Hierarchical Virtual Private LAN Service
draft-khandekar-ppvpn-hvpls-mpls-00

Versions: 00                                                            
Provider Provisioned VPN Working Group                 Sunil Khandekar
Internet Draft                                           Vach Kompella
Expiration Date: June 2002                                   Joe Regan
                                                           Nick Tingle
                                                           TiMetra Inc

Tom Soon                                                Pascal Menezes
SBC Communications                                   Terabeam Networks

Giles Heron                                               Marc Lassere
PacketExchange Ltd.                                Riverstone Networks

Ron Haberman                                          Kireeti Kompella
Rick Wilder                                           Juniper Networks
Masergy Communications
                                                          Marty Borden
                                                            Atrica Inc



                 Hierarchical Virtual Private LAN Service
                 draft-khandekar-ppvpn-hvpls-mpls-00.txt


 Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six
   months and may be updated, replaced, or obsoleted by other
   documents at any time.  It is inappropriate to use Internet-Drafts
   as reference material or to cite them other than as "work in
   progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html


 Abstract

   This document proposes scalable extensions to the Virtual Private
   LAN Segment (VPLS) solution described in [VPLS], by introducing
   hierarchical connectivity.  This document also describes support
   for participation of non-bridging PE devices in a VPLS solution.

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 1.     Placement of this Memo in Sub-IP Area

   RELATED DOCUMENTS

     draft-vkompella-ppvpn-vpsn-mpls-00.txt
     draft-heron-ppvpn-vpsn-reqmts-00.txt
     draft-lasserre-tls-mpls-00.txt

   WHERE DOES THIS FIT IN THE PICTURE OF THE SUB-IP WORK

   This fits in the PPVPN box.

   WHY IS IT TARGETED AT THIS WG

   This work fits in the PPVPN working group charter.  It describes
   scalable extensions to a service that uses an emulation of a Layer
   2 medium to create a provider provisioned virtual private network
   0, specifically, a Transparent LAN service.

   JUSTIFICATION

   We believe the WG should consider this draft because it specifies
   extensions for a class of layer 2 VPN


 2.     Introduction

   The solution described in [VPLS] requires a full mesh of tunnel
   LSPs between all the PE routers that participate in the VPLS
   service.  For each VPLS service, n*(n-1) VCs must be setup between
   the PE routers.  While this creates signaling overhead, the real
   detriment to large-scale deployment is the packet replication
   requirements for each provisioned VCs on a PE router.  Hierarchical
   connectivity, described in this document reduces signaling and
   replication overhead to allow large-scale deployment.

   In many cases, service providers place smaller edge devices in
   multi-tenant buildings and aggregate them into a PE device in a
   large Central Office (CO) facility. In some instances, standard
   IEEE 802.1q (Dot 1Q) tagging techniques may be used to facilitate
   mapping CE interfaces to PE VPLS access points.  When this is done,
   a hierarchical architecture is created outside the context of VPLS;
   no service level signaling is present between the PE router and the
   MTU bridge.

   To avoid issues with Spanning Tree Protocol (STP), 'VLAN' tag
   provisioning and non-Ethernet access networks, it is beneficial to
   extend VPLS service tunneling techniques into the MTU domain.  This


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   can be accomplished by treating the MTU device as a PE device and
   provision VCs between it and every other edge, as described in
   [VPLS].  An alternative is to utilize [MARTINI-ENCAP] VCs between
   the MTU and selected VPLS enabled PE routers.  This document
   focuses on this alternative approach.  The [VPLS] mesh core tier
   VCs (Hub) are augmented with access tier VCs (Spoke) to form a two
   tier hierarchical VPLS (H-VPLS).

   Spoke VCs may be expanded to include any L2 tunneling mechanism,
   expanding the scope of the first tier to include non-bridging VPLS
   PE routers. The non-bridging PE router would extend a Spoke VC from
   a Layer-2 switch or Router that connects to it, through the service
   core network, to a bridging VPLS PE router supporting Hub VCs.

   This document also describes support for participation of non-
   bridging devices (routers) in a VPLS solution.


 3.     Hierarchical connectivity

   This section describes the hub and spoke connectivity model and
   describes the requirements of the bridging capable and non-bridging
   devices for supporting the spoke connections.

   For rest of this discussion we will refer to a bridging capable MTU
   device as MTU-s and a non-bridging capable PE device as PE-r.  A
   routing and bridging capable device will be referred to as PE-rs.



3.1.     Spoke connectivity for bridging-capable devices

   As shown in figure-1, consider the case where an MTU-s device has a
   single connection to the PE-rs device placed in the CO.  The PE-rs
   devices are connected in a full mesh.   To participate in the VPLS
   service, MTU-s device creates a single point-to-point tunnel LSP to
   the PE-rs device in the CO.  We will call this the spoke
   connection.  For each VPLS service, a single spoke VC is setup
   between an MTU-s and the PE-rs based on [MARTINI-SIG] and [MARTINI-
   ENCAP].  Unlike traditional [MARTINI-ENCAP] VCs that terminate on a
   physical port at each end, the spoke VC terminates on a virtual
   bridge instance on the MTU-s and the PE-rs devices.  The MTU-s
   device and the PE-rs device treat each spoke connection like an
   access port of the VPLS service. On access ports, the combination
   of the physical port and the vlan tag is used to associate the
   traffic to a VPLS instance while the combination of vc-id and vc-
   labels (ingress and egress) are used to associate the traffic on
   the virtual spoke port with a VPLS instance.

   The signaling and association of the spoke connection to the VPLS
   service may be done by introducing extensions to the LDP signaling
   as specified in [MARTINI-SIG].  This will be specified in a future
   version of this document.

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                                                          PE2-rs
                                                          ------
                                                         /      \
                                                        |   --   |
                                                        |  /  \  |
    CE-1                                                |  \B /  |
     \                                                   \  --  /
      \                                                  /------
       \   MTU-s                          PE1-rs        /   |
        \ ------                          ------       /    |
         /      \                        /      \     /     |
        | \ --   |      VC-1            |   --   |---/      |
        |  /  \--|- - - - - - - - - - - |--/  \  |          |
        |  \B /  |                      |  \B /  |          |
         \ /--  /                        \  --  / ---\      |
          /-----                          ------      \     |
         /                                             \    |
       ----                                             \ ------
      |Agg |                                             /      \
       ----                                             |  --    |
      /    \                                            | /  \   |
     CE-2  CE-3                                         | \B /   |
                                                         \ --   /
    MTU-s = Bridging capable MTU                          ------
    PE-rs = VPLS capable PE                               PE3-rs
    --
   /  \
   \B / = Virtual VPLS(Bridge)Instance
    --
    Agg = Layer-2 Aggregation


3.1.1.       MTU-s Operation

   The MTU-s device is defined as a device that supports layer-2
   switching functionality and does all the normal bridging functions
   of learning and replication on all its ports, including the virtual
   spoke port.  Packets to unknown destination are replicated to all
   ports in the service including the virtual spoke port.  Once the
   MAC address is learned, traffic between CE1 and CE2 will be
   switched locally by the MTU-s device conserving the link capacity
   of the connection to the PE-rs.  Similarly traffic between CE1 or
   CE2 and any remote destination is switched directly on to the spoke
   connection and sent to the PE-rs over the point-to-point VC LSP.

   Since the MTU-s is bridging capable, only a single VC is required
   per VPLS instance for any number of access connections in the same
   VPLS service.  This further reduces the signaling overhead between
   the MTU-s and PE-rs.


3.1.2.       PE-rs Operation

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   The PE-rs device is a device that supports all the bridging
   functions for VPLS service and supports the routing and MPLS
   encapsulation, i.e. it supports all the functions described in
   [VPLS].   The operation on the PE-rs node is identical to that
   described in [VPLS] with one addition.  A point-to-point VC
   associated with the VPLS is regarded as a virtual port.  The
   operation on the virtual spoke port is identical to the operation
   on an access port as described in the earlier section.  As shown in
   figure-1, each PE-rs device switches traffic between aggregated
   [MARTINI-ENCAP] VCs that look like virtual ports and the network
   side VPLS VCs.


3.2.     Advantages of spoke connectivity

   Spoke connectivity offers several scaling and operational
   advantages for creating large scale VPLS implementations, while
   retaining the ability to offer all the functionality of the VPLS
   service.

     - Eliminates the need for a full mesh of tunnels and full mesh of
       VCs per service between all devices participating in the VPLS
       service.
     - Minimizes signaling overhead since fewer VC-LSPs are required
       for the VPLS service.
     - Segments VPLS nodal discovery.  MTU-s needs to be aware of only
       the PE-rs node although it is participating in the VPLS service
       that spans multiple devices.  On the other hand, every VPLS PE-
       rs must be aware of every other VPLS PE-rs device and all of
       it's locally connected MTU-s and PE-r devices.
     - Addition of other sites requires configuration of the new MTU-s
       device but does not require any provisioning of the existing
       MTU-s devices on that service.
     - Hierarchical connections can be used to create VPLS service
       that spans multiple service provider domains. This is explained
       in a later section.


3.3.     Spoke connectivity for non-bridging devices
   In some cases, a bridging PE-rs device may not be deployed in some
   CO while a PE-r might already be deployed.  If there is a need to
   provide VPLS service from the CO where the PE-rs device is not
   available, the service provider may prefer to use the PE-r device
   in the interim.  In this section, we explain how a PE-r device that
   does not support any of the bridging functionality as described in
   [VPLS] can participate in the VPLS service.







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                                                          PE2-rs
                                                          ------
                                                         /      \
                                                        |   --   |
                                                        |  /  \  |
    CE-1                                                |  \B /  |
     \                                                   \  --  /
      \                                                  /------
       \   PE-r                           PE1-rs        /   |
        \ ------                          ------       /    |
         /      \                        /      \     /     |
        | \      |      VC-1            |   --   |---/      |
        |  ------|- - - - - - - - - - - |--/  \  |          |
        |   -----|- - - - - - - - - - - |--\B /  |          |
         \ /    /                        \  --  / ---\      |
          ------                          ------      \     |
         /                                             \    |
       ----                                             \------
      | Agg|                                            /      \
       ----                                            |  --    |
      /    \                                           | /  \   |
     CE-2  CE-3                                        | \B /   |
                                                        \ --   /
    PE-r = Non-Bridging PE (router)                      ------
    PE-rs = VPLS capable PE                               PE3-rs
    --
   /  \
   \B / = Virtual VPLS(Bridge)Instance
    --
    Agg = Layer-2 Aggregation

   As shown in figure-2, the PE-r device creates a point-to-point
   tunnel LSP to a PE-rs device.  Then for every access port that
   needs to participate in a VPLS service, the PE-r device creates a
   point-to-point [MARTINI-SIG] VC that terminates on the physical
   port at the PE-r and terminates on the virtual bridge instance of
   the VPLS service at the PE-rs.


3.3.1.       PE-r Operation

   The PE-r device is defined as a device that supports routing but
   does not support any bridging functions.  However, it is capable of
   setting up [MARTINI-SIG] VCs between itself and the PE-rs.  For
   every port that is supported in the VPLS service, a [MARTINI-SIG]
   VC is setup from the PE-r to the PE-rs.  Once the VCs are setup,
   there is no learning or replication function required on part of
   the PE-r.  All traffic received on an access port is transmitted on
   the VC associated with that access port.  Similarly all traffic
   received on a VC is transmitted to the access port where the VC
   terminates.  Thus traffic from CE1 destined for CE2 is switched at
   PE-rs and not at PE-r.


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   This approach adds more overhead than the bridging capable (MTU-s)
   spoke approach since a VC is required for every access port that
   participates in the service versus a single VC required per service
   (regardless of access ports) when a MTU-s type device is used.
   However, this approach offers the advantage of offering a VPLS
   service in conjunction with a routed internet service from CO where
   the PE-rs device is not yet deployed while the PE-r device is
   deployed.


3.3.2.       PE-rs Operation

   The operation of PE-rs is independent of the type of device at the
   other end of the spoke connection.  Whether there is a bridging
   capable device (MTU-s) at the other end of the spoke connection or
   there is a non-bridging device (PE-r) at the other end of the spoke
   connection, the operation of PE-rs is exactly the same.  Thus, the
   spoke connection from the PE-r is treated as a virtual port and the
   PE-rs device switches traffic between the virtual port, access
   ports and the network side VPLS VCs once it has learned the MAC
   addresses.


 4.     Redundant Spoke Connections

   An obvious weakness of the hub and spoke approach described thus
   far is that the MTU device has a single connection to the PE-rs
   device.  In case of failure of the connection or the PE-rs device,
   the MTU device suffers total loss of connectivity.

   In this section, we describe how redundant connections can be
   provided to avoid total loss of connectivity from the MTU device.
   The mechanism described is identical for both, MTU-s and PE-r type
   of devices

4.1.     Dual-homed MTU-s OR PE-r device

   To protect from connection failure of the VC or the failure of the
   PE-rs device, the MTU-s device or the PE-r device is dual-homed
   into two PE-rs devices, as shown in figure-3.  The PE-rs devices
   must be part of the same VPLS service instance.

   An MTU-s device will setup two [MARTINI-ENCAP] VCs (one each to
   PE1-rs and PE3-rs) for each VPLS instances. One of the two VC is
   designated as primary and is the one that is actively used under
   normal conditions, while the second VC is designated as secondary
   and is held in a standby state.  The MTU-s device or the PE-r
   device negotiates the VC-labels for both the primary and secondary
   VC, but does not use the secondary VC unless the primary VC fails.
   Since only one link is active at a given time, a loop does not
   exist and hence 802.1D spanning tree is not required.



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                                                          PE2-rs
                                                          ------
                                                         /      \
                                                        |   --   |
                                                        |  /  \  |
    CE-1                                                |  \B /  |
      \                                                  \  --  /
       \                                                 /------
        \  MTU-s                          PE1-rs        /   |
         \------                          ------       /    |
         /      \                        /      \     /     |
        |   --   |   Primary VC         |   --   |---/      |
        |  /  \--|- - - - - - - - - - - |--/  \  |          |
        |  \B /  |                      |  \B /  |          |
         \  -- \/                        \  --  / ---\      |
          ------\                         ------      \     |
          /      \                                     \    |
         /        \                                     \ ------
        /          \                                     /      \
       CE-2         \                                   |  --    |
                     \     Secondary VC                 | /  \   |
                      - - - - - - - - - - - - - - - - - |-\B /   |
                                                         \ --   /
    MTU-s = Bridging capable MTU                          ------
    PE-rs = VPLS capable PE                               PE3-rs
    --
   /  \
   \B / = Virtual VPLS(Bridge)Instance
    --


4.2.      Failure detection and recovery

   The MTU-s device controls the usage of the VC links to the PE-rs
   nodes.  Since LDP signaling is used to negotiate the VC-labels, the
   keepalive messages used for the LDP session are used to detect
   failure of the primary VC.

   Upon failure of the primary VC, the MTU-s device immediately
   switches to the secondary VC.  At this point, the PE3-rs device
   that terminates the secondary VC starts learning MAC addresses on
   the spoke VC.  All other PE-rs nodes in the network think that CE-1
   and CE-2 are behind PE1-rs and may continue to send traffic to PE1-
   rs until they learn that the devices are now behind PE3-rs.  The
   relearning process can take a long time and may adversely affect
   the connectivity of higher level protocols from CE1 and CE2.  To
   enable faster convergence, the PE1-rs device where the primary VC
   failed SHOULD send out a flush message, using the MAC TLV as
   defined in [VPLS], to all other PE-rs devices participating in the
   VPLS service.  Upon receiving the message, all PE-rs flush the MAC
   addresses learned from PE1-rs.  This creates more traffic

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   temporarily, since the remote PE-rs device that is transmitting to
   the CE1 and CE2 must replicate the traffic until it learns that the
   devices are now behind PE3-rs.  This approach, however, speeds upon
   the convergence times when devices move from PE-rs to PE-rs.


 5.     Multi-domain VPLS service

   Hierarchy can also be used to create a large scale VPLS service
   within a single domain or a service that spans multiple domains
   without requiring full mesh connectivity between all VPLS capable
   devices.   Two fully meshed VPLS networks are connected together
   using a single LSP tunnel between the VPLS gateway devices.  A
   single VC is setup per VPLS service to connect the two domains
   together.  The VPLS gateway device joins two VPLS services together
   to form a single multi-domain VPLS service.  The requirements and
   functionality required from a VPLS gateway device will be explained
   in a future version of this document.


 6.     Security Considerations

   No new security issues result from this draft.  It is recommended
   in that LDP security (authentication) methods be applied.  This
   would prevent unauthorized participation by a PE in a VPLS.
   Traffic separation for VPLS is maintained using VC labels or IEEE
   802.1q VLAN tags.  However, for additional levels of security, the
   customer MAY deploy end-to-end security, which is out of the scope
   of this draft.


 7.     References

   IETF Drafts


   [VPSN-REQ]     Heron et al, "Requirements for Virtual Private
                  Switched Networks", (draft-heron-ppvpn-vpsn-reqmts-
                  00.txt), work in progress, July 2001.

   [PPVPN-REQ]    "Service Requirements for Provider Provisioned
                  Virtual Private Networks", M. Carugi, et al.  August
                  2001.  draft-ietf-ppvpn-requirements-02.txt.  Work
                  in progress.

   [VPSN]         VKompella et al, "Virtual Private Switched Network
                  Services over an MPLS Network" , (draft-vkompella-
                  ppvpn-vpsn-mpls-00.txt), work in progress, July
                  2001.




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   [TLS]          Lasserre et al, "Transparent VLAN Services over
                  MPLS". (draft-lasserre-tls-mpls-00.txt), work in
                  progress, August 2001.

   [VPLS]         Vkompella Lasserre et al, "Signaling Virtual Private
                  LAN Segments", work in progress, November 2001.

   [MARTINI-ENCAP]
                  Martini et al, "Encapsulation Methods for
                  Transport of Layer 2 Frames Over IP and MPLS
                  Networks", (draft-martini-l2circuit-encap-mpls-
                  04txt), work in progress, November 2001.

   [MARTINI-SIG]
                  Martini et al, "Transport of Layer 2 Frames
                  Over MPLS", (draft-martini-l2circuit-trans-mpls-
                  08.txt), work in progress, November 2001.

   [LDP]          "LDP Specification", L. Andersson, et al.  RFC
                  3036.January 2001.



 8.     Authors' Addresses

   10. Author Information

      Sunil Khandekar
      TiMetra Networks
      274 Ferguson Dr.
      Mountain View, CA 94043
      Tel.: +1 (650) 237-5105
      Email: sunil@timetra.com

      Vach Kompella
      TiMetra Networks
      274 Ferguson Dr.
      Mountain View, CA 94043
      Tel.: +1 (650) 237-5152
      Email: vkompella@timetra.com

      Joe Regan
      TiMetra Networks
      274 Ferguson Dr.
      Mountain View, CA 94043
      Tel.: +1 (650) 237-5103
      Email: jregan@timetra.com

      Nick Tingle
      TiMetra Networks
      274 Ferguson Dr.
      Mountain View, CA 94043
      Tel.: +1 (650) 237-5105

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      Email: sunil@timetra.com

      Pascal Menezes
      Terabeam
      14833 NE 87th St.
      Redmond, WA, USA
      Email:  Pascal.Menezes@Terabeam.com
      Phone: +1 (206) 686-2001

      Tom S. C. Soon
      SBC Technology Resources Inc.
      4698 Willow Road
      Pleasanton, CA 94588
      Tel.: +1 (925) 598-1227
      Email: sxsoon@tri.sbc.com

      Marc Lasserre
      Riverstone Networks
      5200 Great America Pkwy
      Santa Clara, CA 95054
      Tel.: +1 (408) 878-6550
      Email: marc@riverstonenet.com

      Giles Heron
      PacketExchange Ltd.
      The Truman Brewery
      91 Brick Lane
      LONDON E1 6QL
      United Kingdom
      Tel.: +44 7880 506185
      Email: giles@packetexchange.net

      Ron Haberman
      Masergy Communications
      2901 Telestar Ct.
      Falls Church, VA 22042
      Tel.: +1 (703) 846-0159
      Email: ronh@masergy.com


      Rick Wilder
      Masergy Communications
      2901 Telestar Ct.
      Falls Church, VA 22042
      Tel.: +1 (703) 846-0529
      Email: rwilder@masergy.com


      Kireeti Kompella
      Juniper Networks
      1194 N. Mathilda Ave
      Sunnyvale, CA 94089
      kireeti@juniper.net

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      Marty Borden
      Atrica, Inc.
      30 Shaker Lane
      Littleton, MA  01460
      mborden@atrica.com
















































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