Internet Engineering Task Force (IETF) R. Maglione

Internet Engineering Task Force (IETF) R. Maglione
Request for Comments: 6519 Telecom Italia
Category: Standards Track A. Durand
ISSN: 2070-1721 Juniper Networks
February 2012

RADIUS Extensions for Dual-Stack Lite

Abstract

Dual-Stack Lite is a solution to offer both IPv4 and IPv6
connectivity to customers that are addressed only with an IPv6
prefix. Dual-Stack Lite requires pre-configuration of the Dual-Stack
Lite Address Family Transition Router (AFTR) tunnel information on
the Basic Bridging BroadBand (B4) element. In many networks, the
customer profile information may be stored in Authentication,
Authorization, and Accounting (AAA) servers, while client
configurations are mainly provided through the Dynamic Host
Configuration Protocol (DHCP). This document specifies a new Remote
Authentication Dial-In User Service (RADIUS) attribute to carry the
Dual-Stack Lite AFTR tunnel name; the RADIUS attribute is defined
based on the equivalent DHCPv6 OPTION_AFTR_NAME option. This RADIUS
attribute is meant to be used between the RADIUS server and the
Network Access Server (NAS); it is not intended to be used directly
between the B4 element and the RADIUS server.

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6519.

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RFC 6519 DS-Lite RADIUS Extensions February 2012

Copyright Notice

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Table of Contents

1. Introduction ....................................................3
2. Terminology .....................................................4
3. DS-Lite Configuration with RADIUS and DHCPv6 ....................4
4. RADIUS Attribute ................................................7
4.1. DS-Lite-Tunnel-Name ........................................7
5. Table of Attributes .............................................9
6. Security Considerations .........................................9
7. IANA Considerations .............................................9
8. References .....................................................10
8.1. Normative References ......................................10
8.2. Informative References ....................................10

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RFC 6519 DS-Lite RADIUS Extensions February 2012

1. Introduction

Dual-Stack Lite [RFC6333] is a solution to offer both IPv4 and IPv6
connectivity to customers that are addressed only with an IPv6 prefix
(no IPv4 address is assigned to the attachment device). One of its
key components is an IPv4-over-IPv6 tunnel, but a Dual-Stack-Lite
Basic Bridging BroadBand (B4) element will not know if the network to
which it is attached offers Dual-Stack Lite support. Even if the B4
did know, it would not know the remote end of the tunnel to which it
could establish a connection.

To inform the B4 element of the location of the Address Family
Transition Router (AFTR), a Fully Qualified Domain Name (FQDN) may be
used. Once this information is conveyed, the presence of the
configuration indicating the AFTR's location also informs a host to
initiate Dual-Stack Lite (DS-Lite) service and become a Softwire
Initiator.

[RFC6334] specifies a DHCPv6 option that is meant to be used by a
DS-Lite client (B4 element) to discover its AFTR name. In order to
be able to populate such an option, the DHCPv6 server must be
pre-provisioned with the AFTR name.

In broadband environments, a customer profile may be managed by
Authentication, Authorization, and Accounting (AAA) servers, together
with AAA for users. The Remote Authentication Dial-In User Service
(RADIUS) protocol [RFC2865] is usually used by AAA servers to
communicate with network elements. [RADIUS-IPv6] describes a typical
broadband network scenario in which the Network Access Server (NAS)
acts as the access gateway for the users (hosts or Customer Premises
Equipment (CPE) devices) and also embeds a DHCPv6 server function
that allows it to locally handle any DHCPv6 requests issued by the
clients.

Since the DS-Lite AFTR information can be stored in AAA servers and
the client configuration is mainly provided through DHCP running
between the NAS and the requesting clients, a new RADIUS attribute is
needed to send AFTR information from the AAA server to the NAS.

This document defines a new RADIUS attribute to be used for carrying
the DS-Lite Tunnel Name, based on the equivalent DHCPv6 option
already specified in [RFC6334].

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RFC 6519 DS-Lite RADIUS Extensions February 2012

2. Terminology

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].

The terms DS-Lite Basic Bridging BroadBand element (B4) and the
DS-Lite Address Family Transition Router element (AFTR) are defined
in [RFC6333].

3. DS-Lite Configuration with RADIUS and DHCPv6

Figure 1 illustrates how the RADIUS protocol and DHCPv6 work together
to accomplish DS-Lite configuration on the B4 element when a PPP
session is used to provide connectivity to the user.

The NAS operates as a client of RADIUS and as a DHCP Server. The NAS
initially sends a RADIUS Access-Request message to the RADIUS server,
requesting authentication. Once the RADIUS server receives the
request, it validates the sending client, and if the request is
approved, the AAA server replies with an Access-Accept message
including a list of attribute-value pairs that describe the
parameters to be used for this session. This list MAY also contain
the AFTR tunnel name. When the NAS receives a DHCPv6 client request
containing the DS-Lite tunnel option, the NAS SHALL use the name
returned in the RADIUS DS-Lite-Tunnel-Name attribute to populate the
DHCPv6 OPTION_AFTR_NAME option in the DHCPv6 reply message.

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RFC 6519 DS-Lite RADIUS Extensions February 2012

B4 NAS AAA
| | Server
| | |
|----PPP LCP Config-Request------> | |
| | |
| |----Access-Request ---->|
| | |
| |<---- Access-Accept-----|
| | (DS-Lite-Tunnel-Name) |
|<-----PPP LCP Config-ACK ------- | |
| | |
| | |
|--- PPP IPv6CP Config-Request --->| |
| | |
|<----- PPP IPv6CP Config-ACK -----| |
| | |
|------- DHCPv6 Solicit -------->| |
| | |
|<-------DHCPv6 Advertisement -----| |
| (DHCPv6 OPTION_AFTR_NAME) | |
| | |
|------- DHCPv6 Request -------->| |
| | |
|<-------- DHCPv6 Reply ---------- | |
| (DHCPv6 OPTION_AFTR_NAME) | |

DHCPv6 RADIUS

Figure 1: RADIUS and DHCPv6 Message Flow for a PPP Session

Figure 2 illustrates how the RADIUS protocol and DHCPv6 work together
to accomplish DS-Lite configuration on the B4 element when an IP
session is used to provide connectivity to the user.

The only difference between this message flow and the previous one is
that in this scenario, the interaction between the NAS and the AAA/
RADIUS server is triggered by the DHCPv6 Solicit message received by
the NAS from the B4 acting as a DHCPv6 client, while in the case of a
PPP session, the trigger is the PPP Link Control Protocol (LCP)
Config-Request message received by the NAS.

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RFC 6519 DS-Lite RADIUS Extensions February 2012

B4 NAS AAA
| | Server
|------ DHCPv6 Solicit ---------> | |
| | |
| |----Access-Request ---->|
| | |
| |<---Access-Accept-------|
| | (DS-Lite-Tunnel-Name) |
| | |
|<-------DHCPv6 Advertisement------| |
| (DHCPv6 OPTION_AFTR_NAME) | |
| | |
|------- DHCPv6 Request -------->| |
| | |
| | |
|<----- DHCPv6 Reply ------------- | |
| (DHCPv6 OPTION_AFTR_NAME) | |

DHCPv6 RADIUS

Figure 2: RADIUS and DHCPv6 Message Flow for an IP Session

In the scenario depicted in Figure 2, the Access-Request packet
contains a Service-Type attribute with the value Authorize Only (17);
thus, according to [RFC5080], the Access-Request packet MUST contain
a State attribute.

After receiving the DS-Lite-Tunnel-Name attribute in the initial
Access-Accept packet, the NAS MUST store the received AFTR tunnel
name locally. When the B4 sends a DHCPv6 Renew message to request an
extension of the lifetimes for the assigned address or prefix, the
NAS does not have to initiate a new Access-Request packet towards the
AAA server to request the AFTR tunnel name. The NAS retrieves the
previously stored AFTR tunnel name and uses it in its reply.

According to [RFC3315], if the DHCPv6 server to which the DHCPv6
Renew message was sent at time T1 has not responded, the DHCPv6
client initiates a Rebind/Reply message exchange with any available
server. In this scenario, the NAS receiving the DHCPv6 Rebind
message MUST initiate a new Access-Request message towards the AAA
server. The NAS MAY include the DS-Lite-Tunnel-Name attribute in its
Access-Request message.

If the NAS does not receive the DS-Lite-Tunnel-Name attribute in the
Access-Accept message, it MAY fall back to a pre-configured default
tunnel name, if any. If the NAS does not have any pre-configured

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RFC 6519 DS-Lite RADIUS Extensions February 2012

default tunnel name or if the NAS receives an Access-Reject message,
the IPv4-over-IPv6 tunnel cannot be established; thus, the B4 element
has only IPv6 connectivity.

4. RADIUS Attribute

This section specifies the format of the new RADIUS attribute.

4.1. DS-Lite-Tunnel-Name

The DS-Lite-Tunnel-Name RADIUS attribute contains an FQDN that refers
to the AFTR to which the client is requested to establish a
connection. The NAS SHALL use the name returned in the RADIUS
DS-Lite-Tunnel-Name attribute to populate the DHCPv6 OPTION_AFTR_NAME
option [RFC6334].

This attribute MAY be used in Access-Request packets as a hint to the
RADIUS server; for example, if the NAS is pre-configured with a
default tunnel name, this name MAY be inserted in the attribute. The
RADIUS server MAY ignore the hint sent by the NAS, and it MAY assign
a different AFTR tunnel name.

If the NAS includes the DS-Lite-Tunnel-Name attribute, but the AAA
server does not recognize it, this attribute MUST be ignored by the
AAA server.

If the NAS does not receive the DS-Lite-Tunnel-Name attribute in the
Access-Accept message, it MAY fall back to a pre-configured default
tunnel name, if any. If the NAS does not have any pre-configured
default tunnel name, the tunnel cannot be established.

If the NAS is pre-provisioned with a default AFTR tunnel name and the
AFTR tunnel name received in the Access-Accept message is different
from the configured default, then the AFTR tunnel name received in
the Access-Accept message MUST be used for the session.

If the NAS cannot support the received AFTR tunnel name for any
reason, the tunnel SHOULD NOT be established.

When the Access-Request message is triggered by a DHCPv6 Rebind
message, if the AFTR tunnel name received in the Access-Accept
message is different from the currently used one for that session,
the NAS MUST force the B4 to re-establish the tunnel using the new
AFTR name received in the Access-Accept message.

If an implementation includes Change-of-Authorization (CoA) messages
[RFC5176], they could be used to modify the current established
DS-Lite tunnel. When the NAS receives a CoA Request message

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containing the DS-Lite-Tunnel-Name attribute, the NAS MUST send a
Reconfigure message to a B4 to inform the B4 that the NAS has new or
updated configuration parameters and that the B4 is to initiate a
Renew/Reply or Information-Request/Reply transaction with the NAS in
order to receive the updated information.

Upon receiving an AFTR tunnel name different from the currently used
one, the B4 MUST terminate the current DS-Lite tunnel, and the B4
MUST establish a new DS-Lite tunnel with the specified AFTR.

The DS-Lite-Tunnel-Name RADIUS attribute MAY be present in
Accounting-Request records where the Acct-Status-Type is set to
Start, Stop, or Interim-Update. The DS-Lite-Tunnel-Name RADIUS
attribute MUST NOT appear more than once in a message.

A summary of the DS-Lite-Tunnel-Name RADIUS 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 | DS-Lite-Tunnel-Name (FQDN)...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type:

144 for DS-Lite-Tunnel-Name.

Length:

This field indicates the total length in octets of this
attribute including the Type and Length fields, and the length
in octets of the DS-Lite-Tunnel-Name field.

DS-Lite-Tunnel-Name:

This field contains a single FQDN of the remote tunnel endpoint,
located at the DS-Lite AFTR.

As the DS-Lite-Tunnel-Name attribute is used to populate the DHCPv6
OPTION_AFTR_NAME option, the DS-Lite-Tunnel-Name field is formatted
as required in DHCPv6 (Section 8 of [RFC3315] -- "Representation and
Use of Domain Names"). Briefly, the format described is using a
single octet noting the length of one DNS label (limited to at most
63 octets), followed by the label contents. This repeats until all
labels in the FQDN are exhausted, including a terminating zero-length
label. Any updates to Section 8 of [RFC3315] also apply to the
encoding of this field.

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RFC 6519 DS-Lite RADIUS Extensions February 2012

The data type of the DS-Lite-Tunnel-Name RADIUS attribute is a string
with opaque encapsulation, according to Section 5 of [RFC2865].

5. Table of Attributes

The following tables provide a guide to which attributes may be found
in which kinds of packets, and in what quantity.

Access- Access- Access- Challenge Accounting # Attribute
Request Accept Reject Request
0-1 0-1 0 0 0-1 144 DS-Lite-Tunnel-Name

CoA-Request CoA-ACK CoA-NACK # Attribute
0-1 0 0 144 DS-Lite-Tunnel-Name

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

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

6. Security Considerations

This document has no additional security considerations beyond those
already identified in [RFC2865] for the RADIUS protocol and in
[RFC5176] for CoA messages.

[RFC6333] discusses security issues related to Dual-Stack Lite.

7. IANA Considerations

Per this document, IANA has allocated a new RADIUS attribute type
from the IANA registry "Radius Attribute Types" located at
http://www.iana.org/assignments/radius-types.

DS-Lite-Tunnel-Name - 144

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RFC 6519 DS-Lite RADIUS Extensions February 2012

8. References

8.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)",
RFC 2865, June 2000.

[RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T.,
Perkins, C., and M. Carney, "Dynamic Host
Configuration Protocol for IPv6 (DHCPv6)", RFC 3315,
July 2003.

[RFC5080] Nelson, D. and A. DeKok, "Common Remote Authentication
Dial In User Service (RADIUS) Implementation Issues
and Suggested Fixes", RFC 5080, December 2007.

[RFC6333] Durand, A., Droms, R., Woodyatt, J., and Y. Lee,
"Dual-Stack Lite Broadband Deployments Following IPv4
Exhaustion", RFC 6333, August 2011.

[RFC6334] Hankins, D. and T. Mrugalski, "Dynamic Host
Configuration Protocol for IPv6 (DHCPv6) Option for
Dual-Stack Lite", RFC 6334, August 2011.

8.2. Informative References

[RADIUS-IPv6] Lourdelet, B., Dec, W., Ed., Sarikaya, B., Zorn, G.,
and D. Miles, "RADIUS attributes for IPv6 Access
Networks", Work in Progress, November 2011.

[RFC5176] Chiba, M., Dommety, G., Eklund, M., Mitton, D., and B.
Aboba, "Dynamic Authorization Extensions to Remote
Authentication Dial In User Service (RADIUS)",
RFC 5176, January 2008.

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RFC 6519 DS-Lite RADIUS Extensions February 2012

Authors' Addresses

Roberta Maglione
Telecom Italia
Via Reiss Romoli 274
Torino 10148
Italy

EMail: [email protected]

Alain Durand
Juniper Networks
1194 North Mathilda Avenue
Sunnyvale, CA 94089-1206
USA

EMail: [email protected]

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