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Versions: (draft-key-l2vpn-etree-frwk) 00 01 02 03 04 05 06 07 08 09 10 RFC 7387

L2VPN WG                                           Raymond Key (editor)
Internet Draft                               Lucy Yong, Huawei (editor)
Intended status: Informational                             Simon Delord
Expires: February 2015                                          Telstra
                                             Frederic Jounay, Orange CH
                                                            Lizhong Jin
                                                        August 25, 2014



   A Framework for Ethernet Tree (E-Tree) Service over a Multiprotocol
                      Label Switching (MPLS) Network
                    draft-ietf-l2vpn-etree-frwk-10.txt


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

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on February 25, 2015.



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Copyright Notice

   Copyright (c) 2014 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
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   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.

Table of Contents


   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. IANA Considerations...........................................10
   8. References....................................................11
      8.1. Normative References.....................................11
      8.2. Informative References...................................11
   9. Contributing Authors..........................................12
   10. Acknowledgments..............................................12









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1. Introduction

   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.

   This document extends the existing IETF specified Layer 2 Virtual
   Private Network (L2VPN) framework [RFC4664] to provide the emulation
   of E-Tree services over an MPLS network. It specifies the E-Tree
   architecture reference model and describes the corresponding
   functional components. It also points out the gaps and required
   extension areas in existing L2VPN solutions such as Virtual Private
   LAN Service (VPLS)[RFC4761][RFC4762] and Ethernet Virtual Private
   Network (EVPN)[EVPN] for supporting E-Tree services.

1.1. Terminology

   This document adopts all the terminologies defined in RFC4664
   [RFC4664], RFC4761 [RFC4761], and RFC4762 [RFC4762]. It also uses the
   following terminologies:

   Leaf Attachment Circuit (AC): An AC with Leaf role. An ingress
   Ethernet frame at a Leaf AC (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 E-Tree are: Root AC can
   communicate with other Root ACs and Leaf ACs; Leaf ACs can only
   communicate with Root ACs.








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2. Overview

2.1. Ethernet Bridge Network

   In this document, Ethernet bridge network refers to the Ethernet
   bridge/switch network defined in IEEE802.1Q [IEEE802.1Q]. In a bridge
   network, a data frame is an Ethernet frame; data forwarding is based
   on destination MAC address; MAC reachability is learned in the data
   plane based on the source MAC address and the port (or tagged port)
   on which the frame arrives; and 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 MAC
   destinations, unknown, multicast, or broadcast MAC destinations.
   Unknown, multicast, and broadcast frames are forwarded in a similar
   way, i.e. to every port except the ingress port on which the frame
   arrives. Multicast forwarding can be further constrained when using
   multicast control protocol snooping or multicast MAC registration
   protocols. [IEEE802.1Q]

   An Ethernet host receiving an Ethernet frame checks the destination
   address in the frame to decide whether it is the intended
   destination.

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

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

   o  E-LAN (Ethernet LAN), a multipoint-to-multipoint service

   o  E-Tree (Ethernet Tree), a rooted-multipoint service

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

   Note that 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 of the root UNI and leaf UNI
   defined in MEF10.3 [MEF10.3]. The Root AC and Leaf AC terms are used
   in the following MEF service description.

   For an E-LAN service, all ACs have the Root role, which means that
   any AC can communicate with other ACs in the service. The E-LAN


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   service defined by 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 the communication among the roots and
   between a root and a leaf but prohibits the 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 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 Services
   (VLAN) in MPLS networks, and 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 on
   which the frame arrives. MAC reachability learning is performed in
   the data plane based on the source address and the AC or Pseudowire
   (PW) on which the frame arrives. MAC aging is also the mechanism used
   to remove inactive MAC addresses from a VPLS switching instance (VSI)
   on a Provider Edge (PE). VPLS supports forwarding for known unicast,
   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 multi-homing of CEs and uses
   Multiprotocol Border Gateway Protocol (MP-BGP) control plane to
   advertise MAC address reachability from an ingress PE to egress PEs.
   Thus, a PE learns MAC addresses reachable over local ACs in the data
   plane and other MAC addresses 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 relatively new technique and is still under development in
   IETF L2VPN WG.


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2.3.3. Virtual Private Multicast Service (VPMS)

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

   In the case of Ethernet ACs, VPMS provides single coverage of
   receiver membership, i.e. there is no differentiation among multicast
   groups in one VPN. 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 may support reverse transport in a
   point-to-point manner.

3. E-Tree Architecture Reference Model

   Figure 1 illustrates E-Tree architecture reference model. Three
   provider edges (PEs), PE1, PE2, and PE3 are shown in the Figure. Each
   PE has a Virtual Service Instance (VSI) associated with an E-Tree
   service instance. A CE attaches to the VSI on a PE via an AC. Each AC
   must be configured with a root or leaf role. In Figure 1, AC1 AC2,
   AC5, AC6, AC9, AC10 are Root ACs; AC3, AC4, AC7, AC8, AC11, AC12 are
   Leaf ACs. This implies that a PE (local or remote) processes the
   Ethernet frames from CE01, CE02, etc as if they are originated from a
   Root AC; and processes the Ethernet frames from CE03, CE04, etc as if
   they are originated from a Leaf AC.

   Under this architecture model, the forwarding rules among the ACs,
   regardless whether sending AC and receiving AC are on the same PE or
   on different PEs, are described as follow:

   o  An egress frame (frame to be transmitted over an AC) at an AC with
      Root role must be the result of an ingress frame at an AC (frame
      received at an AC) that has Root or Leaf role attached to the same
      E-tree service instance.

   o  An egress frame at the AC with Leaf role must be the result of an
      ingress frame at an AC that has Root role attached to the same E-
      tree service instance.









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                     <------------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 apply to all frame types, i.e. Known Unicast, Unknown,
   Broadcast, and Multicast. For Known Unicast frames, forwarding in a
   VSI context is based on the destination MAC address.

   A VSI on a PE corresponds to an E-Tree service instance and maintains
   a MAC forwarding table which is isolated from other VSI tables on the
   PE. It also keeps the track of local AC roles.  The VSI receives a
   frame from an AC or across the MPLS core; and forwards the frame to
   another AC over which the destination is reachable according to the
   VSI forwarding table and forwarding rules described above. When the
   target AC is on a remote PE, the VSI forwards the frame to the remote
   PE over the MPLS core. Forwarding over the MPLS core will be
   dependent on the E-tree solution.  For instance, a solution may adopt


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   PWs to mesh VSIs as in VPLS, and forward frames over VSIs subject to
   the E-tree forwarding rules. Alternatively, a solution may adopt the
   EVPN forwarding paradigm constrained by the E-tree forwarding rules.
   Thus, solutions that satisfy the E-tree requirements could be
   extensions to VPLS and EVPN.

   In most use cases, an E-Tree service has only a few Root ACs (root CE
   sites) but many Leaf ACs (leaf CE sites). Furthermore, a PE may have
   only Root ACs or only Leaf ACs. Figure 1 provides a general E-Tree
   architecture model.

4. E-Tree Use Cases

   Table 1 below presents some major use cases for E-Tree.

          +---------------------------+--------------+------------+
          | 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 [1588]    | 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


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   Common to all use cases, direct Layer2 Leaf-to-Leaf communication is
   required to be prohibited. For Mobile backhaul, this may not be valid
   for LTE X2 interfaces; LTE X2 interface [LTE] between two evolved
   node B (eNB) enables the communication in between. E-Tree service is
   appropriate for such use cases.

   Also common to the use cases mentioned above, there may be single or
   multiple Root ACs in one E-Tree service. The need of multiple Root-
   ACs may be driven by redundancy requirement or multiple serving
   sites. Whether a particular E-Tree service needs to support single or
   multiple Root ACs depends on an application.

5. L2VPN Gaps for Emulating MEF E-Tree Service

   E-Tree Service defines special forwarding rules that prohibit
   forwarding Ethernet frames among leaves. This poses some challenges
   to IETF L2VPN solutions such as VPLS and EVPN in emulating E-Tree
   service over an MPLS network. There are two major issues described in
   the following sections.

5.1. No Differentiation on AC Role

   IP/MPLS L2VPN architecture has no distinct role on Attachment Circuit
   (AC) and supports any-to-any connectivity among all ACs. It does not
   have any mechanism to support forwarding constraint based on an AC
   role. However, E-Tree service defines two AC roles, Root and Leaf,
   and defines the forwarding rules based on the frame originating and
   receiving AC roles.

5.2. No AC Role Indication or Advertisement

   In an L2VPN, when a PE, say PE2, receives a frame from another PE,
   say PE1, over the MPLS core, PE2 does not know if the frame from PE1
   is originated from a root AC or leaf AC. This causes the forwarding
   issue on PE2 because the E-Tree forwarding rules require that the
   forwarder must know the role of the frame origin, i.e. from root AC
   or leaf AC. This is specifically important, when PE2 has both root AC
   and leaf AC attached to the VSI. E-Tree forwarding rules apply to all
   types of frames (known unicast destination, unknown unicast
   destination, multicast and broadcast).

5.3. Other Issues

   Some desirable requirements for IETF E-Tree are specific to an
   IP/MPLS L2VPN implementation such as Leaf-only PE. Leaf-only PE is
   the PE that only has Leaf AC(s) in an E-Tree service instance, thus
   other PEs on the same E-Tree service instance do not necessarily


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   forward the frames originated from a Leaf AC to the Leaf-only PE,
   which may save some network resources. It is also desirable for E-
   Tree solution to work with existing PEs that support single-role AC
   and the role is equivalent to the root in an E-Tree Service. These
   requirements are described in the E-Tree requirement document.
   [RFC7152]

6. Security Considerations

   An E-tree service may be deployed for security reasons to prohibit
   communication among sites (leaves). An E-tree solution must enforce
   E-Tree forwarding constraints. The solution must also guarantee that
   Ethernet frames do not leak outside of the E-tree service instance to
   which they belong.

   An E-Tree service prohibits communication among leaf sites but does
   not have knowledge of higher layer security constraint. Therefore, in
   general, higher layer applications can not rely on E-Tree to provide
   the security protection unless all security constraints are fully
   implemented by E-Tree service.

   Enhancing L2VPN for E-Tree service inherits the same security issues
   described in L2VPN framework [RFC4664]. These relate to both control
   plane and data plane security issues that may arise in the following
   areas:

   o  issues fully contained in the provider network

   o  issues fully contained in the customer network

   o  issues in the customer-provider interface network

   The framework has substantial discussions on the security issues and
   potential solutions to address them. An E-Tree solution must consider
   these issues and address them properly. VPLS [RFC4761] [RFC4762]
   and/or EVPN [EVPN] will likely be candidate solutions for E-Tree
   Service over MPLS network. The security capabilities built in these
   solutions will be naturally adopted in supporting E-Tree. For the
   detail, see the security consideration section in [RFC4761],
   [RFC4762], and [EVPN].



7. IANA Considerations

   The document requires no IANA action.



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8. References

8.1. Normative References

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

   [MEF10.3] MEF, "Ethernet Service Attributes Phase 3", MEF10.3,
             October 2013

   [RFC4664] Andersson, L., et al, "Framework for Layer 2 Virtual
             Private Network (L2VPNs)", RFC4664, Sept. 2006

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

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

   [RFC7152] Key, et al., "Requirements for Metro Ethernet Forum (MEF)
             Ethernet-Tree (E-Tree) Support in L2VPN", RFC7152, April
             2011997.

8.2. Informative References

   [IEEE802.1Q] IEEE802.1, "Media Access Control (MAC) Bridges and
             Virtual Bridged Local Area", IEEE802.1Q, 2011

   [1588]    IEEE 1588, "Precision Time Protocol", IEEE 1588, 2013

   [LTE]     3GPP TS, "Evolved Universal Terrestrial Radio Access (E-
             UTRA) and Evolved Universal Terrestrial Radio Access
             Network (E-UTRAN)", V11.2.0, June, 2012

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

   [VPMS]  Kamite, et al., "Framework and Requirements for Virtual
             Private Multicast Service (VPMS)", draft-ietf-l2vpn-vpms-
             frmwk-requirements-05, work in progress

   [EVPN] Sajassi, et al., "BGP MPLS Based Ethernet VPN", draft-ietf-
             l2vpn-evpn-07, work in progress




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9. Contributing Authors

   The following people contribute the document as co-authors.

   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


10. Acknowledgments

   Authors like to thank Nabil Bitar for this detail review and
   suggestions.

Authors' Addresses

   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









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   Frederic Jounay
   Orange CH
   4 rue caudray 1020 Renens
   Switzerland

   Email: frederic.jounay@orange.ch


   Lizhong Jin

   Email: lizho.jin@gmail.com






































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