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Network Working Group N. McGill
Internet-Draft cisco Systems
Expires: June 3, 2008 T. Mistretta
Juniper Networks
I. Goyret
Alcatel-Lucent
M. Townsley
G. Weber
cisco Systems
Dec 2007
RADIUS & L2TP Extended NAS-Port AVPs
draft-ietf-l2tpext-radius-ext-nas-port-02.txt
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Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
This document defines additional Layer 2 Tunneling Protocol (L2TP)
and Remote Authentication Dial In User Service (RADIUS) Attribute-
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Value Pairs (AVPs) to communicate Network Access Server (NAS)
informational UTF-8 text and port usage information between L2TP
peers during call establishment to facilitate authorization,
accounting and logging.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Specification of Requirements . . . . . . . . . . . . . . 4
2. L2TP Extended NAS-Port AVPs . . . . . . . . . . . . . . . . . 4
3. RADIUS Extended NAS-Port AVP . . . . . . . . . . . . . . . . . 7
3.1. Table of Attributes . . . . . . . . . . . . . . . . . . . 10
3.2. Interactions with other RADIUS attributes . . . . . . . . 10
3.3. Diameter Compatibility . . . . . . . . . . . . . . . . . . 10
4. Security Considerations . . . . . . . . . . . . . . . . . . . 11
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
7.1. Normative References . . . . . . . . . . . . . . . . . . . 11
7.2. Informative References . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
Intellectual Property and Copyright Statements . . . . . . . . . . 14
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1. Introduction
It is often desirable to send adjunct and port usage information from
the L2TP Access Concentrator (LAC) to the L2TP Network Server (LNS)
during call setup. Such information MAY be used for:
Logging
to describe system and port related information in a human-
readable, vendor-specific form.
Authorization
to restrict users to particular given access types or
interfaces.
Accounting
to determine port usage on a per-user basis, for example, via
RADIUS accounting [RFC2866].
Auditing
to ensure that the LNS vendor is being allocated the proper
contractual resources by the LAC vendor.
L2TPv2 [RFC2661] and L2TPv3 [RFC3931] already have a Physical Channel
ID AVP that may be used to provide port usage information. However,
its usefulness is limited in multi-vendor LAC/LNS environments where
the vendor- specific bit encoding used for this AVP will often not be
understood by L2TP peers from differing vendors.
This makes the task of de-constructing the Physical Channel ID AVP
contents at the LNS for (RADIUS) authorization/accounting server
extremely difficult.
Additionally, it is length limited to 4 octets of information which
is inadequate in access servers supporting multiple access types and
large numbers of ports.
This document defines extensions whereby such port usage information
may be transferred in a vendor-independent fashion between mixed-
vendor LAC and LNSs, thus facilitating detailed and matching logging
and accounting at each end of the tunnel.
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The following diagram depicts a typical dialin scenario for L2TP with
RADIUS accounting servers at the LNS:
Authen/Accounting
RADIUS server
|
|
|
|
intranet - - - - LNS - - - - - internet - - - -LAC - - - -client
<----------------------------->
L2TP tunnel
1.1. Specification of Requirements
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 [RFC2119].
2. L2TP Extended NAS-Port AVPs
The following collection of Extended NAS-Port AVPs, attribute types
TBD, allow detailed logging and port usage information to be
transmitted between L2TP peers. This format is common to all
Extended NAS-Port AVPs; only the Attribute Type is different for
each:
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 (IETF) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Attribute Type | Attribute Value...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
[until Length is reached]... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NOTES:
o Each Extended NAS-Port AVP is encoded as the IETF Vendor ID 0
o Each AVP has defined behaviour associated with it, namely:
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RELAYED AVP: See [I-D.ietf-l2tpext-tunnel-switching], section 3.
AVP Behavior, for definition. In summary, if this AVP is
received by a node participating in a multi-hop scenario, then
the AVP MUST be copied as-is to the next hop.
STACKED AVP: See [I-D.ietf-l2tpext-tunnel-switching], section 3.
AVP Behavior, for definition. In summary, if this AVP is
received by a node participating in a multi-hop scenario, then
the AVP MUST be copied as-is to the next hop. A locally
generated AVP MUST be generated and appended in the outbound
message to the next hop. If no value is appropriate then an
AVP of Length 6 (minimum AVP length) MUST be appended. This
null attibute value may be used for all AVPs where no value is
appropriate.
o The value of all bits MUST be preserved in any AVPs copied.
The following are valid values for the Attribute Type field in
control channel related messages:
L2TP-AVP-TBD-1 - Platform Information
This AVP, value length 0-253, allows a UTF-8 [RFC3629] string
to be sent with a human-readable description of the platform.
Examples: "Model 457", or "TPX-1700".
This information MUST NOT be parsed and as such termination
action MUST NOT be based on the contents of this attribute.
The M-bit MUST be set to 0. The H-bit MAY be set based on the
current L2TP node's policy. This AVP is a stackable AVP.
L2TP-AVP-TBD-2 - System Identification Information
This AVP, value length 0-253, allows a UTF-8 [RFC3629] string
to be sent with a human-readable description of the router's
identification within the provider's network.
Examples: "CommCo LAC", or "SuperProvider AS".
This information MUST NOT be parsed and as such termination
action MUST NOT be based on the contents of this attribute.
The M-bit MUST be set to 0. The H-bit MAY be set based on the
current L2TP node's policy. This AVP is a stackable AVP.
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L2TP-AVP-TBD-4 - Software Information
This AVP, value length 0-253, allows a UTF-8 [RFC3629] string
to be sent with a human-readable description of the software
running on the platform.
Examples: "Version 4-0.12(c)-2", or "Rev 10.4.2-beta".
This information MUST NOT be parsed and as such termination
action MUST NOT be based on the contents of this attribute.
The M-bit MUST be set to 0. The H-bit MAY be set based on the
current L2TP node's policy. This AVP is a stackable AVP.
For tunnels, these AVPs are valid either on SCCRQ or SCCCN. If
sent on both, the SCCCN AVP MUST override the SCCRP value.
The following are valid values for the Attribute Type field in
session related messages:
L2TP-AVP-TBD-3 - Call Information
This AVP, value length 0-253, allows a UTF-8 [RFC3629] string
to be sent with a human-readable description of the call.
Examples could include "Atlanta POP", or "Neptune-304x using
frame2 module".
This information MUST NOT be parsed and as such termination
action MUST NOT be based on the contents of this attribute.
The M-bit MUST be set to 0. The H-bit MAY be set based on the
current L2TP node's policy. This AVP is a stackable AVP.
L2TP-AVP-TBD-6 - Shelf
L2TP-AVP-TBD-7 - Slot
L2TP-AVP-TBD-8 - Module
L2TP-AVP-TBD-9 - Adapter
L2TP-AVP-TBD-10 - Interface
L2TP-AVP-TBD-11 - Line
L2TP-AVP-TBD-12 - Port
L2TP-AVP-TBD-13 - Channel
L2TP-AVP-TBD-14 - Physical Interface
L2TP-AVP-TBD-15 - Physical Sub-interface
L2TP-AVP-TBD-16 - Virtual Path
L2TP-AVP-TBD-17 - Virtual Circuit
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L2TP-AVP-TBD-18 - Virtual Lan
L2TP-AVP-TBD-18 - Virtual Interface
L2TP-AVP-TBD-20 - Virtual Sub-interface
These AVPs, length 0 or 4, are unsigned octet integers value,
representing a specific Extended NAS-Port AVP value at this
L2TP node.
The M-bit MUST be set to 0. The H-bit MAY be set based on the
current L2TP node's policy. These AVPs are relayed AVPs.
All Extended NAS-Port AVPs SHOULD be used in conjunction with the
port type values defined in [RFC2865] and [RFC2866].
For incoming calls, these AVPs are valid either on ICRQ or ICCN.
If sent on both, the ICCN AVP MUST override the ICRQ value. For
outgoing calls, the AVPs are valid on OCRP and OCCN, with similar
override behavior.
3. RADIUS Extended NAS-Port AVP
The RADIUS Extended NAS-Port AVP closely resembles its L2TP counter-
part and allows detailed port-usage/accounting information to be
provided in multi-vendor environments.
The key distinction is that for RADIUS we have a single new attribute
(due to lack of available RADIUS type attributes) with multiple
Extensions, encoded as string attribute-value pairs of the form
"<extension>=<value>". These Extensions exist in a one-to- one
mapping with the previously defined L2TP AVPs.
The following format is common to all Extended NAS-Port AVPs; only
the Extension string name is different for each:
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 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
|Extnd. NAS-Port| Length | "extension=value"...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Type
RADIUS-AVP-TBD-1 for Extended NAS-Port
Length
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>= 3
Value
This attribute is of string format, with the following definition:
"<extension>=<value>"
Where "<extension>" is one of the following case-sensitive
strings:
"platform" - Platform Information
This AVP extension, length 3-255, allows a UTF-8 [RFC3629]
string to be sent with a human-readable description of the
platform.
Examples: "platform=Model 457", or "platform=TPX-1700".
This information MUST NOT be parsed and as such termination
action MUST NOT be based on the contents of this attribute.
"system-id" - System Identification Information
This AVP extension, length 3-255, allows a UTF-8 [RFC3629]
string to be sent with a human-readable description of the
routers identification within the provider's network.
Examples: "system-id=CommCo LAC", or "system-
id=SuperProvider AS".
This information MUST NOT be parsed and as such termination
action MUST NOT be based on the contents of this attribute.
"call" - Call Information
This AVP extension, length 3-255, allows a UTF-8 [RFC3629]
string to be sent with a human-readable description of the
call.
Examples could include "call=Atlanta POP", or "call=Neptune-
304x using frame2 module".
This information MUST NOT be parsed and as such termination
action MUST NOT be based on the contents of this attribute.
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"software" - Software Information
This AVP extension, length 3-255, allows a UTF-8 [RFC3629]
string to be sent with a human-readable description of the
software running on the platform.
Examples: "software=Version 4-0.12(c)-2", or "software=Rev
10.4.2-beta".
This information MUST NOT be parsed and as such termination
action MUST NOT be based on the contents of this attribute.
"shelf" - Shelf
"slot" - Slot
"module" - Module
"adapter" - Adapter
"intf" - Interface
"line" - Line
"port" - Port
"channel" - Channel
"phys-intf" - Physical Interface
"phys-subintf" - Physical Sub-interface
"vpi" - Virtual Path
"vci" - Virtual Circuit
"vlan" - Virtual Lan
"vintf" - Virtual Interface
"vsubintf" - Virtual Sub-interface
These AVPs, length 3-255, allow a UTF-8 [RFC3629] string to
be sent with the integer value of the relevant Extended NAS-
Port AVP.
Examples: "vpi=3", "vci=0", "vlan=4094"
For L2TP tunnels, these attributes MUST be used, if available, to log
information obtained via the corresponding L2TP Extended NAS-Port
AVPs. See section 2.
To cater for L2TP multi-hop environments, if an L2TP Extended NAS-
Port AVP is available, but without a corresponding value, then the
associated RADIUS AVP MUST be encoded as "<extension>"
The sequence of RADIUS Extended NAS-Port AVPs MUST follow that of any
L2TP Extended NAS-Port AVPs received.
For scenarios without L2TP, these attributes MAY also be used in
preference over the RADIUS NAS-Port attribute to provide finer
granularity during accounting.
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Where an attribute was not received from L2TP it is considered
optional to send.
For non L2TP environments, all Extensions are optional.
All strings are NOT null terminated.
Any numbers encoded as the value part of the Extension MUST be as
strings with a minimum value of "0". Only unsigned values MUST be
sent.
The use of the character '"' in this document is included purely as a
visual aid in identifying the beginning and end of strings. It MUST
NOT be included as part of the end format, unless specifically
encoded as data within the AVP Value section.
3.1. Table of Attributes
The following table provides a guide to which attributes may be found
in which kinds of packets, and in what quantity.
For Authentication:
Request Accept Reject Challenge Attribute
0+ 0 0 0 Extended NAS-Port
For Accounting:
Request Response Attribute
0+ 0 Extended NAS-Port
3.2. Interactions with other RADIUS attributes
Extended NAS-Port overlaps in functionality with NAS-Port. However,
whereas the encoding of NAS-Port is limited to 32 bits and often
vendor specific, Extended NAS-Port is not. NAS-Port may still
continue to be used but preference SHOULD be given to information
received in Extended NAS-Port.
If a RADIUS vendor detects conflicting values between NAS-Port and
Extended NAS-Port, Extended NAS-Port SHOULD be taken as the more
accurate value.
3.3. Diameter Compatibility
The RADIUS Extended NAS-Port attribute defined in this section may be
translated for transmission via Diameter [RFC3588] by AAA Translation
Agents as described by Section 9 of [RFC4005].
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Such a translation might represent the extended NAS-Port information
as a single Diameter attribute of type Grouped. Each RADIUS
<extension> valued defined in section 3 would map to a new Diameter
attribute, all of which would be encapsulated in a single Grouped
Extended-NAS-Port attribute. The ABNF for such an attribute might
look like:
Extended-NAS-Port ::= < AVP Header: DIAMETER-AVP-TBD-1 >
[ NAS-Port-Platform ]
[ NAS-Port-System-Id ]
[ NAS-Port-Call ]
[ NAS-Port-Software ]
[ NAS-Port-Vendor ]
[ NAS-Port-Shelf ]
[ NAS-Port-Slot ]
...
4. Security Considerations
This document describes mechanisms where port termination-related
information can be sent between L2TP peers. Users of these AVPs
should have the understanding that any information sent could be used
for malicious purposes. If this is a concern, any of the L2TP
Extended NAS-Port List AVPs MAY be hidden.
5. IANA Considerations
All values referenced with AVP-TBP need to be assigned an IETF
"Attribute Type" from the "Control Message Attribute Value Pairs"
maintained by IANA for L2TP.
6. Acknowledgements
The authors wish to thank Carlos Pignato for comments received.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J.
Arkko, "Diameter Base Protocol", RFC 3588, September 2003.
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[RFC2661] Townsley, W., Valencia, A., Rubens, A., Pall, G., Zorn,
G., and B. Palter, "Layer Two Tunneling Protocol "L2TP"",
RFC 2661, August 1999.
7.2. Informative References
[RFC2866] Rigney, C., "RADIUS Accounting", RFC 2866, June 2000.
[RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)",
RFC 2865, June 2000.
[RFC3931] Lau, J., Townsley, M., and I. Goyret, "Layer Two Tunneling
Protocol - Version 3 (L2TPv3)", RFC 3931, March 2005.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[I-D.ietf-l2tpext-tunnel-switching]
Jain, V., "PPP over L2TP Tunnel Switching",
draft-ietf-l2tpext-tunnel-switching-08 (work in progress),
March 2007.
[RFC4005] Calhoun, P., Zorn, G., Spence, D., and D. Mitton,
"Diameter Network Access Server Application", RFC 4005,
August 2005.
Authors' Addresses
Neil McGill
cisco Systems
3rd Floor
96 Commercial Street
Edinburgh, EH6 6LX
UK
Email: nmcgill@cisco.com
Tom Mistretta
Juniper Networks
10 Technology Park Drive
Westford, MA 01886
US
Email: thomas.mistretta@verizon.net
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Ignacio Goyret
Alcatel-Lucent
1801 Harbor Bay Parkway
Alameda, CA 94502
Email: igoyret@alcatel-lucent.com
W. Mark Townsley
cisco Systems
Email: mark@townsley.net
Greg Weber
cisco Systems
10850 Murdock Road
Knoxville, TN 37932
US
Email: gdweber@cisco.com
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