Network Working Group G. Zorn

Network Working Group G. Zorn
Request for Comments: 2867 Cisco Systems, Inc.
Category: Informational B. Aboba
Updates: 2866 Microsoft Corporation
D. Mitton
Nortel Networks
June 2000

RADIUS Accounting Modifications for Tunnel Protocol Support

Status of this Memo

This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.

Copyright Notice

Copyright (C) The Internet Society (2000). All Rights Reserved.

Abstract

This document defines new RADIUS accounting Attributes and new values
for the existing Acct-Status-Type Attribute [1] designed to support
the provision of compulsory tunneling in dial-up networks.

Specification of Requirements

In this document, the key words "MAY", "MUST, "MUST NOT", "optional",
"recommended", "SHOULD", and "SHOULD NOT", are to be interpreted as
described in [2].

1. Introduction

Many applications of tunneling protocols such as PPTP [5] and L2TP
[4] involve dial-up network access. Some, such as the provision of
secure access to corporate intranets via the Internet, are
characterized by voluntary tunneling: the tunnel is created at the
request of the user for a specific purpose. Other applications
involve compulsory tunneling: the tunnel is created without any
action from the user and without allowing the user any choice in the
matter, as a service of the Internet service provider (ISP).
Typically, ISPs providing a service want to collect data regarding
that service for billing, network planning, etc. One way to collect
usage data in dial-up networks is by means of RADIUS Accounting [1].
The use of RADIUS Accounting allows dial-up usage data to be
collected at a central location, rather than stored on each NAS.

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RFC 2867 RADIUS Tunnel Accounting Support June 2000

In order to collect usage data regarding tunneling, new RADIUS
attributes are needed; this document defines these attributes. In
addition, several new values for the Acct-Status-Type attribute are
proposed. Specific recommendations for, and examples of, the
application of this attribute for the L2TP protocol can be found in
RFC 2809.

2. Implementation Notes

Compulsory tunneling may be part of a package of services provided by
one entity to another. For example, a corporation might contract
with an ISP to provide remote intranet access to its employees via
compulsory tunneling. In this case, the integration of RADIUS and
tunnel protocols allows the ISP and the corporation to synchronize
their accounting activities so that each side receives a record of
the user's resource consumption. This provides the corporation with
the means to audit ISP bills.

In auditing, the User-Name, Acct-Tunnel-Connection, Tunnel-Client-
Endpoint and Tunnel-Server-Endpoint attributes are typically used to
uniquely identify the call, allowing the Accounting-Request sent by
the NAS to be reconciled with the corresponding Accounting-Request
sent by the tunnel server.

When implementing RADIUS accounting for L2TP/PPTP tunneling, the
Call-Serial-Number SHOULD be used in the Acct-Tunnel-Connection
attribute. In L2TP, the Call-Serial-Number is a 32-bit field and in
PPTP it is a 16-bit field. In PPTP the combination of IP Address and
Call-Serial-Number SHOULD be unique, but this is not required. In
addition, no method for determining the Call-Serial-Number is
specified, which leaves open the possibility of wrapping after a
reboot.

Note that a 16-bit Call-Serial-Number is not sufficient to
distinguish a given call from all other calls over an extended time
period. For example, if the Call-Serial-Number is assigned
monotonically, the NAS in question has 96 ports which are continually
busy and the average call is of 20 minutes duration, then a 16-bit
Call-Serial-Number will wrap within 65536/(96 * 3 calls/hour * 24
hours/day) = 9.48 days.

3. New Acct-Status-Type Values

3.1. Tunnel-Start

Value

9

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RFC 2867 RADIUS Tunnel Accounting Support June 2000

Description

This value MAY be used to mark the establishment of a tunnel
with another node. If this value is used, the following
attributes SHOULD also be included in the Accounting-Request
packet:

User-Name (1)
NAS-IP-Address (4)
Acct-Delay-Time (41)
Event-Timestamp (55)
Tunnel-Type (64)
Tunnel-Medium-Type (65)
Tunnel-Client-Endpoint (66)
Tunnel-Server-Endpoint (67)
Acct-Tunnel-Connection (68)

3.2. Tunnel-Stop

Value

10

Description

This value MAY be used to mark the destruction of a tunnel to
or from another node. If this value is used, the following
attributes SHOULD also be included in the Accounting-Request
packet:

User-Name (1)
NAS-IP-Address (4)
Acct-Delay-Time (41)
Acct-Input-Octets (42)
Acct-Output-Octets (43)
Acct-Session-Id (44)
Acct-Session-Time (46)
Acct-Input-Packets (47)
Acct-Output-Packets (48)
Acct-Terminate-Cause (49)
Acct-Multi-Session-Id (51)
Event-Timestamp (55)
Tunnel-Type (64)
Tunnel-Medium-Type (65)
Tunnel-Client-Endpoint (66)
Tunnel-Server-Endpoint (67)
Acct-Tunnel-Connection (68)
Acct-Tunnel-Packets-Lost (86)

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RFC 2867 RADIUS Tunnel Accounting Support June 2000

3.3. Tunnel-Reject

Value

11

Description

This value MAY be used to mark the rejection of the
establishment of a tunnel with another node. If this value is
used, the following attributes SHOULD also be included in the
Accounting-Request packet:

User-Name (1)
NAS-IP-Address (4)
Acct-Delay-Time (41)
Acct-Terminate-Cause (49)
Event-Timestamp (55)
Tunnel-Type (64)
Tunnel-Medium-Type (65)
Tunnel-Client-Endpoint (66)
Tunnel-Server-Endpoint (67)
Acct-Tunnel-Connection (68)

3.4. Tunnel-Link-Start

Value

12

Description

This value MAY be used to mark the creation of a tunnel link.
Only some tunnel types (e.g., L2TP) support multiple links per
tunnel. This Attribute is intended to mark the creation of a
link within a tunnel that carries multiple links. For example,
if a mandatory tunnel were to carry M links over its lifetime,
2(M+1) RADIUS Accounting messages might be sent: one each
marking the initiation and destruction of the tunnel itself and
one each for the initiation and destruction of each link within
the tunnel. If only a single link can be carried in a given
tunnel (e.g., IPsec in the tunnel mode), this Attribute need
not be included in accounting packets, since the presence of
the Tunnel-Start Attribute will imply the initiation of the
(only possible) link.

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RFC 2867 RADIUS Tunnel Accounting Support June 2000

If this value is used, the following attributes SHOULD also be
included in the Accounting-Request packet:

User-Name (1)
NAS-IP-Address (4)
NAS-Port (5)
Acct-Delay-Time (41)
Event-Timestamp (55)
Tunnel-Type (64)
Tunnel-Medium-Type (65)
Tunnel-Client-Endpoint (66)
Tunnel-Server-Endpoint (67)
Acct-Tunnel-Connection (68)

3.5. Tunnel-Link-Stop

Value

13

Description

This value MAY be used to mark the destruction of a tunnel
link. Only some tunnel types (e.g., L2TP) support multiple
links per tunnel. This Attribute is intended to mark the
destruction of a link within a tunnel that carries multiple
links. For example, if a mandatory tunnel were to carry M
links over its lifetime, 2(M+1) RADIUS Accounting messages
might be sent: one each marking the initiation and destruction
of the tunnel itself and one each for the initiation and
destruction of each link within the tunnel. If only a single
link can be carried in a given tunnel (e.g., IPsec in the
tunnel mode), this Attribute need not be included in accounting
packets, since the presence of the Tunnel-Stop Attribute will
imply the termination of the (only possible) link.

If this value is used, the following attributes SHOULD also be
included in the Accounting-Request packet:

User-Name (1)
NAS-IP-Address (4)
NAS-Port (5)
Acct-Delay-Time (41)
Acct-Input-Octets (42)
Acct-Output-Octets (43)
Acct-Session-Id (44)
Acct-Session-Time (46)
Acct-Input-Packets (47)

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RFC 2867 RADIUS Tunnel Accounting Support June 2000

Acct-Output-Packets (48)
Acct-Terminate-Cause (49)
Acct-Multi-Session-Id (51)
Event-Timestamp (55)
NAS-Port-Type (61)
Tunnel-Type (64)
Tunnel-Medium-Type (65)
Tunnel-Client-Endpoint (66)
Tunnel-Server-Endpoint (67)
Acct-Tunnel-Connection (68)
Acct-Tunnel-Packets-Lost (86)

3.6. Tunnel-Link-Reject

Value

14

Description

This value MAY be used to mark the rejection of the
establishment of a new link in an existing tunnel. Only some
tunnel types (e.g., L2TP) support multiple links per tunnel.
If only a single link can be carried in a given tunnel (e.g.,
IPsec in the tunnel mode), this Attribute need not be included
in accounting packets, since in this case the Tunnel-Reject
Attribute has the same meaning.

If this value is used, the following attributes SHOULD also be
included in the Accounting-Request packet:

User-Name (1)
NAS-IP-Address (4)
Acct-Delay-Time (41)
Acct-Terminate-Cause (49)
Event-Timestamp (55)
Tunnel-Type (64)
Tunnel-Medium-Type (65)
Tunnel-Client-Endpoint (66)
Tunnel-Server-Endpoint (67)
Acct-Tunnel-Connection (68)

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RFC 2867 RADIUS Tunnel Accounting Support June 2000

4. Attributes

4.1. Acct-Tunnel-Connection

Description

This Attribute indicates the identifier assigned to the tunnel
session. It SHOULD be included in Accounting-Request packets
which contain an Acct-Status-Type attribute having the value
Start, Stop or any of the values described above. This
attribute, along with the Tunnel-Client-Endpoint and Tunnel-
Server-Endpoint attributes [3], may be used to provide a means
to uniquely identify a tunnel session for auditing purposes.

A summary of the Acct-Tunnel-Connection Attribute format is shown
below. The fields are transmitted from left to right.

0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | String ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type

68 for Acct-Tunnel-Connection

Length

>= 3

String

The format of the identifier represented by the String field
depends upon the value of the Tunnel-Type attribute [3]. For
example, to fully identify an L2TP tunnel connection, the L2TP
Tunnel ID and Call ID might be encoded in this field. The
exact encoding of this field is implementation dependent.

4.2. Acct-Tunnel-Packets-Lost

Description

This Attribute indicates the number of packets lost on a given
link. It SHOULD be included in Accounting-Request packets
which contain an Acct-Status-Type attribute having the value
Tunnel-Link-Stop.

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RFC 2867 RADIUS Tunnel Accounting Support June 2000

A summary of the Acct-Tunnel-Packets-Lost Attribute 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Lost
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Lost (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type

86 for Acct-Tunnel-Packets-Lost

Length

6

Lost

The Lost field is 4 octets in length and represents the number
of packets lost on the link.

5. Table of Attributes

The following table provides a guide to which attributes may be found
in Accounting-Request packets. No tunnel attributes should be found
in Accounting-Response packets.

Request # Attribute
0-1 64 Tunnel-Type
0-1 65 Tunnel-Medium-Type
0-1 66 Tunnel-Client-Endpoint
0-1 67 Tunnel-Server-Endpoint
0-1 68 Acct-Tunnel-Connection
0 69 Tunnel-Password
0-1 81 Tunnel-Private-Group-ID
0-1 82 Tunnel-Assignment-ID
0 83 Tunnel-Preference
0-1 86 Acct-Tunnel-Packets-Lost

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RFC 2867 RADIUS Tunnel Accounting Support June 2000

The following table defines the meaning of the above table entries.

0 This attribute MUST NOT be present in packet.
0+ Zero or more instances of this attribute MAY be present in
packet.
0-1 Zero or one instance of this attribute MAY be present in
packet.

6. Security Considerations

By "sniffing" RADIUS Accounting packets, it might be possible for an
eavesdropper to perform a passive analysis of tunnel connections.

7. References

[1] Rigney, C., "RADIUS Accounting", RFC 2866, June 2000.

[2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.

[3] Zorn, G., Leifer, D., Rubens, A., Shriver, J., Holdrege, M. and
I. Goyret, "RADIUS Attributes for Tunnel Protocol Support", RFC
2868, June 2000.

[4] Townsley, W., Valencia, A., Rubens, A., Pall, G., Zorn, G. and
B. Palter, "Layer Two Tunneling Protocol "L2TP"", RFC 2661,
August 1999.

[5] Hamzeh, K., Pall, G., Verthein, W., Taarud, J., Little, W. and
G. Zorn, "Point-to-Point Tunneling Protocol (PPTP)", RFC 2637,
July 1999.

8. Acknowledgments

Thanks to Aydin Edguer, Ly Loi, Matt Holdrege and Gurdeep Singh Pall
for salient input and review.

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RFC 2867 RADIUS Tunnel Accounting Support June 2000

9. Authors' Addresses

Questions about this memo can be directed to:

Glen Zorn
Cisco Systems, Inc.
500 108th Avenue N.E., Suite 500
Bellevue, Washington 98004
USA

Phone: +1 425 438 8218
FAX: +1 425 438 1848
EMail: [email protected]

Dave Mitton
Nortel Networks
880 Technology Park Drive
Billerica, MA 01821

Phone: +1 978 288 4570
Fax: +1 978 288 3030
EMail: [email protected]

Bernard Aboba
Microsoft Corporation
One Microsoft Way
Redmond, Washington 98052

Phone: +1 425 936 6605
Fax: +1 425 936 7329
EMail: [email protected]

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RFC 2867 RADIUS Tunnel Accounting Support June 2000

10. Full Copyright Statement

Copyright (C) The Internet Society (2000). All Rights Reserved.

This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
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included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
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followed, or as required to translate it into languages other than
English.

The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.

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TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
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Acknowledgement

Funding for the RFC Editor function is currently provided by the
Internet Society.

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