





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

   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
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   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











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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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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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       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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       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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   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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   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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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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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

































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