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Versions: 00 01 02 03 04 05 RFC 7152

Network Working Group                       Raymond Key (editor), Huawei
Internet Draft                              Simon Delord, Alcatel-Lucent
Category: Informational                       Frederic Jounay, Orange CH
Expires: April 2013                               Lu Huang, China Mobile
                                               Zhihua Liu, China Telecom
                                           Manuel Paul, Deutsche Telekom
                                        Ruediger Kunze, Deutsche Telekom
                                                 Nick Del Regno, Verizon
                                          Josh Rogers, Time Warner Cable


                                                         October 7, 2012


              Requirements for MEF E-Tree Support in L2VPN
                    draft-ietf-l2vpn-etree-reqt-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
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   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on April 7, 2013.


Abstract

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






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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...........................3
   3.2. Difference between E-LAN and E-Tree...........................4
   3.3. E-Tree Use Cases..............................................4
   3.4. Generic E-Tree Service........................................5
   4. Problem Statement...............................................5
   4.1. Motivation....................................................5
   4.2. Leaf-to-Leaf Communication Restriction........................5
   5. Requirements....................................................6
   5.1. Functional Requirements.......................................6
   5.2. Applicability.................................................6
   5.3. Backward Compatibility........................................7
   5.4. External Network Network Interface............................7
   6. Security Consideration..........................................7
   7. IANA Considerations.............................................7
   8. Acknowledgements................................................7
   9. References......................................................7
   9.1. Normative References..........................................7
   9.2. Informative References........................................8
   Appendix
   A. Frequently Asked Questions......................................9
   A.1. Are E-Tree requirements addressed in the
        VPMS requirement draft?.......................................9
   A.2. Are there any potential deployment scenarios
        for a "VPLS Only" solution?..................................10
   Authors' Addresses................................................13
   Intellectual Property and Copyright Statements....................14


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 L2VPN. It is intended
   that potential solutions will use these requirements as guidelines.

   Considerable number of service providers have adopted 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 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.

2.2. 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].

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].

3.1. Similarity between E-LAN and E-Tree

   Data frame is Ethernet frame.



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

   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. 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

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           | 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


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   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.

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 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.

4. Problem Statement

4.1. Motivation

   L2VPN can be used to emulate MEF E-LAN service over MPLS network
   provided that the E-LAN service uses MAC-based forwarding as service
   frame delivery attributes.

   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.

   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 1 below. VPLS is
   used to emulate an E-Tree service over a MPLS network.


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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:
     - 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

   Note: Figure 1 is a hypothetical case solely 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 extension to the current standard VPLS 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

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

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

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

5.2. Applicability

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




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5.3. Backward Compatibility

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

   A solution SHOULD be backward compatible with the existing L2VPN
   solution. 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

   A solution SHOULD support Root 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. Other than that, there
   are no additional security considerations beyond those already
   described in [RFC4761] [RFC4762].

7. IANA Considerations

   This document has no actions for IANA.

8. Acknowledgements

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

9. References

9.1. 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

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

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

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



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

9.2. Informative References

   [Draft EVPN Req]
                Sajassi, Aggarwal, et al., Requirements for Ethernet VPN
                (E-VPN), draft-ietf-l2vpn-evpn-req-00 (work in
                progress), March 2012

   [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-01 (work in
                progress), July 2012

   [Draft VPMS Frmwk]
                Kamite, et al., Framework and Requirements for Virtual
                Private Multicast Service (VPMS),
                draft-ietf-l2vpn-vpms-frmwk-requirements-04 (work in
                progress), July 2011





























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Appendix A. Frequently Asked Questions

A.1. Are E-Tree requirements addressed in the VPMS requirement draft?

   VPMS is Virtual Private Multicast Service. VPMS requirement draft
   refers to [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
   Leafs). 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 Leafs.

   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.

   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 &
       Leafs
     - 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.

   Only for special case E-Tree service where
     - No Unicast traffic from Root destined for a specific Leaf (or
       there is no concern if such Unicast traffic are forwarded to all
       Leafs)
     - No traffic between Roots
   VPMS will be able to meet the requirement. An example is E-Tree
   service for content delivery application.

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





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A.2. Are there any potential deployment scenarios for a "VPLS Only"
     solution?

   Yes, there are potential deployment scenarios for a "VPLS Only"
   solution, some examples below.

   Example 1 -

                                                   Enhanced VPLS with
              <-----Physical P2P Service------><-----E-Tree Support-----
                                               +---------+
              +---+                            |   PE1   |
   +---+      |NTU|                            |  +---+  |
   |CE1+------+---+--V1-----------------AC1----+--+   |  |
   +---+ Root +---+                  (Root AC) |  | V |  |
                                               |  |   |  | Ethernet
              +---+                            |  | S +--+----PW--->PE2
   +---+      |NTU|                            |  |   |  |
   |CE2+------+---+--V2-----------------AC2----+--+ I |  |
   +---+ Root +---+                  (Root AC) |  |   |  |
                                               |  |   |  |
              +---+                            |  |   |  |
   +---+      |NTU|                            |  |   |  |
   |CE3+------+---+--V3-----------------AC3----+--+   |  |
   +---+ Root +---+                  (Root AC) |  |   |  |
                                               |  |   |  |
              +---+                            |  |   |  |
   +---+      |NTU|                            |  |   |  |
   |CE4+------+---+--V4-----------------AC4----+--+   |  |
   +---+ Leaf +---+                  (Leaf AC) |  |   |  |
                                               |  |   |  |
              +---+                            |  |   |  |
   +---+      |NTU|                            |  |   |  |
   |CE5+------+---+--V5-----------------AC5----+--+   |  |
   +---+ Leaf +---+                  (Leaf AC) |  +---+  |
                                               +---------+

















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   Example 2 -

                     Logical P2P Service           Enhanced VPLS with
              <-------via Access Switch-------><-----E-Tree Support-----
                         +---------+           +---------+
                         | Access  |           |   PE1   |
              +---+      | Switch  |           |         |
   +---+      |NTU|      |         |           |  +---+  |
   |CE1+------+---+--V1--+--VLAN1--+--V1--AC1--+--+   |  |
   +---+ Root +---+      |         | (Root AC) |  | V |  |
                         +---------+           |  |   |  | Ethernet
                                               |  | S +--+----PW--->PE2
                         +---------+           |  |   |  |
                         | Access  |           |  | I |  |
              +---+      | Switch  |           |  |   |  |
   +---+      |NTU|      |         |           |  |   |  |
   |CE2+------+---+--V2--+--VLAN2--+--V2--AC2--+--+   |  |
   +---+ Root +---+      |         | (Root AC) |  |   |  |
                         |         |           |  |   |  |
              +---+      |         |           |  |   |  |
   +---+      |NTU|      |         |           |  |   |  |
   |CE3+------+---+--V3--+--VLAN3--+--V3--AC3--+--+   |  |
   +---+ Root +---+      |         | (Root AC) |  |   |  |
                         |         |           |  |   |  |
              +---+      |         |           |  |   |  |
   +---+      |NTU|      |         |           |  |   |  |
   |CE4+------+---+--V4--+--VLAN4--+--V4--AC4--+--+   |  |
   +---+ Leaf +---+      |         | (Leaf AC) |  |   |  |
                         |         |           |  |   |  |
              +---+      |         |           |  |   |  |
   +---+      |NTU|      |         |           |  |   |  |
   |CE5+------+---+--V5--+--VLAN5--+--V5--AC5--+--+   |  |
   +---+ Leaf +---+      |         | (Leaf AC) |  +---+  |
                         +---------+           +---------+



















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   Example 3 -

                     Ethernet Switching            Enhanced VPLS with
              <------with Split Horizon-------><-----E-Tree Support-----
                         +---------+           +---------+
                         | Access  |           |   PE1   |
                         | Switch  |           |         |
                         |         |           |         |
                         |  +---+  |           |  +---+  |
              +---+      |  | V |  |           |  |   |  |
   +---+      |NTU|      |  | L |  |           |  | V |  |
   |CE1+------+---+--V1--+--+ A +--+--V1--AC1--+--+   |  |
   +---+ Root +---+      |  | N |  | (Root AC) |  | S |  |
                         |  | 1 |  |           |  |   |  | Ethernet
                         |  +---+  |           |  | I +--+----PW--->PE2
                         +---------+           |  |   |  |
                                               |  |   |  |
                         +---------+           |  |   |  |
                         | Access  |           |  |   |  |
                         | Switch  |           |  |   |  |
              +---+      |         |           |  |   |  |
   +---+      |NTU|      |  +---+  |           |  |   |  |
   |CE2+------+---+--V2--+--+ V |  |           |  |   |  |
   +---+ Root +---+      |  | L |  |           |  |   |  |
                         |  | A +--+--V2--AC2--+--+   |  |
              +---+      |  | N |  | (Root AC) |  |   |  |
   +---+      |NTU|      |  | 2 |  |           |  |   |  |
   |CE3+------+---+--V2--+--+   |  |           |  |   |  |
   +---+ Root +---+      |  +---+  |           |  |   |  |
                         |         |           |  |   |  |
              +---+      |         |           |  |   |  |
   +---+      |NTU|      |  +---+  |           |  |   |  |
   |CE4+------+---+--V4--+SH+ V |  |           |  |   |  |
   +---+ Leaf +---+      |  | L |  |           |  |   |  |
                         |  | A +--+--V4--AC4--+--+   |  |
              +---+      |  | N |  | (Leaf AC) |  |   |  |
   +---+      |NTU|      |  | 4 |  |           |  |   |  |
   |CE5+------+---+--V4--+SH+   |  |           |  |   |  |
   +---+ Leaf +---+      |  +---+  |           |  +---+  |
                         +---------+           +---------+

   Note:
     - Group Roots and Leafs into two separate VLANs on Access Switch
     - SH means member of split horizon group on Access Switch









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Authors' Addresses

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

   Simon Delord
   Alcatel-Lucent
   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

   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

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Copyright Notice

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