Internet Engineering Task Force (IETF) F. Balus, Ed.
Request for Comments: 7041 Alcatel-Lucent
Category: Informational A. Sajassi, Ed.
ISSN: 2070-1721 Cisco
N. Bitar, Ed.
Verizon
November 2013
Internet Engineering Task Force (IETF) F. Balus, Ed.
Request for Comments: 7041 Alcatel-Lucent
Category: Informational A. Sajassi, Ed.
ISSN: 2070-1721 Cisco
N. Bitar, Ed.
Verizon
November 2013
Extensions to the Virtual Private LAN Service (VPLS) Provider Edge (PE) Model for Provider Backbone Bridging
虚拟专用LAN服务（VPLS）提供商边缘（PE）模型的扩展，用于提供商主干桥接
Abstract
摘要
The IEEE 802.1 Provider Backbone Bridges (PBBs) specification defines an architecture and bridge protocols for interconnection of multiple Provider Bridged Networks (PBNs). Provider backbone bridging was defined by IEEE as a connectionless technology based on multipoint VLAN tunnels. PBB can be used to attain better scalability than Provider Bridges (PBs) in terms of the number of customer Media Access Control addresses and the number of service instances that can be supported.
IEEE 802.1提供商主干网桥（PBB）规范定义了用于多提供商桥接网络（PBN）互连的体系结构和网桥协议。提供商主干桥接由IEEE定义为基于多点VLAN隧道的无连接技术。就客户媒体访问控制地址的数量和可支持的服务实例的数量而言，PBB可用于实现比提供商网桥（PBs）更好的可伸缩性。
The Virtual Private LAN Service (VPLS) provides a framework for extending Ethernet LAN services, using MPLS tunneling capabilities, through a routed MPLS backbone without running the Rapid Spanning Tree Protocol (RSTP) or the Multiple Spanning Tree Protocol (MSTP) across the backbone. As a result, VPLS has been deployed on a large scale in service provider networks.
虚拟专用LAN服务（VPLS）提供了一个框架，用于使用MPLS隧道功能，通过路由MPLS主干扩展以太网LAN服务，而无需在主干上运行快速生成树协议（RSTP）或多生成树协议（MSTP）。因此，VPLS已在服务提供商网络中大规模部署。
This document discusses extensions to the VPLS Provider Edge (PE) model required to incorporate desirable PBB components while maintaining the service provider fit of the initial model.
本文档讨论了VPLS提供商边缘（PE）模型的扩展，该模型需要包含所需的PBB组件，同时保持服务提供商与初始模型的匹配。
Status of This Memo
关于下段备忘
This document is not an Internet Standards Track specification; it is published for informational purposes.
本文件不是互联网标准跟踪规范；它是为了提供信息而发布的。
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Not all documents approved by the IESG are a candidate for any level of Internet Standard; see Section 2 of RFC 5741.
本文件是互联网工程任务组（IETF）的产品。它代表了IETF社区的共识。它已经接受了公众审查，并已被互联网工程指导小组（IESG）批准出版。并非IESG批准的所有文件都适用于任何级别的互联网标准；见RFC 5741第2节。
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc7041.
有关本文件当前状态、任何勘误表以及如何提供反馈的信息，请访问http://www.rfc-editor.org/info/rfc7041.
Copyright Notice
版权公告
Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved.
版权所有（c）2013 IETF信托基金和确定为文件作者的人员。版权所有。
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 carefully, as 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 are provided without warranty as described in the Simplified BSD License.
本文件受BCP 78和IETF信托有关IETF文件的法律规定的约束(http://trustee.ietf.org/license-info)自本文件出版之日起生效。请仔细阅读这些文件，因为它们描述了您对本文件的权利和限制。从本文件中提取的代码组件必须包括信托法律条款第4.e节中所述的简化BSD许可证文本，并提供简化BSD许可证中所述的无担保。
Table of Contents
目录
1. Introduction ....................................................3
2. General Terminology .............................................4
3. PE Reference Model ..............................................6
4. Packet Walkthrough ..............................................9
5. Control Plane ..................................................11
6. Efficient Packet Replication in PBB VPLS .......................12
7. PBB VPLS OAM ...................................................12
8. Security Considerations ........................................12
9. References .....................................................13
9.1. Normative References ......................................13
9.2. Informative References ....................................13
10. Contributors ..................................................14
11. Acknowledgments ...............................................15
1. Introduction ....................................................3
2. General Terminology .............................................4
3. PE Reference Model ..............................................6
4. Packet Walkthrough ..............................................9
5. Control Plane ..................................................11
6. Efficient Packet Replication in PBB VPLS .......................12
7. PBB VPLS OAM ...................................................12
8. Security Considerations ........................................12
9. References .....................................................13
9.1. Normative References ......................................13
9.2. Informative References ....................................13
10. Contributors ..................................................14
11. Acknowledgments ...............................................15
The IEEE 802.1 Provider Backbone Bridges specification [PBB] defines an architecture and bridge protocols for interconnection of multiple Provider Bridged Networks (PBNs). PBB can be used to attain better scalability than Provider Bridges [PB] in terms of the number of customer Media Access Control (MAC) addresses and the number of service instances that can be supported. PBB provides a data-plane hierarchy and new addressing designed to achieve such better scalability in Provider Backbone Networks. A number of Ethernet control-plane protocols, such as the Rapid Spanning Tree Protocol (RSTP), the Multiple Spanning Tree Protocol (MSTP), and Shortest Path Bridging (SPB), could be deployed as the core control plane for loop avoidance and load balancing for PBB. The applicability of these control protocols is out of scope for this document.
IEEE 802.1提供商主干网桥规范[PBB]定义了用于多提供商桥接网络（PBN）互连的体系结构和网桥协议。就客户媒体访问控制（MAC）地址的数量和可支持的服务实例的数量而言，PBB可用于实现比提供商网桥[PB]更好的可伸缩性。PBB提供了数据平面层次结构和新的寻址，旨在在提供商主干网中实现更好的可扩展性。许多以太网控制平面协议，如快速生成树协议（RSTP）、多生成树协议（MSTP）和最短路径桥接（SPB）可以部署为核心控制平面，用于PBB的环路避免和负载平衡。这些控制协议的适用性超出了本文件的范围。
The Virtual Private LAN Service (VPLS) provides a solution for extending Ethernet LAN services, using MPLS tunneling capabilities, through a routed MPLS backbone without requiring the use of a native Ethernet control-plane protocol across the backbone. VPLS use of the structured FEC 129 [RFC4762] also allows for inter-domain, inter-provider connectivity and enables auto-discovery options across the network, improving the service delivery options.
虚拟专用LAN服务（VPLS）提供了一种通过路由MPLS骨干网使用MPLS隧道功能扩展以太网LAN服务的解决方案，而无需跨骨干网使用本机以太网控制平面协议。VPLS使用结构化FEC 129[RFC4762]还允许域间、提供商间的连接，并支持跨网络的自动发现选项，从而改进服务交付选项。
A hierarchical solution for VPLS was introduced in [RFC4761] and [RFC4762] to provide improved scalability and efficient handling of packet replication. These improvements are achieved by reducing the number of Provider Edge (PE) devices connected in a full-mesh topology through the creation of two-tier PEs. A User-facing PE (U-PE) aggregates all the Customer Edge (CE) devices in a lower-tier access network and then connects to the Network-facing PE (N-PE) device(s) deployed around the core domain. In VPLS, Media Access Control (MAC) address learning and forwarding are done based on Customer MAC addresses (C-MACs); this poses scalability issues on the N-PE devices as the number of VPLS instances (and thus C-MACs) increases. Furthermore, since a set of pseudowires (PWs) is maintained on a "per customer service instance" basis, the number of PWs required at N-PE devices is proportional to the number of customer service instances multiplied by the number of N-PE devices in the full-mesh set. This can result in scalability issues (in terms of PW manageability and troubleshooting) as the number of customer service instances grows.
[RFC4761]和[RFC4762]中引入了VPLS的分层解决方案，以提供改进的可扩展性和数据包复制的高效处理。这些改进是通过创建两层PE来减少在全网状拓扑中连接的提供商边缘（PE）设备的数量来实现的。面向用户的PE（U-PE）聚合较低层接入网络中的所有客户边缘（CE）设备，然后连接到部署在核心域周围的面向网络的PE（N-PE）设备。在VPLS中，媒体访问控制（MAC）地址学习和转发基于客户MAC地址（C-MAC）；随着VPLS实例（以及C-MAC）数量的增加，这在N-PE设备上带来了可伸缩性问题。此外，由于一组伪线（PW）是在“每个客户服务实例”的基础上维护的，因此N-PE设备所需的PW数量与客户服务实例数量乘以全网格集中的N-PE设备数量成正比。随着客户服务实例数量的增加，这可能会导致可伸缩性问题（在PW可管理性和故障排除方面）。
This document describes how PBB can be integrated with VPLS to allow for useful PBB capabilities while continuing to avoid the use of MSTP in the backbone. The combined solution referred to in this document
本文档描述了如何将PBB与VPL集成，以实现有用的PBB功能，同时继续避免在主干中使用MSTP。本文件中提及的组合解决方案
as PBB-VPLS results in better scalability in terms of the number of service instances, PWs, and C-MACs that need to be handled in the VPLS PEs.
由于PBB-VPLS在VPLS PEs中需要处理的服务实例、PW和C-MAC的数量方面具有更好的可伸缩性。
Section 2 provides a quick terminology reference. Section 3 covers the reference model for PBB VPLS PEs. Section 4 describes the packet walkthrough. Sections 5 through 7 discuss the PBB-VPLS usage of existing VPLS mechanisms -- the control plane; efficient packet replication; and Operations, Administration, and Maintenance (OAM).
第2节提供了一个快速的术语参考。第3节介绍了PBB VPLS PEs的参考模型。第4节描述了数据包演练。第5节至第7节讨论了PBB-VPLS对现有VPLS机制的使用——控制平面；高效的数据包复制；以及运营、管理和维护（OAM）。
Some general terminology is defined here; most of the terminology used is from [PBB], [PB], [RFC4664], and [RFC4026]. Terminology specific to this memo is introduced as needed in later sections.
这里定义了一些通用术语；使用的大多数术语来自[PBB]、[PB]、[RFC4664]和[RFC4026]。本备忘录的专用术语将根据需要在后面的章节中介绍。
B-BEB: A backbone edge bridge positioned at the edge of a provider backbone bridged network. It contains a B-component that supports bridging in the provider backbone based on Backbone MAC (B-MAC) and B-tag information.
B-BEB：位于提供商主干桥接网络边缘的主干边缘桥接器。它包含一个B组件，支持基于主干MAC（B-MAC）和B-tag信息在提供商主干中桥接。
B-component: A bridging component contained in backbone edge and core bridges that bridges in the backbone space (B-MAC addresses, B-VLAN).
B组件：包含在主干边缘和核心网桥中的桥接组件，在主干空间（B-MAC地址，B-VLAN）桥接。
B-MAC: The backbone source or destination MAC address fields defined in the PBB provider MAC encapsulation header.
B-MAC：在PBB提供者MAC封装报头中定义的主干源或目标MAC地址字段。
B-tag: Field defined in the PBB provider MAC encapsulation header that conveys the backbone VLAN identifier information. The format of the B-tag field is the same as that of an 802.1ad S-tag field.
B-tag：在PBB提供商MAC封装报头中定义的字段，用于传输主干VLAN标识符信息。B标签字段的格式与802.1ad S标签字段的格式相同。
B-Tagged Service Interface: The interface between a BEB and a Backbone Core Bridge (BCB) in a provider backbone bridged network. Frames passed through this interface contain a B-tag field.
B-标记服务接口：在提供商主干桥接网络中，BEB和主干核心网桥（BCB）之间的接口。通过此接口的帧包含一个B标记字段。
B-VID: The specific VLAN identifier carried inside a B-tag.
B-VID：在B-tag中携带的特定VLAN标识符。
B-VLAN: The backbone VLAN associated with a B-component.
B-VLAN：与B组件关联的主干VLAN。
B-PW: The pseudowire used to interconnect B-component instances.
B-PW：用于互连B组件实例的伪线。
BEB: A backbone edge bridge positioned at the edge of a provider backbone bridged network. It can contain an I-component, a B-component, or both I-components and B-components.
BEB：位于提供商主干桥接网络边缘的主干边缘桥接器。它可以包含I组件、B组件或I组件和B组件。
C-VID: The VLAN identifier in a customer VLAN.
C-VID：客户VLAN中的VLAN标识符。
DA: Destination Address.
DA：目的地地址。
I-BEB: A backbone edge bridge positioned at the edge of a provider backbone bridged network. It contains an I-component for bridging in the customer space (customer MAC addresses, service VLAN IDs).
I-BEB：位于提供商主干桥接网络边缘的主干边缘桥接器。它包含一个用于在客户空间桥接的I组件（客户MAC地址、服务VLAN id）。
I-component: A bridging component contained in a backbone edge bridge that bridges in the customer space (customer MAC addresses, service VLAN identifier information (S-VLAN)).
I-component：包含在主干边缘网桥中的桥接组件，桥接客户空间（客户MAC地址、服务VLAN标识符信息（S-VLAN））。
I-SID: The 24-bit service instance field carried inside the I-tag. I-SID defines the service instance that the frame should be "mapped to".
I-SID：I-tag中携带的24位服务实例字段。I-SID定义帧应“映射到”的服务实例。
I-tag: A field defined in the PBB provider MAC encapsulation header that conveys the service instance information (I-SID) associated with the frame.
I-tag：在PBB提供者MAC封装报头中定义的一个字段，用于传递与帧关联的服务实例信息（I-SID）。
I-Tagged Service Interface: The interface defined between the I-components and B-components inside an IB-BEB or between two B-BEBs. Frames passed through this interface contain an I-tag field.
I标签服务接口：IB-BEB内部的I组件和B组件之间或两个B-BEB之间定义的接口。通过此接口的帧包含一个I-tag字段。
IB-BEB: A backbone edge bridge positioned at the edge of a provider backbone bridged network. It contains an I-component for bridging in the customer space (customer MAC addresses, service VLAN IDs) and a B-component for bridging the provider's backbone space (B-MAC, B-tag).
IB-BEB：位于提供商主干桥接网络边缘的主干边缘网桥。它包含一个用于在客户空间桥接的I组件（客户MAC地址、服务VLAN ID）和一个用于桥接提供商主干空间的B组件（B-MAC、B-tag）。
PBs: Provider Bridges (IEEE amendment (802.1ad) to 802.1Q for "QinQ" encapsulation and bridging of Ethernet frames [PB]).
PBs：提供商网桥（IEEE对802.1Q的修订（802.1ad），用于“QinQ”封装和以太网帧桥接[PB]）。
PBBs: Provider Backbone Bridges (IEEE amendment (802.1ah) to 802.1Q for "MAC tunneling" encapsulation and bridging of frames across a provider network [PBB]).
PBB：提供商主干网桥（IEEE对802.1Q的修正案（802.1ah），用于“MAC隧道”封装和跨提供商网络的帧桥接[PBB]）。
PBBN: Provider Backbone Bridged Network.
PBBN：提供商主干桥接网络。
PBN: Provider Bridged Network. A network that employs 802.1ad (QinQ) technology.
PBN：提供商桥接网络。采用802.1ad（QinQ）技术的网络。
PSN: Packet-Switched Network.
分组交换网络。
S-tag: A field defined in the 802.1ad QinQ encapsulation header that conveys the service VLAN identifier information (S-VLAN).
S-tag：在802.1ad QinQ封装头中定义的字段，用于传输服务VLAN标识符信息（S-VLAN）。
S-Tagged Service Interface: The interface defined between the customer (CE) and the I-BEB or IB-BEB components. Frames passed through this interface contain an S-tag field.
S标记服务接口：客户（CE）与I-BEB或IB-BEB组件之间定义的接口。通过此接口的帧包含一个S标记字段。
S-VLAN: The specific service VLAN identifier carried inside an S-tag.
S-VLAN：S-tag中携带的特定服务VLAN标识符。
SA: Source Address.
SA：源地址。
S-VID: The VLAN identifier in a service VLAN.
S-VID：服务VLAN中的VLAN标识符。
Tag: In Ethernet, a header immediately following the Source MAC Address field of the frame.
标记：在以太网中，紧跟在帧的源MAC地址字段之后的一种报头。
The following gives a short primer on the Provider Backbone Bridge (PBB) before describing the PE reference model for PBB-VPLS. The internal components of a PBB bridge module are depicted in Figure 1.
在描述PBB-VPLS的PE参考模型之前，下面给出了一个关于提供商主干网桥（PBB）的简短介绍。PBB网桥模块的内部组件如图1所示。
+-------------------------------+
| PBB Bridge Model |
| |
+---+ | +------+ +-----------+ |
|CE |---------|I-Comp|------| | |
+---+ | | | | |--------
| +------+ | | |
| o | B-Comp | |
| o | |--------
| o | | |
+---+ | +------+ | | |
|CE |---------|I-Comp|------| |--------
+---+ ^ | | | ^ | | | ^
| | +------+ | +-----------+ | |
| +------------|------------------+ |
| | |
| | |
S-tagged I-tagged B-tagged
Service Interface Service I/F Service I/F
(I/F)
+-------------------------------+
| PBB Bridge Model |
| |
+---+ | +------+ +-----------+ |
|CE |---------|I-Comp|------| | |
+---+ | | | | |--------
| +------+ | | |
| o | B-Comp | |
| o | |--------
| o | | |
+---+ | +------+ | | |
|CE |---------|I-Comp|------| |--------
+---+ ^ | | | ^ | | | ^
| | +------+ | +-----------+ | |
| +------------|------------------+ |
| | |
| | |
S-tagged I-tagged B-tagged
Service Interface Service I/F Service I/F
(I/F)
Figure 1: PBB Bridge Model
图1:PBB桥模型
Provider Backbone Bridges (PBBs) [PBB] offer a scalable solution for service providers to build large bridged networks. The focus of PBB is primarily on improving two main areas with provider Ethernet bridged networks:
提供商主干网桥（PBB）[PBB]为服务提供商构建大型桥接网络提供了一种可扩展的解决方案。PBB的重点主要是改进供应商以太网桥接网络的两个主要领域：
- MAC-address table scalability - Service instance scalability
- MAC地址表可伸缩性-服务实例可伸缩性
To obviate the above two limitations, PBB introduces a hierarchical network architecture with associated new frame formats that extend the work completed by Provider Bridges (PBs). In the PBBN architecture, customer networks (using PBs) are aggregated into PBBNs, which utilize the IEEE PBB frame format. The frame format employs a MAC tunneling encapsulation scheme for tunneling customer Ethernet frames within provider Ethernet frames across the PBBN. A VLAN identifier (B-VID) is used to segregate the backbone into broadcast domains, and a new 24-bit service identifier (I-SID) is defined and used to associate a given customer MAC frame with a provider service instance (also called the service delimiter). It should be noted that in [PBB] there is a clear segregation between provider service instances (represented by I-SIDs) and provider VLANs (represented by B-VIDs), which was not the case for PBs.
为了避免上述两个限制，PBB引入了一种分层网络体系结构，该体系结构具有相关的新帧格式，扩展了提供者网桥（PBs）完成的工作。在PBBN体系结构中，用户网络（使用PBs）聚合到PBBN中，PBBN使用IEEE PBB帧格式。帧格式采用MAC隧道封装方案，用于跨PBBN在提供商以太网帧内隧道传输客户以太网帧。VLAN标识符（B-VID）用于将主干分隔为广播域，并定义新的24位服务标识符（I-SID）并用于将给定的客户MAC帧与提供商服务实例（也称为服务分隔符）关联。应该注意的是，在[PBB]中，在提供者服务实例（由I-SID表示）和提供者VLAN（由B-VID表示）之间存在明显的隔离，而PBs的情况并非如此。
As shown in Figure 1, a PBB bridge may consist of a single B-component and one or more I-components. In simple terms, the B-component provides bridging in the provider space (B-MAC, B-VLAN), and the I-component provides bridging in the customer space (C-MAC, S-VLAN). The customer frame is first encapsulated with the provider backbone header (B-MAC, B-tag, I-tag); then, the bridging is performed in the provider backbone space (B-MAC, B-VLAN) through the network till the frame arrives at the destination BEB, where it gets decapsulated and passed to the CE. If a PBB bridge consists of both I-components and B-components, then it is called an IB-BEB, and if it only consists of either B-components or I-components, then it is called a B-BEB or an I-BEB, respectively. The interface between an I-BEB or IB-BEB and a CE is called an S-tagged service interface, and the interface between an I-BEB and a B-BEB (or between two B-BEBs) is called an I-tagged service interface. The interface between a B-BEB or IB-BEB and a Backbone Core Bridge (BCB) is called a B-tagged service interface.
如图1所示，PBB电桥可由单个B组件和一个或多个I组件组成。简单地说，B组件在提供者空间（B-MAC，B-VLAN）中提供桥接，I组件在客户空间（C-MAC，S-VLAN）中提供桥接。首先使用提供商主干报头（B-MAC、B-tag、I-tag）封装客户帧；然后，桥接通过网络在提供商主干空间（B-MAC、B-VLAN）中执行，直到帧到达目的地BEB，在那里它被解除封装并传递到CE。如果PBB网桥由I-组件和B-组件组成，则称为IB-BEB，如果它仅由B-组件或I-组件组成，则分别称为B-BEB或I-BEB。I-BEB或IB-BEB与CE之间的接口称为带S标签的服务接口，I-BEB与B-BEB之间（或两个B-BEB之间）的接口称为带I标签的服务接口。B-BEB或IB-BEB与主干核心网桥（BCB）之间的接口称为带B标签的服务接口。
To accommodate the PBB components, the VPLS model defined in [RFC4664] is extended as depicted in Figure 2.
为了适应PBB组件，对[RFC4664]中定义的VPLS模型进行了扩展，如图2所示。
+----------------------------------------+
| PBB-VPLS-Capable PE Model |
| +---------------+ +------+ |
| | | |VPLS-1|------------
| | |==========|Fwdr |------------ PWs
+--+ | | Bridge ------------ |------------
|CE|-|-- | | +------+ |
+--+ | | Module | o |
| | | o |
| | (PBB | o |
| | bridge) | o |
| | | o |
+--+ | | | +------+ |
|CE|-|-- | ------------VPLS-n|-------------
+--+ | | |==========| Fwdr |------------- PWs
| | | ^ | |-------------
| +---------------+ | +------+ |
| | |
+-------------------------|--------------+
LAN Emulation Interface
+----------------------------------------+
| PBB-VPLS-Capable PE Model |
| +---------------+ +------+ |
| | | |VPLS-1|------------
| | |==========|Fwdr |------------ PWs
+--+ | | Bridge ------------ |------------
|CE|-|-- | | +------+ |
+--+ | | Module | o |
| | | o |
| | (PBB | o |
| | bridge) | o |
| | | o |
+--+ | | | +------+ |
|CE|-|-- | ------------VPLS-n|-------------
+--+ | | |==========| Fwdr |------------- PWs
| | | ^ | |-------------
| +---------------+ | +------+ |
| | |
+-------------------------|--------------+
LAN Emulation Interface
Figure 2: PBB-VPLS-Capable PE Model
图2：支持PBB VPLS的PE型号
The PBB module as defined in the [PBB] specification is expanded to interact with VPLS Forwarders. The VPLS Forwarders are used in [RFC4762] to build a PW mesh or a set of spoke PWs (Hierarchical VPLS (H-VPLS) topologies). The VPLS instances are represented externally in the MPLS context by a Layer 2 Forwarding Equivalence Class (L2FEC) that binds related VPLS instances together. VPLS Signaling advertises the mapping between the L2FEC and the PW labels and implicitly associates the VPLS bridging instance to the VPLS Forwarders [RFC4762].
[PBB]规范中定义的PBB模块扩展为与VPLS转发器交互。[RFC4762]中使用VPLS转发器来构建PW网格或一组辐射PWs（分层VPLS（H-VPLS）拓扑）。VPLS实例在MPLS上下文中由第2层转发等价类（L2FEC）在外部表示，该类将相关VPLS实例绑定在一起。VPLS信令播发L2FEC和PW标签之间的映射，并将VPLS桥接实例隐式关联到VPLS转发器[RFC4762]。
In the PBB-VPLS case, the backbone service instance in the B-component space (B-VID) is represented in the backbone MPLS network using a VPLS instance. In the same way as for the regular VPLS case, existing signaling procedures are used to generate through PW labels the linkage between VPLS Forwarders and the backbone service instance.
在PBB-VPLS情况下，B组件空间（B-VID）中的主干服务实例使用VPLS实例在主干MPLS网络中表示。与常规VPLS情况相同，现有信令过程用于通过PW标签生成VPLS转发器和主干服务实例之间的链接。
Similarly, with the regular H-VPLS, another L2FEC may be used to identify the customer service instance in the I-component space. This will be useful, for example, to address the PBB-VPLS N-PE case where H-VPLS spokes are connecting the PBB-VPLS N-PE to a VPLS U-PE.
类似地，对于常规的H-VPL，可以使用另一个L2FEC来识别I组件空间中的客户服务实例。例如，这将有助于解决PBB-VPLS N-PE情况，其中H-VPLS辐条将PBB-VPLS N-PE连接到VPLS U-PE。
It is important to note that the PBB-VPLS solution inherits the PBB service aggregation capability where multiple customer service instances may be mapped to a backbone service instance. In the PBB-VPLS case, this means multiple customer VPNs can be transported using a single VPLS instance corresponding to the backbone service instance, thus substantially reducing resource consumption in the VPLS core.
需要注意的是，PBB-VPLS解决方案继承了PBB服务聚合功能，其中多个客户服务实例可以映射到主干服务实例。在PBB-VPLS情况下，这意味着可以使用与主干服务实例相对应的单个VPLS实例来传输多个客户VPN，从而大大减少VPLS核心中的资源消耗。
Since the PBB bridge module inherently performs forwarding, the PE reference model of Figure 2 can be expanded as shown in Figure 3.
由于PBB网桥模块固有地执行转发，因此图2的PE参考模型可以如图3所示进行扩展。
Furthermore, the B-component is connected via several virtual interfaces to the PW Forwarder module. The function of the PW Forwarder is defined in [RFC3985]. In this context, the PW Forwarder simply performs the mapping of the PWs to the virtual interface on the B-component, without the need for any MAC lookup.
此外，B组件通过几个虚拟接口连接到PW转发器模块。PW转发器的功能在[RFC3985]中定义。在此上下文中，PW转发器仅执行PWs到B组件上的虚拟接口的映射，而不需要任何MAC查找。
This simplified model takes full advantage of the PBB module -- where all the [PBB] procedures, including C-MAC/B-MAC forwarding and PBB encapsulation/decapsulation, take place -- and thus avoids the need to specify any of these functions in this document.
该简化模型充分利用了PBB模块——所有的[PBB]过程，包括C-MAC/B-MAC转发和PBB封装/去封装，都在PBB模块中进行——因此无需在本文档中指定任何这些功能。
Because of text-based graphics, Figure 3 only shows PWs on the core-facing side; however, in the case of MPLS access with spoke PWs, the PE reference model is simply extended to include the same PW Forwarder function on the access-facing side. To avoid cluttering the figure, but without losing any generality, the access-side PW Forwarder (Fwdr) is not depicted.
由于基于文本的图形，图3仅显示了面向堆芯一侧的PWs；然而，在使用辐射PWs的MPLS接入的情况下，PE参考模型被简单地扩展为在接入面向侧包括相同的PW转发器功能。为了避免图中出现混乱，但又不失去任何通用性，未描述接入侧PW转发器（Fwdr）。
+------------------------------------------------+
| PBB-VPLS-Capable PE Model |
| +---------------+ +------+ |
| | | | | |
| +------+ | ======== ---------
+--+ | | | | | | --------- PWs
|CE|-|-- | I- ==== ======== PW ---------
+--+ | | Comp | | | | Fwdr |
| +------+ | | | --------- PWs
| | B-Comp ======== ---------
| | | ^ | | |
| +------+ | | | +------+ |
+--+ | | I- | | OOOOOOOOOOOOOOOOOOOOOOOO B-tag
|CE|-|-- | Comp ==== | | | I/Fs
+--+ | | |^ | OOOOOOOOOOOOOOOOOOOOOOOO
| +------+| | | | |
| | +---------------+ | |
| | | |
+-----------|--------------------|---------------+
| |
Internal I-tag I/Fs Virtual Interfaces (I/Fs)
+------------------------------------------------+
| PBB-VPLS-Capable PE Model |
| +---------------+ +------+ |
| | | | | |
| +------+ | ======== ---------
+--+ | | | | | | --------- PWs
|CE|-|-- | I- ==== ======== PW ---------
+--+ | | Comp | | | | Fwdr |
| +------+ | | | --------- PWs
| | B-Comp ======== ---------
| | | ^ | | |
| +------+ | | | +------+ |
+--+ | | I- | | OOOOOOOOOOOOOOOOOOOOOOOO B-tag
|CE|-|-- | Comp ==== | | | I/Fs
+--+ | | |^ | OOOOOOOOOOOOOOOOOOOOOOOO
| +------+| | | | |
| | +---------------+ | |
| | | |
+-----------|--------------------|---------------+
| |
Internal I-tag I/Fs Virtual Interfaces (I/Fs)
+---------------+ +--------------+
| C-MAC DA,SA | | PSN Header |
|---------------| |--------------|
| S-VID, C-VID | | PW Label |
|---------------| |--------------|
| Payload | | B-MAC DA,SA |
+---------------+ |--------------|
| PBB I-tag |
|--------------|
| C-MAC DA,SA |
|--------------|
| S-VID, C-VID |
|--------------|
| Payload |
+--------------+
+---------------+ +--------------+
| C-MAC DA,SA | | PSN Header |
|---------------| |--------------|
| S-VID, C-VID | | PW Label |
|---------------| |--------------|
| Payload | | B-MAC DA,SA |
+---------------+ |--------------|
| PBB I-tag |
|--------------|
| C-MAC DA,SA |
|--------------|
| S-VID, C-VID |
|--------------|
| Payload |
+--------------+
Figure 3: Packet Walkthrough for PBB VPLS PE
图3:PBB VPLS PE的数据包演练
In order to better understand the data-plane walkthrough, let us consider the example of a PBB packet arriving over a Backbone pseudowire (B-PW). The PSN header is used to carry the PBB encapsulated frame over the backbone while the PW label will point to the related Backbone Service Instance (B-SI), in the same way as for regular VPLS. The PW label has in this case an equivalent role with the backbone VLAN identifier on the PBB B-tagged interface.
为了更好地理解数据平面演练，让我们考虑到达骨干伪线（B-PW）的PBB分组的例子。PSN报头用于在主干上承载PBB封装的帧，而PW标签将指向相关的主干服务实例（B-SI），方式与常规VPL相同。在这种情况下，PW标签具有与PBB标记接口上的主干VLAN标识符相同的角色。
An example of the PBB packet for the regular Ethernet PW is depicted on the right-hand side of Figure 3. The MPLS packet from the MPLS core network is received by the PBB-VPLS PE. The PW Forwarder function of the PE uses the PW label to derive the virtual interface-id on the B-component, and then, after removing the PSN and PW encapsulation, it passes the packet to the B-component. From there on, the processing and forwarding are performed according to [PBB], where bridging based on the Backbone MAC (B-MAC) Destination Address (DA) is performed. This scenario results in one of the following outcomes:
图3的右侧描绘了用于常规以太网PW的PBB分组的示例。PBB-VPLS PE接收来自MPLS核心网络的MPLS数据包。PE的PW转发器功能使用PW标签导出B组件上的虚拟接口id，然后在移除PSN和PW封装后，将数据包传递给B组件。此后，根据[PBB]执行处理和转发，其中执行基于骨干MAC（B-MAC）目的地地址（DA）的桥接。这种情况会导致以下结果之一：
1. The packet is forwarded to a physical interface on the B-component. In this case, the PBB Ethernet frame is forwarded as is.
1. 数据包被转发到B组件上的物理接口。在这种情况下，PBB以太网帧按原样转发。
2. The packet is forwarded to a virtual interface on the B-component. This is not typically the case, because of a single split-horizon group within a VPLS instance; however, if there is more than one split-horizon group, then such forwarding takes place. In this case, the PW Forwarder module adds the PSN and PW labels before sending the packet out.
2. 数据包被转发到B组件上的虚拟接口。通常情况并非如此，因为VPLS实例中有一个单独的拆分地平线组；但是，如果存在多个拆分地平线组，则会发生此类转发。在这种情况下，PW转发器模块在发送数据包之前添加PSN和PW标签。
3. The packet is forwarded toward the access side via one of the I-tagged service interfaces connected to the corresponding I-components. In this case, the I-component removes the B-MAC header according to [PBB] and bridges the packet using the C-MAC DA.
3. 该分组经由连接到相应I组件的I标签服务接口之一被转发到接入侧。在这种情况下，I组件根据PBB移除B-MAC报头，并使用C-MAC DA桥接分组。
If the destination B-MAC is an unknown MAC address or a Group MAC address (multicast or broadcast), then the B-component floods the packet to one or more of the three destinations described above.
如果目的地B-MAC是未知MAC地址或组MAC地址（多播或广播），则B组件将分组洪泛到上述三个目的地中的一个或多个。
The control-plane procedures described in [RFC6074], [RFC4761], and [RFC4762] can be reused in a PBB-VPLS to set up the PW infrastructure in the service provider and/or customer bridging space. This allows porting the existing control-plane procedures (e.g., BGP Auto-Discovery (BGP-AD), PW setup, VPLS MAC flushing, PW OAM) for each domain.
[RFC6074]、[RFC4761]和[RFC4762]中描述的控制平面程序可在PBB-VPLS中重复使用，以在服务提供商和/或客户桥接空间中建立PW基础设施。这允许为每个域移植现有的控制平面过程（例如，BGP自动发现（BGP-AD）、PW设置、VPLS MAC刷新、PW OAM）。
The PBB VPLS architecture takes advantage of the existing VPLS features addressing packet replication efficiency. The H-VPLS hierarchy may be used in both customer and backbone service instances to reduce the redundant distribution of packets over the core. IGMP and PIM snooping may be applied on a "per customer service instance" basis to control the distribution of the multicast traffic to non-member sites.
PBB VPLS体系结构利用了现有的VPLS功能来提高数据包复制效率。H-VPLS层次结构可在客户和主干服务实例中使用，以减少核心上数据包的冗余分布。IGMP和PIM窥探可在“每个客户服务实例”的基础上应用，以控制多播通信量到非成员站点的分布。
[IEEE-802.1Q] specifies the use of the Multiple MAC Registration Protocol (MMRP) for flood containment in the backbone instances. The same solution can be ported in the PBB-VPLS solution.
[IEEE-802.1Q]指定在主干实例中使用多MAC注册协议（MMRP）进行洪水控制。相同的解决方案可以移植到PBB-VPLS解决方案中。
Further optimizations of the packet replication in PBB-VPLS are out of the scope of this document.
PBB-VPLS中数据包复制的进一步优化超出了本文档的范围。
The existing VPLS, PW, and MPLS OAM procedures may be used in each customer service instance or backbone service instance to verify the status of the related connectivity components.
现有的VPLS、PW和MPLS OAM过程可用于每个客户服务实例或主干服务实例，以验证相关连接组件的状态。
PBB OAM procedures make use of the IEEE Ethernet Connectivity Fault Management [CFM] and ITU-T Y.1731 [Y.1731] tools in both I-components and B-components.
PBB OAM程序在I组件和B组件中使用IEEE以太网连接故障管理[CFM]和ITU-T Y.1731[Y.1731]工具。
Both sets of tools (PBB and VPLS) may be used for the combined PBB-VPLS solution.
两套工具（PBB和VPLS）可用于组合PBB-VPLS解决方案。
No new security issues are introduced beyond those described in [RFC4761] and [RFC4762].
除[RFC4761]和[RFC4762]中所述的安全问题外，未引入任何新的安全问题。
[RFC4761] Kompella, K., Ed., and Y. Rekhter, Ed., "Virtual Private LAN Service (VPLS) Using BGP for Auto-Discovery and Signaling", RFC 4761, January 2007.
[RFC4761]Kompella，K.，Ed.，和Y.Rekhter，Ed.，“使用BGP进行自动发现和信令的虚拟专用LAN服务（VPLS）”，RFC 4761，2007年1月。
[RFC4762] Lasserre, M., Ed., and V. Kompella, Ed., "Virtual Private LAN Service (VPLS) Using Label Distribution Protocol (LDP) Signaling", RFC 4762, January 2007.
[RFC4762]Lasserre，M.，Ed.，和V.Kompella，Ed.，“使用标签分发协议（LDP）信令的虚拟专用LAN服务（VPLS）”，RFC 4762，2007年1月。
[RFC6074] Rosen, E., Davie, B., Radoaca, V., and W. Luo, "Provisioning, Auto-Discovery, and Signaling in Layer 2 Virtual Private Networks (L2VPNs)", RFC 6074, January 2011.
[RFC6074]Rosen，E.，Davie，B.，Radoaca，V.，和W.Luo，“第二层虚拟专用网络（L2VPN）中的资源调配、自动发现和信令”，RFC 6074，2011年1月。
[RFC3985] Bryant, S., Ed., and P. Pate, Ed., "Pseudo Wire Emulation Edge-to-Edge (PWE3) Architecture", RFC 3985, March 2005.
[RFC3985]Bryant，S.，Ed.，和P.Pate，Ed.，“伪线仿真边到边（PWE3）架构”，RFC 39852005年3月。
[RFC4664] Andersson, L., Ed., and E. Rosen, Ed., "Framework for Layer 2 Virtual Private Networks (L2VPNs)", RFC 4664, September 2006.
[RFC4664]Andersson，L.，Ed.，和E.Rosen，Ed.，“第二层虚拟专用网络（L2VPN）框架”，RFC 4664，2006年9月。
[PBB] Clauses 25 and 26 of "IEEE Standard for Local and metropolitan area networks - Media Access Control (MAC) Bridges and Virtual Bridged Local Area Networks", IEEE Std 802.1Q-REV, 2013.
[PBB]IEEE Std 802.1Q-REV，2013年，“局域网和城域网IEEE标准-媒体访问控制（MAC）网桥和虚拟桥接局域网”第25条和第26条。
[PB] Clauses 15 and 16 of "IEEE Standard for Local and metropolitan area networks - Media Access Control (MAC) Bridges and Virtual Bridged Local Area Networks", IEEE Std 802.1Q-REV, 2013.
[PB]IEEE Std 802.1Q-REV，2013年“IEEE局域网和城域网标准-媒体访问控制（MAC）网桥和虚拟桥接局域网”第15条和第16条。
[CFM] CFM clauses of "IEEE Standard for Local and metropolitan area networks - Media Access Control (MAC) Bridges and Virtual Bridged Local Area Networks", IEEE Std 802.1Q-REV, 2013.
《IEEE局域网和城域网标准-媒体访问控制（MAC）网桥和虚拟桥接局域网》的[CFM]CFM条款，IEEE Std 802.1Q-REV，2013年。
[IEEE-802.1Q] "IEEE Standard for Local and metropolitan area networks - Media Access Control (MAC) Bridges and Virtual Bridged Local Area Networks", IEEE Std 802.1Q-REV, 2013.
[IEEE-802.1Q]“局域网和城域网IEEE标准-媒体访问控制（MAC）网桥和虚拟桥接局域网”，IEEE标准802.1Q-REV，2013年。
[Y.1731] ITU-T Recommendation Y.1731, "OAM functions and mechanisms for Ethernet based networks", July 2011.
[Y.1731]ITU-T建议Y.1731，“基于以太网的网络的OAM功能和机制”，2011年7月。
[RFC4026] Andersson, L. and T. Madsen, "Provider Provisioned Virtual Private Network (VPN) Terminology", RFC 4026, March 2005.
[RFC4026]Andersson，L.和T.Madsen，“提供商提供的虚拟专用网络（VPN）术语”，RFC 4026，2005年3月。
The following people made significant contributions to this document:
以下人员对本文件做出了重大贡献：
Matthew Bocci Alcatel-Lucent Voyager Place Shoppenhangers Road Maidenhead Berks, UK
Matthew Bocci Alcatel-Lucent Voyager Place Shoppenivers Road Maidenhead Berks，英国
EMail: matthew.bocci@alcatel-lucent.com
EMail: matthew.bocci@alcatel-lucent.com
Raymond Zhang Alcatel-Lucent
张雷蒙阿尔卡特朗讯
EMail: raymond.zhang@alcatel.com
EMail: raymond.zhang@alcatel.com
Geraldine Calvignac Orange 2, avenue Pierre-Marzin 22307 Lannion Cedex France
Geraldine Calvignac Orange 2，Pierre Marzin大街22307拉尼翁塞德斯法国
EMail: geraldine.calvignac@orange.com
EMail: geraldine.calvignac@orange.com
John Hoffmans KPN Regulusweg 1 2516 AC Den Haag The Netherlands
John Hoffmans KPN Regulusweg 1 2516 AC Den Haag荷兰
EMail: john.hoffmans@kpn.com
EMail: john.hoffmans@kpn.com
Olen Stokes Extreme Networks PO Box 14129 RTP, NC 27709 USA
美国北卡罗来纳州27709奥伦斯托克斯极限网络公司邮政信箱14129 RTP
EMail: ostokes@extremenetworks.com
EMail: ostokes@extremenetworks.com
The authors would like to thank Wim Henderickx, Mustapha Aissaoui, Dimitri Papadimitriou, Pranjal Dutta, Jorge Rabadan, Maarten Vissers, and Don Fedyk for their insightful comments and probing questions.
作者要感谢Wim Henderickx、Mustapha Aissaoui、Dimitri Papadimitriou、Pranjal Dutta、Jorge Rabadan、Maarten Vissers和Don Fedyk，感谢他们富有洞察力的评论和探索性的问题。
Authors' Addresses
作者地址
Florin Balus (editor) Alcatel-Lucent 701 E. Middlefield Road Mountain View, CA 94043 USA
Florin Balus（编辑）阿尔卡特朗讯701 E.米德尔菲尔德路山景城，美国加利福尼亚州94043
EMail: florin.balus@alcatel-lucent.com
EMail: florin.balus@alcatel-lucent.com
Ali Sajassi (editor) Cisco 170 West Tasman Drive San Jose, CA 95134 USA
Ali Sajassi（编辑）美国加利福尼亚州圣何塞西塔斯曼大道170号，邮编95134
EMail: sajassi@cisco.com
EMail: sajassi@cisco.com
Nabil Bitar (editor) Verizon 60 Sylvan Road Waltham, MA 02145 USA
Nabil Bitar（编辑）Verizon 60 Sylvan Road Waltham，马萨诸塞州02145
EMail: nabil.n.bitar@verizon.com
EMail: nabil.n.bitar@verizon.com