regno, Verizon
   Josh Rogers, Time Warner Cable

9. Acknowledgements

   The authors would like to thank Lizhong Jin, Lucy Yong, Yuji Kamite
   and Wim Henderickx for their valuable input and support.

10. References

10.1. Normative References

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

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



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

   [MEF22.1]    Metro Ethernet Forum, Mobile Backhaul Implementation
                Agreement - Phase 2, January 2012

   [MEF26.1]    Metro Ethernet Forum, External Network Network Interface
                (ENNI) - Phase 2, January 2012

   [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

10.2. Informative References

   [Draft EVPN Req]   Sajassi, et al., Requirements for Ethernet VPN
                      (EVPN), draft-ietf-l2vpn-evpn-req-04
                      (work in progress), July 2013

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

   [Draft ETree Frwk] Key, et al., A Framework for E-Tree Service over
                      MPLS Network, draft-ietf-l2vpn-etree-frwk-02
                      (work in progress), February 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




















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Appendix A. Frequently Asked Questions

A.1. Are E-Tree requirements addressed in the Virtual Private Multicast
     Service (VPMS) requirements?

   VPMS requirements are defined in [Draft VPMS Frmwk].

   The focus of VPMS is to provide point-to-multipoint connectivity.

   VPMS provides single coverage of receiver membership (i.e., there is
   no distinct differentiation for multiple multicast groups). A VPMS
   service supports single or multiple Root ACs. All traffic from a Root
   AC will be forwarded to all Leaf ACs (i.e., P2MP, from Root to all
   Leaves). Destination address in Ethernet frame is not used in data
   forwarding. As an optional capability, a VPMS service may support
   reverse traffic from a Leaf AC to a Root AC (i.e., P2P, from Leaf to
   Root).

   In contrast, the focus of MEF E-Tree is that a Leaf can only
   communicate with Roots but not Leaves.

   A generic MEF E-Tree service supports multiple Root endpoints.
   Whether a particular E-Tree service needs to support single or
   multiple Root endpoints depends on the target application.

   As discussion in a previous section, a generic MEF E-Tree service
   supports all the following traffic flows:
     - Ethernet Unicast bidirectional Root to/from Root
     - Ethernet Unicast bidirectional Root to/from Leaf
     - Ethernet Broadcast/Multicast unidirectional Root to all Roots &
       Leaves
     - Ethernet Broadcast/Multicast unidirectional Leaf to all Roots.
   A particular E-Tree service may need to support all the above or only
   a subset depending on the target application.

   IETF's VPMS definition and MEF's E-Tree definition are significantly
   different.

   VPMS may be acceptable in cases where E-Tree service is needed, such
   as in the following cases:
     - No Unicast traffic from Root destined for a specific Leaf (or
       there is no concern if such Unicast traffic is forwarded to all
       Leaves)
     - No traffic between Roots

   For generic E-Tree service, VPMS will not be able to meet the
   requirements.






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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

   Lu Huang
   China Mobile
   Unit 2, 28 Xuanwumenxi Ave, Xuanwu District
   Beijing 100053, China
   Email: huanglu@chinamobile.com

   Zhihua Liu
   China Telecom
   109 Zhongshan Ave., Guangzhou
   510630, China
   Email: zhliu@gsta.com

   Manuel Paul
   Deutsche Telekom
   Winterfeldtstr. 21-27
   10781 Berlin, Germany
   Email: manuel.paul@telekom.de




















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Contributors' Addresses

   Ruediger Kunze
   Deutsche Telekom
   Winterfeldtstr. 21-27
   10781 Berlin, Germany
   Email: ruediger.kunze@telekom.de

   Nick Del Regno
   Verizon
   400 International Pkwy
   Richardson, TX 75081, USA
   Email: nick.delregno@verizon.com

   Josh Rogers
   Time Warner Cable
   11921 N Mo Pac Expy
   Suite 210B
   Austin, TX 78759, USA
   Email: josh.rogers@twcable.com

Copyright Notice

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

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


















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