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rfc:rfc6519

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.

Maglione & Durand Standards Track [Page 1] RFC 6519 DS-Lite RADIUS Extensions February 2012

Copyright Notice

 Copyright (c) 2012 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.
 This document may contain material from IETF Documents or IETF
 Contributions published or made publicly available before November
 10, 2008.  The person(s) controlling the copyright in some of this
 material may not have granted the IETF Trust the right to allow
 modifications of such material outside the IETF Standards Process.
 Without obtaining an adequate license from the person(s) controlling
 the copyright in such materials, this document may not be modified
 outside the IETF Standards Process, and derivative works of it may
 not be created outside the IETF Standards Process, except to format
 it for publication as an RFC or to translate it into languages other
 than English.

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

Maglione & Durand Standards Track [Page 2] 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].

Maglione & Durand Standards Track [Page 3] 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.

Maglione & Durand Standards Track [Page 4] 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.

Maglione & Durand Standards Track [Page 5] 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

Maglione & Durand Standards Track [Page 6] 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

Maglione & Durand Standards Track [Page 7] RFC 6519 DS-Lite RADIUS Extensions February 2012

 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.

Maglione & Durand Standards Track [Page 8] 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

Maglione & Durand Standards Track [Page 9] 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.

Maglione & Durand Standards Track [Page 10] RFC 6519 DS-Lite RADIUS Extensions February 2012

Authors' Addresses

 Roberta Maglione
 Telecom Italia
 Via Reiss Romoli 274
 Torino  10148
 Italy
 EMail: roberta.maglione@telecomitalia.it
 Alain Durand
 Juniper Networks
 1194 North Mathilda Avenue
 Sunnyvale, CA  94089-1206
 USA
 EMail: adurand@juniper.net

Maglione & Durand Standards Track [Page 11]

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