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RFC 6361

Proposed STD
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PPP Transparent Interconnection of Lots of Links (TRILL) Protocol Control Protocol


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Internet Engineering Task Force (IETF)                        J. Carlson
Request for Comments: 6361                                   WorkingCode
Category: Standards Track                                D. Eastlake 3rd
ISSN: 2070-1721                                                   Huawei
                                                             August 2011

   PPP Transparent Interconnection of Lots of Links (TRILL) Protocol
                            Control Protocol


   The Point-to-Point Protocol (PPP) defines a Link Control Protocol
   (LCP) and a method for negotiating the use of multiprotocol traffic
   over point-to-point links.  This document describes PPP support for
   the Transparent Interconnection of Lots of Links (TRILL) Protocol,
   allowing direct communication between Routing Bridges (RBridges) via
   PPP links.

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

Copyright Notice

   Copyright (c) 2011 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
   ( 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
   2. PPP TRILL Negotiation ...........................................3
      2.1. TNCP Packet Format .........................................3
      2.2. TNP Packet Format ..........................................4
      2.3. TLSP Packet Format .........................................5
   3. TRILL PPP Behavior ..............................................5
   4. Security Considerations .........................................6
   5. IANA Considerations .............................................6
   6. References ......................................................7
      6.1. Normative References .......................................7
      6.2. Informative References .....................................7
   7. Acknowledgements ................................................8

1.  Introduction

   The TRILL Protocol [RFC6325] defines a set of mechanisms used to
   communicate between RBridges.  These devices can bridge together
   large 802 networks using link-state protocols in place of the
   traditional spanning tree mechanisms [RFC5556].

   Over Ethernet, TRILL uses two separate Ethertypes to distinguish
   between encapsulation headers, which carry user data, and link-state
   messages, which compute network topology using a protocol based on
   [IS-IS] [RFC6326].  These two protocols must be distinguished from
   one another, and segregated from all other traffic.

   In a network where PPP [RFC1661] is used to interconnect routers
   (often over telecommunications links), it may be advantageous to be
   able to bridge between Ethernet segments over those PPP links, and
   thus integrate remote networks with an existing TRILL cloud.  The
   existing Bridging Control Protocol (BCP) [RFC3518] allows direct
   bridging of Ethernet frames over PPP.  However, this mechanism is
   inefficient and inadequate for TRILL, which can be optimized for use
   over PPP links.

   To interconnect these devices over PPP links, three protocol numbers
   are needed, and are reserved as follows:

      Value (in hex)  Protocol Name
      --------------  -------------------------------------
       005d           TRILL Network Protocol (TNP)
       405d           TRILL Link State Protocol (TLSP)
       805d           TRILL Network Control Protocol (TNCP)

   The usage of these three protocols is described in detail in the
   following section.

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

2.  PPP TRILL Negotiation

   The TRILL Network Control Protocol (TNCP) is responsible for
   negotiating the use of the TRILL Network Protocol (TNP) and TRILL
   Link State Protocol (TLSP) on a PPP link.  TNCP uses the same option
   negotiation mechanism and state machine as described for LCP
   (Section 4 of [RFC1661]).

   TNCP packets MUST NOT be exchanged until PPP has reached the Network-
   Layer Protocol phase.  Any TNCP packets received when not in that
   phase MUST be silently ignored.

   The encapsulated network layer data, carried in TNP packets, and
   topology information, carried in TLSP packets, MUST NOT be sent
   unless TNCP is in the Opened state.  If a TNP or TLSP packet is
   received when TNCP is not in the Opened state and LCP is in the
   Opened state, an implementation MUST silently discard the unexpected
   TNP or TLSP packet.

2.1.  TNCP Packet Format

   Exactly one TNCP packet is carried in the PPP Information field, with
   the PPP Protocol field set to hex 805d (TNCP).  A summary of the TNCP
   packet format is shown below.  The fields are transmitted from left
   to right.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      |     Code      |  Identifier   |            Length             |
      |    Data ...


      Only LCP Code values 1 through 7 (Configure-Request,
      Configure-Ack, Configure-Nak, Configure-Reject, Terminate-Request,
      Terminate-Ack, and Code-Reject) are used.  All other codes SHOULD
      result in a TNCP Code-Reject reply.

   Identifier and Length

      These are as documented for LCP.

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      This field contains data formatted as described in Section 5 of
      [RFC1661].  Codes 1-4 use Type-Length-Data sequences, Codes 5
      and 6 use uninterpreted data, and Code 7 uses a Rejected-Packet,
      all as described in [RFC1661].

   Because no Configuration Options have been defined for TNCP,
   negotiating the use of the TRILL Protocol with IS-IS for the link
   state protocol is the default when no options are specified.  A
   future document may specify the use of Configuration Options to
   enable different TRILL operating modes, such as the use of a
   different link state protocol.

2.2.  TNP Packet Format

   When TNCP is in the Opened state, TNP packets are sent by setting the
   PPP Protocol field to hex 005d (TNP) and placing TRILL-encapsulated
   data representing exactly one encapsulated packet in the PPP
   Information field.

   A summary of this format is provided below:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      | V | R |M|Op-Length| Hop Count | Egress (RB2) Nickname         |
      | Ingress (RB1) Nickname        | Inner Destination MAC ...

   This is identical to the TRILL Ethernet format (Section 4.1 of
   [RFC6325], "Ethernet Data Encapsulation"), except that the Outer MAC
   (Media Access Control) header and Ethertype are replaced by the PPP
   headers and Protocol Field, and the Ethernet Frame Check Sequence
   (FCS) is not present.  Both user data and End-Station Address
   Distribution Information (ESADI) packets are encoded in this format.

   The PPP FCS follows the encapsulated data on links where the PPP FCS
   is in use.

   Unlike the TRILL Ethernet encapsulation, PPP nodes do not have MAC
   addresses, so no outer MAC is present.  (High-Level Data Link Control
   (HDLC) addresses MAY be present in some situations; such usage is
   outside the scope of this document.)

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2.3.  TLSP Packet Format

   When TNCP is in the Opened state, TLSP packets are sent by setting
   the PPP Protocol field to hex 405d (TLSP) and placing exactly one
   IS-IS Payload (Section 4.2.3 of [RFC6325], "TRILL IS-IS Frames") in
   the PPP Information field.

   Note that point-to-point IS-IS links have only an arbitrary circuit
   ID, and do not use MAC addresses for identification.

3.  TRILL PPP Behavior

   1. On a PPP link, TRILL always uses point-to-point (P2P) Hellos.
      There is no need for TRILL-Hello frames, nor is per-port
      configuration necessary.  P2P Hello messages, per "Point-to-Point
      IS to IS hello PDU" (Section 9.7 of [IS-IS]), do not use Neighbor
      IDs in the same manner as on Ethernet.  However, per
      Section of [RFC6325], the three-way IS-IS handshake using
      extended circuit IDs is required on point-to-point links, such
      as PPP.

   2. RBridges are never appointed forwarders on PPP links.  If an
      implementation includes BCP [RFC3518], then it MUST ensure that
      only one of BCP or TNCP is negotiated on a link, and not both.  If
      the peer is an RBridge, then there is no need to pass
      unencapsulated frames, as the link can have no TRILL-ignorant peer
      to be concerned about.  If the peer is not an RBridge, then TNCP
      negotiation fails and TRILL is not used on the link.

   3. An implementation that has only PPP links might have no
      Organizationally Unique Identifier (OUI) that can form an IS-IS
      System ID.  Resolving that issue is outside the scope of this
      document; however, it is strongly RECOMMENDED that all TRILL
      implementations have at least one zero-configuration mechanism to
      obtain a valid System ID.  Refer to ISO/IEC 10589 [IS-IS]
      regarding System ID uniqueness requirements.

   4. TRILL MTU-probe and TRILL MTU-ack messages (Section 4.3.2 of
      [RFC6325]) are not needed on a PPP link.  Implementations MUST NOT
      send MTU-probe messages and SHOULD NOT reply to these messages.
      The MTU computed by LCP SHOULD be used instead.  Negotiating an
      LCP MTU of at least 1524, to allow for an inner Ethernet payload
      of 1500 octets, is RECOMMENDED.

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4.  Security Considerations

   Existing PPP and IS-IS security mechanisms may play important roles
   in a network of RBridges interconnected by PPP links.  At the TRILL
   IS-IS layer, the IS-IS authentication mechanism [RFC5304] [RFC5310]
   prevents fabrication of link-state control messages.

   Not all implementations need to include specific security mechanisms
   at the PPP layer, for example if they are designed to be deployed
   only in cases where the networking environment is trusted or where
   other layers provide adequate security.  A complete enumeration of
   possible deployment scenarios and associated threats and options is
   not possible and is outside the scope of this document.  For
   applications involving sensitive data, end-to-end security should
   always be considered in addition to link security to provide security
   in depth.

   However, in case a PPP layer authentication mechanism is needed to
   protect the establishment of a link and identify a link with a known
   peer, implementation of the PPP Challenge Handshake Authentication
   Protocol (CHAP) [RFC1994] is RECOMMENDED.  Should greater flexibility
   than that provided by CHAP be required, the Extensible Authentication
   Protocol (EAP) [RFC3748] is a good alternative.

   If TRILL-over-PPP packets also require confidentiality, the PPP
   Encryption Control Protocol (ECP) link encryption mechanisms
   [RFC1968] can protect the confidentiality and integrity of all
   packets on the PPP link.

   And when PPP is run over tunneling mechanisms, such as the Layer Two
   Tunneling Protocol (L2TP) [RFC3931], tunnel security protocols may be

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

5.  IANA Considerations

   IANA has assigned three PPP Protocol field values, 005d, 405d, and
   805d, as described in Section 1 of this document.

   IANA has created a new "PPP TNCP Configuration Option Types" registry
   in the PPP-Numbers registry, using the same format as the existing
   "PPP LCP Configuration Option Types" registry.

   All TNCP Configuration Option Types except 0 are "Unassigned" and
   available for future use, based on "IETF Review", as described in
   BCP 26 [RFC5226].  Option 0 is allocated for use with Vendor-Specific
   Options, as described in [RFC2153].

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6.  References

6.1.  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.

   [RFC5226]   Narten, T. and H. Alvestrand, "Guidelines for Writing an
               IANA Considerations Section in RFCs", BCP 26, RFC 5226,
               May 2008.

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

6.2.  Informative References

   [IS-IS]     International Organization for Standardization,
               "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)", ISO/IEC
               10589:2002, Second Edition, November 2002.

   [RFC1968]   Meyer, G., "The PPP Encryption Control Protocol (ECP)",
               RFC 1968, June 1996.

   [RFC1994]   Simpson, W., "PPP Challenge Handshake Authentication
               Protocol (CHAP)", RFC 1994, August 1996.

   [RFC2153]   Simpson, W., "PPP Vendor Extensions", RFC 2153, May 1997.

   [RFC3518]   Higashiyama, M., Baker, F., and T. Liao, "Point-to-Point
               Protocol (PPP) Bridging Control Protocol (BCP)",
               RFC 3518, April 2003.

   [RFC3748]   Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
               Levkowetz, Ed., "Extensible Authentication Protocol
               (EAP)", RFC 3748, June 2004.

   [RFC3931]   Lau, J., Ed., Townsley, M., Ed., and I. Goyret, Ed.,
               "Layer Two Tunneling Protocol - Version 3 (L2TPv3)",
               RFC 3931, March 2005.

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   [RFC5304]   Li, T. and R. Atkinson, "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.

   [RFC5556]   Touch, J. and R. Perlman, "Transparent Interconnection of
               Lots of Links (TRILL): Problem and Applicability
               Statement", RFC 5556, May 2009.

   [RFC6326]   Eastlake, D., Banerjee, A., Dutt, D., Perlman, R., and A.
               Ghanwani, "Transparent Interconnection of Lots of Links
               (TRILL) Use of IS-IS", RFC 6326, July 2011.

7.  Acknowledgements

   The authors thank Jari Arkko, Stewart Bryant, Ralph Droms, Linda
   Dunbar, Adrian Farrel, Stephen Farrell, Radia Perlman, Mike Shand,
   and William A. Simpson for their comments and help.

Authors' Addresses

   James Carlson
   25 Essex Street
   North Andover, MA 01845 USA

   Phone: +1-781-301-2471

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

   Phone: +1-508-333-2270