RFC 7387

A Framework for Ethernet Tree (E-Tree) Service over a Multiprotocol Label Switching (MPLS) Network

📅 published October 2014, from ietf

A Framework for Ethernet Tree (E-Tree) Service over a Multiprotocol Label Switching (MPLS) Network

Okay bestie, let's start with the paperwork 📄✨ This is RFC 7387, published in October 2014 by the IETF (Internet Engineering Task Force). It's marked as Informational, which means it's sharing ideas rather than being a standard you have to follow 💅 The ISSN is 2070-1721. R. Key and L. Yong are the editors (both marked Ed.), and S. Delord, F. Jounay and L. Jin are also credited as authors. The affiliations listed are Huawei under L. Yong, Telstra for S. Delord and Orange CH for F. Jounay. No affiliation appears next to R. Key or L. Jin. The header doesn't list any RFCs that this one obsoletes or updates.

Abstract

This document describes an Ethernet-Tree (E-Tree) solution framework for supporting the Metro Ethernet Forum (MEF) E-Tree service 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.

Status of This Memo

Honestly, the status is giving "for info only" 🧠 This document is not an Internet Standards Track specification. It's published for informational purposes.

This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community, and it has gotten public review and been approved for publication by the Internet Engineering Steering Group (IESG). Not every IESG-approved document 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 document, any errata, and how to give feedback can be found at http://www.rfc-editor.org/info/rfc7387.

Copyright Notice

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 those documents carefully, because 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 they're provided without warranty as described in the Simplified BSD License. 💖

1. Introduction ....................................................3
   1.1. Terminology ................................................3
2. Overview ........................................................4
   2.1. Ethernet Bridge Network ....................................4
   2.2. MEF Multipoint Ethernet Services: E-LAN and E-Tree .........4
   2.3. IETF L2VPN .................................................5
        2.3.1. Virtual Private LAN Service (VPLS) ..................5
        2.3.2. Ethernet VPN (EVPN) .................................5
        2.3.3. Virtual Private Multicast Service (VPMS) ............6
3. E-Tree Architecture Reference Model .............................6
4. E-Tree Use Cases ................................................8
5. L2VPN Gaps for Emulating MEF E-Tree Service .....................9
   5.1. No Differentiation on AC Role ..............................9
   5.2. No AC Role Indication or Advertisement .....................9
   5.3. Other Issues ...............................................9
6. Security Considerations ........................................10
7. References .....................................................11
   7.1. Normative References ......................................11
   7.2. Informative References ....................................11
Acknowledgments ...................................................12
Contributors ......................................................12
Authors' Addresses ................................................13

1. Introduction ✨

This document extends the existing IETF-specified Layer 2 Virtual Private Network (L2VPN) framework [RFC4664] so it can emulate E-Tree services over an MPLS network. It lays out the E-Tree architecture reference model and describes the functional components that go with it. It also points out the gaps and the extension areas that still need work in existing L2VPN solutions, like Virtual Private LAN Service (VPLS) [RFC4761] [RFC4762] and Ethernet Virtual Private Network (EVPN) [EVPN], when they're used for E-Tree services 🦋

1.1. Terminology

This document adopts all the terminology defined in RFC 4664 [RFC4664], RFC 4761 [RFC4761], and RFC 4762 [RFC4762]. It also uses the following terms:

Leaf Attachment Circuit (AC): An AC with Leaf role. An ingress Ethernet frame at a Leaf AC (an Ethernet frame arriving over an AC at the Provider Edge (PE) of an MPLS network) can only be delivered to one or more Root ACs in an E-Tree service instance. An ingress Ethernet frame at a Leaf AC must not be delivered to any Leaf ACs in the E-Tree service instance. 🍓

Root AC: An AC with Root role. An ingress Ethernet frame at a Root AC can be delivered to one or more of the other ACs in the associated E-Tree service instance. 👑

E-Tree: An Ethernet VPN service in which each AC is assigned the role of a Root or Leaf. The forwarding rules in an E-Tree are as follows:

The Root AC can communicate with other Root ACs and Leaf ACs.
Leaf ACs can only communicate with Root ACs.

2. Overview 🧚

2.1. Ethernet Bridge Network

In this document, "Ethernet bridge network" refers to the Ethernet bridge/switch network defined in IEEE 802.1Q [IEEE802.1Q]. In a bridge network, a data frame is an Ethernet frame. Data forwarding is based on the destination Media Access Control (MAC) address. MAC reachability is learned in the data plane based on the source MAC address and the port (or tagged port) the frame arrives on. The MAC aging mechanism is used to remove inactive MAC addresses from the MAC forwarding table on an Ethernet switch. 🔥

Data frames arriving at a switch may be destined to known unicast, unknown unicast, multicast, or broadcast MAC destinations. Unknown unicast, multicast, and broadcast frames are forwarded in a similar way, meaning they go to every port except the ingress port the frame arrived on. Multicast forwarding can be further constrained when using multicast control protocol snooping or using multicast MAC registration protocols [IEEE802.1Q].

An Ethernet host receiving an Ethernet frame checks the destination address in the frame to decide whether it's the intended destination 🙈

2.2. MEF Multipoint Ethernet Services: E-LAN and E-Tree

MEF 6.1 [MEF6.1] defines two multipoint Ethernet Service types:

E-LAN (Ethernet LAN), a multipoint-to-multipoint service
E-Tree (Ethernet Tree), a rooted-multipoint service

The MEF defines the User-Network Interface (UNI) in a multipoint service as the Ethernet interface between Customer Equipment (CE) and a Provider Edge (PE). In other words, the PE can send and receive Ethernet frames to and from the CE. The MEF also defines UNI roles in a multipoint service. One role is Root, and the other is Leaf 💜

Note that a MEF UNI in a service is equivalent to the Attachment Circuit (AC) defined in L2VPN [RFC4664]. The Root AC and Leaf AC defined in this document are the same as the Root UNI and Leaf UNI defined in MEF 10.3 [MEF10.3]. The terms "Root AC" and "Leaf AC" are used in the following MEF service description.

For an E-LAN service, all ACs have the Root role, which means any AC can communicate with other ACs in the service. The E-LAN service defined by the MEF may be implemented by IETF L2VPN solutions such as VPLS and EVPN [EVPN].

An E-Tree service has one or more Root ACs and at least two Leaf ACs. An E-Tree service supports communication among the roots and between a root and a leaf, but it prohibits communication among the leaves. Existing IETF L2VPN solutions can't support the E-Tree service. This document specifies the E-Tree architecture reference model that supports the E-Tree service defined by the MEF [MEF6.1]. Section 4 will discuss different E-Tree use cases 🎀

2.3. IETF L2VPN

2.3.1. Virtual Private LAN Service (VPLS)

VPLS [RFC4761] [RFC4762] is an L2VPN solution that provides multipoint-to-multipoint Ethernet connectivity across IP/MPLS networks. VPLS emulates traditional Ethernet Virtual LAN (VLAN) services in MPLS networks, and it may support MEF E-LAN services 🌈

A data frame in VPLS is an Ethernet frame. Data forwarding in a VPLS instance is based on the destination MAC address and the VLAN the frame arrives on. MAC reachability learning is performed in the data plane based on the source address and the AC or pseudowire (PW) the frame arrives on. MAC aging is the mechanism used to remove inactive MAC addresses from a VPLS switching instance (VSI) on a PE. VPLS supports forwarding for known unicast frames, as well as unknown unicast, broadcast, and multicast Ethernet frames.

Many service providers have deployed VPLS in their networks to provide L2VPN services to customers 💅

2.3.2. Ethernet VPN (EVPN)

Ethernet VPN [EVPN] is an enhanced L2VPN solution that emulates an Ethernet LAN or virtual LAN(s) across MPLS networks. ⭐

EVPN supports active-active multihoming of CEs. It uses the Multiprotocol Border Gateway Protocol (MP-BGP) control plane to advertise MAC address reachability from an ingress PE to egress PEs. So a PE learns MAC addresses that are reachable over local ACs in the data plane, and it learns other MAC addresses that are reachable across the MPLS network over remote ACs via the EVPN MP-BGP control plane. As a result, EVPN aims to support large-scale L2VPN with better resiliency compared to VPLS 🧠

EVPN is a relatively new technique and is still under development in the IETF L2VPN WG. 🙈

2.3.3. Virtual Private Multicast Service (VPMS)

VPMS [VPMS] is an L2VPN solution that provides point-to-multipoint connectivity across MPLS networks. It supports various attachment circuit (AC) types, including Frame Relay, ATM, Ethernet, PPP, etc. 🦋

With Ethernet ACs, VPMS provides single coverage of receiver membership, meaning there is no differentiation among multicast groups in one VPN. The destination address in the Ethernet frame is not used in data forwarding. 🫶

VPMS supports unidirectional point-to-multipoint transport from a sender to multiple receivers, and it may support reverse transport in a point-to-point manner.

3. E-Tree Architecture Reference Model 🧚

okay so Figure 1 is the whole E-Tree architecture reference model, and it is giving main character energy 🎀 There are three Provider Edges here: PE1, PE2, and PE3 💅 Each PE has a Virtual Service Instance (VSI) tied to an E-Tree service instance. A CE plugs into the VSI on a PE through an AC, and every AC has to be configured with either a Root or Leaf role. In the figure, AC1, AC2, AC5, AC6, AC9, and AC10 are Root ACs, and AC3, AC4, AC7, AC8, AC11, and AC12 are Leaf ACs. So a PE, whether it's local or remote, handles the Ethernet frames from CE01, CE02, and so on as if they came in on a Root AC, and handles the frames from CE03, CE04, and so on as if they came in on a Leaf AC 🫶

Now the forwarding rules, which apply no matter whether the sending AC and the receiving AC live on the same PE or on different PEs 👑

An egress frame (the frame going out over an AC) at an AC with Root role has to be the result of an ingress frame (the frame received at an AC) that has Root or Leaf role and is attached to the same E-Tree service instance.
An egress frame at an AC with Leaf role has to be the result of an ingress frame at an AC that has Root role and is attached to the same E-Tree service instance.

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

These rules cover all frame types: known unicast, unknown unicast, broadcast, and multicast 🌈 For known unicast frames, forwarding inside a VSI is based on the destination MAC address ✨

Each VSI on a PE is the E-Tree service instance, and it keeps its own MAC forwarding table that stays isolated from the other VSI tables on that PE. It also tracks the local AC roles 🍓 The VSI takes in a frame from an AC or from across the MPLS core, then forwards it to whichever other AC can reach the destination, according to the VSI forwarding table and the rules above. If the target AC sits on a remote PE, the VSI sends the frame over the MPLS core to that PE. How the traffic crosses the core depends on the E-Tree solution. One option is PWs meshing the VSIs, like in VPLS, with frames forwarded across the VSIs under the E-Tree forwarding rules. Another option is the EVPN forwarding paradigm, constrained by those same rules. So solutions that meet the E-Tree requirements could be extensions to VPLS and EVPN 🦋

Most use cases have only a few Root ACs (root CE sites) but lots of Leaf ACs (leaf CE sites) 🥹 A PE can also have only Root ACs or only Leaf ACs. Figure 1 is just a general model of E-Tree architecture, so think of it as the starter pack 🧃

4. E-Tree Use Cases 💖

Here are some of the big E-Tree use cases, all laid out in Table 1 📋

       +---------------------------+--------------+------------+
       | Use Case                  | Root AC      | Leaf AC    |
   +---+---------------------------+--------------+------------+
   | 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 [IEEE1588]| PTP Server   | PTP Client |
   |   | Clock Synchronization     |              |            |
   +---+---------------------------+--------------+------------+
   | 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     |
   +---+---------------------------+--------------+------------+

Where:

   RAN: Radio Access Network       NC: Network Controller
   BS: Base Station                PTP: Precision Time Protocol
   BNG: Broadband Network Gateway

                      Table 1: E-Tree Use Cases

For every one of these use cases, direct Layer 2 leaf-to-leaf communication is required to be prohibited 🙅‍♀️ Mobile backhaul is the one that gets a little tricky: for LTE X2 interfaces it may not apply 🫠 An LTE X2 interface [LTE] lets two evolved Node Bs (eNBs) talk to each other, and E-Tree service is still a good fit for those cases 🌸

Also, across all of the use cases above, one E-Tree service can have one Root AC or several 🌟 Multiple Root ACs might be there for redundancy or because there are several serving sites. Whether a given E-Tree service needs one or many Root ACs really depends on the application 🤷‍♀️

5. L2VPN Gaps for Emulating MEF E-Tree Service 🔥

okay real talk, the MEF E-Tree service has special forwarding rules that stop Ethernet frames from moving between leaves 😭 That's a real headache for IETF L2VPN solutions like VPLS and EVPN when they try to emulate E-Tree over an MPLS network. Two major issues come up, and they're covered in the subsections below 🧩

5.1. No Differentiation on AC Role

IP/MPLS L2VPN architecture doesn't have distinct roles on Attachment Circuits (ACs). It supports any-to-any connectivity across all ACs, and there's no mechanism for forwarding constraints based on AC role 🙈 The MEF E-Tree service, though, defines two AC roles, Root and Leaf, and sets its forwarding rules based on the originating and receiving AC roles of each frame. big mismatch bestie 💀

5.2. No AC Role Indication or Advertisement

In an L2VPN, when a PE (say PE2) gets a frame from another PE (say PE1) over the MPLS core, PE2 has no idea whether that frame came from a Root AC or a Leaf AC 😵 That's a forwarding problem on PE2, because the E-Tree forwarding rules need the forwarder to know the role of the frame's origin, meaning Root AC or Leaf AC. It matters the most when PE2 has both Root and Leaf ACs attached to the VSI. And the E-Tree forwarding rules apply to every frame type: known unicast, unknown unicast, multicast, and broadcast 🥀

5.3. Other Issues

Some of the E-Tree requirements are specific to an IP/MPLS L2VPN implementation, like the Leaf-only PE 🍭 A Leaf-only PE is a PE that has only Leaf AC(s) in an E-Tree service instance. Because of that, other PEs on the same E-Tree service instance don't have to forward frames from a Leaf AC to the Leaf-only PE, which can save some network resources 🫧 It's also desirable for an E-Tree solution to work with existing PEs that support single-role ACs, where the role is equivalent to the root in an E-Tree service 💜 All of these requirements are described in the E-Tree requirement document [RFC7152] 📄

6. Security Considerations 🔐

Okay, this section is serious, so listen up 🚨 An E-Tree service might be deployed for security reasons, to stop sites (leaves) from communicating with each other. An E-Tree solution has to enforce the E-Tree forwarding constraints. It also has to guarantee that Ethernet frames don't leak outside the E-Tree service instance they belong to 🛑

An E-Tree service blocks communication among leaf sites, but it knows nothing about higher-layer security constraints 😬 So, in general, higher-layer applications can't rely on E-Tree for security protection unless every security constraint is fully implemented by the E-Tree service itself.

Enhancing L2VPN for E-Tree services inherits the same security issues described in the L2VPN framework document [RFC4664] ⚠️ Those issues cover both the control plane and the data plane, and they can show up in these areas:

issues fully contained in the provider network
issues fully contained in the customer network
issues in the customer-provider interface network

The framework document goes deep on these security issues and on possible solutions 📚 An E-Tree solution must consider these issues and address them properly. VPLS [RFC4761] [RFC4762] and/or EVPN [EVPN] will likely be the candidate solutions for an E-Tree service over an MPLS network 💅 The security capabilities built into those solutions will naturally be adopted when E-Tree is supported. For details, check the Security Considerations sections in [RFC4761], [RFC4762], and [EVPN] 🫶

7. References 🦋

7.1. Normative References

okay so these are the docs you have to read before any of this makes sense, bestie 📚✨ the MUST-level stuff lives here, so no skipping 🙈

[MEF6.1]     Metro Ethernet Forum, "Ethernet Services Definitions -
             Phase 2", MEF 6.1, April 2008.

[MEF10.3]    Metro Ethernet Forum, "Ethernet Service Attributes -
             Phase 3", MEF 10.3, October 2013.

[RFC4664]    Andersson, L., Ed., and E. Rosen, Ed., "Framework for
             Layer 2 Virtual Private Networks (L2VPNs)", RFC 4664,
             September 2006,
             <http://www.rfc-editor.org/info/rfc4664>.

[RFC4761]    Kompella, K., Ed., and Y. Rekhter, Ed., "Virtual Private
             LAN Service (VPLS) Using BGP for Auto-Discovery and
             Signaling", RFC 4761, January 2007,
             <http://www.rfc-editor.org/info/rfc4761>.

[RFC4762]    Lasserre, M., Ed., and V. Kompella, Ed., "Virtual
             Private LAN Service (VPLS) Using Label Distribution
             Protocol (LDP) Signaling", RFC 4762, January 2007,
             <http://www.rfc-editor.org/info/rfc4762>.

[RFC7152]    Key, R., Ed., DeLord, S., Jounay, F., Huang, L., Liu,
             Z., and M. Paul, "Requirements for Metro Ethernet Forum
             (MEF) Ethernet-Tree (E-Tree) Support in Layer 2 Virtual
             Private Network (L2VPN)", RFC 7152, March 2014,
             <http://www.rfc-editor.org/info/rfc7152>.

7.2. Informative References

these ones are the extra reading 🧚 helpful for the vibe, but you don't need them to get the core stuff 💅

[IEEE802.1Q] IEEE, "IEEE Standard for Local and metropolitan area
             networks -- Media Access Control (MAC) Bridges and
             Virtual Bridged Local Area", IEEE Std 802.1Q, 2011.

[IEEE1588]   IEEE, "IEEE Standard for a Precision Clock
             Synchronization Protocol for Networked Measurement and
             Control Systems", IEEE Std 1588, July 2008.

[LTE]        3GPP, "Evolved Universal Terrestrial Radio Access
             (E-UTRA) and Evolved Universal Terrestrial Radio Access
             Network (E-UTRAN)", 3GPP TS 36.300 v11.2.0, July 2012.

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

[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,
             draft-ietf-l2vpn-vpms-frmwk-requirements-05,
             October 2012.

[EVPN]       Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,
             and J. Uttaro, "BGP MPLS Based Ethernet VPN", Work in
             Progress, draft-ietf-l2vpn-evpn-11, October 2014.

Acknowledgments ✨

the authors wanna give a huge shoutout to Nabil Bitar and Adrian Farrel 🫶 they gave super detailed reviews and suggestions, and the doc is way better because of them 💖

Contributors 🎀

these people contributed a ton to this doc, no cap 👑

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

Authors' Addresses 💌

and here are the people who actually wrote it 🦋

Raymond Key (editor)

EMail: raymond.key@ieee.org


Lucy Yong (editor)
Huawei USA

EMail: lucy.yong@huawei.com


Simon Delord
Telstra

EMail: simon.delord@gmail.com


Frederic Jounay
Orange CH
4 rue caudray 1020 Renens
Switzerland

EMail: frederic.jounay@orange.ch


Lizhong Jin

EMail: lizho.jin@gmail.com

📦 where this page comes from

ietf: rfc7387 2014-10
💖 girlified by claude-haiku-5-5 on 2026-10-18: a language model's rewrite of the original, under its terms

RFC 7387

A Framework for Ethernet Tree (E-Tree) Service over a Multiprotocol Label Switching (MPLS) Network

Abstract

Status of This Memo

Copyright Notice

Table of Contents

1. Introduction ✨

1.1. Terminology

2. Overview 🧚

2.1. Ethernet Bridge Network

2.2. MEF Multipoint Ethernet Services: E-LAN and E-Tree

2.3. IETF L2VPN

2.3.1. Virtual Private LAN Service (VPLS)

2.3.2. Ethernet VPN (EVPN)

2.3.3. Virtual Private Multicast Service (VPMS)

3. E-Tree Architecture Reference Model 🧚

4. E-Tree Use Cases 💖

5. L2VPN Gaps for Emulating MEF E-Tree Service 🔥

5.1. No Differentiation on AC Role

5.2. No AC Role Indication or Advertisement

5.3. Other Issues

6. Security Considerations 🔐

7. References 🦋

7.1. Normative References

7.2. Informative References

Acknowledgments ✨

Contributors 🎀

Authors' Addresses 💌