rfc3046.txt

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   IP Spoofing

      The circuit access device may associate the IP address assigned by
      a DHCP server in a forwarded DHCP Ack packet with the circuit to
      which it was forwarded.  The circuit access device MAY prevent
      forwarding of IP packets with source IP addresses -other than-
      those it has associated with the receiving circuit.  This prevents
      simple IP spoofing attacks on the Central LAN, and IP spoofing of
      other hosts.

   Client Identifier Spoofing

      By using the agent-supplied Agent Remote ID option, the untrusted
      and as-yet unstandardized client identifier field need not be used
      by the DHCP server.

   MAC Address Spoofing

      By associating a MAC address with an Agent Remote ID, the DHCP
      server can prevent offering an IP address to an attacker spoofing
      the same MAC address on a different remote ID.

5.0 Security Considerations

   DHCP as currently defined provides no authentication or security
   mechanisms.  Potential exposures to attack are discussed in section 7
   of the DHCP protocol specification in RFC 2131 [1].

   This document introduces mechanisms to address several security
   attacks on the operation of IP address assignment, including IP
   spoofing, Client ID spoofing, MAC address spoofing, and DHCP server



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   address exhaustion.  It relies on an implied trusted relationship
   between the DHCP Relay Agent and the DHCP server, with an assumed
   untrusted DHCP client.  It introduces a new identifer, the "Remote
   ID", that is also assumed to be trusted.  The Remote ID is provided
   by the access network or modem and not by client premise equipment.
   Cryptographic or other techniques to authenticate the remote ID are
   certainly possible and encouraged, but are beyond the scope of this
   document.

   This option is targeted towards environments in which the network
   infrastructure -- the relay agent, the DHCP server, and the entire
   network in which those two devices reside -- is trusted and secure.
   As used in this document, the word "trusted" implies that
   unauthorized DHCP traffic cannot enter the trusted network except
   through secured and trusted relay agents and that all devices
   internal to the network are secure and trusted.  Potential deployers
   of this option should give careful consideration to the potential
   security vulnerabilities that are present in this model before
   deploying this option in actual networks.

   Note that any future mechanisms for authenticating DHCP client to
   server communications must take care to omit the DHCP Relay Agent
   option from server authentication calculations.  This was the
   principal reason for organizing the DHCP Relay Agent Option as a
   single option with sub-options, and for requiring the relay agent to
   remove the option before forwarding to the client.

   While it is beyond the scope of this document to specify the general
   forwarding algorithm of public data circuit access units, note that
   automatic reforwarding of IP or ARP broadcast packets back downstream
   exposes serious IP security risks.  For example, if an upstream
   broadcast DHCP-DISCOVER or DHCP-REQUEST were re-broadcast back
   downstream, any public host may easily spoof the desired DHCP server.

6.0 IANA Considerations

   IANA is required to maintain a new number space of "DHCP Relay Agent
   Sub-options", located in the BOOTP-DHCP Parameters Registry.  The
   initial sub-options are described in section 2.0 of this document.

   IANA assigns future DHCP Relay Agent Sub-options with a "IETF
   Consensus" policy as described in RFC 2434 [3].  Future proposed
   sub-options are to be referenced symbolically in the Internet-Drafts
   that describe them, and shall be assigned numeric codes by IANA when
   approved for publication as an RFC.






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7.0 Intellectual Property Notices

   This section contains two notices as required by [5] for standards
   track documents.

   The IETF takes no position regarding the validity or scope of any
   intellectual property 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; neither does it represent that it
   has made any effort to identify any such rights.  Information on the
   IETF's procedures with respect to rights in standards-track and
   standards-related documentation can be found in BCP-11.  Copies of
   claims of rights made available for publication 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 implementors or users of this specification can
   be obtained from the IETF Secretariat.

   The IETF has been notified of intellectual property rights claimed in
   regard to some or all of the specification contained in this
   document.  For more information consult the online list of claimed
   rights.

8.0 References

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

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

   [3]  Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
        Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.

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

   [5]  Bradner, S., "The Internet Standards Process -- Revision 3", BCP
        9, RFC 2026, October 1996.

   [6]  Kent, S. and R. Atkinson, "Security Architecture for the
        Internet Protocol", RFC 2401, November 1998.








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9.0 Glossary

   DSLAM   Digital Subscriber Link Access Multiplexer
   IANA    Internet Assigned Numbers Authority
   LIS     Logical IP Subnet
   MAC     Message Authentication Code
   RAS     Remote Access Server

10.0 Author's Address

   Michael Patrick
   Motorola Broadband Communications Sector
   20 Cabot Blvd., MS M4-30
   Mansfield, MA 02048

   Phone: [phone]
   EMail: [e-mail]


































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11.0  Full Copyright Statement

   Copyright (C) The Internet Society (2001).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS 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.

Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.



















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