RFC5192

Network Working Group L. Morand Request for Comments: 5192 France Telecom R&D Category: Standards Track A. Yegin

                                                             Samsung
                                                            S. Kumar
                                                   Tech Mahindra Ltd
                                                      S. Madanapalli
                                                             Samsung
                                                            May 2008

   DHCP Options for Protocol for Carrying Authentication for
          Network Access (PANA) Authentication Agents

Status 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.

Abstract

This document defines new DHCPv4 and DHCPv6 options that contain a list of IP addresses to locate one or more PANA (Protocol for carrying Authentication for Network Access) Authentication Agents (PAAs). This is one of the methods that a PANA Client (PaC) can use to locate PAAs.

Introduction

The Protocol for carrying Authentication for Network Access (PANA) RFC5191 defines a new Extensible Authentication Protocol (EAP) RFC3748 lower layer that uses IP between the protocol end-points.

The PANA protocol is run between a PANA Client (PaC) and a PANA Authentication Agent (PAA) in order to perform authentication and authorization for the network access service.

This document specifies DHCPv4 RFC2131 and DHCPv6 RFC3315 options that allow PANA clients (PaCs) to discover PANA Authentication Agents (PAAs). This is one of the methods for locating PAAs.

The DHCP options defined in this document are used only as a PAA discovery mechanism. These DHCP options MUST NOT be used to perform any negotiation of the use of PANA between the PaC and a PAA.

Specification of Requirements

In this document, several words are used to signify the requirements of the specification. These words are often capitalized. 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.

Terminology

This document uses the DHCP terminology defined in RFC2131, RFC2132, and RFC3315.

This document uses the PANA terminology defined in RFC5191. In particular, the following terms are defined:

  PANA Client (PaC):

     The client side of the protocol that resides in the access
     device (e.g., laptop, PDA, etc.).  It is responsible for
     providing the credentials in order to prove its identity
     (authentication) for network access authorization.  The PaC and
     the EAP peer are co-located in the same access device.

  PANA Authentication Agent (PAA):

     The protocol entity in the access network whose responsibility
     it is to verify the credentials provided by a PANA client (PaC)
     and authorize network access to the access device.  The PAA and

     the EAP authenticator (and optionally the EAP server) are
     colocated in the same node.

PANA Authentication Agent DHCPv4 Option

This DHCPv4 option carries a list of 32-bit (binary) IPv4 addresses indicating PANA Authentication Agents (PAAs) available to the PANA client (PaC).

The DHCPv4 option for PANA Authentication Agent has the format shown in Figure 1.

  0                   1
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |  option-code  | option-length |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                               |
  +      PAA IPv4 Address         +
  |                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |             ...               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     Figure 1: PAA DHCPv4 option

  option-code:        OPTION_PANA_AGENT (136).

  option-length:      Length of the 'options' field in octets;
                      MUST be a multiple of four (4).

  PAA IPv4 Address:   IPv4 address of a PAA for the client to use.
                      The PAAs are listed in the order of preference
                      for use by the client.

A PaC (DHCPv4 client) SHOULD request the PAA DHCPv4 Option in a Parameter Request List, as described in RFC2131 and RFC2132.

If configured with a (list of) PAA address(es), a DHCPv4 server SHOULD send a client the PAA DHCPv4 option, even if this option is not explicitly requested by the client.

A PaC (DHCPv4 client) receiving the PAA DHCPv4 option SHOULD use the (list of) IP address(es) to locate PAA(s).

The PaC (DHCPv4 client) MUST try the records in the order listed in the PAA DHCPv4 option received from the DHCPv4 server.

PANA Authentication Agent DHCPv6 Option

This DHCPv6 option carries a list of 128-bit (binary) IPv6 addresses indicating PANA Authentication Agents (PAAs) available to the PANA client (PaC).

The DHCPv6 option for PANA Authentication Agent has the format shown in Figure 2.

  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-code             |       option-length           |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                                                               |
  +                                                               +
  |                                                               |
  +                         PAA IPv6 Address                      +
  |                                                               |
  +                                                               +
  |                                                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                    Figure 2: PAA DHCPv6 option

  option-code:        OPTION_PANA_AGENT (40).

  option-length:      Length of the 'options' field in octets;
                      MUST be a multiple of sixteen (16).

  PAA IPv6 Address:   IPv6 address of a PAA for the client to use.
                      The PAAs are listed in the order of preference
                      for use by the client.

A PaC DHCPv6 client SHOULD request the PAA DHCPv6 option in an Options Request Option (ORO) as described in the DHCPv6 specification RFC3315.

If configured with a (list of) PAA address(es), a DHCPv6 server SHOULD send a client the PAA DHCPv6 option, even if this option is not explicitly requested by the client.

A PaC (DHCPv6 client) receiving the PAA DHCPv6 option SHOULD use the (list of) IP address(es) to locate PAA(s).

The PaC (DHCPv6 client) MUST try the records in the order listed in the PAA DHCPv6 option received from the DHCPv6 server.

IANA Considerations

The following DHCPv4 option code for PANA Authentication Agent options has been assigned by IANA:

  Option  Name           Value       Described in
  -----------------------------------------------
  OPTION_PANA_AGENT       136         Section 4

The following DHCPv6 option code for PANA Authentication Agent options has been assigned by IANA:

  Option  Name            Value       Described in
  ------------------------------------------------
  OPTION_PANA_AGENT        40         Section 5

Security Considerations

The security considerations in RFC2131, RFC2132, and RFC3315 apply. If an adversary manages to modify the response from a DHCP server or insert its own response, a PANA Client could be led to contact a rogue PANA Authentication Agent, possibly one that then intercepts authentication requests and/or denies network access to the access device.

In most networks, the DHCP exchange that delivers the options prior to network access authentication is neither integrity protected nor origin authenticated. Therefore, the options defined in this document MUST NOT be used to perform any negotiation on the use of PANA between the PANA Client and a PANA Authentication Agent. Using the presence (or absence) of these DHCP options as an indication of network mandating PANA authentication (or not) is an example of such a negotiation mechanism. This negotiation would allow bidding-down attacks by making the clients choose to use a lower-grade security mechanism (or even no security at all).

Acknowledgements

We would like to thank Ralph Droms, Stig Venaas, Ted Lemon, Andre Kostur and Bernie Volz for their valuable comments. We would also like to thank Jari Arkko, Thomas Narten and Bernard Aboba that provided several reviews, as well as all members of the PANA and DHC working groups that contribute to improve this document.

References

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.

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.

RFC5191 Forsberg, D., Ohba, Y., Patil, B., Tschofenig, H., and A.

          Yegin, "Protocol for Carrying Authentication for Network
          Access (PANA)", RFC 5191, May 2008.

Informative References

RFC3748 Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.

          Levkowetz, "Extensible Authentication Protocol (EAP)",
          RFC 3748, June 2004.

Authors' Addresses

Lionel Morand France Telecom R&D

EMail: [email protected]

Alper E. Yegin Samsung

EMail: [email protected]

Suraj Kumar Tech Mahindra Ltd

EMail: [email protected]

Syam Madanapalli Samsung

EMail: [email protected]

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