Network Working Group Raymond Key (editor), Huawei Internet Draft Simon Delord, Telstra Category: Informational Frederic Jounay, Orange CH Expires: October 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 April 4, 2013 Requirements for MEF E-Tree Support in L2VPN draft-ietf-l2vpn-etree-reqt-04 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 October 4, 2013. Key, et al. Expires October 2013 [Page 1] Internet Draft Requirement E-Tree in L2VPN April 2013 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 Virtual Private Multicast Service (VPMS) requirements?................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]. Key, et al. Expires October 2013 [Page 2] Internet Draft Requirement E-Tree in L2VPN April 2013 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 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 (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. 2.2. E-VPN E-VPN is an enhanced Layer-2 service that emulates an Ethernet VLAN 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 Following are the similarities between E-LAN and E-Tree services. - Data frame is Ethernet frame. - Data forwarding can be MAC-based forwarding, to be specified by service provider as service frame delivery attributes in the particular service definition. Key, et al. Expires October 2013 [Page 3] Internet Draft Requirement E-Tree in L2VPN April 2013 - 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 Network | RAN Base | | | | Controller | Station | +---+---------------------------+--------------+------------+ | 4 | IEEE 1588 PTPv2 | PTP Server | PTP Client | | | Clock Synchronisation | | | +---+---------------------------+--------------+------------+ | 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 Key, et al. Expires October 2013 [Page 4] Internet Draft Requirement E-Tree in L2VPN April 2013 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 [MEF22.1]. 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 an MPLS network provided that the E-LAN service uses MAC-based forwarding as a 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. VPLS treats all attachment circuits (ACs) equal (i.e. not classified into Root or Leaf) and provides any-to-any connectivity among all ACs. VPLS does not include any mechanism of communication restriction between specific ACs, therefore it is insufficient for emulating generic E-Tree service over 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 over an MPLS network. Key, et al. Expires October 2013 [Page 5] Internet Draft Requirement E-Tree in L2VPN April 2013 <------------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 frame to PE1 via AC2 - CE2 sends a Unicast frame to PE1 via AC2 with 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 extension 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 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 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. Key, et al. Expires October 2013 [Page 6] Internet Draft Requirement E-Tree in L2VPN April 2013 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 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]. 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 [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 Key, et al. Expires October 2013 [Page 7] Internet Draft Requirement E-Tree in L2VPN April 2013 [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 [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-02 (work in progress), February 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 Key, et al. Expires October 2013 [Page 8] Internet Draft Requirement E-Tree in L2VPN April 2013 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 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 is 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. Key, et al. Expires October 2013 [Page 9] Internet Draft Requirement E-Tree in L2VPN April 2013 A.2. Are there any potential deployment scenarios for a "VPLS Only" solution? Yes, there are potential deployment scenarios for a "VPLS Only" solution with enhancements to support E-Tree services, 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) | +---+ | +---------+ Key, et al. Expires October 2013 [Page 10] Internet Draft Requirement E-Tree in L2VPN April 2013 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) | +---+ | +---------+ +---------+ Key, et al. Expires October 2013 [Page 11] Internet Draft Requirement E-Tree in L2VPN April 2013 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 Key, et al. Expires October 2013 [Page 12] Internet Draft Requirement E-Tree in L2VPN April 2013 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 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 Key, et al. Expires October 2013 [Page 13] Internet Draft Requirement E-Tree in L2VPN April 2013 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 publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Key, et al. Expires October 2013 [Page 14]