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Network Working Group                                           R. DromsRequest for Comments: 4014                                 J. SchnizleinCategory: Standards Track                                  Cisco Systems                                                           February 2005Remote Authentication Dial-In User Service (RADIUS)Attributes Suboption for theDynamic Host Configuration Protocol (DHCP)                     Relay Agent Information OptionStatus of This Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2005).Abstract   The RADIUS Attributes suboption enables a network element to pass   identification and authorization attributes received during RADIUS   authentication to a DHCP server.  When the DHCP server receives a   message from a relay agent containing a RADIUS Attributes suboption,   it extracts the contents of the suboption and uses that information   in selecting configuration parameters for the client.1.  Introduction and Background   The RADIUS Attributes suboption for the DHCP Relay Agent option   provides a way in which a NAS can pass attributes obtained from a   RADIUS server to a DHCP server [1].  IEEE 802.1X [2] is an example of   a mechanism through which a NAS such as a switch or a wireless LAN   access point can authenticate the identity of the user of a device   before providing layer 2 network access with RADIUS as the   Authentication Service, as specified inRFC 3580 [8].  In IEEE 802.1X   authenticated access, a device must first exchange some   authentication credentials with the NAS.  The NAS then supplies these   credentials to a RADIUS server, which eventually sends either an   Access-Accept or an Access-Reject in response to an Access-Request.   The NAS, based on the reply of the RADIUS server, then allows or   denies network access to the requesting device.Droms & Schnizlein          Standards Track                     [Page 1]

RFC 4014              RADIUS Attributes Suboption          February 2005   Figure 1 summarizes the message exchange among the participants in   IEEE 802.1X authentication.                        +-----------------+                        |Device requesting|                        | network access  |                        +-----------------+                         |         ^                         |         |                        (1) Request for access                         |         |                         |        (4) Success/Failure                         v         |                        +-----------------+                        |       NAS       |                        |(IEEE 802.1X and |                        |DHCP relay agent}|                        +-----------------+                           |     ^                           |     |                          (2) Request for authentication                           |     |                           |    (3) Access-Accept/Reject                           v     |                        +-----------------+                        |     RADIUS      |                        |     Server      |                        +-----------------+                             Figure 1   The access device acts as an IEEE 802.1X Authenticator and adds a   DHCP relay agent option that includes a RADIUS Attributes suboption   to DHCP messages.  At the successful conclusion of IEEE 802.1X   authentication, a RADIUS Access-Accept provides attributes for   service authorizations to the NAS.  The NAS stores these attributes   locally.  When the NAS subsequently relays DHCP messages from the   network device, the NAS adds these attributes in a RADIUS Attributes   suboption.  The RADIUS Attributes suboption is another suboption of   the Relay Agent Information option [5].   The RADIUS Attributes suboption described in this document is not   limited to use in conjunction with IEEE 802.1X and can be used to   carry RADIUS attributes obtained by the relay agent for any reason.   That is, the option is not limited to use with IEEE 802.1X but is   constrained by RADIUS semantics (seeSection 4).Droms & Schnizlein          Standards Track                     [Page 2]

RFC 4014              RADIUS Attributes Suboption          February 2005   The scope of applicability of this specification is such that robust   interoperability is only guaranteed for RADIUS service   implementations that exist within the same scope as does the DHCP   service implementation, i.e., within a single, localized   administrative domain.  Global interoperability of this   specification, across administrative domains, is not required.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 inRFC 2119 [3].   Within this specification, the use of the key words "MUST", "MUST   NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT",   "RECOMMENDED", "MAY", and "OPTIONAL" is with respect to RADIUS   clients and servers that implement the optional features of this   specification.  The use of these key words does not create any   normative requirements outside of that scope, and does not modify the   base RADIUS specifications, such asRFC 2865 [4].2.1.  DHCP Terminology   The following terms are used as defined inRFC 2131 andRFC 3046:   DHCP relay agent, DHCP server, DHCP client.2.2.  RADIUS Terminology   The following terms are used in conjunction with RADIUS:   RADIUS server: A RADIUS server is responsible for receiving user      connection requests, authenticating the user, and then returning      all configuration information necessary for the client to deliver      service to the user.   Attribute: A Type-Length-Value tuple encapsulating data elements as      defined inRFC 2865 [4].   NAS:  A Network Access Server (NAS) provides access to the network      and operates as a client of RADIUS.  The client is responsible for      passing user information to designated RADIUS servers and then      acting on the response that is returned.  Unlike a traditional      dial NAS, the NAS considered here may not have a protocol such as      PPP through which it can pass configuration information from the      RADIUS attributes to the client.Droms & Schnizlein          Standards Track                     [Page 3]

RFC 4014              RADIUS Attributes Suboption          February 20052.3.  IEEE 802.1X Terminology   The following terms are used as defined in the IEEE 802.1X protocol:   Authenticator, Supplicant.3.  RADIUS Attributes Suboption Format   The RADIUS Attributes suboption is a new suboption for the DHCP Relay   Agent option.   The format of the RADIUS Attributes suboption is as follows:        SubOpt   Len     RADIUS attributes         code       +-------+-----+------+------+------+------+--...-+------+       |   7   |  N  |  o1  |  o2  |  o3  |  o4  |      |  oN  |       +-------+-----+------+------+------+------+--...-+------+   The RADIUS attributes are encoded according to the encoding rules inRFC 2865, in octets o1...oN.   The DHCP relay agent truncates the RADIUS attributes to fit in the   RADIUS Attributes suboption.4.  DHCP Relay Agent Behavior   When the DHCP relay agent receives a DHCP message from the client, it   MAY append a DHCP Relay Agent Information option containing the   RADIUS Attributes suboption, along with any other suboptions it is   configured to supply.  The RADIUS Attributes suboption MUST only   contain the attributes provided in the RADIUS Access/Accept message.   The DHCP relay agent MUST NOT add more than one RADIUS Attributes   suboption in a message.   The relay agent MUST include the User-Name and Framed-Pool attributes   in the RADIUS Attributes suboption, if they are available, and MAY   include other attributes.   To avoid dependencies between the address allocation and other state   information between the RADIUS server and the DHCP server, the DHCP   relay agent SHOULD include only the attributes in the table below in   an instance of the RADIUS Attributes suboption.  The table, based on   the analysis inRFC 3580 [8], lists attributes that MAY be included:Droms & Schnizlein          Standards Track                     [Page 4]

RFC 4014              RADIUS Attributes Suboption          February 2005           #   Attribute         ---   ---------           1   User-Name (RFC 2865 [3])           6   Service-Type (RFC 2865)          26   Vendor-Specific (RFC 2865)          27   Session-Timeout (RFC 2865)          88   Framed-Pool (RFC 2869)         100   Framed-IPv6-Pool (RFC 3162 [7])5.  DHCP Server Behavior   When the DHCP server receives a message from a relay agent containing   a RADIUS Attributes suboption, it extracts the contents of the   suboption and uses that information in selecting configuration   parameters for the client.  If the relay agent relays RADIUS   attributes not included in the table inSection 4, the DHCP server   SHOULD ignore them.  If the DHCP server uses attributes not specified   here, it might result in side effects not anticipated in the existing   RADIUS specifications.6.  DHCP Client Behavior   Relay agent options are exchanged only between relay agents and the   DHCP server, so DHCP clients are never aware of their use.7.  Security Considerations   Message authentication in DHCP for intradomain use where the   out-of-band exchange of a shared secret is feasible is defined inRFC3118 [6].  Potential exposures to attack are discussed insection 7   of the DHCP protocol specification inRFC 2131 [1].   The DHCP Relay Agent option depends on a trusted relationship between   the DHCP relay agent and the server, as described in section 5 ofRFC3046 [5].  Although the introduction of fraudulent relay-agent   options can be prevented by a perimeter defense that blocks these   options unless the relay agent is trusted, a deeper defense using the   authentication option for relay agent options [9] or IPsec [10]   SHOULD be deployed as well.8.  IANA Considerations   IANA has assigned the value of 7 for the DHCP Relay Agent Information   option suboption code for this suboption.  This document does not   define any new namespaces or other constants for which IANA must   maintain a registry.Droms & Schnizlein          Standards Track                     [Page 5]

RFC 4014              RADIUS Attributes Suboption          February 20059.  Acknowledgements   Expert advice from Bernard Aboba, Paul Funk, David Nelson, Ashwin   Palekar, and Greg Weber on avoiding RADIUS entanglements is   gratefully acknowledged.10.  References10.1.  Normative References   [1]  Droms, R., "Dynamic Host Configuration Protocol",RFC 2131,        March 1997.   [2]  Institute of Electrical and Electronics Engineers, "Local and        Metropolitan Area Networks: Port based Network Access Control",        IEEE Standard 802.1X, March 2001.   [3]  Bradner, S., "Key words for use in RFCs to Indicate Requirement        Levels",BCP 14,RFC 2119, March 1997.   [4]  Rigney, C., Willens, S., Rubens, A., and W. Simpson, "Remote        Authentication Dial In User Service (RADIUS)",RFC 2865, June        2000.   [5]  Patrick, M., "DHCP Relay Agent Information Option",RFC 3046,        January 2001.10.2.  Informative References   [6]  Droms, R. and W. Arbaugh, "Authentication for DHCP Messages",RFC 3118, June 2001.   [7]  Aboba, B., Zorn, G., and D. Mitton, "RADIUS and IPv6",RFC 3162,        August 2001.   [8]  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.   [9]  Stapp, M. and T. Lemon, "The Authentication Suboption for the        DHCP Relay Agent Option", Work in Progress, October 2003.   [10] Droms, R., "Authentication of DHCP Relay Agent Options Using        IPsec", Work in Progress, September 2003.Droms & Schnizlein          Standards Track                     [Page 6]

RFC 4014              RADIUS Attributes Suboption          February 2005Authors' Addresses   Ralph Droms   Cisco Systems   1414 Massachusetts Avenue   Boxborough, MA  01719   USA   EMail: rdroms@cisco.com   John Schnizlein   Cisco Systems   9123 Loughran Road   Fort Washington, MD  20744   USA   EMail: jschnizl@cisco.comDroms & Schnizlein          Standards Track                     [Page 7]

RFC 4014              RADIUS Attributes Suboption          February 2005Full Copyright Statement   Copyright (C) The Internet Society (2005).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   This document and the information contained herein are provided on an   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the IETF's procedures with respect to rights in IETF Documents can   be found inBCP 78 andBCP 79.   Copies of IPR disclosures made to the IETF Secretariat and any   assurances of licenses to be made available, or the result of an   attempt made to obtain a general license or permission for the use of   such proprietary rights by implementers or users of this   specification can be obtained from the IETF on-line IPR repository athttp://www.ietf.org/ipr.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights that may cover technology that may be required to implement   this standard.  Please address the information to the IETF at ietf-   ipr@ietf.org.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Droms & Schnizlein          Standards Track                     [Page 8]