RADIUS Attribute for IPv6 Rapid Deployment on IPv4 Infrastructures (6rd)
RFC 6930

Internet Engineering Task Force (IETF)                            D. Guo
Request for Comments: 6930                                 S. Jiang, Ed.
Category: Standards Track                   Huawei Technologies Co., Ltd
ISSN: 2070-1721                                               R. Despres
                                                               RD-IPtech
                                                             R. Maglione
                                                           Cisco Systems
                                                              April 2013

               RADIUS Attribute for IPv6 Rapid Deployment
                     on IPv4 Infrastructures (6rd)

Abstract

   The IPv6 Rapid Deployment on IPv4 Infrastructures (6rd) provides both
   IPv4 and IPv6 connectivity services simultaneously during the
   IPv4/IPv6 coexistence period.  The Dynamic Host Configuration
   Protocol (DHCP) 6rd option has been defined to configure the 6rd
   Customer Edge (CE).  However, in many networks, the configuration
   information may be stored in the Authentication Authorization and
   Accounting (AAA) servers, while user configuration is mainly acquired
   from a Broadband Network Gateway (BNG) through the DHCP protocol.
   This document defines a Remote Authentication Dial-In User Service
   (RADIUS) attribute that carries 6rd configuration information from
   the AAA server to BNGs.

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/rfc6930.

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Copyright Notice

   Copyright (c) 2013 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.

Table of Contents

   1. Introduction ....................................................3
   2. Terminology .....................................................3
   3. IPv6 6rd Configuration with RADIUS ..............................4
   4. Attributes ......................................................6
      4.1. IPv6-6rd-Configuration Attribute ...........................6
      4.2. Table of Attributes ........................................9
   5. Diameter Considerations .........................................9
   6. Security Considerations .........................................9
   7. IANA Considerations ............................................10
   8. Acknowledgments ................................................10
   9. References .....................................................10
      9.1. Normative References ......................................10
      9.2. Informative References ....................................11

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1.  Introduction

   Recently, providers have started to deploy IPv6 and to consider
   transition to IPv6.  The IPv6 Rapid Deployment (6rd) [RFC5969]
   provides both IPv4 and IPv6 connectivity services simultaneously
   during the IPv4/IPv6 coexistence period.  6rd is used to provide IPv6
   connectivity service through legacy IPv4-only infrastructure.  6rd
   uses the Dynamic Host Configuration Protocol (DHCP) [RFC2131], and
   the 6rd Customer Edge (CE) uses the DHCP 6rd option [RFC5969] to
   discover a 6rd Border Relay and to configure an IPv6 prefix and
   address.

   In many networks, user-configuration information is managed by
   Authentication, Authorization, and Accounting (AAA) servers.  The
   Remote Authentication Dial-In User Service (RADIUS) protocol
   [RFC2865] is usually used by AAA servers to communicate with network
   elements.  In a fixed-line broadband network, the Broadband Network
   Gateways (BNGs) act as the access gateway for users.  The BNGs are
   assumed to embed a DHCP server function that allows them to handle
   locally any DHCP requests issued by hosts.

   Since the 6rd configuration information is stored in AAA servers, and
   user configuration is mainly through DHCP between BNGs and hosts/CEs,
   new RADIUS attributes are needed to propagate the information from
   AAA servers to BNGs.

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 6rd Customer Edge (6rd CE) and 6rd Border Relay (BR) are
   defined in [RFC5969].  "MAC" stands for Media Access Control.

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3.  IPv6 6rd Configuration with RADIUS

   Figure 1 illustrates how DHCP and the RADIUS protocol cooperate to
   provide 6rd CE with 6rd configuration information.

      6rd CE                       BNG                       AAA Server
         |                          |                             |
         |-------DHCPDISCOVER------>|                             |
         |(Parameter Request w/ 6rd option)                       |
         |                          |--Access-Request(6rd Attr)-->|
         |                          |                             |
         |                          |<--Access-Accept(6rd Attr)---|
         |<-------DHCPOFFER---------|                             |
         |      (6rd option)        |                             |
         |                          |                             |
                   DHCP                         RADIUS

             Figure 1: The Cooperation between DHCP and RADIUS
                 When Combined with RADIUS Authentication

   The BNG acts as a client of RADIUS and as a DHCP server.  First, the
   6rd CE MAY initiate a DHCPDISCOVER message that includes a Parameter
   Request option (55) [RFC2132] with the 6rd option [RFC5969].  When
   the BNG receives the DHCPDISCOVER, it SHOULD initiate a RADIUS
   Access- Request message to the RADIUS server. In that message,

   -  the User-Name attribute (1) SHOULD be filled by the 6rd CE MAC
      address, and

   -  the User-Password attribute (2) SHOULD be filled by the shared 6rd
      password that has been preconfigured on the DHCP server.

   The BNG requests authentication, as defined in [RFC2865], with the
   IPv6-6rd-Configuration attribute (Section 4.1) in the desired
   attribute list.  If the authentication request is approved by the AAA
   server, an Access-Accept message MUST be acknowledged with the
   IPv6-6rd-Configuration attribute.  Then, the BNG SHOULD respond to
   the 6rd CE with a DHCPOFFER message, which contains a DHCP 6rd
   option.  The recommended format of the MAC address is as defined in
   Calling-Station-Id ([RFC3580], Section 3.20) without the SSID
   (Service Set Identifier) portion.

   Figure 2 describes another scenario -- later re-authorization -- in
   which the authorization operation is not coupled with authentication.
   Authorization relevant to 6rd is done independently after the
   authentication process.

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      6rd CE                       BNG                       AAA Server
         |                          |                             |
         |--------DHCPREQUEST------>|                             |
         |(Parameter Request w/ 6rd option)                       |
         |                          |--Access-Request(6rd Attr)-->|
         |                          |                             |
         |                          |<--Access-Accept(6rd Attr)---|
         |                          |                             |
         |<---------DHCPACK---------|                             |
         |      (6rd option)        |                             |
         |                          |                             |
                   DHCP                         RADIUS

             Figure 2: The Cooperation between DHCP and RADIUS
                 When Decoupled from RADIUS Authentication

   In this scenario, the Access-Request packet SHOULD contain a Service-
   Type attribute (6) with the value Authorize Only (17); thus,
   according to [RFC5080], the Access-Request packet MUST contain a
   State attribute that it obtains from the previous authentication
   process.

   In both above-mentioned scenarios, Message-Authenticator (type 80)
   [RFC2865] SHOULD be used to protect both Access-Request and Access-
   Accept messages.

   After receiving the IPv6-6rd-Configuration attribute in the initial
   Access-Accept, the BNG SHOULD store the received 6rd configuration
   parameters locally.  When the 6rd CE sends a DHCP Request message to
   request an extension of the lifetime for the assigned address, the
   BNG does not have to initiate a new Access-Request towards the AAA
   server to request the 6rd configuration parameters.  The BNG could
   retrieve the previously stored 6rd configuration parameters and use
   them in its reply.

   If the BNG does not receive the IPv6-6rd-Configuration attribute in
   the Access-Accept, it MAY fall back to a preconfigured default 6rd
   configuration, if any.  If the BNG does not have any preconfigured
   default 6rd configuration or if the BNG receives an Access-Reject,
   the tunnel cannot be established.

   As specified in [RFC2131], Section 4.4.5 ("Reacquisition and
   expiration"), if the DHCP server to which the DHCP Request message
   was sent at time T1 has not responded by time T2 (typically
   0.375*duration_of_lease after T1), the 6rd CE (the DHCP client)
   SHOULD enter the REBINDING state and attempt to contact any server.

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RFC 6930                     RADIUS for 6rd                   April 2013

   In this situation, the secondary BNG receiving the new DHCP message
   MUST initiate a new Access-Request towards the AAA server.  The
   secondary BNG MAY include the IPv6-6rd-Configuration attribute in its
   Access-Request.

4.  Attributes

   This section defines the IPv6-6rd-Configuration attribute that is
   used in both above-mentioned scenarios.  The attribute design follows
   [RFC6158] and refers to [RFC6929].

4.1.  IPv6-6rd-Configuration Attribute

   The specification requires that multiple IPv4 addresses are
   associated with one IPv6 prefix.  Given that RADIUS currently has no
   recommended way of grouping multiple attributes, the design below
   appears to be a reasonable compromise.  The IPv6-6rd-Configuration
   attribute is structured as follows:

       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     |    SubType1   |    SubLen1    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          IPv4MaskLen                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    SubType2   |    SubLen2    |  Reserved     |  6rdPrefixLen |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      +                                                               +
      |                                                               |
      +                           6rdPrefix                           +
      |                                                               |
      +                                                               +
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   SubType3    |    SubLen3    |        6rdBRIPv4Address       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |        6rdBRIPv4Address       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       Type

         173

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       Length

         28 + n*6 (the length of the entire attribute in octets, where n
         is the number of BR IPv4 addresses and minimum n is 1)

       SubType1

         1 (SubType number, for the IPv4 Mask Length suboption)

       SubLen1

         6 (the length of the IPv4 Mask Length suboption)

       IPv4MaskLen

         The number of high-order bits that are identical across all CE
         IPv4 addresses within a given 6rd domain.  This may be any
         value between 0 and 32.  Any value greater than 32 is invalid.
         Since [RFC6158], Appendix A.2.1, has forbidden 8-bit fields, a
         32-bit field is used here.

       SubType2

         2 (SubType number for the 6rd prefix suboption)

       SubLen2

         20 (the length of the 6rd prefix suboption)

       Reserved

         Set to all 0 for now.  Reserved for future use.  To be
         compatible with other IPv6 prefix attributes in the RADIUS
         protocol, the bits MUST be set to zero by the sender and MUST
         be ignored by the receiver.

       6rdPrefixLen

         The IPv6 Prefix length of the Service Provider's 6rd IPv6
         prefix in number of bits.  The 6rdPrefixLen MUST be less than
         or equal to 128.

       6rdPrefix

         The Service Provider's 6rd IPv6 prefix represented as a
         16-octet IPv6 address.  The bits after the 6rdPrefixlen number
         of bits in the prefix SHOULD be set to zero.

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       SubType3

         3 (SubType number, for the 6rd Border Relay IPv4 address
         suboption)

       SubLen3

         6 (the length of the 6rd Border Relay IPv4 address suboption)

       6rdBRIPv4Address

         One or more IPv4 addresses of the 6rd Border Relay(s) for a
         given 6rd domain.  The maximum RADIUS attribute length of 255
         octets results in a limit of 37 IPv4 addresses.

   Since the subtypes have values, they can appear in any order.  If
   multiple 6rdBRIPv4Address (subtype 3) appear, they are RECOMMENDED to
   be placed together.

   The IPv6-6rd-Configuration attribute is normally used in Access-
   Accept messages.  It MAY be used in Access-Request packets as a hint
   to the RADIUS server; for example, if the BNG is preconfigured with a
   default 6rd configuration, these parameters MAY be inserted in the
   attribute.  The RADIUS server MAY ignore the hint sent by the BNG,
   and it MAY assign different 6rd parameters.

   If the BNG includes the IPv6-6rd-Configuration attribute, but the AAA
   server does not recognize it, this attribute MUST be ignored by the
   AAA server.

   If the BNG does not receive the IPv6-6rd-Configuration attribute in
   the Access-Accept, it MAY fallback to a preconfigured default 6rd
   configuration, if any.  If the BNG does not have any preconfigured
   default 6rd configuration, the 6rd tunnel cannot be established.

   If the BNG is pre-provisioned with a default 6rd configuration and
   the 6rd configuration received in Access-Accept is different from the
   configured default, then the 6rd configuration received in the
   Access-Accept message MUST be used for the session.

   If the BNG cannot support the received 6rd configuration for any
   reason, the tunnel SHOULD NOT be established.

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4.2.  Table of Attributes

   The following table adds to the one in [RFC2865], Section 5.44,
   providing a guide to the quantity of IPv6-6rd-Configuration
   attributes that may be found in each kind of packet.

   Request Accept Reject Challenge Accounting  #  Attribute
                                    Request
    0-1     0-1     0      0         0-1      173  IPv6-6rd-
                                                   Configuration
    0-1     0-1     0      0         0-1      1    User-Name
    0-1     0       0      0         0-1      2    User-Password
    0-1     0-1     0      0         0-1      6    Service-Type
    0-1     0-1     0-1    0-1       0-1      80   Message-Authenticator

   The following key defines the meanings 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.
   1     Exactly one instance of this attribute MUST be present in
         packet.

5.  Diameter Considerations

   This attribute is usable within either RADIUS or Diameter [RFC6733].
   Since the attribute defined in this document has been allocated from
   the standard RADIUS type space, no special handling is required by
   Diameter entities.

6.  Security Considerations

   In 6rd scenarios, both CE and BNG are within a provider network,
   which can be considered as a closed network and a lower-threat
   environment.  A similar consideration can be applied to the RADIUS
   message exchange between the BNG and the AAA server.

   In 6rd scenarios, the RADIUS protocol is run over IPv4.  Known
   security vulnerabilities of the RADIUS protocol are discussed in
   [RFC2607], [RFC2865], and [RFC2869].  Use of IPsec [RFC4301] for
   providing security when RADIUS is carried in IPv6 is discussed in
   [RFC3162].

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RFC 6930                     RADIUS for 6rd                   April 2013

   To get unauthorized 6rd configuration information, a malicious user
   may use MAC address spoofing and/or a dictionary attack on the shared
   6rd password that has been preconfigured on the DHCP server.  The
   relevant security issues have been considered in Section 12 of
   [RFC5969].

   Security issues that may arise specifically between the 6rd CE and
   BNG are discussed in [RFC5969].  Furthermore, generic DHCP security
   mechanisms can be applied to DHCP intercommunication between 6rd CE
   and BNG.

   Security considerations for the Diameter protocol are discussed in
   [RFC6733].

7.  IANA Considerations

   Per this document, IANA has assigned one new RADIUS Attribute Type in
   the "Radius Types" registry (currently located at
   http://www.iana.org/assignments/radius-types) for the following
   attribute:

      IPv6-6rd-Configuration (173)

8.  Acknowledgments

   The authors would like to thank Alan DeKok, Yong Cui, Leaf Yeh, Sean
   Turner, Joseph Salowey, Glen Zorn, Dave Nelson, Bernard Aboba, Benoit
   Claise, Barry Lieba, Stephen Farrell, Adrian Farrel, Ralph Droms, and
   other members of the SOFTWIRE WG, RADEXT WG, AAA Doctors, and
   Security Directorate for valuable comments.

9.  References

9.1.  Normative References

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

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol", RFC
              2131, March 1997.

   [RFC2132]  Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
              Extensions", RFC 2132, March 1997.

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

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   [RFC3162]  Aboba, B., Zorn, G., and D. Mitton, "RADIUS and IPv6", RFC
              3162, August 2001.

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, December 2005.

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

   [RFC5969]  Townsley, W. and O. Troan, "IPv6 Rapid Deployment on IPv4
              Infrastructures (6rd) -- Protocol Specification", RFC
              5969, August 2010.

   [RFC6158]  DeKok, A., Ed., and G. Weber, "RADIUS Design Guidelines",
              BCP 158, RFC 6158, March 2011.

   [RFC6733]  Fajardo, V., Ed., Arkko, J., Loughney, J., and G. Zorn,
              Ed., "Diameter Base Protocol", RFC 6733, October 2012.

9.2.  Informative References

   [RFC2607]  Aboba, B. and J. Vollbrecht, "Proxy Chaining and Policy
              Implementation in Roaming", RFC 2607, June 1999.

   [RFC2869]  Rigney, C., Willats, W., and P. Calhoun, "RADIUS
              Extensions", RFC 2869, June 2000.

   [RFC3580]  Congdon, P., Aboba, B., Smith, A., Zorn, G., and J. Roese,
              "IEEE 802.1X Remote Authentication Dial In User Service
              (RADIUS) Usage Guidelines", RFC 3580, September 2003.

   [RFC6929]  DeKok, A. and A. Lior, "Remote Authentication Dial-In User
              Service (RADIUS) Protocol Extensions", RFC 6929, April
              2013.

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Authors' Addresses

   Dayong Guo
   Huawei Technologies Co., Ltd
   Q14 Huawei Campus, 156 BeiQi Road,
   ZhongGuan Cun, Hai-Dian District, Beijing 100095
   P.R. China

   EMail: guoseu@huawei.com

   Sheng Jiang (Editor)
   Huawei Technologies Co., Ltd
   Q14 Huawei Campus, 156 BeiQi Road,
   ZhongGuan Cun, Hai-Dian District, Beijing 100095
   P.R. China

   EMail: jiangsheng@huawei.com

   Remi Despres
   RD-IPtech
   3 rue du President Wilson
   Levallois
   France

   EMail: despres.remi@laposte.net

   Roberta Maglione
   Cisco Systems
   181 Bay Street
   Toronto, ON
   M5J 2T3
   Canada

   EMail: robmgl@cisco.com

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