Network Working Group                                           R. Droms
Internet-Draft                                             Cisco Systems
Expires: November 12, 2002                                  May 14, 2002


        DHCP Auto-configure Option (Option code 116) Deprecated
                  draft-droms-rfc2563-deprecate-00.txt

Status of this Memo

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Copyright Notice

   Copyright (C) The Internet Society (2002).  All Rights Reserved.

Abstract


1. Introduction

   RFC2563 defines the DHCP Auto-configure option, which controls
   whether a DHCP client uses address auto-configuration.  Because of
   the potential threat of a denial of service attack, the use of
   RFC2563 is deprecated.

2. Requirements

   The key words MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
   SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL in this document are to be



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   interpreted as described in RFC2119 [1].

3. Deprecation of DHCP Auto-configure option

   RFC2563 [2] defines the Auto-configure option (option code 116) for
   DHCP [3].  This option is sent from a DHCP server to a DHCP client.
   When the option value is 0, the DHCP client does not perform address
   autoconfiguration.

   Because DHCP does not enforce any authentication of servers, a DHCP
   server can mount a denial of service attack on DHCP clients.  A DHCP
   server on an isolated link with no attached routers can respond to
   DHCP clients with an Auto-configure option instructing the clients
   not to use address auto-configuration.  Those clients will then not
   have an IP address and not be able to exchange datagrams with other
   hosts on the same link.

   The DHC working group knows of no current or planned implementations
   of the DHCP Auto-configure option.  Representatives from several
   vendors of DHCP implementations have said that the DHCP Auto-
   configure option has no known application, presents an opportunity
   for a denial of service attack and that they will never consider
   implementing it.

4. IANA Considerations

   IANA is asked to mark the DHCP Auto-configure option (option code
   116) as "Deprecated" in its reference list of DHCP options.

5. Security considerations

   The DHCP Auto-configure option may be used to moutn a denial of
   service attack on DHCP clients.  The use of the DHCP Auto-configure
   option is deprecated.

6. Acknowledgments

   Stuart Cheshire, Bernard Aboba and Myron Hattig, among others, have
   noted the security threat posed by the DHCP Auto-configure option.

References

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

   [2]  Troll, R., "DHCP Option to Disable Stateless Auto-Configuration
        in IPv4 Clients", RFC 2563, May 1999.




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


Author's Address

   Ralph Droms
   Cisco Systems
   250 Apollo Drive
   Chelmsford, MA  01824
   USA

   Phone: +1 978 497 4733
   EMail: rdroms@cisco.com





































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Acknowledgement

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