Extensions to the Virtual Private LAN Service (VPLS) Provider Edge (PE) Model for Provider Backbone Bridging
draft-ietf-l2vpn-pbb-vpls-pe-model-07

L2VPN Working Group                                    F. Balus (editor)
Internet Draft                                            Alcatel-Lucent
Intended Status: Informational
Expires: April 2013                                 Ali Sajassi (editor)
                                                                   Cisco

                                                    Nabil Bitar (editor)
                                                                 Verizon





                                                       October 22, 2012


        Extensions to VPLS PE model for Provider Backbone Bridging
                 draft-ietf-l2vpn-pbb-vpls-pe-model-06.txt


Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
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   publication of this document. Please review these documents
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Abstract

   IEEE 802.1ah standard [IEEE802.1ah], also known as Provider Backbone
   Bridges (PBB) defines an architecture and bridge protocols for
   interconnection of multiple Provider Bridge Networks (PBNs). PBB was
   defined in IEEE as a connectionless technology based on multipoint
   VLAN tunnels. MSTP is used as the core control plane for loop
   avoidance and load balancing. As a result, the coverage of the
   solution is limited by STP scale in the core of large service
   provider networks. PBB on the other hand can be used to attain better
   scalability in terms of number of customer MAC addresses and number
   of service instances that can be supported.

   Virtual Private LAN Service (VPLS) [RFC4664] provides a framework for
   extending Ethernet LAN services, using MPLS tunneling capabilities,
   through a routed MPLS backbone without running (M)STP across the
   backbone. As a result, VPLS has been deployed on a large scale in
   service provider networks.

   This draft discusses extensions to the VPLS PE model required to
   incorporate desirable PBB components while maintaining the Service
   Provider fit of the initial model.

   Table of Contents

   1. Introduction...................................................3
   2. General terminology............................................4
   3. PE Reference Model.............................................5
   4. Packet Walkthrough.............................................8
   5. Control Plane.................................................10
   6. Efficient Packet replication in PBB VPLS......................11
   7. PBB VPLS OAM..................................................11
   8. Security Considerations.......................................11
   9. IANA Considerations...........................................11
   10. References...................................................11
      10.1. Normative References....................................11
      10.2. Informative References..................................12
   11. Contributors.................................................12
   12. Acknowledgments..............................................12



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1. Introduction

   IEEE 802.1ah standard [IEEE802.1ah], also known as Provider Backbone
   Bridges (PBB) defines an architecture and bridge protocols for
   interconnection of multiple Provider Bridge Networks (PBNs). PBB
   provides data plane hierarchy and new addressing designed to improve
   the scalability of MAC addresses and service instances in Provider
   Backbone Networks. MSTP is still used as the core control plane for
   loop avoidance and load balancing. As a result, the coverage of the
   solution is limited by STP scale in the core of large service
   provider networks.

   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 (M)STP 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.

   A hierarchical solution for VPLS was introduced in [RFC4762] for the
   purpose of improved scalability and to provide efficient handling of
   packet replication. These improvements are achieved by reducing the
   number of PE devices connected in a full-mesh topology through the
   creation of two-tier PEs. A U-PE aggregates all the CE devices in a
   lower-tier access network and then connects to the N-PE device(s)
   deployed around the core domain. In VPLS, MAC address learning and
   forwarding are done based on customer MAC addresses (C-MACs), which
   poses scalability issues on the N-PE devices as the number of VPLS
   instances (and thus customer MAC addresses) 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 (in terms of PW manageability and troubleshooting) as the
   number of customer service instances grows.

   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 in this document as
   PBB-VPLS results in better scalability in terms of number of service
   instances, PWs and C-MACs that need to be handled in the VPLS PEs.

   Section 2 gives a quick terminology reference. Section 3 covers the
   reference model for PBB VPLS PE. Section 4 describes the packet
   walkthrough. Section 5 to 7 discusses the PBB-VPLS usage of existing
   VPLS mechanisms - control plane, efficient packet replication, OAM.


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2. General terminology

   Some general terminology is defined here; most of the terminology
   used is from [IEEE802.1ah], [RFC4664] and [RFC4026]. Terminology
   specific to this memo is introduced as needed in later sections.

   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.

   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 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.

   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 I and B components.

   B-component: A bridging component contained in backbone edge and
   core bridges that bridges in the backbone space (B-MAC addresses,
   B-VLAN)

   B-TAG:  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 provider backbone bridged network. Frames passed through
   this interface contain a B-TAG field.

   B-VID: The specific VLAN identifier carried inside a B-TAG

   B-PW: The pseudowire used to interconnect B-component instances.

   I-component: A bridging component contained in a backbone edge bridge
   that bridges in the customer space (customer MAC addresses, S-VLAN)





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   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).

   I-BEB: A backbone edge bridged 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-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-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 the interface defined between the I
   and B components inside an IB-BEB or between two B-BEB. Frames passed
   through this interface contain an I-TAG field

   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 identifier information (S-VLAN).

   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



3. PE Reference Model

   The following gives a short primer on PBB before describing the PE
   reference model for PBB-VPLS. The internal components of a PBB bridge
   module are depicted in Figure 1.



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                   +-------------------------------+
                   |      802.1ah Bridge Model     |
                   |                               |
        +---+      |  +------+      +-----------+  |
        |CE |---------|I-Comp|------|           |  |
        +---+      |  |      |      |           |--------
                   |  +------+      |           |  |
                   |     o          |   B-Comp  |  |
                   |     o          |           |--------
                   |     o          |           |  |
        +---+      |  +------+      |           |  |
        |CE |---------|I-Comp|------|           |--------
        +---+  ^   |  |      |  ^   |           |  |   ^
               |   |  +------+  |   +-----------+  |   |
               |   +------------|------------------+   |
               |                |                      |
               |                |                      |
             S-tagged         I-tagged              B-tagged
             Service I/F      Service I/F           Service I/F

                        Figure 1: PBB Bridge Model

   Provider Backbone Bridges (PBBs) [IEEE 802.1ah] offers 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:

     - MAC-address table scalability
     - Service instance scalability

   To obviate the above two limitations, PBB introduces a hierarchical
   network architecture with associated new frame formats which extend
   the work completed by Provider Bridges (IEEE 802.1ad). In the PBBN
   architecture, customer networks (using IEEE 802.1Q or 802.1ad
   bridging) are aggregated into Provider Backbone Bridge Networks
   (PBBNs) which utilize the IEEE 802.1ah 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 [802.1ah] 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
   802.1ad.


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   As shown in the 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 provider space (B-MAC, B-VLAN) and the
   I-component provides bridging in 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 de-encapsulated
   and passed to the CE. If a PBB bridge consists of both I & B
   components, then it is called IB-BEB and if it only consists of
   either B-component or I-component, then it is called B-BEB or I-BEB
   respectively. The interface between an I-BEB or IB-BEB and a CE is
   called S-tagged service interface and the interface between an I-BEB
   and a B-BEB (or between two B-BEBs) is called I-tagged service
   interface. The interface between a B-BEB or IB-BEB and a Backbone
   Core Bridge (BCB) is called B-Tagged service interface.

   To accommodate the PBB components the VPLS model defined in [RFC4664]
   is extended as depicted in figure 1.


        +----------------------------------------+
        |       PBB-VPLS-capable PE model        |
        |   +---------------+          +------+  |
        |   |               |          |VPLS-1|------------
        |   |               |==========|Fwdr  |------------ PWs
   +--+ |   |     Bridge    ------------      |------------
   |CE|-|-- |               |          +------+  |
   +--+ |   |     Module    |             o      |
        |   |               |             o      |
        |   |   (802.1ah    |             o      |
        |   |    bridge)    |             o      |
        |   |               |             o      |
   +--+ |   |               |          +------+  |
   |CE|-|-- |               ------------VPLS-n|-------------
   +--+ |   |               |==========| Fwdr |------------- PWs
        |   |               |     ^    |      |-------------
        |   +---------------+     |    +------+  |
        |                         |              |
        +-------------------------|--------------+
                         LAN emulation Interface

                    Figure 2: PBB-VPLS capable PE Model





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   The PBB Module as defined in [IEEE802.1ah] 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 (HVPLS
   topologies). The VPLS instances are represented externally in the
   MPLS context by a L2FEC which 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].

   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. Same 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.

   Similarly with the regular HVPLS, 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
   HVPLS spokes are connecting the PBB-VPLS N-PE to a 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 reducing substantially resource consumption in the
   VPLS core.

4. Packet Walkthrough

   Since PBB bridge module inherently performs forwarding, the PE
   reference model of Figure 2 can be expanded as the one shown in
   Figure 3.

   Furthermore, the B-component is connected via several virtual
   interfaces to the PW Forwarder module. The function of 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.

   This simplified model takes full advantage of PBB bridge module where
   all the [IEEE 802.1ah] procedures including the C-MAC/B-MAC
   forwarding and PBB encapsulation/decapsulation takes place and thus
   avoids specifying any of these functions in here.




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   Because of text-based graphics, the Figure 3 only shows PWs on the
   core-facing side; however, in 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, the access-side PW Forwarder is not depicted without loss of
   any generality.


        +------------------------------------------------+
        |               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 I/Fs

    +----------+                                      +------------+
    |CMAC DA,SA|                                      | PSN header |
    |----------|                                      |------------|
    |SVID, CVID|                                      | PW Label   |
    |----------|                                      |------------|
    | Payload  |                                      | BMAC DA,SA |
    +----------+                                      |------------|
                                                      | PBB I-tag  |
                                                      |------------|
                                                      | CMAC DA,SA |
                                                      |------------|
                                                      | SVID, CVID |
                                                      |------------|
                                                      |  Payload   |
                                                      +------------+

               Figure 3: Packet Walkthrough for PBB VPLS PE


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   In order to better understand the data plane walkthrough let us
   consider the example of a PBB packet arriving over a 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), same as for regular VPLS. The PW Label has in this
   case an equivalent role with the Backbone VLAN id on the PBB B-tagged
   interface.

   An example of the PBB packet for regular Ethernet PW is depicted in
   Figure 3 on the right hand side. The MPLS packet from MPLS core
   network is received by the PBB-VPLS PE. The PW Forwarder function of
   the PE uses 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 is performed according to the [IEEE 802.1ah] where
   bridging based on B-MAC DA is performed which result in one of the
   three outcomes:

     1. The packet is forwarded to a physical interface on the B-
       component. In this case, the 802.1ah Ethernet frame is forwarded
       as is.

     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.

     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 scenario, the I-component removes the B-MAC
       header according to [IEEE 802.1ah] and bridges the packet using
       C-MAC DA.

     4. If the destination B-MAC is an unknown 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.

5. Control Plane

   The control plane procedures described in [RFC6074], [RFC4761] and
   [RFC4762] can be re-used in a PBB-VPLS to setup the PW infrastructure
   in the service provider and/or customer bridging space. This allows
   porting the existing control plane procedures (e.g. BGP-AD, PW setup,
   VPLS MAC Flush, PW OAM) for each domain.


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6. Efficient Packet replication in PBB VPLS

   The PBB VPLS architecture takes advantage of the existing VPLS
   features addressing packet replication efficiency. HVPLS 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 to control
   the distribution of the Multicast traffic to non-member sites.

   [IEEE802.1ah] specifies also the use of MMRP protocol [IEEE802.1ak]
   for flood containment in the backbone instances. The same solution
   can be ported in the PBB-VPLS solution.

   Further optimizations of the packet replication in PBB-VPLS are out
   of the scope of this draft.

7. PBB VPLS OAM

   The existing VPLS, PW and MPLS OAM procedures may be used in each
   customer or backbone service instance to verify the status of the
   related connectivity components.

   PBB OAM procedures make use of the IEEE 802.1ag and Y.1731 tools in
   both I-component and B-component.

   Both set of tools (PBB and VPLS) may be used for the combined PBB-
   VPLS solution.

8. Security Considerations

   No new security issues are introduced beyond those that are described
   in [RFC4761] and [RFC4762].

9. IANA Considerations

   IANA does not need to take any action for this draft.

10. References

10.1. Normative References

   [RFC4761] Kompella, K. and Rekhter, Y. (Editors), "Virtual Private
             LAN Service (VPLS) Using BGP for Auto-Discovery and
             Signaling", RFC 4761, January 2007.




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   [RFC4762] Lasserre, M. and Kompella, V. (Editors), "Virtual Private
             LAN Service (VPLS) Using Label Distribution Protocol (LDP)
             Signaling", RFC 4762, January 2007.

   [RFC6074] E. Rosen, et Al. "Provisioning, Autodiscovery and
             Signaling in L2VPNs", RFC 6074, January 2011


10.2. Informative References

   [RFC3985] Bryant, S. and Pate, P. (Editors)," Pseudo Wire Emulation
             Edge-to-Edge (PWE3) Architecture", RFC 3985, May 2005.

   [RFC4664] Andersson, L. and Rosen, E. (Editors),"Framework for Layer
             2 Virtual Private Networks (L2VPNs)", RFC 4664, Sept 2006

   [IEEE802.1ah] IEEE 802.1ah "Virtual Bridged Local Area Networks,
             Amendment 6: Provider Backbone Bridges", Approved Standard
             June 12th, 2008

   [IEEE802.1ak] IEEE Draft P802.1ak/D8.0 "Virtual Bridged Local Area
             Networks, Amendment 7: Multiple Registration Protocol",
             Work in Progress, November 29, 2006

   [RFC4026] Andersson, L. et Al., "Provider Provisioned Virtual Private
             Network (VPN) Terminology", RFC 4026, May 2005.

11. Contributors

   The following authors contributed to this document: John Hoffmans
   (KPN), Geraldine Calvignac (France Telecom), Olen Stokes (Extreme
   Networks), Raymond Zhang and Matthew Bocci (Alcatel-Lucent).


12. Acknowledgments

   The authors would like to thank Wim Henderickx, Mustapha Aissaoui,
   Dimitri Papadimitriou, Pranjal Dutta, Jorge Rabadan and Maarten
   Vissers for their insightful comments and probing questions.









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Authors' Addresses

   Ali Sajassi
   Cisco
   170 West Tasman Drive
   San Jose, CA  95134, U.S.
   Email: sajassi@cisco.com

   Nabil Bitar
   Verizon
   40 Sylvan Road
   Waltham, MA 02145
   Email: nabil.bitar@verizon.com

   Florin Balus
   Alcatel-Lucent
   701 E. Middlefield Road
   Mountain View, CA, USA 94043
   Email: florin.balus@alcatel-lucent.com

   Matthew Bocci
   Alcatel-Lucent,
   Voyager Place
   Shoppenhangers Road
   Maidenhead
   Berks, UK
   e-mail: matthew.bocci@alcatel-lucent.co.uk

   Raymond Zhang
   BT
   2160 E. Grand Ave.
   El Segundo, CA 900245 USA
   EMail: raymond.zhang@bt.com

   Geraldine Calvignac
   France Telecom
   2, avenue Pierre-Marzin
   22307 Lannion Cedex
   France
   Email: geraldine.calvignac@orange-ftgroup.com

   John Hoffmans
   KPN
   Regulusweg 1
   2516 AC Den Haag
   Nederland
   Email: john.hoffmans@kpn.com

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   Olen Stokes
   Extreme Networks
   PO Box 14129
   RTP, NC 27709
   USA
   Email: ostokes@extremenetworks.com









































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