





Internet Engineering Task Force (IETF)                           L. Yong
Request for Comments: 7173                               D. Eastlake 3rd
Category: Standards Track                                      S. Aldrin
ISSN: 2070-1721                                                   Huawei
                                                               J. Hudson
                                                                 Brocade
                                                                May 2014


     Transparent Interconnection of Lots of Links (TRILL) Transport
                           Using Pseudowires

Abstract

   This document specifies how to interconnect a pair of Transparent
   Interconnection of Lots of Links (TRILL) switch ports using
   pseudowires under existing TRILL and Pseudowire Emulation End-to-End
   (PWE3) standards.

Status of This Memo

   This is an Internet Standards Track document.

   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).  Further information on
   Internet Standards is available in 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/rfc7173.

Copyright Notice

   Copyright (c) 2014 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.




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Table of Contents

   1. Introduction.....................................................2
      1.1. Conventions Used in This Document...........................2
   2. PWE3 Interconnection of TRILL Switches...........................3
      2.1. PWE3 Type-Independent Details...............................3
      2.2. PPP PWE3 Transport of TRILL.................................4
   3. Security Considerations..........................................6
   Appendix A. Use of Other Pseudowire Types ..........................7
   Acknowledgements ...................................................8
   Normative References ...............................................9
   Informative References ............................................10

1.  Introduction

   The Transparent Interconnection of Lots of Links (TRILL) protocol
   [RFC6325] provides optimal pair-wise data frame routing without
   configuration in multi-hop networks with arbitrary topology.  TRILL
   supports multipathing of both unicast and multicast traffic.  Devices
   that implement TRILL are called TRILL switches or Routing Bridges
   (RBridges).

   Links between TRILL switches can be based on arbitrary link
   protocols, for example, PPP [RFC6361], as well as Ethernet [RFC6325].
   A set of connected TRILL switches together form a TRILL campus that
   is bounded by end stations and Layer 3 routers.

   This document specifies how to interconnect a pair of TRILL switch
   ports using a pseudowire under existing TRILL and PWE3 (Pseudowire
   Emulation End-to-End) standards.

1.1.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   [RFC2119].

   Acronyms used in this document include the following:

      IS-IS - Intermediate System to Intermediate System [IS-IS]

      MPLS - Multi-Protocol Label Switching

      PPP - Point-to-Point Protocol [RFC1661]

      PW - Pseudowire [RFC3985]




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      PWE3 - PW Emulation End-to-End

      RBridge - Routing Bridge, an alternative name for a TRILL switch

      TRILL - Transparent Interconnection of Lots of Links [RFC6325]

      TRILL Switch - A device implementing the TRILL protocol

2.  PWE3 Interconnection of TRILL Switches

   When a pseudowire is used to interconnect a pair of TRILL switch
   ports, a PPP [RFC4618] pseudowire is used as described below.  The
   pseudowire between such ports can be signaled [RFC4447] or manually
   configured.  In this context, the TRILL switch ports at the ends of
   the pseudowire are acting as native service processing (NSP) elements
   [RFC3985] and, assuming that the pseudowires are over MPLS or IP
   [RFC4023] networks, as label switched or IP routers at the TRILL
   switch ports.

   Pseudowires provide transparent transport, and the two TRILL switch
   ports appear directly interconnected with a transparent link.  With
   such an interconnection, the TRILL adjacency over the link is
   automatically discovered and established through TRILL IS-IS control
   messages [RFC7177].

   A pseudowire is carried over a packet switched network tunnel
   [RFC3985], for example, an MPLS or MPLS-TP label switched path tunnel
   in MPLS networks.  Either a signaling protocol or manual
   configuration can be used to configure a label switched path tunnel
   between two TRILL switch ports.  This application needs no additions
   to the existing pseudowire standards.

2.1.  PWE3 Type-Independent Details

   The sending pseudowire TRILL switch port SHOULD map the inner
   priority of the TRILL Data packets being sent to the Traffic Class
   field of the pseudowire label [RFC5462] so as to minimize the
   probability that higher priority TRILL Data packets will be discarded
   due to excessive TRILL Data packets of lower priority.

   TRILL IS-IS PDUs critical to establishing and maintaining adjacency
   (Hello and MTU PDUs) SHOULD be sent with the MPLS Traffic Class that
   calls for handling with the maximum priority.  Other TRILL IS-IS PDUs
   SHOULD be sent with the MPLS Traffic Class denoting the highest
   priority that is less than the maximum priority.  TRILL Data packets
   SHOULD be sent with appropriate MPLS Traffic Classes, typically
   mapped from the TRILL Data packet priority, such that TRILL Data
   packet Traffic Classes denote priorities less than the priorities



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   used for TRILL IS-IS PDUs.  This minimizes the probability of other
   traffic interfering with these important control PDUs and causing
   false loss of adjacency or other control problems.

   If a pseudowire supports fragmentation and reassembly (a feature that
   has received little or no deployment), then there is no reason to do
   TRILL MTU testing on it, and the pseudowire will not be a constraint
   on the TRILL campus-wide MTU size (Sz) (see Section 4.3.1 of
   [RFC6325]).  If the pseudowire does not support fragmentation (the
   more common case), then the available TRILL IS-IS packet payload size
   over the pseudowire (taking into account MPLS encapsulation with a
   control word) or some lower value, MUST be used in helping to
   determine MTU size (Sz) (see Section 5 of [RFC7180]).

   An intervening MPLS label switched router or similar packet switched
   network device has no awareness of TRILL.  Such devices will not
   change the TRILL Header hop count.

2.2.  PPP PWE3 Transport of TRILL

   For a PPP pseudowire (PW type = 0x0007), the two TRILL switch ports
   being connected are configured to form a pseudowire with PPP
   encapsulation [RFC4618].  After the pseudowire is established and
   TRILL use is negotiated within PPP, the two TRILL switch ports appear
   directly connected with a PPP link [RFC1661] [RFC6361].

   If pseudowire interconnection of two TRILL switch ports is signaled
   [RFC4447], the initiating TRILL switch port MUST attempt the
   connection setup with pseudowire type PPP (0x0007).

   Behavior for TRILL with a PPP pseudowire continues to follow that of
   TRILL over PPP as specified in Section 3 of [RFC6361].



















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   The following figures show what a TRILL Data packet and TRILL IS-IS
   packet look like over such a pseudowire in the MPLS case, assuming no
   TRILL Header extensions:

   +--------------------------------+
   |   Server MPLS Tunnel Label(s)  |  n*4 octets (4 octets per label)
   +--------------------------------+
   |           PW Label             |  4 octets
   +--------------------------------+
   |         Control Word           |  4 octets
   +--------------------------------+
   |      PPP Header 0x005d         |  2 octets
   +--------------------------------+
   |         TRILL Header           |  6 octets
   +--------------------------------+
   |    Destination MAC Address     |  6 octets
   +--------------------------------+
   |      Source MAC Address        |  6 octets
   +--------------------------------+
   |          Data Label            |  4 or 8 octets
   +--------------------------------+
   |         Payload Body           |  variable
   +--------------------------------+

                 Figure 1: TRILL Data Packet in Pseudowire

   "Data Label" is the VLAN Label or Fine-Grained Label [RFC7172] of the
   payload.

   +--------------------------------+
   |   Server MPLS Tunnel Label(s)  |  n*4 octets (4 octets per label)
   +--------------------------------+
   |           PW Label             |  4 octets
   +--------------------------------+
   |         Control Word           |  4 octets
   +--------------------------------+
   |      PPP Header 0x405d         |  2 octets
   +--------------------------------+
   |     Common IS-IS Header        |  8 octets
   +--------------------------------+
   | IS-IS PDU Type Specific Header |  variable
   +--------------------------------+
   |          IS-IS TLVs            |  variable
   +--------------------------------+

                Figure 2: TRILL IS-IS Packet in Pseudowire





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   The PPP Header fields (0x005d and 0x405d, respectively) for TRILL
   Data and IS-IS packets shown above are specified in [RFC6361].

3.  Security Considerations

   TRILL-level security mechanisms, such as the ability to use
   authentication with TRILL IS-IS PDUs [RFC6325], are not affected by
   link technology, such as the use of pseudowire links as specified in
   this document.

   Link security may be useful in improving TRILL campus security.
   TRILL is transported over pseudowires as TRILL over PPP over
   pseudowires, pseudowires are over MPLS or IP, and MPLS and IP are
   over some lower-level link technology.  Thus, link security below the
   TRILL level for a pseudowire link could be provided by PPP security,
   pseudowire security, MPLS or IP security, or security of the link
   technology supporting MPLS or IP.

   PPP TRILL security considerations are discussed in [RFC6361].  For
   security considerations introduced by carrying PPP TRILL links over
   pseudowires, see [RFC3985], which discusses the risks introduced by
   sending protocols that previously assumed a point-to-point link on a
   pseudowire built on a packet switched network (PSN).  However, the
   PPP layer in TRILL transport by pseudowire is somewhat vestigial and
   intended primarily as a convenient way to use existing PPP code
   points to identify TRILL Data packets and TRILL IS-IS packets.
   Furthermore, existing PPP security standards are arguably
   questionable in terms of current security criteria.  For these
   reasons, it is NOT RECOMMENDED to use PPP security in the transport
   of TRILL by pseudowires as specified in this document.

   It is RECOMMENDED that link security be provided at the layers
   supporting pseudowires transporting TRILL, that is, at the MPLS or IP
   layer or the link layer transporting MPLS or IP.

   For applications involving sensitive data, end-to-end security should
   always be considered, in addition to link security, to provide
   security in depth.  In this context, such end-to-end security should
   be between the end stations involved so as to protect the entire path
   to, through, and from the TRILL campus.

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









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Appendix A.  Use of Other Pseudowire Types

   This informational appendix briefly discusses the use of pseudowire
   types other than PPP for the transport of TRILL.

   The use of Ethernet pseudowires [RFC4448] was examined by the authors
   and would be possible without change to such pseudowires; however,
   this would require an additional 12 or 16 bytes per packet within the
   payload being transmitted over the pseudowire for a TRILL Data packet
   (Figure 3) and a TRILL IS-IS packet (Figure 4) over such an Ethernet
   pseudowire in the MPLS case, assuming no TRILL Header extensions
   (compare with Figures 1 and 2):

   +--------------------------------+
   |   Server MPLS Tunnel Label(s)  |  n*4 octets (4 octets per label)
   +--------------------------------+
   |          PW Label              |  4 octets
   +--------------------------------+
   |    Optional Control Word       |  4 octets
   +--------------------------------+
   |  TRILL Hop Dest. MAC Address   |  6 octets
   +--------------------------------+
   |  TRILL Hop Source MAC Address  |  6 octets
   +--------------------------------+
   |Optional VLAN and/or other tags |  variable
   +--------------------------------+
   |   TRILL Ethertype (0x22f3)     |  2 octets
   +--------------------------------+
   |         TRILL Header           |  6 octets
   +--------------------------------+
   |    Destination MAC Address     |  6 octets
   +--------------------------------+
   |      Source MAC Address        |  6 octets
   +--------------------------------+
   |          Data Label            |  4 or 8 octets
   +--------------------------------+
   |         Payload Body           |  variable
   +--------------------------------+

            Figure 3: TRILL Data Packet in Ethernet Pseudowire

   "Data Label" is the VLAN Label or Fine-Grained Label [RFC7172] of the
   payload.








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   +--------------------------------+
   |   Server MPLS Tunnel Label(s)  |  n*4 octets (4 octets per label)
   +--------------------------------+
   |          PW Label              |  4 octets
   +--------------------------------+
   |    Optional Control Word       |  4 octets
   +--------------------------------+
   |  TRILL Hop Dest. MAC Address   |  6 octets
   +--------------------------------+
   |  TRILL Hop Source MAC Address  |  6 octets
   +--------------------------------+
   |Optional VLAN and/or other tags |  variable
   +--------------------------------+
   | Layer 2 IS-IS Ethertype 0x22f4 |  2 octets
   +--------------------------------+
   |       Common IS-IS Header      |  8 octets
   +--------------------------------+
   | IS-IS PDU Type Specific Header |  variable
   +--------------------------------+
   |          IS-IS TLVs            |  variable
   +--------------------------------+

            Figure 4: TRILL IS-IS Packet in Ethernet Pseudowire

   It would also be possible to specify a new pseudowire type for TRILL
   traffic, but the authors feel that any efficiency gain over PPP
   pseudowires would be too small to be worth the complexity of adding
   such a specification.  Furthermore, using PPP pseudowire encoding
   means that any traffic dissector that understands TRILL PPP encoding
   [RFC6361] and PPP pseudowires [RFC4618] will automatically be able to
   recursively decode TRILL transported by pseudowire.

Acknowledgements

   Thanks for the valuable comments from the following, who are listed
   in alphabetic order:

      Stewart Bryant, Stephen Farrell, Brian Haberman, Christer
      Holmberg, Joel Jaeggli, Barry Leiba, Erik Nordmark, Yaron Sheffer,
      and Yaakov (J) Stein.











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Normative References

   [RFC1661]  Simpson, W., Ed., "The Point-to-Point Protocol (PPP)",
              STD 51, RFC 1661, July 1994.

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

   [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.

   [RFC4618]  Martini, L., Rosen, E., Heron, G., and A. Malis,
              "Encapsulation Methods for Transport of PPP/High-Level
              Data Link Control (HDLC) over MPLS Networks", RFC 4618,
              September 2006.

   [RFC5462]  Andersson, L. and R. Asati, "Multiprotocol Label Switching
              (MPLS) Label Stack Entry: "EXP" Field Renamed to "Traffic
              Class" Field", RFC 5462, February 2009.

   [RFC6325]  Perlman, R., Eastlake 3rd, D., Dutt, D., Gai, S., and A.
              Ghanwani, "Routing Bridges (RBridges): Base Protocol
              Specification", RFC 6325, July 2011.

   [RFC6361]  Carlson, J. and D. Eastlake 3rd, "PPP Transparent
              Interconnection of Lots of Links (TRILL) Protocol Control
              Protocol", RFC 6361, August 2011.

   [RFC7172]  Eastlake 3rd, D., Zhang, M., Agarwal, P., Perlman, R., and
              D. Dutt, "Transparent Interconnection of Lots of Links
              (TRILL): Fine-Grained Labeling", RFC 7172, May 2014.

   [RFC7180]  Eastlake 3rd, D., Zhang, M., Ghanwani, A., Manral, V., and
              A. Banerjee, "Transparent Interconnection of Lots of Links
              (TRILL): Clarifications, Corrections, and Updates",
              RFC 7180, May 2014.














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Informative References

   [IS-IS]    ISO/IEC 10589:2002, Second Edition, "Information
              technology -- Telecommunications and information exchange
              between systems -- Intermediate System to Intermediate
              System intra-domain routeing information exchange protocol
              for use in conjunction with the protocol for providing the
              connectionless-mode network service (ISO 8473)", 2002.

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

   [RFC4023]  Worster, T., Rekhter, Y., and E. Rosen, Ed.,
              "Encapsulating MPLS in IP or Generic Routing Encapsulation
              (GRE)", RFC 4023, March 2005.

   [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.

   [RFC7177]  Eastlake 3rd, D., Perlman, R., Ghanwani, A., Yang, H., and
              V. Manral, "Transparent Interconnection of Lots of Links
              (TRILL): Adjacency", RFC 7177, May 2014.




























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Authors' Addresses

   Lucy Yong
   Huawei Technologies
   5340 Legacy Drive
   Plano, TX  75024
   USA

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


   Donald E. Eastlake 3rd
   Huawei Technologies
   155 Beaver Street
   Milford, MA  01757
   USA

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


   Sam Aldrin
   Huawei Technologies
   2330 Central Expressway
   Santa Clara, CA  95050
   USA

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


   Jon Hudson
   Brocade
   130 Holger Way
   San Jose, CA  95134
   USA

   Phone: +1-408-333-4062
   EMail: jon.hudson@gmail.com











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