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Versions: 00 01                                                         
TRILL Working Group                                            Lucy Yong
INTERNET-DRAFT                                           Donald Eastlake
Intended status: Informational                                Sam Aldrin
                                                          Huawei R&D USA
                                                              Jon Hudson
Expires: September 9, 2012                                March 10, 2012

       Transparent Interconnection of Lots of Links (TRILL) over
                           MPLS Pseudo Wires


   This informational document describes ways to interconnect TRILL
   RBridges by using MPLS Pseudo Wire (PW) services with existing TRILL
   and MPLS standards so as to form a unified TRILL campus.

Status of This Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Distribution of this document is unlimited. Comments should be sent
   to the TRILL working group mailing list <rbridge@postel.org>.

   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-

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

   The list of current Internet-Drafts can be accessed at

   The list of Internet-Draft Shadow Directories can be accessed at

D. Eastlake, et al                                              [Page 1]

INTERNET-DRAFT                                        TRILL over MPLS PW

Table of Contents

      1. Introduction............................................3
      1.1 Conventions used in this document......................3

      2. Use Cases...............................................4
      2.1 Point-To-Point Interconnection.........................4
      2.1.1 Direct Point-to-Point................................5
      2.1.2 Provider Point-to-Point Service......................5
      2.2 Multi-Access Link Interconnection......................6

      3. RBridge Behavior for MPLS Pseudo Wire...................9

      4. IANA Considerations....................................10
      5. Security Considerations................................10
      6. Acknowledgements.......................................10
      7. Normative References...................................11
      8. Informative References.................................12

D. Eastlake, et al                                              [Page 2]

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1. Introduction

   The IETF TRILL (Transparent Interconnection of Lots of Links)
   standard [RFC6325] [RFC6326] provides optimal pair-wise data frame
   forwarding without configuration in multi-hop networks with arbitrary
   topology and link technology, and supports multipathing of both
   unicast and multicast traffic. TRILL enables a new method to
   construct a campus or data center network. Devices that implement
   TRILL are called RBridges (Routing Bridges) or TRILL Switches.

   This document describes the use of MPLS Pseudo Wire or VPLS links by

1.1 Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

   Acronyms used in this document include the following:

      AC - Attachment Circuit

      IS-IS - Intermediate System to Intermediate System

      MPLS - Multi-Protocol Label Switching

      PE - Provider Edge

      PPP - Point-to-Point Protocol

      PW - Pseudo Wire

      QoS - Quality of Service

      RB - RBridge

      RBridge - Routing Bridge

      TRILL - Transparent Interconnection of Lots of Links

      TRILL Switch - An alternative term for an RBridge

      VPLS - Virtual Private LAN Service

      VSI - Virtual Service Instance

D. Eastlake, et al                                              [Page 3]

INTERNET-DRAFT                                        TRILL over MPLS PW

2. Use Cases

   TRILL campuses at different locations may interconnect by networks
   that are implemented with different technologies to form a unified
   RBridge campus. This section describes use cases assuming that
   IP/MPLS technology is available. From the MPLS network view, a pair
   of RBridges can be directly connected with a pseudo wire or an
   RBridge can act as a Customer Edge device that connects to a Provider
   Edge device via an attachment circuit. RBridge ports [RFC6325], by
   default, support both point-to-point links and multi-access links.

   Section 2.1 describes point-to-point links, i.e. TRILL over an
   Ethernet or PPP point-to-point link that is over an MPLS network.
   Section 2.2 describes TRILL over a bridged LAN or equivalent that is
   implemented by MPLS/VPLS.

2.1 Point-To-Point Interconnection

   Either an Ethernet or PPP link over an MPLS network interconnets two
   RBridge ports. This can be either a direct pseudo wire between the
   RBridges or by attachment circuits from each RBridge port to Provider
   Edge devices that provide a transparent tunnel between the provider
   edge attachment points.

   MPLS already supports many pseudo wire transport encapsulations
   [RFC4446].  Two types of TRILL links between RBridges have been
   standardized are Ethernet [RFC6325] and PPP [RFC6361]. Pseudo wire
   encapsulations for these two interfaces are specified in [RFC4448]
   and [RFC4618], respectively.

   The method described in 2.1.1 below is typically suitable when the
   TRILL and MPLS facilities have common management while the method
   described in 2.1.2 is typically suittable when the TRILL and MPLS
   facilities are separately managed.  In the case of different
   management, the core MPLS operator can sell a VPWS service to an
   RBridge operator.

   In both cases, the MPLS label switched routers involved need no
   awareness of TRILL.

   A pseudo wire may cross multiple MPLS domains [RFC5659]. In these
   cases, RBridges may be considered to connect to T-PEs and it works in
   the same way as a single domain. The MPLS network can provide
   transport resiliency for a pseudo wire. The dual homing (two
   attachment circuits) can be used for attachment circuit protection.
   In this case, two TRILL links are established; RBridges can perform
   load balancing over two links.

D. Eastlake, et al                                              [Page 4]

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2.1.1 Direct Point-to-Point

   Two RBridge ports can be connected directly by an MPLS pseudo wire.
   This implies that the RBridges, which are TRILL routers, are also
   acting as label switched routers. The pseudo wire can be either
   Ethernet over MPLS or PPP over MPLS but PPP over MPLS is recommended
   because it saves 16 bytes per frame. The pseudo wire between two
   RBridge ports can be auto-configured [RFC4447] or manually
   configured; the two RBridges then appear directly interconnected with
   a transparent link.

   (Technically speaking, it is possible to create a specially
   designated TRILL encapsulated pseudo wire for point-to-point TRILL
   over MPLS. However, the authors think that this is not worth the
   effort in this case because of available technologies, particularly
   the highly-efficient PPP link technology.)

   From a customer/provider point of view, this can also be though of as
   shown in the following diagram:

               *---------*                        *---------*
               | TRILL   |<---- TRILL Link------->| TRILL   |
               | Site A  |    (Customer Layer)    | Site B  |
               |         |                        |         |
               |     +-------+     +---+      +-------+     |
               |     | RB/PE |-----| P |------| PE/RB |     |
               |     +-------+     +---+      +-------+     |
               |         |<---------PW ---------->|         |
               |         |    (Provider Layer)    |         |
               *---------*                        *---------*
                         {      MPLS Network      }

              {               One RBridge Campus             }

   The interworking between the RBridge network and the MPLS network is
   within the combined TRILL/MPLS device. This has a similar
   architecture to MPLS/VPLS [RFC4762].

2.1.2 Provider Point-to-Point Service

   Two RBridge ports may also be connected by attachment circuits (ACs)
   to Provider Edge (PE) devices that are part of a typically separately
   managed provider network. The provider network then provides a
   transparent path between these attachment circuits, connecting the
   RBridge ports. The following diagram illustrates this arrangement:

D. Eastlake, et al                                              [Page 5]

INTERNET-DRAFT                                        TRILL over MPLS PW

                     <-------------TRILL Link------------>
           *--------*       <----------PW---------->      *--------*
           | TRILL  |                                     | TRILL  |
           | Site A |                                     | Site B |
           |      +--+  AC  +----+   +---+   +----+  AC  +--+      |
           |      |RB|------| PE |---| P |---| PE |------|RB|      |
           |      +--+      +----+   +---+   +----+      +--+      |
           |        |       {   Provider Network   }      |        |
           *--------*                                     *--------*
           {                   One RBridge Campus                  }

   If the attachment circuits are Ethernet, the two PEs would be
   configured to form a pseudo wire with Ethernet encapsulation
   [RFC4448]. This pseudo wire can be auto-configured [RFC4447] or
   manually configured; the two RBridges then appear directly
   interconnected with an Ethernet link. The provider edge devices
   SHOULD use the Raw mode and non-service-delimiting, which provides a
   transparent Ethernet transport.

   If the attachment circuits are PPP link type, the two PEs must be
   configured to form a PW with PPP encapsulation [RFC4618]. After the
   pseudo wire is established between two PEs, the two RBridges then
   appear directly connected with a PPP link. The PPP link configuration
   will be more efficient than the Ethernet point-to-point
   configuration; it saves about 16 bytes per frame by replacing the
   TRILL Outer.MacDA, Outer.MacSA, Outer.VLAN, and outer Ethertype with
   a PPP code point [RFC6361].

   In both case, the pseudo wire provides transparent transport between
   attachment circuits. The TRILL link and the connectivity over that
   link is automatically discovered and established through TRILL IS-IS
   control messages.

2.2 Multi-Access Link Interconnection

   Multiple RBridges may interconnect via an [802.1Q] Bridged LAN that
   acts as a hub. The bridged LAN simply forwards on the outer Ethernet
   header of the TRILL over Ethernet frames. This configuration creates
   what appears to each connected RBridge as a multi-access link. In
   other words, each RBridge connecting to a bridged LAN normally has
   connectivity to every other RBridge connecting to the same bridged

   MPLS/VPLS can provide the same capability when multiple parts of an
   RBridge campus are interconnected over an IP/MPLS network and make
   each RBridge attaching to the VPLS appear as having a multi-access
   TRILL link. The diagram below shows one RBridge campus is split
   between three different sites and the use of MPLS/VPLS for RBridge

D. Eastlake, et al                                              [Page 6]

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   interconnection. Ethernet attachment circuits and pseudo wires are

       *-------*      ...........................     *-------*
       |       |      .             MPLS/VPLS   .     |       |
       | TRILL |AC +----+       PW           +----+ AC| TRILL |
       | Site 1+---|VSI ********************** VSI|---+ Site 2|
       |       |   | PE *****            ***** PE |   |       |
       |       |   +----+    ****    ****    +----+   |       |
       |       |      .         +*--*+          .     *-------*
       *-------*      ..........|VSI |...........
                                | PE |
                             |  TRILL  |
                             |  Site 3 |
                             |         |

   One VPLS instance is configured on three Provider Edge (PE) devices
   and the pseudo wires are configured for the VPLS instance. Each
   RBridge Site connects to the VSI on a PE via an attachment circuit.
   The VSI on a PE forwards TRILL frames based on the outer Ethernet
   header of the frames [RFC6325]. Either BGP [RFC4761] or LDP [RFC4762]
   protocol can be used to automatically construct the VPLS instance on
   the PEs.

   The choice of three VSIs and three singly connected sites was for
   illustrative purposes. There could be two or more than three.
   Furthermore, each TRILL site could have multiple connections to the
   VPLS network and/or direct connection via other technologies or VPLS
   networks to one or more of the other sites. TRILL sorts all this out
   and router properly.

   A PE may connect to several different RBridge campuses that belong to
   different customers. Separated VPLS instances are configured for
   individual customers and customer traffic is isolated by VPLS
   instance. The PE treats an RBridge as a generic Ethernet customer
   devices and has no awareness of TRILL.  The outer Ethernet MAC of
   TRILL frames may be either a next-hop RBridge MAC address (for
   unicast frames) or one of TRILL defined multicast addresses (ALL-IS-
   IS-RBridges and All-RBridges) [RFC6325]. The VSI at each PE learns
   the source MAC addresses on each VSI interface and forward the frame
   based on the destination MAC. For the multicast frames, the VSI
   replicates the frames to all pseudo wires it associates. If a VPLS is
   configured with some optimization capability [VPLS-BCAST], the
   multicast frames can be delivered over a point-to-multipoint pseudo
   wire while unicast frames are carried over a point-to-point pseudo

D. Eastlake, et al                                              [Page 7]

INTERNET-DRAFT                                        TRILL over MPLS PW


   The scenario above can also be extended to multiple RBridge
   interconnections when a device serves both the RBridge and PE
   functions, similarly to the case in Section 2.1.2 and 2.1.1 above.

   Note: If the customer devices associated with one VPLS instances
   happen to include some RBridges and some end stations or IEEE 802.1Q
   bridges providing paths to end stations, TRILL will, by default, be
   able to handle this by providing both through service and end station
   service. However, the end station addresses will be visible to the
   VPLS instance. If, in such a case, all the RBridge ports connected to
   the VPLS are configured as trunk ports (see Section 4.9.2 of
   [RFC6325]), then they will not provide any end station service.

D. Eastlake, et al                                              [Page 8]

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3. RBridge Behavior for MPLS Pseudo Wire

   This section describes RBridge behaviors for TRILL Ethernet or TRILL
   PPP links over MPLS pseudo wire (PW) as described in Sections 2.1.

   1. For two RBridge ports connecting via a PPP pseudo wire, the ports
      MUST be configured as IS-IS point-to-point because there are no
      subnetwork point of attachment (SNPA/MAC) addresses of the end
      points at the PPP protocol layer. Thus TRILL will use IS-IS P2P
      Hellos that, as described in "Point-to-Point IS to IS Hello PDU"
      (section 9.7 of [IS-IS]), do not use Neighbor TLVs or require
      SNPAs. However, as described section of [RFC6325], three-
      way IS-IS handshake using extended circuit IDs is required.

   2. Any MPLS forwarder within an MPLS label switched path does not
      change the TRILL Header Hop Count. RBridges are not aware of the
      packet forwarders in with the MPLS network.

   3. If it is desired for MPLS label switched routers to perform QoS in
      the same way as RBridges do, an Ethernet path MUST be used and
      RBridges MUST be configured to send an Outer.VLAN tag on the
      RBridge port leading to the pseudo wire. The PE can then copy the
      priority value from the Outer.VLAN tag to the COS field of the
      pseudo wire label prior to the forwarding [RFC5462].

   4. TRILL MTU-probe and TRILL MTU-ack messages (section 4.3.2 of
      [RFC6325]) are not needed on a pseudo wire link.  Implementations
      MUST NOT send MTU-probe and SHOULD NOT reply to these messages.
      The MTU pseudo wire interface parameter SHOULD be used instead.
      PE MUST configure the MTU size as the originating RBridges Size
      specified in Section 4.3.1 of [RFC6325].

D. Eastlake, et al                                              [Page 9]

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4. IANA Considerations

   No IANA action is required by this document. RFC Editor: Please
   remove this section before publication.

5. Security Considerations

   The IS-IS authentication mechanism [RFC5304] [RFC5310], at the TRILL
   IS-IS layer, can be used to prevent fabrication of link-state control
   messages over TRILL links including those discussed in this document.

   For general TRILL protocol security considerations, see [RFC6325].

   Use cases in which the path between RBridges transits a provider
   network under separate administration may represent a substantial
   increase in the threat of observation, deletion, modification, or
   insertion of data or control information. Under such circumstances
   consideration should be give to the use of security at the TRILL link
   level, such as [802.1AE] if the path between the RBridge ports is
   Ethernet or security as suggested in [RFC6361] if that path is PPP.

6. Acknowledgements

   The authors sincerely acknowledge the contributions of Ben Mack-Crane
   and Sue Hares.

D. Eastlake, et al                                             [Page 10]

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7. Normative References

   [RFC2119] - Bradner, S., "Key words for use in RFCs to Indicate
         Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4446] Martini, L., "IANA Allocations for Pseudowire Edge to
         EdgeEmulation (PWE3)", BCP 116, RFC 4446, April 2006.

   [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.

   [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.

   [RFC4618] Martini, L., "Encapsulation Methods for Transport of
         PPP/High-Level Data Link Control (HDLC) over MPLS Networks",
         BCP 116, RFC 4618, September 2006.

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

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

   [RFC2119] S. Bradner, "Key words for use in RFCs to Indicate
         Requirement Levels," BCP 14 and RFC 2119, March 1997

   [RFC5304] Li, T. and Atkinson, R, "IS-IS Cryptographic
         Authentication," RFC 5304, October 2008

   [RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
         and M. Fanto, "IS-IS Generic Cryptographic Authentication", RFC
         5310, February 2009

   [RFC5462] Andersson, L. and Asati, R., "Multiprotocol Label Switching
         (MPLS) Label Stack entry: "Exp" Field Rename to "Traffic Class"
         Field", RFC5462, February 2009

   [RFC5659] Bocci, M and Bryant, S, "An Architecture for Multi-Segment
         Pseudowire Emulation Edge-to-Edge", RFC 5659, October2009.

   [RFC6325] Perlman, R., Eastlake 3rd, D., Dutt, D., Gai, S., and A.
         Ghanwani, "Routing Bridges (RBridges): Base Protocol
         Specification", RFC6325, July 2011.

   [RFC6326] Eastlake 3rd, D., Banerjee, A., Dutt, D., Perlman, R.,

D. Eastlake, et al                                             [Page 11]

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         andGhanwani, A. "Transparent Interconnection of Lots of
         Links(TRILL) Use of IS-IS", RFC6326, July 2011.

   [RFC6361] Carlson, J., and D. Eastlake, "PPP Transparent
         Interconnection of Lots of Links (TRILL) Protocol Control
         Protocol", RFC6361, August 2011.

8. Informative References

   [802.1AE] "IEEE Standard for Local and metropolitan area networks /
         Media Access Control (MAC) Security", 802.1AE-2006, 18 August

   [802.1Q] IEEE 802.1, "IEEE Standard for Local and metropolitan area
         networks - Virtual Bridged Local Area Networks", IEEE Std
         802.1Q-2011, May 2011.

   [IS-IS] International Organization for Standardization, "Intermediate
         system to Intermediate system intra-domain routing information
         exchange protocol for use in conjunction with the protocol for
         providing the connectionless-mode Network Service (ISO 8473)",
         ISO/IEC10589:2002, Second Edition, Nov 2002

   [VPLS-BCAST] Delord, S, and Key, R., "Extension to LDP-VPLS for
         Ethernet Broadcast and Multicast", draft-ietf-l2vpn-ldp-vpls-
         broadcast-exten-02, work in progress, 2011.

D. Eastlake, et al                                             [Page 12]

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Authors' Addresses

   Lucy Yong
   Huawei R&D USA
   5340 Legacy Drive
   Plano, TX 75025

   Phone: +1-469-227-5837
   Email: lucy.yong@huawei.com

   Donald E. Eastlake, 3rd
   Huawei R&D USA
   155 Beaver Street
   Milford, MA 01757 USA

   Phone: +1-508-333-2270
   Email: d3e3e3@gmail.com

   Sam Aldrin
   Huawei R&D USA
   2330 Central Expressway
   Santa Clara, CA 95050

   Phone: +1-408-330-4517
   Email: sam.aldrin@huawei.com

   Jon Hudson
   130 Holger Way
   San Jose, CA 95134

   Phone: +1-408-333-4062

D. Eastlake, et al                                             [Page 13]

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D. Eastlake, et al                                             [Page 14]