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+Network Working Group                                  V. Kalusivalingam
+Request for Comments: 4075         Cisco Systems (India) Private Limited
+Category: Standards Track                                       May 2005
+
+
+  Simple Network Time Protocol (SNTP) Configuration Option for DHCPv6
+
+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.
+
+Copyright Notice
+
+   Copyright (C) The Internet Society (2005).
+
+Abstract
+
+   This document describes a new DHCPv6 option for passing a list of
+   Simple Network Time Protocol (SNTP) server addresses to a client.
+
+1.  Introduction
+
+   This document describes a new option, called the SNTP [3] servers
+   option, for passing information about SNTP servers in DHCPv6 [1].
+
+2.  Requirements
+
+   The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
+   SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this
+   document, are to be interpreted as described in RFC 2119 [2].
+
+3.  Terminology
+
+   This document uses terminology specific to IPv6 and DHCPv6 as defined
+   in the "Terminology" section of the DHCPv6 specification [1].
+
+4.  Simple Network Time Protocol (SNTP) Servers Option
+
+   The Simple Network Time Protocol servers option provides a list of
+   one or more IPv6 addresses of SNTP [3] servers available to the
+   client for synchronization.  The clients use these SNTP servers to
+   synchronize their system time to that of the standard time servers.
+   Clients MUST treat the list of SNTP servers as an ordered list.  The
+   server MAY list the SNTP servers in decreasing order of preference.
+
+
+
+Kalusivalingam              Standards Track                     [Page 1]
+
+RFC 4075          SNTP Configuration Option for DHCPv6          May 2005
+
+
+   The option defined in this document can only be used to configure
+   information about SNTP servers that can be reached using IPv6.  The
+   DHCP option to configure information about IPv4 SNTP servers can be
+   found in RFC 2132 [4].  Mechanisms for configuring IPv4/IPv6 dual-
+   stack applications are being considered, but are not specified in
+   this document.
+
+   The format of the Simple Network Time Protocol servers option is as
+   shown below:
+
+       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_SNTP_SERVERS       |        option-len            |
+      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+      |                                                               |
+      |                  SNTP server (IPv6 address)                   |
+      |                                                               |
+      |                                                               |
+      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+      |                                                               |
+      |                  SNTP server (IPv6 address)                   |
+      |                                                               |
+      |                                                               |
+      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+      |                              ...                              |
+      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+
+      option-code: OPTION_SNTP_SERVERS (31)
+
+      option-len:  Length of the 'SNTP server' fields, in octets;
+                   it must be a multiple of 16
+
+      SNTP server: IPv6 address of SNTP server
+
+5.  Appearance of This Option
+
+   The SNTP servers option MUST NOT appear in messages other than the
+   following: Solicit, Advertise, Request, Renew, Rebind, Information-
+   Request, and Reply.  If this option appears in messages other than
+   those specified above, the receiver SHOULD ignore it.
+
+   The option number for this option MAY appear in the Option Request
+   Option [1] in the following messages:  Solicit, Request, Renew,
+   Rebind, Information-Request, and Reconfigure.  If this option number
+   appears in the Option Request Option in messages other than those
+   specified above, the receiver SHOULD ignore it.
+
+
+
+Kalusivalingam              Standards Track                     [Page 2]
+
+RFC 4075          SNTP Configuration Option for DHCPv6          May 2005
+
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+6.  Security Considerations
+
+   The SNTP servers option may be used by an intruder DHCPv6 server to
+   cause DHCPv6 clients to contact a rogue SNTP server, resulting in
+   invalid synchronization of time in the client, finally leading to
+   time-critical applications running inaccurately in the client
+   machine.  Time accuracy can be crucial to some security algorithms.
+   For example, expired certificates may gain a new life, making the
+   applications running on the client machine less secure.  The
+   inaccuracy can even cause clients to set their time incorrectly,
+   making them vulnerable to replay attacks in protocols that use time
+   stamps to detect replays.
+
+   To avoid attacks through these options, the DHCPv6 client SHOULD use
+   authenticated DHCPv6 (see the "Authentication of DHCP messages"
+   section in the DHCPv6 specification [1]).
+
+7.  IANA Considerations
+
+   The IANA has assigned an option code to the following from the
+   option-code space defined in the "DHCPv6 Options" section of the
+   DHCPv6 specification [1].
+
+   Option Name            Value    Described in
+   OPTION_SNTP_SERVERS    31       Section 4.
+
+8.  Acknowledgements
+
+   Thanks to the DHC Working Group for their time and input on the
+   specification.  In particular, thanks to (in alphabetical order)
+   Bernie Volz, Jim Bound, Margaret Wasserman, Pekka Savola, Ralph
+   Droms, Robert Elz, and Thomas Narten for their thorough review.
+
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+Kalusivalingam              Standards Track                     [Page 3]
+
+RFC 4075          SNTP Configuration Option for DHCPv6          May 2005
+
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+9.  Normative References
+
+   [1]  Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M.
+        Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
+        RFC 3315, July 2003.
+
+   [2]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
+        Levels", BCP 14, RFC 2119, March 1997.
+
+10.  Informative References
+
+   [3]  Mills, D., "Simple Network Time Protocol (SNTP) Version 4 for
+        IPv4, IPv6 and OSI", RFC 2030, October 1996.
+
+   [4]  Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
+        Extensions", RFC 2132, March 1997.
+
+Author's Address
+
+   Vijayabhaskar A. Kalusivalingam
+   Cisco Systems (India) Private Limited,
+   No: 9, Brunton Road,
+   Bangalore - 560025
+   India
+
+   Phone: +91-80-51036615
+   EMail: vibhaska@cisco.com
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+Kalusivalingam              Standards Track                     [Page 4]
+
+RFC 4075          SNTP Configuration Option for DHCPv6          May 2005
+
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+Full Copyright Statement
+
+   Copyright (C) The Internet Society (2005).
+
+   This document is subject to the rights, licenses and restrictions
+   contained in BCP 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
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+   pertain to the implementation or use of the technology described in
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+
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+
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+
+Acknowledgement
+
+   Funding for the RFC Editor function is currently provided by the
+   Internet Society.
+
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+Kalusivalingam              Standards Track                     [Page 5]
+