Network Working Group V. Kalusivalingam
Internet-Draft Cisco Systems (India) Private Limited
Category: Standards Track October 2004
Simple Network Time Protocol Configuration Option for DHCPv6
draft-ietf-dhc-dhcpv6-opt-sntp-01
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Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
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 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].
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3. Terminology
This document uses terminology specific to IPv6 and DHCPv6 as defined
in "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 the order of preference.
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 (tbd)
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 other than the following
messages: Solicit, Advertise, Request, Renew, Rebind,
Information-Request and Reply. If this option appears in other than the
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messages specified above, the receiver SHOULD ignore the option.
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 appear
in the Option Request Option in other than the messages specified above,
the receiver SHOULD ignore the option number.
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 client and finally leading to
time critical applications running inaccurately in client machine.
The time accuracy can be crucial to some security algorithms. For
example, it may cause expired certificates to gain a new life, making
the applications running on the client machine less secure. It 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 "Authentication of DHCP messages" section
in the DHCPv6 specification [1]).
7. IANA Considerations
IANA is requested to assign an option code to the following options
from the option-code space defined in "DHCPv6 Options" section of the
DHCPv6 specification [1].
Option Name Value Described in
OPTION_SNTP_SERVERS tbd Section 4.
8. Normative References
[1] Bound, J., Carney, M., Perkins, C., Lemon, T., Volz, B. and R.
Droms (ed.), "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.
9. Informative References
[3] D. Mills. Simple Network Time Protocol (SNTP) Version 4 for
IPv4, IPv6 and OSI. Request for Comments (Informational) 2030,
Internet Engineering Task Force, October 1996.
[4] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
Extensions", RFC 2132, March 1997.
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Acknowledgements
Thanks to the DHC Working Group for their time and input into 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.
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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