RFC 7152
Requirements for Metro Ethernet Forum (MEF) Ethernet-Tree (E-Tree) Support in Layer 2 Virtual Private Network (L2VPN)
Requirements for Metro Ethernet Forum (MEF) Ethernet-Tree (E-Tree) Support in Layer 2 Virtual Private Network (L2VPN) 🎀
okay bestie, here's the title block tea ☕ this is an Internet Engineering Task Force (IETF) doc, and it's giving RFC 7152 💖
- Category: Informational
- ISSN: 2070-1721
- Date: March 2014
- Authors: R. Key, Ed.; S. Delord (Telstra); F. Jounay (Orange CH); L. Huang (China Mobile); Z. Liu (China Telecom); M. Paul (Deutsche Telekom)
- Obsoletes / Updates: none are listed in this header 🙈
Abstract 💜
This doc gives the functional requirements for supporting Metro Ethernet Forum (MEF) Ethernet Tree (E-Tree) in multipoint Layer 2 Virtual Private Network solutions (referred to as simply "L2VPN") ✨ The idea is that potential solutions will use these requirements as guidelines 🧚
Status of This Memo 🎀
ngl this one is not an Internet Standards Track spec. It's published for informational purposes 🌸
It's a product of the Internet Engineering Task Force (IETF), so it represents the consensus of the IETF community 🫶 It got public review and was approved for publication by the Internet Engineering Steering Group (IESG). Not every IESG-approved doc is a candidate for any level of Internet Standard, so see Section 2 of RFC 5741 for that 💅
Info about the current status of this doc, any errata, and how to give feedback can be found at http://www.rfc-editor.org/info/rfc7152 🦋
Copyright Notice 🌈
Copyright (c) 2014 IETF Trust and the persons identified as the document authors. All rights reserved ✨
This doc is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) as in effect on the date of publication. Please read these carefully, because they spell out your rights and restrictions for this doc 📜 Code Components pulled from this doc must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions, and they come without warranty as described in the Simplified BSD License 💖
Table of Contents 🗂️
1. Introduction ....................................................3
1.1. Conventions Used in This Document ..........................3
2. IETF Multipoint Ethernet L2VPN Services .........................3
2.1. VPLS .......................................................3
2.2. Ethernet Virtual Private Network (E-VPN) ...................3
3. MEF Multipoint Ethernet Services ................................4
3.1. Similarities between E-LAN and E-Tree ......................4
3.2. Differences 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 ..............................................8
5.3. Backward Compatibility .....................................8
5.4. External Network Network Interface (ENNI) ..................8
6. Security Considerations .........................................8
7. Contributors ....................................................8
8. Acknowledgements ................................................9
9. References ......................................................9
9.1. Normative References .......................................9
9.2. Informative References ....................................10
Appendix A. Frequently Asked Question .............................11
A.1. Are E-Tree Requirements Addressed in the Virtual
Private Multicast Service (VPMS) Requirements? ...............111. Introduction ✨
This doc gives the functional requirements for supporting Metro Ethernet Forum (MEF) Ethernet Tree (E-Tree) in multipoint Layer 2 Virtual Private Network solutions (referred to as simply "L2VPN") 🌸 The idea is that potential solutions will use these requirements as guidelines 🧚
A lot of service providers have adopted Virtual Private LAN Service (VPLS) to deliver MEF Ethernet LAN (E-LAN) services to customers 💅 Right now, service providers need a simple and effective way to emulate E-Tree services alongside E-LAN services on their MPLS networks 🫶
Service providers also expect E-Tree support in any newly developed L2VPN technologies 🔥
1.1. Conventions Used in This Document 📝
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this doc are to be interpreted as described in [RFC2119] 🍓
2. IETF Multipoint Ethernet L2VPN Services 🌈
2.1. VPLS 🦋
VPLS [RFC4761] [RFC4762] is an L2VPN service that gives you multipoint-to-multipoint connectivity for Ethernet across an IP or MPLS-enabled IP Packet Switched Network (IP/MPLS PSN) 💖 It emulates the Ethernet VLAN functionality of traditional Ethernet networks ✨ So in VPLS, the customer Ethernet frame gets carried over the IP/MPLS PSN from the ingress Provider Edge (PE) to the egress PE. The destination is then connected based on the Ethernet frame's destination Media Access Control (MAC) address, within the virtual switching instance (VSI) the frame belongs to 🧠
2.2. Ethernet Virtual Private Network (E-VPN) 💜
E-VPN is an enhanced L2 service that emulates an Ethernet VLAN across an IP/MPLS PSN 🌸 It's mainly aimed at large scale L2VPNs with resiliency requirements that other L2VPN solutions don't satisfy 👑
E-VPN is still under development, so please refer to [EVPN] 🛠️
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 the full specs, check out [MEF6.1] and [MEF10.2] 📜
3.1. Similarities between E-LAN and E-Tree 🫧
Here's what E-LAN and E-Tree have in common, and honestly it's a lot 😭
- 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 💅
Inside a multipoint Ethernet service, every endpoint is labelled either a Root or a Leaf 🦋 A Root can talk to all the other endpoints in the same service. A Leaf, though, can only talk to Roots, not to other 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.
3.3. E-Tree Use Cases 🍓
Table 1 shows some of the big 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 Access | RAN Base |
| | | Network (RAN)| Station |
| | | Network | |
| | | Controller | |
+---+---------------------------+--------------+------------+
| 4 | IEEE 1588 PTPv2 | Precision | PTP Client |
| | Clock Synchronisation | Time Protocol| |
| | [IEEE1588] | (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 CasesAcross all of these use cases, direct L2 Leaf-to-Leaf communication is not required, or it must be inhibited 🙅♀️
If direct L2 Leaf-to-Leaf communication isn't allowed because of a security concern, then E-Tree should be used to block 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 👑 Needing multiple Roots is usually driven by a redundancy requirement 🫶 Whether a particular E-Tree service needs single or multiple Roots depends on the target application 🎯
A generic E-Tree service supports all of 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 and Leaves
- Ethernet Broadcast/Multicast from Leaf to Roots
A particular E-Tree service may need to support all of the above, or only a subset, depending on the target application 🦋
4. Problem Statement 🌸
4.1. Motivation 💜
L2VPN can be used to emulate the 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
Okay so in this section they use VPLS as the example, but literally the same problem shows up in other L2VPN techs too 🎀
VPLS treats every attachment circuit (AC) the same, basically like they're all Roots even though they're not actually labelled Root or Leaf 🙈 It gives any-to-any connectivity across all ACs 💅 and it has zero mechanism for blocking communication between specific ACs. So it's not enough to emulate a generic E-Tree service over an IP/MPLS PSN. Not it 💀
Let's look at Figure 1 🦋 There are two PEs, each with a Root AC and a Leaf AC, and VPLS is being used to emulate an E-Tree service between them over an IP/MPLS PSN:
<------------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 gets a frame from PE1 over the Ethernet pseudowire (PW), it's kinda stuck 😭
- PE2 doesn't know which AC on PE1 the frame came in on
- PE2 doesn't know whether that ingress AC is a Leaf AC
- PE2 doesn't have enough info to enforce the Leaf-to-Leaf communication restriction
Here are the examples where things go wrong 🙈
- Customer Edge 2 (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 matching CE4's MAC address
Note: Figure 1 is a hypothetical case that only exists to explain the problem. It is NOT meant to represent a typical E-Tree service 💅
There are some ways to work around this without extending existing VPLS solutions 🧚, but every single one comes with serious design complexity or deployment constraints 😩
5. Requirements ✨
5.1. Functional Requirements 🎀
Here are the E-Tree L2VPN functional requirements 💖
(1) A solution MUST prohibit communication between any two Leaf ACs in an L2VPN instance.
(2) A solution MUST allow multiple Root ACs in an L2VPN instance.
(3) A solution MUST allow a Root AC and Leaf AC of an L2VPN instance to coexist on any PE.
5.2. Applicability 🦋
A solution MUST identify the L2VPN technology ([RFC4761], [RFC4762], [EVPN]) it applies to 💅
5.3. Backward Compatibility 🫶
A solution SHOULD minimise the impact on VPLS and E-VPN L2VPN solutions, especially for the MEF E-LAN services that are already in operation 🌸
A solution SHOULD be backward compatible with the VPLS and E-VPN L2VPN solutions. It SHOULD allow a case where one common L2VPN instance is made of both PEs that support the solution and PEs that don't, 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, as specified in [MEF26.1] ⭐
6. Security Considerations 💀
This document introduces a requirement to prohibit communication between any two Leaf ACs in an L2VPN instance. In some use cases this requirement is imposed for security reasons. Other than that, there are no additional security considerations beyond those already described in [RFC4761], [RFC4762], and [EVPN]. This part is SERIOUS, bestie 🔥
7. Contributors 🧚
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
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", Technical Specification MEF 6.1, April 2008, <http://metroethernetforum.org/Assets/Technical_Specifications/PDF/MEF6-1.pdf>.
[MEF10.2] Metro Ethernet Forum, "Ethernet Services Attributes Phase 2", Technical Specification MEF 10.2, October 2009, <http://metroethernetforum.org/Assets/Technical_Specifications/PDF/MEF10.2.pdf>.
[MEF26.1] Metro Ethernet Forum, "External Network Network Interface (ENNI) Phase 2", Technical Specification, MEF 26.1, January 2012, <http://metroethernetforum.org/Assets/Technical_Specifications/PDF/MEF_26.1.pdf>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4761] Kompella, K., Ed., and Y. Rekhter, Ed., "Virtual Private LAN Service (VPLS) Using BGP for Auto-Discovery and Signaling", RFC 4761, January 2007.
[RFC4762] Lasserre, M., Ed., and V. Kompella, Ed., "Virtual Private LAN Service (VPLS) Using Label Distribution Protocol (LDP) Signaling", RFC 4762, January 2007.
9.2. Informative References 📖
[EVPN] Sajassi, A., Aggarwal, R., Uttaro, J., Bitar, N., Henderickx, W., and A. Isaac, "Requirements for Ethernet VPN (EVPN)", Work in Progress, February 2014.
[IEEE1588] IEEE, "1588-2008 Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems", July 2008.
[TR-101] Broadband Forum, "Migration to Ethernet-Based DSL Aggregation", Technical Report, DSL Forum TR-101, April 2006, <http://www.broadband-forum.org/technical/download/TR-101.pdf>.
[VPMS] Kamite, Y., Jounay, F., Niven-Jenkins, B., Brungard, D., and L. Jin, "Framework and Requirements for Virtual Private Multicast Service (VPMS)", Work in Progress, October 2012.
Appendix A. Frequently Asked Question 🎀
A.1. Are E-Tree Requirements Addressed in the Virtual Private Multicast Service (VPMS) Requirements? 🤔
VPMS requirements are defined in [VPMS] 📝
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., Point-to-Multipoint (P2MP), from Root to all Leaves). The destination address in an 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., point-to-point (P2P), from Leaf to Root) 💫
In contrast, the focus of MEF E-Tree is that a Leaf can only communicate with Roots, 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 discussed 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 and Leaves
- Ethernet Broadcast/Multicast unidirectional Leaf to all Roots
A particular E-Tree service may need to support all of the above or only a subset, depending on the target application 🧚
The 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 💀
Authors' Addresses 💌
Raymond Key (editor) 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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