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Network Working Group                                  V. KalusivalingamRequest for Comments: 4075         Cisco Systems (India) Private LimitedCategory: Standards Track                                       May 2005Simple Network Time Protocol (SNTP) Configuration Option for DHCPv6Status 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 inRFC 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 inRFC 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 server5.  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 20056.  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    31Section 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.Kalusivalingam              Standards Track                     [Page 3]

RFC 4075          SNTP Configuration Option for DHCPv6          May 20059.  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.comKalusivalingam              Standards Track                     [Page 4]

RFC 4075          SNTP Configuration Option for DHCPv6          May 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 procedures with respect to rights in RFC 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.Kalusivalingam              Standards Track                     [Page 5]