Network Working Group Raymond Key
Internet Draft Simon Delord
Category: Informational Frederic Jounay, France Telecom
Expires: October 2010
April 7, 2010
Requirements for MEF E-Tree Support in VPLS
draft-key-l2vpn-vpls-etree-reqt-00.txt
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Abstract
This document provides functional requirements for Metro Ethernet
Forum (MEF) Ethernet Tree (E-Tree) support in Virtual Private LAN
Service (VPLS). It is intended that potential solutions will use
these requirements as guidelines.
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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].
Table of Contents
1. Introduction....................................................3
2. Virtual Private LAN Service.....................................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...........................3
3.3. E-Tree Use Cases..............................................4
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........................................6
6. Security Consideration..........................................7
7. IANA Considerations.............................................7
8. Acknowledgements................................................7
9. References......................................................7
9.1. Normative References..........................................7
9.2. Informative References........................................7
Authors' Addresses.................................................8
Intellectual Property and Copyright Statements.....................8
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1. Introduction
This document provides functional requirements for Metro Ethernet
Forum (MEF) Ethernet Tree (E-Tree) support in Virtual Private LAN
Service (VPLS). 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.
2. Virtual Private LAN Service
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.
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 MUST be Ethernet frame.
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.
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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 | Broadcast Video | Video Source | Subscriber |
| | (unidirectional only) | | |
+---+---------------------------+--------------+------------+
| 2 | Broadcast/Multicast Video | Video Source | Subscriber |
| | plus Control Channel | | |
+---+---------------------------+--------------+------------+
| 3 | Internet Access | BNG Router | Subscriber |
+---+---------------------------+--------------+------------+
| 4 | IEEE 1588 PTPv2 | PTP Server | PTP Client |
| | Clock Synchronisation | | |
+---+---------------------------+--------------+------------+
| 5 | Mobile Backhaul | RAN NC | RAN BS |
+---+---------------------------+--------------+------------+
| 6 | Hub & Spoke VPN | Hub Site | Spoke Site |
+---+---------------------------+--------------+------------+
| 7 | Wholesale Access | Customer's | Customer's |
| | | Interconnect | Subscriber |
+---+---------------------------+--------------+------------+
| 8 | Device Management | Management | Managed |
| | | System | Device |
+---+---------------------------+--------------+------------+
Table 1: E-Tree Use Cases
Common to all use cases, direct Leaf-to-Leaf communication is not
required. For Mobile backhaul, this may not be valid for LTE X2
interfaces in the future.
If direct 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.
Also common to the use cases mentioned above, there may be single or
multiple Root endpoints in one E-Tree service. The need for multiple
Root endpoints is usually driven by redundancy requirement. Whether a
particular E-Tree service needs to support single or multiple Root
endpoints depends on the target application.
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A generic E-Tree service supports the following traffic flows:
- Unicast bidirectional Root to/from Root
- Unicast bidirectional Root to/from Leaf
- Broadcast/Multicast unidirectional Root to all Roots and Leafs
- 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.
4. Problem Statement
4.1. Motivation
VPLS 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.
Considerable number of service providers have adopted VPLS to provide
MEF 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.
4.2. Leaf-to-Leaf Communication Restriction
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.
Let's look at the scenario illustrated in Figure 1 below. VPLS is
used to emulate an E-Tree service over a MPLS network.
<------------E-Tree------------>
+---------+ +---------+
| PE1 | | PE2 |
+----+ | +---+ | | +---+ | +----+
|CE01+----AC1----+--+ | | | | +--+----AC5----+CE05|
+----+ (Root AC) | | V | | | | V | | (Root AC) +----+
+----+ | | | | | | | | +----+
|CE02+----AC2----+--+ | | Ethernet | | +--+----AC6----+CE06|
+----+ (Root AC) | | S +--+-----PW-----+--+ S | | (Root AC) +----+
+----+ | | | | | | | | +----+
|CE03+----AC3----+--+ | | | | +--+----AC7----+CE07|
+----+ (Leaf AC) | | I | | | | I | | (Leaf AC) +----+
+----+ | | | | | | | | +----+
|CE04+----AC4----+--+ | | | | +--+----AC8----+CE08|
+----+ (Leaf AC) | +---+ | | +---+ | (Leaf AC) +----+
| | | |
+---------+ +---------+
Figure 1: Reference Model for Leaf-to-Leaf Communication Restriction
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When PE2 receives a frame from PE1 via the 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
5. Requirements
5.1. Functional Requirements
A solution MUST prohibit communication between any two Leaf ACs in a
VPLS instance.
A solution MUST allow multiple Root ACs in a VPLS instance.
A solution MUST allow Root AC and Leaf AC of a VPLS instance co-exist
on any PE.
5.2. Applicability
There are two distinct VPLS standards, performing similar functions
in different manners.
- [RFC4761], commonly known as BGP-VPLS
- [RFC4762], commonly known as LDP-VPLS
A solution MUST identify which VPLS standards the solution is
applicable to, [RFC4761] or [RFC4762] or both.
Service providers may use single or multiple technologies to deliver
an end-to-end E-Tree service.
- Case 1: Single technology "Just VPLS"
- Case 2: Multiple technologies "VPLS + Others"
- e.g. VPLS + Ethernet network, VPLS + OTN
- Case 3: Single/multiple technologies "No VPLS"
- e.g. Ethernet network, Ethernet network + OTN
- out of scope for this document
A solution MUST identify which of the above cases the solution is
applicable to. For Case 2, further details may be required to specify
the applicable deployment scenarios.
5.3. Backward Compatibility
A solution should minimise the impact on existing VPLS solution,
especially for the MEF E-LAN services already in operation.
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A solution should be backward compatible with the existing VPLS
solution. It should allow a case where a common VPLS 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.
6. Security Considerations
This will be added in later version of this document.
7. IANA Considerations
This will be added in later version of this document.
8. Acknowledgements
This will be added in later version of this document.
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
[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
[RFC4762] Lasserre & Kompella, Virtual Private LAN Service (VPLS)
Using Label Distribution Protocol (LDP) Signaling,
January 2007
9.2. Informative References
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Authors' Addresses
Raymond Key
Australia
Email: raymond.key@ieee.org
Simon Delord
Australia
Email: simon.delord@gmail.com
Frederic Jounay
France Telecom
2, avenue Pierre-Marzin
22307 Lannion Cedex, France
Email: frederic.jounay@orange-ftgroup.com
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