L2TP Disconnect Cause Information (RFC3145)
Original Publication Date: 2001-Jul-01
Included in the Prior Art Database: 2019-Feb-13
Internet Society Requests For Comment (RFCs)
R. Verma: AUTHOR [+2]
This document provides an extension to the Layer 2 Tunneling Protocol ("L2TP"), a mechanism for tunneling Point-to-Point Protocol (PPP) sessions. [STANDARDS-TRACK]
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 (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.
L2TP  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", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 .
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  format that can be displayed to the user or i...