Network Working Group Raymond Key (editor), Huawei
Internet Draft Simon Delord, Alcatel-Lucent
Category: Informational Frederic Jounay, Orange CH
Expires: April 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
October 13, 2012
Requirements for MEF E-Tree Support in L2VPN
draft-ietf-l2vpn-etree-reqt-03
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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.
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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...........................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
VPMS requirement draft?.......................................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].
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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 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 is a L2VPN service that provides multipoint-to-multipoint
connectivity for Ethernet across an IP or MPLS-enabled IP Packet
Switched Network. VPLS emulates the Ethernet VLAN functionality of
traditional Ethernet network.
VPLS is a current IETF standard, please refer to [RFC4761] [RFC4762].
Data frame is Ethernet frame.
Data forwarding is MAC-based forwarding, which includes MAC address
learning and aging.
2.2. E-VPN
E-VPN is an enhanced Layer-2 service that emulates an Ethernet (V)LAN
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
Data frame is Ethernet frame.
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Data forwarding can be MAC-based forwarding or something else, to be
specified by service provider as service frame delivery attributes
in the particular service definition.
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 NC | RAN BS |
+---+---------------------------+--------------+------------+
| 4 | IEEE 1588 PTPv2 | PTP Server | PTP Client |
| | Clock Synchronisation | | |
+---+---------------------------+--------------+------------+
| 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 |
+---+---------------------------+--------------+------------+
Table 1: E-Tree Use Cases
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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 in the future.
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 MPLS network
provided that the E-LAN service uses MAC-based forwarding as 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.
Current standard VPLS treats all ACs equal (i.e. not classified into
Root or Leaf) and provides any-to-any connectivity among all ACs. The
current standard VPLS does not include any mechanism of communication
restriction between specific ACs, therefore is insufficient for
emulating generic E-Tree service over MPLS network.
A problem occurs when there are two or more PEs with both Root AC and
Leaf AC.
Let's look at the scenario illustrated in Figure 1 below. VPLS is
used to emulate an E-Tree service over a MPLS network.
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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:
- CE2 sends a Broadcast/Multicast frame to PE1 via AC2
- CE2 sends a Unicast frame to PE1 via AC2, destination address in
Ethernet header equal to CE4's MAC address
Note: Figure 1 is a hypothetical case solely 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 the current standard VPLS 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
co-exist on any PE.
5.2. Applicability
A solution MUST identify the L2VPN technology ([RFC4761], [RFC4761],
E-VPN) the solution is applicable to.
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5.3. Backward Compatibility
A solution SHOULD minimise the impact on existing L2VPN solution,
especially for the MEF E-LAN services already in operation.
A solution SHOULD be backward compatible with the existing L2VPN
solution. 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 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. 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
[MEF26.1] Metro Ethernet Forum, External Network Network Interface
(ENNI) - Phase 2, January 2012
[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
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[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-00 (work in
progress), March 2012
[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-01 (work in
progress), July 2012
[Draft VPMS Frmwk]
Kamite, et al., Framework and Requirements for Virtual
Private Multicast Service (VPMS),
draft-ietf-l2vpn-vpms-frmwk-requirements-04 (work in
progress), July 2011
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Appendix A. Frequently Asked Questions
A.1. Are E-Tree requirements addressed in the VPMS requirement draft?
VPMS is Virtual Private Multicast Service. VPMS requirement draft
refers to [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 are 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.
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A.2. Are there any potential deployment scenarios for a "VPLS Only"
solution?
Yes, there are potential deployment scenarios for a "VPLS Only"
solution, 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) | +---+ |
+---------+
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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) | +---+ |
+---------+ +---------+
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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
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Authors' Addresses
Raymond Key (editor)
Huawei
Email: raymond.key@ieee.org
Simon Delord
Alcatel-Lucent
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
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Copyright Notice
Copyright (c) 2012 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
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described in the Simplified BSD License.
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