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.
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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.
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RFC 4075 SNTP Configuration Option for DHCPv6 May 2005
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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RFC 4075 SNTP Configuration Option for DHCPv6 May 2005
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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RFC 4075 SNTP Configuration Option for DHCPv6 May 2005
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