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Versions: 00 01 02                                                      
PPP Working Group                                          Pat R. Calhoun
INTERNET DRAFT                                     Sun Microsystems, Inc.
Category: Informational                                        Ken Peirce
Title: draft-ietf-pppext-l2tp-mpls-01.txt                3Com Corporation
Date: July 1998

                  Layer Two Tunneling Protocol "L2TP"
                Multi-Protocol Label Switching Extension

Status of this Memo

   This document is an Internet-Draft. 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.  Internet-Drafts may be updated, replaced, or obsoleted by
   other documents at any time.  It is not appropriate to use Internet-
   Drafts as reference material or to cite them other than as a
   ``working draft'' or ``work in progress.''

   To learn the current status of any Internet-Draft, please check the
   1id-abstracts.txt listing contained in the Internet-Drafts Shadow
   Directories on ftp.ietf.org, nic.nordu.net, ftp.nisc.sri.com, or


   The L2TP document [1] defines the base protocol which describes the
   method of tunneling PPP [2] data. The L2TP base protocol does not
   address any MPLS extensions.

   The goal of MPLS is to speed forwarding of packets by reducing the
   lookup required in routing. This draft proposes a method to allow
   L2TP Data Sessions to be assigned a Multi-Protocol Label.

Table of Contents

      1.0 Introduction
      1.1 Conventions

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      2.0 Multi-Protocol Label Switching
      2.1 Multi-Protocol Label AVP
      2.2 Error Reporting
      3.0 References
      4.0 Authors' Addresses

1.0 Introduction

   The L2TP protocol specification does not discuss Multi-Protocol Label
   Switching(MPLS) [4] in any way. This document will describe how two
   L2TP peers can negotiate an Multi-Protocol Label (Mlabel) for an L2TP
   session. This will provide either the LNS or LAC with an Mlabel with
   which to initiate the creation of an MPLS Label Switched Path to the
   peer. The application of an MPLS should speed the forwarding of the
   L2TP packets by reducing the header analysis/lookup.

   This L2TP extension allows individual sessions within a tunnel to
   have their own Mlabel.

   Note that this document does not cover the negotiation of the LSP.
   This is a function of the Label Distribution Protocol which has not
   yet been determined. However, having the L3 address and it's
   contextually meaningful Mlabel should provide the components needed
   to create the LSP regardless of the final LDP design.

   The mechanism defined in this document assumes that the Tunnel
   Initiator determines what the user's appropriate label is and sends
   the value in either the ICRQ or OCRQ messages.

   The Tunnel Terminator can respond to the message by stating what it
   believes is the user's appropriate label.

   In the case where the Tunnel Terminator does not propose ANY
   indicator (which is infered by the absence of the MPLS AVPs in either
   the ICRP or OCRP) the Tunnel Initiator will assume its Mlabel is
   acceptable or, if it did not send one in the ICRQ or OCRQ, that no
   Mlabel is assigned to the session.

   A tunnel peer which violates the negotiated label value is unlikely
   to successfully create an LSP.

1.1 Conventions

   The following language conventions are used in the items of specifi-
   cation in this document:

         o  MUST, SHALL, or MANDATORY -- This item is an absolute

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INTERNET DRAFT                                                 July 1998

            requirement of the specification.

         o  SHOULD or RECOMMEND -- This item should generally be followed
            for all but exceptional circumstances.

         o  MAY or OPTIONAL -- This item is truly optional and may be
            followed or ignored according to the needs of the

2.0 Multi-Protocol Label Switching

   This section will define the new AVP which is required for the MPLS
   label distribution extension of the L2TP protocol. The AVP allows the
   designation of an Mlabel for a specific data channel or group of data

2.1 Multi-Protocol Label AVP

   The Mlabel is an opaque object for an L2TP session used in a method
   similar to [5]. The following AVP holds the Mlabel without any
   knowledge of its composition.

   The Multi-Protocol Label AVP MAY be present in ICRQ, ICRP, OCRQ and
   OCRP. This message is used to inform the tunnel peer that a specific
   Mlabel SHOULD be used for all packets related to the data channel
   associated with the Tunnel and Call Identifiers in the L2TP header

   A tunnel peer which violates the negotiated label value is unlikely
   to successfully create an LSP.

       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
      |1|1|0|0|        Length         |              43               |
      |                1              |  Multi-Protocol Label Value   |
      |  Multi-Protocol Label Value   |

      This AVP MAY be present in the messages shown above. It is encoded
      with a Vendor ID of 43 (3Com Corporation) with the attribute set
      to 2, marked as optional, with the indicator value as data. This

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INTERNET DRAFT                                                 July 1998

      AVP SHOULD NOT be hidden and is optional. When present, the L2TP
      peer is indicating that Multi-Protocol Labels are to be used at
      the link layer.

2.2 Error Reporting

   In the event that the peer did not accept the Mlabel provided, or is
   unable to support MPLS a Call-Disconnect-Notify is returned to the

   If the Mlabel provided cannot be used by the peer, the Call-
   Disconnect-Notify message will include the Multi-Protocol Label AVP
   as provided in the message that caused the Call-Disconnect-Notify.

3.0 References

   [1] K. Hamzeh, T. Kolar, M. Littlewood, G. Singh Pall, J. Taarud,
       A. J. Valencia, W. Verthein, W.M. Townsley, B. Palter,
       A. Rubens "Layer Two Tunneling Protocol (L2TP)",
       Internet draft, October 1997

   [2] E. Rosen, Y. Rekhter, D. Tappan, D. Farinacci, G. Fedorkow,
       T. Li, A. Conta, "MPLS Label Stack Encoding",         draft-
   ietf-mpls-label-encaps-01.txt, February 1998.

   [3] E. Rosen, A. Viswanathan, R. Callon, "A Proposed Architecture
       for MPLS", draft-ietf-mpls-arch-00.txt, August 1997.

   [4] R. Callon, P. Doolan, N. Feldman, A. Fredette, G. Swallow,
       A. Viswanathan, "A Framework for Multiprotocol Label Switching",
           draft-ietf-mpls-framework-02.txt, November 1997.

   [5] B. Davie, Y. Rekhter, E. Rosen, A. Viswanathan, V, Srinivasan,
       "Use of Label Switching With RSVP", draft-davie-mpls-rsvp-01.txt,
           November 1997.

4.0 Authors' Addresses

   Questions about this memo can be directed to:

      Pat R. Calhoun
      Technology Development
      Sun Microsystems, Inc.
      15 Network Circle
      Menlo Park, California, 94025

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INTERNET DRAFT                                                 July 1998

       Phone:  1-650-786-7733
         Fax:  1-650-786-6445
      E-mail:  pcalhoun@eng.sun.com

      Ken Peirce
      3Com Corporation
      1800 Central Ave.
      Mount Prospect, Il, 60056

       Phone:  1-847-342-6794
         Fax:  1-847-222-2424
      E-mail:  Ken_Peirce@mw.3com.com

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