L2TP Disconnect Cause Information
RFC 3145

Document Type RFC - Proposed Standard (July 2001; No errata)
Authors James Carlson  , Rohit verma  , Madhvi Verma 
Last updated 2013-03-02
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Network Working Group                                           R. Verma
Request for Comments: 3145                           Deloitte Consulting
Category: Standards Track                                       M. Verma
                                                        3Com Corporation
                                                              J. Carlson
                                                        Sun Microsystems
                                                               July 2001

                   L2TP Disconnect Cause Information

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2001).  All Rights Reserved.


   This document provides an extension to the Layer 2 Tunneling Protocol
   ("L2TP"), a mechanism for tunneling Point-to-Point Protocol (PPP)
   sessions.  L2TP lacks a mechanism for a host to provide PPP-related
   disconnect cause information to another host.  This information,
   provided by the extension described in this document, can be useful
   for accounting and debugging purposes.

1.  Introduction

   L2TP [1] defines a general-purpose mechanism for tunneling PPP over
   various media.  By design, it insulates L2TP operation from the
   details of the PPP session that is being encapsulated by L2TP.  There
   are, however, cases where it may be desirable for PPP-specific
   disconnect information to be provided to an L2TP host (L2TP Access
   Concentrator [LAC] or L2TP Network Server [LNS]) in a descriptive
   format.  The lack of this information is especially a problem when
   the LAC and LNS are not owned or managed by the same entities.

   The Result and Error Codes defined for L2TP specify only L2TP-
   specific disconnect information.  This document provides an
   additional Attribute Value Pair (AVP), called PPP Disconnect Cause
   Code, that MAY be used by an L2TP host to provide PPP-specific

Verma, et al.               Standards Track                     [Page 1]
RFC 3145           L2TP Disconnect Cause Information           July 2001

   disconnect information to its peer.  This AVP should be used in
   conjunction with, and not as a replacement for, the L2TP Result and
   Error Code AVPs.

   The PPP Disconnect Cause Code AVP can also be used to provide a
   human-readable disconnect reason to the user.  This AVP should not
   have any effect on either the functioning of the tunnel or the
   functioning of the PPP session; it is for informational and logging
   purposes only.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in BCP 14 [2].

2.  PPP Disconnect Cause Code AVP

   The AVP is valid in the L2TP Call-Disconnect-Notify (CDN) message
   only, and it MUST NOT be marked Mandatory.

   The PPP Disconnect Cause Code AVP is encoded with Vendor ID 0 and an
   Attribute Type of PPP Disconnect Cause Code (46).  The length of the
   Value field MUST be at least 11 octets.  If the length is more than
   11 octets, the additional octets MUST contain a descriptive text in
   UTF-8 [3] format that can be displayed to the user or in a log file.
   The format of the AVP is shown 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
      |M|H| rsvd  |      Length       |          Vendor ID          |
      |         Attribute Type        |       Disconnect Code       |
      |    Control Protocol Number    |   Direction   | Message...

                  Figure 1: PPP Disconnect Cause Code AVP

   Mandatory (M) bit: MUST be 0.

   Hidden (H) bit: MAY be 1 if the attribute is hidden.

   Length: The length of the entire attribute in octets, expressed as a
   single octet.  The length MUST be at least 11.

   Vendor ID: A two octet value in network byte order; set to 0 to
   indicate that this is an IETF-assigned attribute.

Verma, et al.               Standards Track                     [Page 2]
RFC 3145           L2TP Disconnect Cause Information           July 2001

   Attribute Type: A two octet value in network byte order; set to 46
   (PPP Disconnect Cause Code).

   Disconnect Code: A two octet value in network byte order.  (Described
   in section 3 of this document.)
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