Internet Draft
Network Working Group Rohit Verma
Internet Draft Deloitte Consulting
Expires November 2000 Madhvi Verma
3Com Corporation
James Carlson
Sun Microsystems
May 2000
L2TP Disconnect Cause Information
<draft-ietf-l2tpext-ppp-discinfo-00.txt>
Status of this Memo
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Abstract
The Layer 2 Tunneling Protocol (``L2TP'') defines a mechanism for
tunneling PPP sessions. The current RFC lacks a mechanism for the
LNS to provide PPP related disconnect cause information to the LAC.
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
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disconnect information to be provided to an L2TP host (LAC/LNS) in a
descriptive format. The lack of this information is especially a
problem when the LAC and LNS are not managed by the same entities.
The Result and Error Codes defined for L2TP specify only L2TP-
specific disconnect information. This document provides an additional
AVP that MAY be used by an L2TP host to provide PPP specific discon-
nect information to its peer for accounting and debugging purposes.
This AVP should be used in conjunction with, and not as a replacement
for, the 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. The following AVP
should not have any effect on either the functioning of the tunnel or
the functioning of the PPP session.
2. AVP
2.1. PPP Disconnect Cause Code
The AVP is valid in the CDN message only, and it MUST NOT be marked
Mandatory.
The PPP Disconnect Cause Code AVP is encoded as Vendor ID 43 (3Com
Corporation), with an Attribute Type of PPP Disconnect Cause Code
(46). The attribute value is one of the values discussed in section
2.1.1. The length of the value field MUST be at least 11 octets. If
the length is more than 11 octets, the additional octets SHOULD con-
tain a descriptive text in ASCII format that can be displayed to the
user or in a log file.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CP Number | Direction | Message... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1.1 PPP Disconnect Cause code AVP
Mandatory (M) bit: MUST be 0.
Hidden (H) bit: MAY be 1 if the attribute is hidden.
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Length: The length of the entire attribute in octets, expressed as a
single octet. MUST be at least 11.
Vendor ID: A two octet value in network byte order; set to 43 (3Com
Corporation).
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.
CP Number: Primary failing Control Protocol, if any. This field may
be 0 unless mentioned otherwise in the description of the Disconnect
Cause Codes in section 2.1.1.
Direction(D) Flag: A single octet value; specifies the direction in
which the Disconnect code applies.
The valid values of this field are:
0: global error
1: at peer
2: at local
3-255: Reserved
This field may be 0 unless mentioned otherwise in the description of
the Disconnect Cause Codes in section 2.1.1.
2.1.1. Disconnect Cause Codes
This section contains the list of well-known values of the Disconnect
Code field in the PPP Disconnect Cause Code AVP. The IANA will main-
tain a registry of the up-to-date values. These values should be used
in conjunction with the Direction flag and the Control Protocol
Number to get the specific error code.
2.1.1.1. Global Errors
The global error codes, given in the list below, are Disconnect Codes
that do not relate to one particular control protocol. The CP Number
for these errors MUST be set to 0 and the Direction (D) flag MUST
also be set to 0 unless specified otherwise for a given code.
0 No information available.
1 Administrative disconnect.
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2 LCP renegotiation at LNS disabled; LNS expects proxy LCP
information, LAC did not send it.
3 Normal Disconnection, LCP Terminate-Request sent.
Valid Direction flags:
1: By peer
2: By local
4 Compulsory encryption required by a PPP peer was refused by the
other.
Valid Direction flags are:
1: Required by local; refused by peer
2: Required by peer; refused by local
2.1.1.2. LCP Errors
The LCP error codes, listed below, are disconnect reasons that are
directly related to failure of PPP peers to negotiate mutually agree-
able link parameters. The CP Number for such errors MUST be set to
0xCO21 and the direction flag to the direction of the failure.
5 FSM Timeout error.
6 No recognizable LCP packets were received.
7 LCP failure-Magic number error; link possibly looped back.
8 LCP link failure-Echo Request timeout.
9 Peer has unexpected Endpoint-Discriminator for existing MP
bundle.
10 Peer has unexpected MRRU for existing MP bundle.
11 Peer has unexpected Short-Sequence-Number option for existing
MP bundle.
12 Compulsory callback required by a PPP peer was refused by the
other.
Valid Direction flags are:
1: Required by local; refused by peer
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2: Required by peer; refused by local
2.1.1.3. Authentication Errors
The authentication errors codes, listed below, are disconnect reasons
that are directly related to authentication failures between the PPP
peers. The CP Number for such errors MUST correspond to the control
protocol number for the authentication protocol in use and the direc-
tion flag to the direction of the failure.
13 FSM Timeout error.
14 Peer has unexpected authenticated name for existing MP bundle.
15 PPP authentication failure-Authentication protocol unacceptable.
Valid Direction flags are:
1: All local authentication protocols were rejected by the
peer.
2: All authentication protocols requested by peer were
unacceptable or unimplemented locally.
16 PPP authentication failure-Authentication failed (bad name,
password, or secret).
Valid Direction flags are:
1: Authentication of peer identity by local system.
2: Authentication of local identity by peer system.
2.1.1.4. Network Control Protocol Errors
NCP Errors are disconnect reasons that are directly related to the
failure of PPP peers to negotiate a mutually agreeable set of parame-
ters for the network protocols. The CP Number for such errors MUST
correspond to the network control protocol number in use and the
direction flag to the direction of the failure. Where multiple net-
work protocols are in use, multiple copies of this AVP may be given
to indicate failure reasons for each NCP.
The Control Protocol field in the following cases will be the last or
primary failing NCP.
17 FSM Timeout error.
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18 No NCPs available (all disabled or rejected); no NCPs went to
Opened state.
19 NCP failure: failed to converge on acceptable addresses.
20 NCP failure: user not permitted to use any addresses.
3. Notes
This AVP MAY always be sent by the LNS to the LAC. However, at the
LAC, this AVP would be more useful diagnostically in the compulsory
case than in the voluntary case. In a voluntary model, it can be
presumed that local PPP traces are always present.
4. IANA Considerations
This AVP includes an enumerated cause code value. Values 0 through
20 are described in this document. New values may be assigned by the
IANA.
5. References
[1] W. Townsley, A. Valencia, A. Rubens, G. Pall, G. Zorn,
B. Palter, ``Layer 2 Tunnel Protocol (L2TP)'', RFC2661,
August 1999.
6. Acknowledgements
The Authors would like to thank W. Mark Townsley for his useful com-
ments to an earlier version of this document.
7. Contacts
7.1. L2TP Working Group Chair
W. Mark Townsley
Cisco Systems
7025 Kit Creek Road
PO Box 14987
Research Triangle Park, NC 27709
Email:
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7.2. Authors
Rohit Verma
180 N. Stetson Avenue
Chicago IL 60601
Phone: +1 312 374 2475
Fax: +1 312 870 2475
Email:
Madhvi Verma
1800 W. Central Road
Mount Prospect IL 60056
Phone: +1 847 797 6528
Fax: +1 847 222 2424
Email:
James Carlson
Sun Microsystems
1 Network Drive MS UBUR02-212
Burlington MA 01803-2757
Email:
Voice: +1 781 442 2084
Fax: +1 781 442 1677
8. Notices
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tain to the implementation or use of the technology described in this
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The IETF invites any interested party to bring to its attention any
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this standard. Please address the information to the IETF Executive
Director.
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