Network Working Group A.K. Vijayabhaskar
Internet-Draft Hewlett-Packard
Expires: August 17, 2002 17 Feb 2002
Time Configuration Options for DHCPv6
draft-ietf-dhc-dhcpv6-opt-timeconfig-00.txt
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Copyright Notice
Copyright (C) The Internet Society (2002). All Rights Reserved.
Abstract
This document describes the options for Time related configuration
information in DHCPv6: NTP Servers and IEEE 1003.1 POSIX Timezone
specifier.
1. Introduction
This document describes the options for time related configuration
information in DHCPv6 [4].
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 [1]
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3. Terminology
This document uses terminology specific to IPv6 and DHCPv6 as defined
in section "Terminology" of the DHCP specification.
4. Network Time Protocol (NTP) Servers option
The Network Time Protocol Servers option provides a list of one or
more IP addresses of NTP [2] servers available to the client. The
NTP servers SHOULD be listed in the order of preference.
The format of the 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_NTP_SERVERS | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| NTP server (IP address) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| NTP server (IP address) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code: OPTION_NTP_SERVERS (tbd)
option-len: Length of the 'NTP server' fields in octets; It must be
a multiple of 16
NTP server: IP address of NTP server
5. IEEE 1003.1 POSIX Timezone option
The IEEE 1003.1 POSIX Timezone option is used by the server to
convey client's timezone information to the client.
The format of the IEEE 1003.1 POSIX Timezone option is:
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_TIME_ZONE | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| time-zone |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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option-code: OPTION_TIME_ZONE (tbd)
option-len: Length of the 'time-zone' field in octets
time-zone: Time zone of the client in IEEE 1003.1 POSIX Timezone
format [3].
The format of the IEEE 1003.1 POSIX timezone string is specified as
follows:
StdOffset[Dst[Offset],[Start[/Time],End[/Time]]]
where '[' and ']' enclose optional fields, '|' indicates choice
of exactly one of the alternatives, ',' and '/' represent literal
characters present in the string.
Std Three or more octets for the standard timezone (Std).
Any character (or case) except a leading colon, digits,
comma, minus or plus sign is allowed.
Offset Indicates the value one must add to local time to
arrive at UTC, of the form: [+|-]hh[:mm[:ss]]. Offset
following Std is required. Digits are always interpreted
as decimal number. If preceded by a '-', the timezone is
east of the Prime Meridian, otherwise it is west ('+' is
optional) The permissible values for hh[:mm[:ss]] are as
follows:
hh 0 <= hh <= 23
mm 0 <= mm <= 60
ss 0 <= ss <= 60
Offset has no default value.
Dst Three or more octets for the daylight savings timezone.
If Dst is missing, then daylight savings time does not
apply in this locale. If no Offset follows Dst, then
Dst is assumed to be one hour ahead of standard time.
Any character (or case) except a leading colon, digits,
comma, minus or plus sign is allowed.
Start Indicates the day of the year, in one of the formats
indicated below, when to change to daylight savings time.
The ``Time'' field (which follows immediately after a
``/'' character, if present) indicates when the change is
made, in local time.
End Indicates the day of the year, in one of the formats
indicated below, when to change back from daylight
savings time. The ``Time'' field (which follows
immediately after a ``/'' character, if present)
indicates when the change is made, in local time.
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Time Time has the same format as Offset, except that no
leading ``-'' or ``+'' is permitted. The default is
02:00:00.
The day of the year needs to be given in any of the following
formats:
Jn The julian day n, (1 <= n <= 365). Leap days are not
counted.
n Zero-based julian day, (0 <= n <= 365). Leap days are
counted so it is possible to refer to Feb 29.
Mm.n.d The ``d''th day, (0 <= d <= 6) of week ``n'' of month
``m'' of the year (1 <= n <= 5, 1 <= m <= 12, where week
5 means last ``d'' day in month ``m'' which may occur in
either the fourth or the fifth week. Week ``1'' is the
first week in which the ``d'' day occurs.
An Example:
For Eastern USA time zone, 1986, the Posix timezone string is as
shown below:
EST5EDT4,116/02:00:00,298/02:00:00
In this case, ``5'' is the Offset for Std, and ``4'' is the Offset
for Dst. Start is the 116th day at 2am, and End is 298th day at 2am.
6. Appearance of these option
The NTP servers and IEEE 1003.1 POSIX Timezone options MUST appear
only in the following messages: Solicit, Advertise, Request,
Confirm, Renew, Rebind, Information-Request, Reply.
7. Security Considerations
The NTP servers option may be used by an intruder DHCP server to
cause DHCP clients to contact an intruder NTP server, resulting in
invalid synchronization of time in client and finally leading to
time critical applications running inaccurately in client machine.
The IEEE 1003.1 POSIX Timezone option may be used by an intruder
DHCP server to assign invalid time zones, leading to timing issues
for the applications running on the client machine.
To avoid attacks through these options, the DHCP client SHOULD use
authenticated DHCP (see section "Authentication of DHCP messages"
in the DHCPv6 specification [4]).
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8. IANA Considerations
IANA is requested to assign an option code to these options from the
option-code space defined in section "DHCPv6 Options" of the DHCPv6
specification [4].
References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] 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.
[3] IEEE, "1003.1 POSIX Timezone Specification", 1988.
[4] Bound, J., Carney, M., Perkins, C., Lemon, T., Volz, B. and R.
Droms (ed.), "Dynamic Host Configuration Protocol for IPv6
(DHCPv6)", draft-ietf-dhc-dhcpv6-23 (work in progress), February
2002.
Author's Addresses
Vijayabhaskar A K
Hewlett-Packard ESD-I
29, Cunningham Road
Bangalore - 560052
India
Phone: +91-080-2051424
E-Mail: vijayak@india.hp.com
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