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rfc:rfc7080

Internet Engineering Task Force (IETF) A. Sajassi Request for Comments: 7080 S. Salam Category: Informational Cisco ISSN: 2070-1721 N. Bitar

                                                               Verizon
                                                              F. Balus
                                                        Nuage Networks
                                                         December 2013
        Virtual Private LAN Service (VPLS) Interoperability
                   with Provider Backbone Bridges

Abstract

 The scalability of Hierarchical Virtual Private LAN Service (H-VPLS)
 with Ethernet access networks (RFC 4762) can be improved by
 incorporating Provider Backbone Bridge functionality in the VPLS
 access.  Provider Backbone Bridging has been standardized as IEEE
 802.1ah-2008.  It aims to improve the scalability of Media Access
 Control (MAC) addresses and service instances in Provider Ethernet
 networks.  This document describes different interoperability
 scenarios where Provider Backbone Bridge functionality is used in
 H-VPLS with Ethernet or MPLS access network to attain better
 scalability in terms of number of customer MAC addresses and number
 of service instances.  The document also describes the scenarios and
 the mechanisms for incorporating Provider Backbone Bridge
 functionality within H-VPLS with existing Ethernet access and
 interoperability among them.  Furthermore, the document discusses the
 migration mechanisms and scenarios by which Provider Backbone Bridge
 functionality can be incorporated into H-VPLS with existing MPLS
 access.

Status of This Memo

 This document is not an Internet Standards Track specification; it is
 published for informational purposes.
 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.
 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/rfc7080.

Sajassi, et al. Informational [Page 1] RFC 7080 VPLS Interoperability with PBB December 2013

Copyright Notice

 Copyright (c) 2013 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
 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.

Table of Contents

 1. Introduction ....................................................3
 2. Terminology .....................................................3
 3. Applicability ...................................................5
 4. H-VPLS with Homogeneous PBBN Access .............................6
    4.1. Service Interfaces and Interworking Options ................8
    4.2. H-VPLS with PBBN Access: Type I Service Interface .........10
    4.3. H-VPLS with PBBN Access: Type II Service Interface ........11
 5. H-VPLS with Mixed PBBN Access and PBN Access ...................14
    5.1. H-VPLS with Mixed PBBN and PBN Access: Modified PBN PE ....15
    5.2. H-VPLS with Mixed PBBN and PBN Access: Regular PBN PE .....16
 6. H-VPLS with MPLS Access ........................................17
    6.1. H-VPLS with MPLS Access: PBB U-PE .........................17
    6.2. H-VPLS with MPLS Access: PBB N-PE .........................19
 7. H-VPLS with MPLS Access: PBB Migration Scenarios ...............21
    7.1. 802.1ad Service Frames over VPLS Core .....................21
    7.2. PBB Service Frames over VPLS Core .........................22
    7.3. Mixed 802.1ad and PBB over VPLS Core ......................23
 8. Acknowledgments ................................................24
 9. Security Considerations ........................................24
 10. References ....................................................24
    10.1. Normative References .....................................24
    10.2. Informative References ...................................25

Sajassi, et al. Informational [Page 2] RFC 7080 VPLS Interoperability with PBB December 2013

1. Introduction

 The scalability of Hierarchical Virtual Private LAN Service (H-VPLS)
 with Ethernet access networks [RFC4762] can be improved by
 incorporating Provider Backbone Bridge (PBB) functionality in the
 VPLS access.  Provider Backbone Bridging has been standardized as
 IEEE 802.1ah-2008 [802.1ah], which is an amendment to IEEE 802.1Q to
 improve the scalability of Media Access Control (MAC) addresses and
 service instances in Provider Ethernet networks.  This document
 describes interoperability scenarios where IEEE 802.1ah functionality
 is used in H-VPLS with Ethernet or MPLS access network to attain
 better scalability in terms of the number of customer MAC addresses
 and the number of services.
 This document also covers the interoperability scenarios for
 deploying H-VPLS with Provider Backbone Bridging Ethernet access when
 other types of access networks are deployed, including existing
 802.1ad Ethernet and MPLS access in either single or multiple service
 domains.  Furthermore, the document explores the scenarios by which
 an operator can gradually migrate an existing H-VPLS network to
 Provider Backbone Bridging over VPLS.
 Section 2 gives a quick terminology reference and Section 3
 highlights the applicability of Provider Backbone Bridging
 interoperation with VPLS.  Section 4 describes H-VPLS with
 homogeneous Provider Backbone Bridge Access Network.  Section 5
 discusses H-VPLS with mixed 802.1ah/802.1ad access.  Section 6
 focuses on Provider Backbone Bridging in H-VPLS with MPLS Access
 Network including PBB function on U-PE and on N-PE variants.
 Finally, Section 7 describes gradual migration scenarios from
 existing H-VPLS to Provider Backbone Bridging over H-VPLS.

2. Terminology

 802.1ad: IEEE specification for "QinQ" encapsulation and bridging of
    Ethernet frames.
 802.1ah: IEEE specification for "MAC tunneling" encapsulation and
    bridging of frames across a Provider Backbone Bridged Network
    (PBBN).
 B-BEB: A backbone edge bridge positioned at the edge of a PBBN.  It
    contains a B-component that supports bridging in the provider
    backbone based on B-MAC and B-TAG information.
 B-MAC: The backbone source or destination MAC address fields defined
    in the 802.1ah provider MAC encapsulation header.

Sajassi, et al. Informational [Page 3] RFC 7080 VPLS Interoperability with PBB December 2013

 BCB: A backbone core bridge running in the core of a provider
    backbone bridged network.  It bridges frames based on B-TAG
    information just as an 802.1ad provider bridge will bridge frames
    based on a Service VLAN (S-VLAN) identifier.
 B-Component: The backbone component of a Provider Backbone edge
    bridge as defined in [802.1ah].
 BEB: A backbone edge bridge positioned at the edge of a provider
    backbone bridged network.  It can contain an I-component,
    B-component, or both.
 B-MACs: Backbone MAC addresses -- outer MAC addresses of a PBB-
    encapsulated frame.
 B-TAG: A field defined in the 802.1ah 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-Tagged Service Interface: This is the interface between a BEB and
    BCB in a PBB network.  Frames passed through this interface
    contain a B-TAG field.
 B-VID: This is the specific VLAN identifier carried inside a B-TAG
 C-MACs: Customer MAC addresses are the inner MAC addresses of a PBB-
    encapsulated frame.
 H-VPLS: Hierarchical Virtual Private LAN Service.
 I-component: A bridging component contained in a backbone edge bridge
    that bridges in the customer space (customer MAC addresses,
    S-VLAN).
 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, S-VLAN IDs) and a
    B-component for bridging the provider's backbone space (B-MAC,
    B-TAG).
 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, S-VLAN IDs).
 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".

Sajassi, et al. Informational [Page 4] RFC 7080 VPLS Interoperability with PBB December 2013

 I-TAG: A field defined in the 802.1ah provider MAC encapsulation
    header that conveys the service instance information (I-SID)
    associated with the frame.
 I-Tagged Service Interface: This is the interface defined between the
    I-component and B-component inside an IB-BEB or between two
    B-BEBs.  Frames passed through this interface contain an I-TAG
    field.
 N-PE: Network-facing Provider Edge
 PBB: Provider Backbone Bridge
 PBBN: Provider Backbone Bridged Network
 PBN: Provider Bridged Network.  A network that employs 802.1ad (QinQ)
    technology.
 S-TAG: A field defined in the 802.1ad QinQ encapsulation header that
    conveys the Service VLAN (S-VLAN) identifier information.
 S-Tagged Service Interface: This 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-VLAN: The specific Service VLAN identifier carried inside an S-TAG
 U-PE: User-facing Provider Edge
 VPLS: Virtual Private LAN Service

3. Applicability

 [RFC4762] describes a two-tier hierarchical solution for VPLS for the
 purpose of improved pseudowire (PW) scalability.  This improvement is
 achieved by reducing the number of PE devices connected in a full-
 mesh topology through connecting CE devices via the lower-tier access
 network, which in turn is connected to the top-tier core network.
 [RFC4762] describes two types of H-VPLS network topologies -- one
 with an MPLS access network and another with an IEEE 802.1ad (QinQ)
 Ethernet access network.  In both types of H-VPLS, the learning and
 forwarding of MAC addresses is based on customer MAC addresses
 (C-MACs), which poses scalability issues as the number of VPLS
 instances (and thus C-MACs) increases.  Furthermore, since a set of
 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

Sajassi, et al. Informational [Page 5] RFC 7080 VPLS Interoperability with PBB December 2013

 (in terms of PW manageability and troubleshooting) as the number of
 customer service instances grows.
 In addition to the above, H-VPLS with an 802.1ad Ethernet access
 network has another scalability issue in terms of the maximum number
 of service instances that can be supported in the access network as
 described in [RFC4762].  Since the number of provider VLANs (S-VLANs)
 is limited to 4094 and each S-VLAN represents a service instance in
 an 802.1ad network, then the maximum number of service instances that
 can be supported is 4094.  These issues are highlighted in [RFC6246].
 This document describes how IEEE 802.1ah (aka Provider Backbone
 Bridges) can be integrated with H-VPLS to address these scalability
 issues.  In the case of H-VPLS with 802.1ah Ethernet access, the
 solution results in better scalability in terms of both number of
 service instances and number of C-MACs in the Ethernet access network
 and the VPLS core network, as well as number of PWs in VPLS core
 network.  And in the case of H-VPLS with MPLS access, Provider
 Backbone Bridging functionality can be used at the U-PE or N-PE,
 which results in reduction of customer MAC addresses and the number
 of PWs in the VPLS core network.
 The interoperability scenarios depicted in this document fall into
 the following two categories:
  1. Scenarios in which Provider Backbone Bridging seamlessly works

with current VPLS implementations (e.g., Section 4.2).

  1. Scenarios in which VPLS-PE implementations need to be upgraded in

order to work with Provider Backbone Bridging (e.g., Sections 4.3

    and 5.1).

4. H-VPLS with Homogeneous PBBN Access

 PBBN access offers MAC-address-table scalability for H-VPLS PE nodes.
 This is due to the MAC tunneling encapsulation scheme of PBB, which
 only exposes the provider's own MAC addresses to PE nodes (B-MACs of
 Provider's PBB-capable devices in the access network), as opposed to
 customers' MAC addresses in conventional H-VPLS with MPLS or 802.1ad
 access.
 PBBN access also offers service-instance scalability when compared to
 H-VPLS with 802.1Q/802.1ad access networks.  This is due to the new
 24-bit service identifier (I-SID) used in PBB encapsulation, which
 allows up to 16M services per PBB access network, compared to 4094
 services per 802.1Q/802.1ad access network.

Sajassi, et al. Informational [Page 6] RFC 7080 VPLS Interoperability with PBB December 2013

 Another important advantage of PBBN access is that it offers clear
 separation between the service layer (represented by I-SID) and the
 network layer (represented by B-VLAN).  B-VLANs segregate a PBB
 access network into different broadcast domains and possibly unique
 spanning-tree topologies, with each domain being able to carry
 multiple services (i.e., I-SIDs).  In 802.1ad access networks, the
 network and service layers are the same (represented by S-VLAN).
 This separation allows the provider to manage and optimize the PBB
 access network topology independent of the number of service
 instances that are supported.
 In this section and those following, we look into different flavors
 of H-VPLS with PBBN access.  This section discusses the case in which
 H-VPLS is deployed with homogeneous PBBN access.  Section 5 describes
 the case in which at least one of the access networks has PBN access
 (QinQ/802.1ad) while the others are PBBNs.
 On a macro scale, a network that employs H-VPLS with PBBN access can
 be represented as shown in Figure 1 below.
                         +--------------+
                         |              |
         +---------+     |    IP/MPLS   |    +---------+
 +----+  |         |   +----+        +----+  |         |  +----+
 | CE |--|         |   |VPLS|        |VPLS|  |         |--| CE |
 +----+  |  PBBN   |---| PE |        | PE |--|  PBBN   |  +----+
 +----+  | 802.1ah |   +----+        +----+  | 802.1ah |  +----+
 | CE |--|         |     |   Backbone   |    |         |--| CE |
 +----+  +---------+     +--------------+    +---------+  +----+
                  Figure 1: H-VPLS with PBBN Access
 In the context of PBBN and H-VPLS interoperability, "I-SID Domain"
 and "B-VLAN Domain" can be defined as follows:
  1. "I-SID Domain" refers to a network administrative boundary under

which all the PBB BEBs and VPLS-PE devices use the same I-SID

    space.  That is, the I-SID assignment is carried out by the same
    administration.  This effectively means that a given service
    instance has the same I-SID designation on all devices within an
    I-SID Domain.
  1. "B-VLAN Domain" refers to a network administrative boundary under

which all the PBB BEBs and VPLS-PE devices employ consistent I-SID

    to B-VLAN bundling.  For example, the grouping of I-SIDs to
    B-VLANs is the same in that domain.  Although the two B-VLANs in
    two PBBNs that represent the same group of I-SIDs do not need to

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    use the same B-VID value, in practice, they often use the same
    value because once the I-SID grouping is made identical in two
    PBBNs.  It is very easy to make the values of the corresponding
    B-VIDs identical also.
 Consequently, three different kinds of "Service Domains" are defined
 in the following manner:
  1. Tightly Coupled Service Domain - Different PBBNs' access belonging

to the same I-SID Domain and B-VLAN Domain. However, the network

    control protocols (e.g., xSTP) run independently in each PBBN
    access.
  1. Loosely Coupled Service Domain - Different PBBNs' access belonging

to the same I-SID Domain. However, each PBBN access maintains its

    own independent B-VLAN Domain.  Again, the network control
    protocols (e.g., xSTP) run independently in each PBBN access.
  1. Different Service Domain - In this case, each PBBN access

maintains its own independent I-SID Domain and B-VLAN Domain, with

    independent network control protocols (e.g., xSTP) in each PBBN
    access.
 In general, correct service connectivity spanning networks in a
 Tightly Coupled Service Domain can be achieved via B-VID mapping
 between the networks (often even without B-VID translation).
 However, correct service connectivity spanning networks in a Loosely
 Coupled Service Domain requires I-SID to B-VID remapping (i.e.,
 unbundling and rebundling of I-SIDs into B-VIDs).  Furthermore,
 service connectivity spanning networks in Different Service Domains
 requires both I-SID translation and I-SID to B-VID remapping.

4.1. Service Interfaces and Interworking Options

 Customer devices will interface with PBBN edge bridges using existing
 Ethernet interfaces including IEEE 802.1Q and IEEE 802.1ad.  At the
 PBBN edge, C-MAC frames are encapsulated in a PBB header that
 includes service provider source and destination MAC addresses
 (B-MACs) and are bridged up to the VPLS-PE.  The PBB-encapsulated
 C-MAC frame is then injected into the VPLS backbone network,
 delivered to the remote VPLS-PE node(s), and switched onto the remote
 PBBN access.  From there, the PBBN bridges the encapsulated frame to
 a PBBN edge bridge where the PBB header is removed and the customer
 frame is sent to the customer domain.

Sajassi, et al. Informational [Page 8] RFC 7080 VPLS Interoperability with PBB December 2013

 Interoperating between PBBN devices and VPLS-PE nodes can leverage
 the BEB functions already defined in [802.1ah].  When I-SID
 visibility is required at the VPLS-PE nodes, a new service interface
 based on I-SID tag will need to be defined.
 Moreover, by mapping a bridge domain (e.g., B-VLAN) to a VPLS
 instance, and bundling multiple end-customer service instances
 (represented by I-SID) over the same bridge domain, service providers
 will be able to significantly reduce the number of full-mesh PWs
 required in the core.  In this case, I-SID visibility is not required
 on the VPLS-PE and the I-SID will serve as the means of
 multiplexing/de-multiplexing individual service instances in the PBBN
 over a bundle (e.g., B-VLAN).
 When I-SID visibility is expected across the service interface at the
 VPLS-PE, the VPLS-PE can be considered to offer service-level
 interworking between PBBN access and the IP/MPLS core.  Similarly,
 when the PE is not expected to have visibility of the I-SID at the
 service interface, the VPLS-PE can be considered to offer network-
 level interworking between PBBN access and the MPLS core.
 A VPLS-PE is always part of the IP/MPLS core, and it may optionally
 participate in the control protocols (e.g., xSTP) of the access
 network.  When connecting to a PBBN access, the VPLS-PE needs to
 support one of the following two types of service interfaces:
  1. Type I: B-Tagged Service Interface with B-VID as Service

Delimiter

 The PE connects to a Backbone Core Bridge (BCB) in the PBBN access.
 The handoff between the BCB and the PE is B-Tagged PBB-encapsulated
 frames.  The PE is transparent to PBB encapsulations and treats these
 frames as 802.1ad frames since the B-VID EtherType is the same as the
 S-VID EtherType.  The PE does not need to support PBB functionality.
 This corresponds to conventional VPLS-PEs' tagged service interface.
 When using Type I service interface, the PE needs to support either
 raw mode or tagged mode Ethernet PW.  Type I service interface is
 described in detail in Section 4.2.
  1. Type II: I-Tagged Service Interface with I-SID as Service

Delimiter

 The PE connects to a B-BEB (backbone edge bridge with B-component) in
 the PBBN access.  The PE itself also supports the B-BEB functionality
 of [802.1ah].  The handoff between the B-BEB in the PBBN access and
 the PE is an I-Tagged PBB-encapsulated frame.  With Type II service

Sajassi, et al. Informational [Page 9] RFC 7080 VPLS Interoperability with PBB December 2013

 interface, the PE supports the existing raw mode and tagged mode PW
 types.  Type II service interface is described in detail in Section
 4.3.

4.2. H-VPLS with PBBN Access: Type I Service Interface

 This is a B-Tagged service interface with B-VID as service delimiter
 on the VPLS-PE.  It does not require any new functionality on the
 VPLS-PE.  As shown in Figure 2, the PE is always part of the IP/MPLS
 core.  The PE may also be part of the PBBN access (e.g., VPLS-PE on
 right side of Figure 2) by participating in network control protocols
 (e.g., xSTP) of the PBBN access.
      PBBN Access       IP/MPLS Core      PBBN Access
                      +--------------+
      +---------+     |              | +---------------+
      |         |    +----+          | |               |
      |      +---+   |VPLS|   +-+    | |    +---+      |
      |      |BCB|---| PE |---|P|    | |    |BCB|      |
      |      +---+  /+----+  /+-+   | |   /+---+      |
      |+---+    |  / +----+ /     +----+ /       +---+|
 +--+ ||IB-| +---+/  |VPLS|/  +-+  |VPLS|/  +---+ |IB-|| +--+
 |CE|-||BEB|-|BCB|---| PE |---|P|--| PE |---|BCB|-|BEB|--|CE|
 +--+ |+---+ +---+ ^ +----+   +-+  +----+ ^ +---+ +---+| +--+
      |         |  |  |              | |  |            |
      +---------+  |  |              | +--|------------+
                   |  +--------------+    |
                   |                      |
                 Type I                  Type I
   Figure 2: H-VPLS with PBBN Access and Type I Service Interface
 Type I service interface is applicable to networks with Tightly
 Coupled Service Domains, where both I-SID Domains and B-VLAN Domains
 are the same across all PBBN access networks.
 The BCB and the VPLS-PE will exchange PBB-encapsulated frames that
 include source and destination B-MACs, a B-VID, and an I-SID.  The
 service delimiter, from the perspective of the VPLS-PE, is the B-VID;
 in fact, this interface operates exactly as a current 802.1Q/ad
 interface into a VPLS-PE does today.  With Type I service interface,
 the VPLS-PE can be considered to provide network-level interworking
 between PBBN and MPLS domains, since VPLS-PE does not have visibility
 of I-SIDs.
 The main advantage of this service interface, when compared to other
 types, is that it allows the service provider to save on the number
 of full-mesh PWs required in the core.  This is primarily because

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 multiple service instances (I-SIDs) are bundled over a single full-
 mesh PW corresponding to a bridge domain (e.g., B-VID), instead of
 requiring a dedicated full-mesh PW per service instance.  Another
 advantage is the MAC address scalability in the core since the core
 is not exposed to C-MACs.
 The disadvantage of this interface is the comparably excessive
 replication required in the core: since a group of service instances
 share the same full-mesh of PWs, an unknown unicast, multicast, or
 broadcast on a single service instance will result in a flood over
 the core.  This, however, can be mitigated via the use of flood
 containment per I-SID (B-MAC multicast pruning).
 Three different modes of operation are supported by Type I service
 interface:
  1. Port Mode: All traffic over an interface in this mode is mapped to

a single VPLS instance. Existing PW signaling and Ethernet raw

    mode (0x0005) PW type, defined in [RFC4447] and [RFC4448], are
    supported.
  1. VLAN Mode: all traffic associated with a particular VLAN

identified by the B-VID is mapped to a single VPLS instance.

    Existing PW signaling and Ethernet raw mode (0x0005) PW type,
    defined in [RFC4447] and [RFC4448], are supported.
  1. VLAN Bundling Mode: all traffic associated with a group or range

of VLANs or B-VIDs is mapped to a single VPLS instance. Existing

    PW signaling and Ethernet raw mode (0x0005) PW type, defined in
    [RFC4447] and [RFC4448], are supported.
 For the VLAN mode, it is also possible to use Ethernet tagged mode
 (0x0004) PW, as defined in [RFC4447] and [RFC4448], for
 interoperability with equipment that does not support raw mode.  The
 use of raw mode is recommended to be the default though.

4.3. H-VPLS with PBBN Access: Type II Service Interface

 This is an I-Tagged service interface with I-SID as service delimiter
 on the VPLS-PE.  It requires the VPLS-PE to include the B-component
 of PBB BEB for I-SID processing in addition to the capability to map
 an I-SID Bundle to a VPLS instance.  As shown in Figure 3, the PE is
 always part of the IP/MPLS core and connects to one or more B-BEBs in
 the PBBN access.

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      PBBN Access      IP/MPLS Core      PBBN Access
                     +--------------+
      +---------+    |              |    +---------+
      |         |    |              |    |         |
      |      +---+  +-----+         |    |  +---+  |
      |      |B- |  |PE w/| +-+     |    |  |BCB|  |
      |      |BEB|--|B-BEB|-|P|     |    |  +---+  |
      |      +---+ /+-----+ +-+     |    | /   |   |
      |+---+ +---+/ +-----+/    +-----+ +---+ +---+|
 +--+ ||IB-| |B- |  |PE w/| +-+ |PE w/| |B- | |IB-|| +--+
 |CE|-||BEB|-|BEB|--|B-BEB|-|P|-|B-BEB|-|BEB| |BEB|--|CE|
 +--+ |+---+ +---+ ^+-----+ +-+ +-----+^+---+ +---+| +--+
      |         |  |  |             |  | |         |
      +---------+  |  |             |  | +---------+
                   |  +-------------+  |
                   |                   |
               Type II             Type II
 Figure 3: H-VPLS with PBBN Access and Type II Service Interface
 Type II service interface is applicable to Loosely Coupled Service
 Domains and Different Service Domains.  B-VLAN Domains can be
 independent and the B-VID is always locally significant in each PBBN
 access: it does not need to be transported over the IP/MPLS core.
 Given the above, it should be apparent that Type II service interface
 is applicable to Tightly Coupled Service Domains as well.
 By definition, the B-BEB connecting to the VPLS-PE will remove any
 B-VLAN tags for frames exiting the PBBN access.  The B-BEB and
 VPLS-PE will exchange PBB-encapsulated frames that include source and
 destination B-MACs and an I-SID.  The service delimiter, from the
 perspective of the VPLS-PE, is the I-SID.  Since the PE has
 visibility of I-SIDs, the PE provides service-level interworking
 between PBBN access and IP/MPLS core.
 Type II service interface may operate in I-SID Bundling Mode: all
 traffic associated with a group or range of I-SIDs is mapped to a
 single VPLS instance.  The PE maintains a mapping of I-SIDs to a PE
 local bridge domain (e.g., B-VID).  The VPLS instance is then
 associated with this bridge domain.  With Loosely Coupled service
 Domains, no I-SID translation needs to be performed.  Type II Service
 interface also supports Different Service Domains in this mode, since
 the B-BEB link in the PE connecting to the local PBBN can perform the
 translation of PBBN-specific I-SID to a local I-SID within the
 IP/MPLS core, which may then be translated to the other PBBN-specific
 I-SID on the egress PE.  Such translation can also occur in the B-BEB
 of PBBN access.  Existing PW signaling and Ethernet raw mode
 (0x0005), defined in [RFC4447] and [RFC4448], is supported.  It is

Sajassi, et al. Informational [Page 12] RFC 7080 VPLS Interoperability with PBB December 2013

 also possible to use a tagged mode (0x0004) PW for purpose of
 interoperability with equipment that does not support raw mode.
 Type II service interface provides operators with the flexibility to
 trade off PW state for multicast flooding containment, since a full-
 mesh of PWs can be set up:
 a. per I-SID,
 b. per group of I-SIDs, or
 c. for all I-SIDs.
 For (a) and (b), the advantage that Type II service interface has
 compared to Type I is that it can reduce replication in the core
 without the need for a mechanism that provides flood containment per-
 I-SID (B-MAC multicast pruning).  This is mainly due to the increased
 segregation of service instances over disjoint full meshes of PWs.
 For (c), both Type II and Type I service interfaces are at par with
 regard to flood containment.
 For (a) and (b), the disadvantage of this service interface, compared
 to Type I, is that it may require a larger number of full-mesh PWs in
 the core.  For (c), both Type II and Type I service interfaces are at
 par with regard to PW state.  However, for all three scenarios, the
 number of full-mesh PWs can still be fewer than the number required
 by H-VPLS without PBBN access, since an I-SID can multiplex many
 S-VLANs.
 It is expected that this interface type will be used for customers
 with significant multicast traffic (but without multicast pruning
 capability in the VPLS-PE) so that a separate VPLS instance is set up
 per group of customers with similar geographic locality (per I-SID
 group).
 Note: Port mode is not called out in Type II service interface since
 it requires the mapping of I-SIDs to be identical on different
 I-Tagged interfaces across VPLS network.  If this is indeed the case,
 Port mode defined in Type I service interface (Section 4.2) can be
 used.

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5. H-VPLS with Mixed PBBN Access and PBN Access

 It is foreseeable that service providers will want to interoperate
 their existing Provider Bridged Networks (PBNs) with Provider
 Backbone Bridged Networks (PBBNs) over H-VPLS.  Figure 4 below shows
 the high-level network topology.
                         +--------------+
                         |              |
         +---------+     |    IP/MPLS   |    +---------+
 +----+  |         |   +----+        +----+  |         |  +----+
 | CE |--|   PBN   |   |VPLS|        |VPLS|  |         |--| CE |
 +----+  |  (QinQ) |---| PE1|        | PE2|--|  PBBN   |  +----+
 +----+  | 802.1ad |   +----+        +----+  | 802.1ah |  +----+
 | CE |--|         |     |   Backbone   |    |         |--| CE |
 +----+  +---------+     +--------------+    +---------+  +----+
     Figure 4: H-VPLS with Mixed PBN and PBBN Access Networks
 Referring to Figure 4 above, two possibilities come into play
 depending on whether the interworking is carried out at PE1 or PE2.
 These are described in the following subsections.

Sajassi, et al. Informational [Page 14] RFC 7080 VPLS Interoperability with PBB December 2013

5.1. H-VPLS with Mixed PBBN and PBN Access: Modified PBN PE

 As shown in Figure 5, the operation of VPLS-PE2 (connecting to the
 PBBN access on the right) is no different from what was discussed in
 Section 4.  Type II service interface, as discussed in the above
 section, is applicable.  It is the behavior of VPLS-PE1 (connecting
 to the PBN access on the left) that is the focus of this section.
       PBN Access       IP/MPLS Core      PBBN Access
        (802.1ad)     +--------------+     (802.1ah)
                      |              |    +---------+
       +---------+    |              |    |         |
       |         |   +-----+         |    |  +---+  |
       |      +---+  |PE w/| +-+     |    |  |BCB|  |
       |      |PCB|--|IBBEB|-|P|     |    |  +---+  |
       |      +---+ /+-----+ +-+     |    | /   |   |
       |         | / +-----+/    +-----+ +---+ +---+|
  +--+ |+---+ +---+  |PE w/| +-+ |PE w/| |B- | |IB-|| +--+
  |CE|-||PEB|-|PCB|--|IBBEB|-|P|-|B-BEB|-|BEB| |BEB|--|CE|
  +--+ |+---+ +---+ ^+-----+ +-+ +-----+^+---+ +---+| +--+
       |         |  |  |PE1       PE2|  | |         |
       +---------+  |  |             |  | +---------+
                    |  +-------------+  |
                    |                   |
                S-Tagged           Type II (I-Tagged)
 Figure 5: H-VPLS with Mixed PBN and PBBN Access: Modified PBN PE
 Some assumptions made for this topology include:
  1. CE is directly connected to PBBN via S-Tagged or port-based

interface.

  1. I-SID in PBBN access represents the same customer as S-VID in PBN

access.

  1. At S-Tagged service interface of PE with IB-BEB functionality

(e.g., PE1 in Figure 5), the only viable service is 1:1 mapping of

    S-VID to I-SID.  However, towards the core network side, the same
    PE can support I-SID bundling into a VPLS instance.
  1. PE1 participates in the local I-SID Domain of the IP/MPLS core so

the model accommodates for the rest of the PBB network any of the

    three domain types described in Section 4 -- Tightly Coupled,
    Loosely Coupled, and Different Service Domains.

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  1. For ease of provisioning in these disparate access networks, it is

recommended to use the same I-SID Domain among the PBBN access

    networks and the PEs with IB-BEB functionality (those connecting
    to PBN).
 This topology operates in I-SID Bundling Mode: at a PE connecting to
 PBN access, each S-VID is mapped to an I-SID and subsequently a group
 of I-SIDs is mapped to a VPLS instance.  Similarly, at a PE
 connecting to PBBN access, each group of I-SIDs is mapped to a VPLS
 instance.  Similar to Type II service interface, no I-SID translation
 is performed for the I-SID bundling case.  Existing PW signaling and
 Ethernet raw mode (0x0005) PW type, defined in [RFC4447] and
 [RFC4448], are supported.  It is possible to use tagged mode (0x0004)
 PW for backward compatibility as well.

5.2. H-VPLS with Mixed PBBN and PBN Access: Regular PBN PE

 As shown in Figure 6, the operation of VPLS-PE1 (connecting to the
 PBN access on the left) is no different from existing VPLS-PEs.  It
 is the behavior of VPLS-PE2 (connecting to the PBBN access on the
 right) that is the focus of this section.
       PBN Access       IP/MPLS Core      PBBN Access
        (802.1ad)     +--------------+     (802.1ah)
                      |              |    +---------+
       +---------+    |              |    |         |
       |         |   +-----+         |    |  +---+  |
       |      +---+  |  PE | +-+     |    |  |BCB|  |
       |      |PCB|--|     |-|P|     |    |  +---+  |
       |      +---+ /+-----+ +-+     |    | /   |   |
       |         | / +-----+/    +-----+ +---+ +---+|
  +--+ |+---+ +---+  |  PE | +-+ |PE w/| |B- | |IB-|| +--+
  |CE|-||PEB|-|PCB|--|     |-|P|-|IBBEB|-|BEB| |BEB|--|CE|
  +--+ |+---+ +---+ ^+-----+ +-+ +-----+^+---+ +---+| +--+
       |         |  |  |PE1       PE2|  | |         |
       +---------+  |  |             |  | +---------+
                    |  +-------------+  |
                    |                   |
                S-Tagged           Type II (I-Tagged)
 Figure 6: H-VPLS with Mixed PBN and PBBN Access: Regular PBN PE
 Some assumptions made for this topology include:
  1. The CE is directly connected to the PBBN access via an S-Tagged or

port-based Interface.

Sajassi, et al. Informational [Page 16] RFC 7080 VPLS Interoperability with PBB December 2013

  1. The I-SID in the PBBN access represents the same customer as the

S-VID in the PBN access.

  1. There is 1:1 mapping between the I-SID and the VPLS instance.
  1. At the S-Tagged service interface of the PE connecting to PBN

(e.g., PE1 in Figure 6), the PE only provides 1:1 mapping of S-VID

    to the VPLS instance.  S-VID bundling is not a viable option since
    it does not correspond to anything in the PBBN access.
  1. The PE connecting to the PBBN access (e.g., PE2 in Figure 6),

supports IB-BEB functionality and the I-component is connected to

    the VPLS Forwarder (i.e., the I-component faces the IP/MPLS core
    whereas the B-component faces the PBBN access network).  One or
    more I-SIDs can be grouped into a B-VID in the PBBN access.
  1. Since C-VID grouping in different PBBN access networks must be

consistent, it is assumed that same I-SID Domain is used across

    these PBBN access networks.
 Unlike the previous case, I-SID bundling mode is not supported in
 this case.  This is primarily because the VPLS core operates in the
 same manner as today.  The PE with IB-BEB functionality connecting to
 PBBN access performs the mapping of each VPLS instance to an I-SID
 and one or more of these I-SIDs may be mapped onto a B-VID within the
 PBBN access network.

6. H-VPLS with MPLS Access

 In this section, the case of H-VPLS with MPLS access network is
 discussed.  The integration of PBB functionality into VPLS-PE for
 such access networks is described to improve the scalability of the
 network in terms of the number of MAC addresses and service instances
 that are supported.
 For this topology, it is possible to embed PBB functionality in
 either the U-PE or the N-PE.  Both of these cases are described in
 the following subsections.

6.1. H-VPLS with MPLS Access: PBB U-PE

 As stated earlier, the objective for incorporating PBB function at
 the U-PE is to improve the scalability of H-VPLS networks in terms of
 the number of MAC addresses and service instances that are supported.
 In current H-VPLS, the N-PE must learn customer MAC addresses
 (C-MACs) of all VPLS instances in which it participates.  This can
 easily add up to hundreds of thousands or even millions of C-MACs at

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 the N-PE.  When the U-PE performs PBB encapsulation, the N-PE only
 needs to learn the MAC addresses of the U-PEs, which is a significant
 reduction.  Furthermore, when PBB encapsulation is used, many I-SIDs
 are multiplexed within a single bridge domain (e.g., B-VLAN).  If the
 VPLS instance is set up per B-VLAN, then one can also achieve a
 significant reduction in the number of full-mesh PWs.  It should be
 noted that this reduction in full-mesh PWs comes at the cost of
 potentially increased replication over the full-mesh of PWs: customer
 multicast and/or broadcast frames are effectively broadcasted within
 the B-VLAN.  This may result in additional frame replication because
 the full-mesh PWs corresponding to a B-VLAN are most likely bigger
 than the full-mesh PWs corresponding to a single I-SID.  However,
 flood containment per I-SID (B-MAC multicast pruning) can be used to
 remedy this drawback and have multicast traffic replicated
 efficiently for each customer (i.e., for each I-SID).
 Figure 7 below illustrates the scenario for H-VPLS with MPLS access.
 As illustrated, customer networks or hosts (CE) connect into the U-PE
 nodes using standard Ethernet interfaces [802.1D-REV], [802.1Q], or
 [802.1ad].  The U-PE is connected upstream to one or more VPLS N-PE
 nodes by MPLS PWs (per VPLS instance).  These, in turn, are connected
 via a full mesh of PWs (per VPLS instance) traversing the IP/MPLS
 core.  The U-PE is outfitted with PBB Backbone Edge Bridge (BEB)
 functions where it can encapsulate/decapsulate customer MAC frames in
 provider B-MACs and perform I-SID translation if needed.
      PBB                                                PBB
      BEB                  +----------+                  BEB
       |                   |          |                   |
       |   +-----------+   |    IP    |   +-----------+   |
       |   | MPLS      |   |   MPLS   |   |    MPLS   |   |
       V   | Access +----+ |   Core   | +----+ Access |   V
 +--+  +----+       |VPLS|-|          |-|VPLS|       +----+  +--+
 |CE|--|U-PE|       |N-PE| |          | | PE |       |U-PE|--|CE|
 +--+  +----+       +----+ |          | +----+       +----+  +--+
           |           |   |          |   |           |
           +-----------+   +----------+   +-----------+
        Figure 7: H-VPLS with MPLS Access Network and PBB U-PE
 The U-PE still provides the same type of services toward its
 customers as before and they are:
  1. Port mode (either 802.1D, 802.1Q, or 802.1ad)
  2. VLAN mode (either 802.1Q or 802.1ad)
  3. VLAN-bundling mode (either 802.1Q or 802.1ad)

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 By incorporating a PBB function, the U-PE maps each of these services
 (for a given customer) onto a single I-SID based on the configuration
 at the U-PE.  Many I-SIDs are multiplexed within a single bridge
 domain (e.g., B-VLAN).  The U-PE can then map a bridge domain onto a
 VPLS instance and the encapsulated frames are sent over the PW
 associated with that VPLS instance.  Furthermore, the entire Ethernet
 bridging operation over the VPLS network is performed as defined in
 [RFC4762].  In other words, MAC forwarding is based on the B-MAC
 address space and service delimiter is based on VLAN ID, which is
 B-VID in this case.  There is no need to inspect or deal with I-SID
 values in the VPLS N-PEs.
 In the case of PBB U-PEs in a single I-SID Domain, I-SID assignment
 is performed globally across all MPLS access networks and therefore
 there is no need for I-SID translation.  This scenario supports I-SID
 bundling mode, and it is assumed that the mapping of the I-SIDs to
 the bridge domain (e.g., B-VLAN) is consistent across all the
 participating PE devices.  In the case of the I-SID bundling mode, a
 bridge domain (e.g., B-VLAN) is mapped to a VPLS instance and an
 existing Ethernet raw mode (0x0005) or tagged mode (0x0004) PW type
 is used as defined in [RFC4447] and [RFC4448].
 I-SID mode can be considered to be a degenerate case of I-SID
 bundling where a single bridge domain is used per I-SID.  However,
 that results in an increased number of bridge domains and PWs in the
 PEs.  PBB flood containment (B-MAC multicast pruning) per I-SID can
 be used in conjunction with I-SID bundling mode to limit the scope of
 flooding per I-SID thus removing the need for I-SID mode.

6.2. H-VPLS with MPLS Access: PBB N-PE

 In this case, the PBB function is incorporated at the N-PE to improve
 the scalability of H-VPLS networks in terms of the numbers of MAC
 addresses and service instances that are supported.
 Customer networks or hosts (CE) connect into the U-PE nodes using
 standard Ethernet interfaces [802.1D-REV], [802.1Q], or [802.1ad].
 The U-PE is connected upstream to one or more VPLS N-PE nodes by MPLS
 PWs (per customer).  These, in turn, are connected via a full mesh of
 PWs (per customer or group of customers) traversing the IP/MPLS core.
 The U-PE still provides the same type of services toward its
 customers as before and they are:
  1. Port mode (either 802.1D, 802.1Q, or 802.1ad)
  2. VLAN mode (either 802.1Q or 802.1ad)
  3. VLAN-bundling mode (either 802.1Q or 802.1ad)

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 The spoke PW from the U-PE to the N-PE is not service multiplexed
 because there is no PBB functionality on the U-PE, i.e., one service
 per PW.
                       PBB              PBB
                       BEB +----------+ BEB
                         | |          | |
           +-----------+ | |    IP    | | +-----------+
           | MPLS      | V |   MPLS   | V |    MPLS   |
           | Access +----+ |   Core   | +----+ Access |
 +--+  +----+       |VPLS|-|          |-|VPLS|       +----+  +--+
 |CE|--|U-PE|       |N-PE| |          | | PE |       |U-PE|--|CE|
 +--+  +----+       +----+ |          | +----+       +----+  +--+
           |           |   |          |   |           |
           +-----------+   +----------+   +-----------+
     Figure 8: H-VPLS with MPLS Access Network and PBB N-PE
 By incorporating a PBB function, the N-PE maps each of these services
 (for a given customer) onto a single I-SID based on the configuration
 at the N-PE.  Many I-SIDs can be multiplexed within a single bridge
 domain (e.g., B-VLAN).  The N-PE can, then, either map a single I-SID
 into a VPLS instance or map a bridge domain (e.g., B-VLAN) onto a
 VPLS instance, according to its configuration.  Next, the
 encapsulated frames are sent over the set of PWs associated with that
 VPLS instance.
 In the case of PBB N-PEs in a single I-SID Domain, I-SID assignment
 is performed globally across all MPLS access networks and therefore
 there is no need for I-SID translation.  This scenario supports I-SID
 bundling mode, and it is assumed that the mapping of the I-SIDs to
 the bridge domain (e.g., B-VLAN) is consistent across all the
 participating PE devices.  In the case of the I-SID bundling mode, a
 bridge domain (e.g., B-VLAN) is mapped to a VPLS instance and an
 existing Ethernet raw mode (0x0005) or tagged mode (0x0004) PW type
 as defined in [RFC4447] and [RFC4448], can be used.
 I-SID mode can be considered to be a degenerate case of I-SID
 bundling where a single bridge domain is used per I-SID.  However,
 that results in an increased number of bridge domains and PWs in the
 PE.  PBB flood containment (B-MAC multicast pruning) per I-SID can be
 used in conjunction with I-SID bundling mode to limit the scope of
 flooding per I-SID thus removing the need for I-SID mode.

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7. H-VPLS with MPLS Access: PBB Migration Scenarios

 Operators and service providers that have deployed H-VPLS with either
 MPLS or Ethernet are unlikely to migrate to PBB technology over night
 because of obvious cost implications.  Thus, it is imperative to
 outline migration strategies that will allow operators to protect
 investments in their installed base while still taking advantage of
 the scalability benefits of PBB technology.
 In the following subsections, we explore three different migration
 scenarios that allow a mix of existing H-VPLS access networks to
 coexist with newer PBB-based access networks.  The scenarios differ
 in whether or not the Ethernet service frames passing over the VPLS
 core are PBB-encapsulated.  The first scenario, in Section 7.1,
 involves passing only frames that are not PBB-encapsulated over the
 core.  The second scenario, in Section 7.2, stipulates passing only
 PBB-encapsulated frames over the core.  Whereas, the final scenario,
 in Section 7.3, depicts a core that supports a mix of PBB-
 encapsulated and non-PBB-encapsulated frames.  The advantages and
 disadvantages of each scenario will be discussed in the respective
 sections.

7.1. 802.1ad Service Frames over VPLS Core

 In this scenario, existing access networks are left unchanged.  All
 N-PEs would forward frames based on C-MACs.  In other words, Ethernet
 frames that are traversing the VPLS core (within PWs) would use the
 802.1ad frame format, as in current VPLS.  Hence, the N-PEs in
 existing access networks do not require any modification.  For new
 MPLS access networks that have PBB functions on the U-PE, the
 corresponding N-PE must incorporate built-in IB-BEB functions in
 order to terminate the PBB encapsulation before the frames enter the
 core.  A key point here is that while both the U-PE and N-PE nodes
 implement PBB IB-BEB functionality, the former has the I-component
 facing the customer (CE) and the B-component facing the core; whereas
 the latter has the I-component facing the core and the B-component
 facing the customer (i.e., access network).

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                                        PBB            PBB
                           +----------+ IB-BEB         IB-BEB
                           |          | |               |
           +-----------+   |    IP    | | +-----------+ |
           | MPLS      |   |   MPLS   | V |    MPLS   | |
           | Access +----+ |   Core   | +----+ Access | V
 +--+  +----+       |VPLS|-|          |-|VPLS|       +----+  +--+
 |CE|--|U-PE|       |N-PE| |          | | PE |       |U-PE|--|CE|
 +--+  +----+       +----+ |          | +----+       +----+  +--+
           | (Existing)|   |          |   |  (New)    |
           +-----------+   +----------+   +-----------+
 Figure 9: Migration with 802.1ad Service Frames over VPLS Core
 The main advantage of this approach is that it requires no change to
 existing access networks or existing VPLS N-PEs.  The main
 disadvantage is that these N-PEs will not leverage the advantages of
 PBB in terms of MAC address and PW scalability.  It is worth noting
 that this migration scenario is an optimal option for an H-VPLS
 deployment with a single PBB-capable access network.  When multiple
 PBB-capable access networks are required, then the scenario in
 Section 7.3 is preferred, as it provides a more scalable and optimal
 interconnect amongst the PBB-capable networks.

7.2. PBB Service Frames over VPLS Core

 This scenario requires that the VPLS N-PE connecting to existing MPLS
 access networks be upgraded to incorporate IB-BEB functions.  All
 Ethernet service frames passing over the VPLS core would be PBB-
 encapsulated.  The PBB over MPLS access networks would require no
 special requirements beyond what is captured in Section 6 of this
 document.  In this case, both the U-PE and N-PE, which implement
 IB-BEB functionality, have the I-component facing the customer and
 the B-component facing the core.
                       PBB                             PBB
                    IB-BEB +----------+              IB-BEB
                         | |          |                 |
           +-----------+ | |    IP    |   +-----------+ |
           | MPLS      | V |   MPLS   |   |    MPLS   | |
           | Access +----+ |   Core   | +----+ Access | V
 +--+  +----+       |VPLS|-|          |-|VPLS|       +----+  +--+
 |CE|--|U-PE|       |N-PE| |          | | PE |       |U-PE|--|CE|
 +--+  +----+       +----+ |          | +----+       +----+  +--+
           | (Existing)|   |          |   |  (New)    |
           +-----------+   +----------+   +-----------+
  Figure 10: Migration with PBB Service Frames over VPLS Core

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 The main advantage of this approach is that it allows better
 scalability of the VPLS N-PEs in terms of MAC address and pseudowire
 counts.  The disadvantage is that it requires upgrading the VPLS
 N-PEs of all existing MPLS access networks.

7.3. Mixed 802.1ad and PBB over VPLS Core

 In this scenario, existing access networks are left unchanged, and
 they exchange Ethernet frames with 802.1ad format over the PWs in the
 core.  The newly added access networks, which incorporate PBB
 functionality exchange Ethernet frames that are PBB-encapsulated
 amongst each other over core PWs.  For service connectivity between
 existing access network (non-PBB-capable) and new access network (PBB
 based), the VPLS N-PE of the latter network employs IB-BEB
 functionality to decapsulate the PBB header from frames outbound to
 the core and encapsulate the PBB header for frames inbound from the
 core.  As a result, a mix of PBB-encapsulated and 802.1ad Ethernet
 service frames are exchanged over the VPLS core.
 This mode of operation requires new functionality on the VPLS N-PE of
 the PBB-capable access network, so that the PE can send frames in
 802.1ad format or PBB format, on a per PW basis, depending on the
 capability of the destination access network.  Effectively, the PE
 would have to incorporate B-BEB as well as IB-BEB functions.
 A given PE needs to be aware of the capability of its remote peer in
 order to determine whether it connects to the right PW Forwarder.
 This can be achieved either via static configuration or by extending
 the VPLS control plane (BGP-based auto-discovery and LDP Signaling)
 discussed in [RFC6074].  The latter approach and the details of the
 extensions required are out of scope for this document.
                                        PBB
                                        B-BEB          PBB
                           +----------+ IB-BEB         IB-BEB
                           |          | |               |
           +-----------+   |    IP    | | +-----------+ |
           | MPLS      |   |   MPLS   | V |    MPLS   | |
           | Access +----+ |   Core   | +----+ Access | V
 +--+  +----+       |VPLS|-|          |-|VPLS|       +----+  +--+
 |CE|--|U-PE|       |N-PE| |          | |N-PE|       |U-PE|--|CE|
 +--+  +----+       +----+ |          | +----+       +----+  +--+
           | (Existing)|   |          |   |  (New)    |
           +-----------+   +----------+   +-----------+
              Figure 11: Migration with Mixed 802.1ad and
                   PBB Service Frames over VPLS Core

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 The U-PE and N-PE of the PBB-capable access network both employ BEB
 functionality.  The U-PE implements IB-BEB functionality where the
 I-component faces the customer (CE) and the B-component faces the
 core.  The N-PE, on the other hand, implements IB-BEB functionality
 with the I-component facing the core and the B-component facing the
 customer (access network).  In addition, the N-PE implements
 standalone B-BEB functionality.
 This scenario combines the advantages of both previous scenarios
 without any of their shortcomings, namely: it does not require any
 changes to existing access networks and it allows the N-PE to
 leverage the scalability benefits of 802.1ah for PBBN to PBBN
 connectivity.  The disadvantage of this option is that it requires
 new functionality on the N-PE of the PBBN access.  A second
 disadvantage is that this option requires two P2MP LSPs to be set up
 at the ingress N-PE: one for the N-PEs that support PBB encapsulation
 and another one for the N-PEs that don't support PBB encapsulation.

8. Acknowledgments

 The authors would like to thank Chris Metz and Dinesh Mohan for their
 valuable feedback and contributions.

9. Security Considerations

 This document does not introduce any additional security aspects
 beyond those applicable to VPLS/H-VPLS.  VPLS/H-VPLS security
 considerations are already covered in [RFC4111] and [RFC4762].

10. References

10.1. Normative References

 [802.1ad]    "IEEE Standard for and metropolitan area networks --
              Virtual Bridged Local Area Networks -- Provider
              Bridges", 802.1ad-2005, August 2005.
 [802.1ah]    "IEEE Standard for Local and metropolitan area networks
              -- Virtual Bridged Local Area Networks Amendment 7:
              Provider Backbone Bridges", IEEE Std. 802.1ah-2008,
              August 2009.
 [RFC4447]    Martini, L., Ed., Rosen, E., El-Aawar, N., Smith, T.,
              and G. Heron, "Pseudowire Setup and Maintenance Using
              the Label Distribution Protocol (LDP)", RFC 4447, April
              2006.

Sajassi, et al. Informational [Page 24] RFC 7080 VPLS Interoperability with PBB December 2013

 [RFC4448]    Martini, L., Ed., Rosen, E., El-Aawar, N., and G. Heron,
              "Encapsulation Methods for Transport of Ethernet over
              MPLS Networks", RFC 4448, April 2006.
 [RFC4762]    Lasserre, M., Ed., and V. Kompella, Ed., "Virtual
              Private LAN Service (VPLS) Using Label Distribution
              Protocol (LDP) Signaling", RFC 4762, January 2007.
 [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.

10.2. Informative References

 [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(tm), 2012 Edition,
              October 2012.
 [802.1D-REV] "IEEE Standard for Local and metropolitan area networks
              Media Access Control (MAC) Bridges", IEEE Std. 802.1D,
              June 2004.
 [RFC6246]    Sajassi, A., Ed., Brockners, F., Mohan, D., Ed., and Y.
              Serbest, "Virtual Private LAN Service (VPLS)
              Interoperability with Customer Edge (CE) Bridges", RFC
              6246, June 2011.
 [RFC4111]    Fang, L., Ed., "Security Framework for Provider-
              Provisioned Virtual Private Networks (PPVPNs)", RFC
              4111, July 2005.

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Authors' Addresses

 Ali Sajassi
 Cisco
 EMail: sajassi@cisco.com
 Samer Salam
 Cisco
 EMail: ssalam@cisco.com
 Nabil Bitar
 Verizon Communications
 EMail : nabil.n.bitar@verizon.com
 Florin Balus
 Nuage Networks
 EMail: florin.balus@nuagenetworks.net

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