Internet DRAFT - draft-ietf-l2vpn-etree-reqt
draft-ietf-l2vpn-etree-reqt
Network Working Group Raymond Key (editor), Huawei
Internet Draft Simon Delord, Telstra
Category: Informational Frederic Jounay, Orange CH
Expires: January 2014 Lu Huang, China Mobile
Zhihua Liu, China Telecom
Manuel Paul, Deutsche Telekom
July 29, 2013
Requirements for Metro Ethernet Forum (MEF)
Ethernet-Tree (E-Tree) Support in L2VPN
draft-ietf-l2vpn-etree-reqt-05
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
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This Internet-Draft will expire on January 29, 2014.
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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...........................4
3.2. Difference 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.................................................7
5.3. Backward Compatibility........................................8
5.4. External Network Network Interface............................8
6. Security Consideration..........................................8
7. IANA Considerations.............................................8
8. Contributors....................................................8
9. Acknowledgements................................................8
10. References.....................................................8
10.1. Normative References.........................................8
10.2. Informative References.......................................9
Appendix
A. Frequently Asked Questions.....................................10
A.1. Are E-Tree requirements addressed in the Virtual
Private Multicast Service (VPMS) requirements?...............10
Authors' Addresses................................................11
Contributors' Addresses...........................................12
Intellectual Property and Copyright Statements....................12
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 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 Virtual Private
LAN Service (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 (IP/MPLS 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 in the context of the virtual
switching instance (VSI) to which it belongs.
2.2. Ethernet Virtual Private Network (E-VPN)
E-VPN is an enhanced Layer-2 service that emulates an Ethernet VLAN
across an IP/MPLS 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].
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3.1. Similarities between E-LAN and E-Tree
Following are the similarities between E-LAN and E-Tree services.
- 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
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 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.
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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 | Radio Area | RAN Base |
| | | Network (RAN)| Station |
| | | Network | |
| | | Controller | |
+---+---------------------------+--------------+------------+
| 4 | IEEE 1588 PTPv2 | Precision | PTP Client |
| | Clock Synchronisation | time Protocol| |
| | | (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 Cases
Common to all use cases, direct layer 2 Leaf-to-Leaf communication is
not required or must be inhibited.
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.
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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 other Roots & Leaves
- 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 IP/MPLS PSN.
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) equally (essentially as
Roots, although they not classified into Root or Leaf) and provides
any-to-any connectivity among all ACs. VPLS does not include any
mechanism for communication restriction between specific ACs.
Therefore it is insufficient for emulating generic E-Tree service
over an 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 interconnecting these ACs over an IP/MPLS PSN.
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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 where the problems arise:
- 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 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 extensions 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
Following are the E-Tree L2VPN functional requirements:
(1) A solution MUST prohibit communication between any two Leaf ACs
in a L2VPN instance.
(2) A solution MUST allow multiple Root ACs in a L2VPN instance.
(3) 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.
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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 (ENNI)
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] [Draft EVPN Req].
7. IANA Considerations
This document has no actions for IANA.
8. Contributors
Ruediger Kunze, Deutsche Telekom
Nick Del Regno, Verizon
Josh Rogers, Time Warner Cable
9. Acknowledgements
The authors would like to thank Lizhong Jin, Lucy Yong, Yuji Kamite
and Wim Henderickx for their valuable input and support.
10. References
10.1. Normative References
[RFC2119] Bradner, S., Key words for use in RFCs to Indicate
Requirement Levels, BCP 14, RFC 2119, March 1997
[MEF6.1] Metro Ethernet Forum, Ethernet Services Definitions -
Phase 2, April 2008
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[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
[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
10.2. Informative References
[Draft EVPN Req] Sajassi, et al., Requirements for Ethernet VPN
(EVPN), draft-ietf-l2vpn-evpn-req-04
(work in progress), July 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
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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
Leaves). 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 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 discussion 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 &
Leaves
- 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.
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.
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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
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Contributors' Addresses
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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