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rfc:rfc7037

Internet Engineering Task Force (IETF) L. Yeh Request for Comments: 7037 Freelancer Technologies Category: Standards Track M. Boucadair ISSN: 2070-1721 France Telecom

                                                          October 2013
              RADIUS Option for the DHCPv6 Relay Agent

Abstract

 The DHCPv6 RADIUS option provides a mechanism to exchange
 authorization and identification information between the DHCPv6 relay
 agent and DHCPv6 server.  This architecture assumes that the Network
 Access Server (NAS) acts as both a DHCPv6 relay agent and RADIUS
 client.  When receiving messages from the DHCPv6 clients, the NAS
 consults the RADIUS server and adds the RADIUS response when
 forwarding the DHCPv6 client's messages to the DHCPv6 server.  The
 DHCPv6 server then uses that additional information to generate an
 appropriate response to the DHCPv6 client's requests.

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/rfc7037.

Yeh & Boucadair Standards Track [Page 1] RFC 7037 DHCPv6 RADIUS Option October 2013

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
 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.

Table of Contents

 1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
 2.  Terminology and Language  . . . . . . . . . . . . . . . . . .   3
 3.  Network Scenarios . . . . . . . . . . . . . . . . . . . . . .   3
 4.  DHCPv6 RADIUS Option  . . . . . . . . . . . . . . . . . . . .   6
   4.1.  RADIUS Attributes Permitted in DHCPv6 RADIUS Option . . .   7
 5.  DHCPv6 Relay Agent Behavior . . . . . . . . . . . . . . . . .   7
 6.  DHCPv6 Server Behavior  . . . . . . . . . . . . . . . . . . .   7
 7.  DHCPv6 Client Behavior  . . . . . . . . . . . . . . . . . . .   7
 8.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
 9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
 10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
 11. References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
   11.1.  Normative References . . . . . . . . . . . . . . . . . .   9
   11.2.  Informative References . . . . . . . . . . . . . . . . .  10

1. Introduction

 DHCPv6 provides a mechanism that allows the server to assign or
 delegate both stateful and stateless configuration parameters to
 clients.  The stateful configuration parameters include IPv6
 addresses [RFC3315] and IPv6 prefixes [RFC3633].  The stateless
 configuration parameters [RFC3736] include, for example, DNS
 [RFC3646], or a Fully Qualified Domain Name (FQDN) of an Address
 Family Transition Router (AFTR) [RFC6334].  In the scenarios
 described in this document, the DHCPv6 server is deployed in the
 central part of an ISP network.
 RADIUS [RFC2865] is widely used as the centralized authentication,
 authorization, and user management mechanism for service provision in
 a Broadband access network.  [RFC3162], [RFC4818], [RFC6519], and
 [RFC6911] specify the attributes that support the service provision

Yeh & Boucadair Standards Track [Page 2] RFC 7037 DHCPv6 RADIUS Option October 2013

 for IPv6-only and IPv6-transition access.  The RADIUS server
 authorizes the Network Access Server (NAS) to assign an IPv6 address
 or prefix from the indicated pool, or to assign an IPv6 address or
 prefix with an explicitly indicated value, and to indicate other
 configuration parameters as per the RADIUS attributes for the
 subscribers.
 When the NAS acts as the distributed DHCPv6 server and RADIUS client
 simultaneously, it communicates with the RADIUS server after
 receiving a request from the DHCPv6 client.  Upon receiving the
 Access-Accept message from the RADIUS server, the NAS then responds
 to the DHCPv6 client's requests per the associated authorization
 information indicated by the RADIUS attributes in the Access-Accept
 message.  When NAS acts as the DHCPv6 relay agent and RADIUS client
 simultaneously, and the centralized DHCPv6 server is co-located with
 the RADIUS server, they may share the same database of users.
 However, when the centralized DHCPv6 server is not located in the
 same place as the RADIUS server, a new communication mechanism is
 needed for the DHCPv6 relay agent to transfer the authorization
 information indicated by the RADIUS attributes to the DHCPv6 server.

2. Terminology and Language

 This document specifies a new DHCPv6 option for the DHCPv6 Relay
 Agent to transfer the authorization information of RADIUS attributes
 received in the Access-Accept message from the RADIUS server to the
 centralized DHCPv6 server.  Definitions for terms and acronyms not
 specified in this document are defined in [RFC2865] and [RFC3315].
 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].

3. Network Scenarios

 Figures 1 and 2 show the typical network scenarios where the
 communication mechanism introduced in this document is necessary.  In
 these scenarios, the centralized DHCPv6 server is not co-located with
 the RADIUS server, but both are in the same administrative domain.
 The NAS acts as the DHCPv6 relay agent and the RADIUS client
 simultaneously.  Figure 1 shows the sequence of DHCPv6 and RADIUS
 messages for the IP over Ethernet (IPoE) access model, when the
 access loop adopts the direct Ethernet encapsulation.  Figure 2 shows
 the sequence of DHCPv6 and RADIUS messages for the PPP over Ethernet
 (PPPoE) access model.

Yeh & Boucadair Standards Track [Page 3] RFC 7037 DHCPv6 RADIUS Option October 2013

 The mechanism introduced in this document is a generic mechanism and
 might also be employed in other network scenarios where the DHCPv6
 relay agent and the RADIUS client are located in the same device.
 +-------+                   +-------+                    +-------+
 |DHCPv6 |   Access Model:   |  NAS  |                    |RADIUS |
 |Client |       IPoE        |       |                    |Server |
 +-------+                   +-------+                    +-------+
                    RADIUS Client/DHCPv6 Relay Agent
     |                           |                            |
     |---Solicit---------------->|                            |
     |                           |---Access-Request---------->|
     |                           |                            |
     |                           |<--Access-Accept------------|
     |                           |(e.g. Delegated-IPv6-Prefix)|
     |                           |                            |
            DHCPv6 messages             RADIUS messages
                                                          +-------+
                                                          |DHCPv6 |
                                                          |Server |
                                                          +-------+
     |                           |                            |
     |                           |---Relay-forward----------->|
     |                           |  (OPTION_RADIUS)           |
     |                           |                            |
     |                           |<--Relay-reply -------------|
     |<--Advertise---------------|                            |
     |  (e.g., IA_PD)            |                            |
     |                           |                            |
     |---Request---------------->|                            |
     |  (e.g., IA_PD)            |---Relay-forward----------->|
     |                           |  (OPTION_RADIUS)           |
     |                           |                            |
     |                           |<--Relay-reply -------------|
     |<--Reply-------------------|                            |
     |  (e.g., IA_PD)            |                            |
     |                           |                            |
            DHCPv6 messages             DHCPv6 messages
 Figure 1: Network Scenario and Message Sequence When Employing DHCPv6
                     RADIUS Option in IPoE Access

Yeh & Boucadair Standards Track [Page 4] RFC 7037 DHCPv6 RADIUS Option October 2013

 +-------+                   +-------+                    +-------+
 |DHCPv6 |   Access Model:   |  NAS  |                    |RADIUS |
 |Client |      PPPoE        |       |                    |Server |
 +-------+                   +-------+                    +-------+
                    RADIUS Client/DHCPv6 Relay Agent
     |                           |                            |
     |--PPP LCP Config-Request-->|                            |
     |                           |---Access-Request---------->|
     |                           |                            |
     |                           |<--Access-Accept------------|
     |<----PPP LCP Config-ACK----|(e.g. Delegated-IPv6-Prefix)|
     |                           |                            |
             PPP messages               RADIUS messages
                                                          +-------+
                                                          |DHCPv6 |
                                                          |Server |
                                                          +-------+
     |                           |                            |
     |---Solicit---------------->|                            |
     |                           |---Relay-forward----------->|
     |                           |  (OPTION_RADIUS)           |
     |                           |                            |
     |                           |<--Relay-reply -------------|
     |<--Advertise---------------|                            |
     |  (e.g., IA_PD)            |                            |
     |                           |                            |
     |---Request---------------->|                            |
     |  (e.g., IA_PD)            |---Relay-forward----------->|
     |                           |  (OPTION_RADIUS)
     |                           |                            |
     |                           |<--Relay-reply -------------|
     |<--Reply-------------------|                            |
     |  (e.g., IA_PD)            |                            |
     |                           |                            |
            DHCPv6 messages             DHCPv6 messages
 Figure 2: Network Scenario and Message Sequence When Employing DHCPv6
                     RADIUS Option in PPPoE Access
 If the authentication or the authorization through RADIUS fails, the
 associated message sequences will stop.  The NAS acting as the DHCPv6
 relay agent will not forward the message received from the client to
 the DHCPv6 server.  If the authentication or the authorization
 through RADIUS passes, the NAS MUST store the information indicated

Yeh & Boucadair Standards Track [Page 5] RFC 7037 DHCPv6 RADIUS Option October 2013

 in the RADIUS attributes received in the Access-Accept message from
 the RADIUS server during the whole session.  How the NAS manages this
 information during the RADIUS session is out of the scope of this
 document.
 After receiving a RENEW (5) message from the DHCPv6 client, the NAS
 SHOULD NOT initiate a new Access-Request/Access-Accept message
 exchange with the RADIUS server.  After receiving a REBIND (6)
 message from the DHCPv6 client, the NAS MUST initiate a new Access-
 Request/Access-Accept message exchange with the RADIUS server, unless
 RADIUS capability is disabled on the NAS.

4. DHCPv6 RADIUS Option

 The OPTION_RADIUS is a DHCPv6 option used by the DHCPv6 relay agent
 to carry the authorization information of RADIUS attributes received
 in the Access-Accept message from the RADIUS server.
 The format of the OPTION_RADIUS option is defined 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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         OPTION_RADIUS         |          option-len           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |            option-data (List of RADIUS Attributes)
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 option-code      81
 option-len       Length of the option-data in octets
 option-data      List of one or more RADIUS attributes
 The option-data of OPTION_RADIUS is a list of one or more RADIUS
 attributes received in the Access-Accept message from the RADIUS
 server.  The format of RADIUS attributes is defined in Section 5 of
 [RFC2865] as well as Sections 2.1 and 2.2 of [RFC6929].  If multiple
 attributes with the same type (including the Long Extended Type
 defined in Section 2.2 of [RFC6929]) are present, the order of
 attributes with the same type MUST be the same as that received from
 the RADIUS server.  The OPTION_RADIUS can only contain the RADIUS
 attributes listed in the "RADIUS Attributes Permitted in DHCPv6
 RADIUS Option" registry.

Yeh & Boucadair Standards Track [Page 6] RFC 7037 DHCPv6 RADIUS Option October 2013

 According to the network scenarios described in Section 3, the
 OPTION_RADIUS should appear in the RELAY-FORW (12) message relaying
 SOLICIT (1), REQUEST (3), and REBIND (6) from the DHCPv6 client and
 may appear in the RELAY-FORW (12) relaying any other message from the
 DHCPv6 client.

4.1. RADIUS Attributes Permitted in DHCPv6 RADIUS Option

 The RADIUS attributes listed in the following table are the initial
 attributes registered in the "RADIUS Attributes Permitted in DHCPv6
 RADIUS Option" registry.  New RADIUS attributes can be added to this
 list after Expert Review [RFC5226].
 Type Code  Attribute                   Reference
 26         Vendor-Specific             [RFC2865]
 123        Delegated-IPv6-Prefix       [RFC4818]
 144        DS-Lite-Tunnel-Name         [RFC6519]
 168        Framed-IPv6-Address         [RFC6911]
 169        DNS-Server-IPv6-Address     [RFC6911]
 171        Delegated-IPv6-Prefix-Pool  [RFC6911]
 172        Stateful-IPv6-Address-Pool  [RFC6911]
 Note: The RADIUS attribute's 'Length' defined in Section 5 of
 [RFC2865] includes the length of 'Type' and 'Length' fields.

5. DHCPv6 Relay Agent Behavior

 If the Relay Agent is configured to send OPTION_RADIUS, and the
 Access-Accept message from the RADIUS server contained RADIUS
 attributes permitted for use in OPTION_RADIUS, the Relay Agent MUST
 include OPTION_RADIUS in the RELAY-FORW (12) message.  The DHCPv6
 relay agent adds the permitted RADIUS attributes into OPTION_RADIUS
 one by one; if multiple attributes with the same type are present,
 the order of attributes with the same type MUST be the same as that
 received from the RADIUS server.

6. DHCPv6 Server Behavior

 Upon receipt of the RELAY-FORW (12) message with OPTION_RADIUS from a
 relay agent, the DHCPv6 server that supports OPTION_RADIUS SHOULD
 extract and interpret the RADIUS attributes in the OPTION_RADIUS and
 use that information to select configuration parameters for the
 requesting client.  If the DHCPv6 server does not support
 OPTION_RADIUS, the DHCPv6 server MUST silently discard this option.

Yeh & Boucadair Standards Track [Page 7] RFC 7037 DHCPv6 RADIUS Option October 2013

7. DHCPv6 Client Behavior

 OPTION_RADIUS is only exchanged between the relay agents and the
 servers.  DHCPv6 clients are not aware of the usage of OPTION_RADIUS.
 DHCPv6 clients MUST NOT send OPTION_RADIUS and MUST ignore
 OPTION_RADIUS if received.

8. Security Considerations

 Known security vulnerabilities of the DHCPv6 and RADIUS protocols may
 apply to their options.  Security issues related with DHCPv6 are
 described in Section 23 of [RFC3315].  Security issues related with
 RADIUS are described in Section 8 of [RFC2865], Section 5 of
 [RFC3162], and Section 11 of [RFC6929].
 The mechanism described in this document may introduce a new attack
 vector against the DHCPv6 server in cases where the DHCPv6 relay
 agent is compromised.  By forging the RADIUS attributes contained in
 the OPTION_RADIUS of the RELAY-FORW (12) messages, the attacker may
 influence the parameter assignment on the DHCPv6 server for the
 DHCPv6 clients.  However, as described in the Section 3, NAS always
 belongs to the same administrative domain of the DHCPv6 server in the
 real deployment.
 Network administrators should be aware that although RADIUS messages
 are encrypted, DHCPv6 messages are always unencrypted.  It is
 possible that some RADIUS vendor-specific attributes might contain
 sensitive or confidential information.  Network administrators are
 strongly advised to prevent such information from being included in
 DHCPv6 messages.
 If the use of vendor-specific attributes with confidential content is
 required, administrators are advised to use IPsec with encryption to
 protect the confidentiality of the RADIUS attributes.  Relay agents
 and servers implementing this specification MUST support the use of
 IPsec Encapsulating Security Payload (ESP) with encryption in
 transport mode, according to Section 3.1.1 of [RFC4303] and
 Section 21.1 of [RFC3315].

9. IANA Considerations

 IANA has assigned OPTION_RADIUS (81) in the "DHCP Option Codes"
 registry, as defined in Section 4.  In addition, IANA has created a
 new registry entitled "RADIUS Attributes Permitted in DHCPv6 RADIUS
 Option" in the "Dynamic Host Configuration Protocol for IPv6
 (DHCPv6)" registry, as defined in Section 4.1.  The new registry
 enumerates the RADIUS Attributes Types
 (http://www.iana.org/assignments/radius-types) that are permitted for

Yeh & Boucadair Standards Track [Page 8] RFC 7037 DHCPv6 RADIUS Option October 2013

 inclusion in the DHCPv6 RADIUS option.  The allocation policy of this
 "RADIUS Attributes Permitted in DHCPv6 RADIUS Option" registry is
 Expert Review per [RFC5226].  Designated experts should carefully
 consider the security implications of allowing the relay agent to
 include new RADIUS attributes to this registry.

10. Acknowledgements

 Thanks to Tomek Mrugalski, Bernie Volz, Gaurav Halwasia, and Roberta
 Maglione for their thorough review comments in the DHC working group
 mailing list.  Thanks also to Ted Lemon for his continuous
 encouragement and technical guidance.

11. References

11.1. 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., Bound, J., Volz, B., Lemon, T., Perkins, C.,
            and M. Carney, "Dynamic Host Configuration Protocol for
            IPv6 (DHCPv6)", RFC 3315, July 2003.
 [RFC4303]  Kent, S., "IP Encapsulating Security Payload (ESP)", RFC
            4303, December 2005.
 [RFC4818]  Salowey, J. and R. Droms, "RADIUS Delegated-IPv6-Prefix
            Attribute", RFC 4818, April 2007.
 [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
            IANA Considerations Section in RFCs", BCP 26, RFC 5226,
            May 2008.
 [RFC6519]  Maglione, R. and A. Durand, "RADIUS Extensions for Dual-
            Stack Lite", RFC 6519, February 2012.
 [RFC6911]  Dec, W., Sarikaya, B., Zorn, G., Miles, D., and B.
            Lourdelet, "RADIUS Attributes for IPv6 Access Networks",
            RFC 6911, April 2013.
 [RFC6929]  DeKok, A. and A. Lior, "Remote Authentication Dial In User
            Service (RADIUS) Protocol Extensions", RFC 6929, April
            2013.

Yeh & Boucadair Standards Track [Page 9] RFC 7037 DHCPv6 RADIUS Option October 2013

11.2. Informative References

 [RFC3162]  Aboba, B., Zorn, G., and D. Mitton, "RADIUS and IPv6", RFC
            3162, August 2001.
 [RFC3633]  Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
            Host Configuration Protocol (DHCP) version 6", RFC 3633,
            December 2003.
 [RFC3646]  Droms, R., "DNS Configuration options for Dynamic Host
            Configuration Protocol for IPv6 (DHCPv6)", RFC 3646,
            December 2003.
 [RFC3736]  Droms, R., "Stateless Dynamic Host Configuration Protocol
            (DHCP) Service for IPv6", RFC 3736, April 2004.
 [RFC6334]  Hankins, D. and T. Mrugalski, "Dynamic Host Configuration
            Protocol for IPv6 (DHCPv6) Option for Dual-Stack Lite",
            RFC 6334, August 2011.

Authors' Addresses

 Leaf Y. Yeh
 Freelancer Technologies
 P. R. China
 EMail: leaf.yeh.sdo@gmail.com
 Mohamed Boucadair
 France Telecom
 France
 EMail: mohamed.boucadair@orange.com

Yeh & Boucadair Standards Track [Page 10]

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