wdiff draft-ietf-dhc-dhcpv6-opt-timeconfig-01.txt draft-ietf-dhc-dhcpv6-opt-timeconfig-02.txt

Network Working Group A.K. Vijayabhaskar
Internet-Draft Hewlett-Packard
Expires: November 10, 2002 10 May 2002 August 26, 2003 26 Feb 2003

Time Configuration Options for DHCPv6
draft-ietf-dhc-dhcpv6-opt-timeconfig-01.txt
draft-ietf-dhc-dhcpv6-opt-timeconfig-02.txt

Status of this Memo

This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.

Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.

Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."

The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.

The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.

This Internet-Draft will expire on August 17, 2002. 26, 2003.

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]. [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 [1] [4]

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 |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 format as
follows:

StdOffset[Dst[Offset],[Start[/Time],End[/Time]]] explained below.

Std[Offset[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.

If "Offset" is specified, then the time-zone is represented in the
IEEE 1003.1 POSIX timezone format [3].

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. If the time-zone
is not represented in IEEE 1003.1 POSIX timezone format [3],
then Std is treated as the index to the timezone database,
for example, a file name, from where additional information
about the timezone may be obtained.

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. required, if the timezone is represented
in IEEE 1003.1 POSIX timezone format. 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.

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: Day ``0'' refers
Sunday, day ``1'' refers Monday and so on.

Examples:

i) Indian Standard Time zone is represented as:

IST-5:30

Here, ``IST'' refers the standard timezone and ``-5:30'' is the offset.
`-' sign in the offset says that the timezone is 5 hours and 30 minutes
ahead of UTC. Absence of ``Dst'' says that daylight savings doesn't apply
to this locale.

ii) 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''

It says:

The standard time zone is the Offset
for Dst. Start in 5 hours behind UTC. The Daylight Savings
Timezone is the 116th day 4 hours behind UTC. Day light savings starts at 2am, 116 day, i.e.,
April 27 02:00 AM standard time and End is 298th day ends at 2am. 298th day, i.e., October 26
02:00 AM daylight time.

It can also represented as:

EST5EDT,116/02:00:00,298/02:00:00

Since no offset follows the ``Dst'', daylight savings time is 1 hour
ahead of standard time, thus, it is 4 hours behind UTC.

iii) Representing ii) in the non POSIX standard way is:

America/New-York

It says that the locale belongs to New-York timezone in America, which
will be used as the index in to a timezone database to get more
information of the timezone.

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,
Information-Request and Reply.

The option number for these options MAY appear in the Option Request
Option [1] in the following messages: Solicit, Request, Confirm, Renew,
Rebind, Information-Request and Reconfigure.

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 time accuracy can be crucial to some security algorithms. For
example, it may cause expired certificates to gain a new life, making
the application less secured.

The 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]). [1]).

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]. [1].

9. Normative References

[1] Bradner, S., "Key words Bound, J., Carney, M., Perkins, C., Lemon, T., Volz, B. and R.
Droms (ed.), "Dynamic Host Configuration Protocol for use IPv6
(DHCPv6)", draft-ietf-dhc-dhcpv6-28 (work in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997. progress), November
2002.

10. Informative References

[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 Bradner, S., "Key words for IPv6
(DHCPv6)", draft-ietf-dhc-dhcpv6-23 (work use in progress), February
2002. RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.

Author's Addresses

Vijayabhaskar A K
Hewlett-Packard ESD-I
29, Cunningham Road
Bangalore - 560052
India

Phone: +91-80-2051424 +91-80-2053085
E-Mail: vijayak@india.hp.com

Full Copyright Statement

This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.

The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.

This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS 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.

Acknowledgement

Funding for the RFC Editor function is currently provided by the
Internet Society. 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 and Bound, Ralph Droms Droms, Robert Elz for their thorough
review. Special thanks to Robert Elz for his suggestions and help in
making this document more readable. Thanks to Mike Carney for his abstract
on Time Zone option.