IPP Mail Archive: IPP> Time-related DHCP options

IPP Mail Archive: IPP> Time-related DHCP options

IPP> Time-related DHCP options

Ira McDonald (imcdonal@sdsp.mc.xerox.com)
Thu, 27 May 1999 10:18:51 -0400

Hi folks, Wednesday (26 May 1999)

I did some research on time-related BOOTP/DHCP options. I also found
the interesting (but poorly documented) DHCP option 100 'Printer Name'.
The relevant RFCs for BOOTP and DHCP are listed at the end of this note.

- Ira McDonald


0012 Network Time Protocol. D. Mills. September 1989. (Format: TXT=193
bytes) (Also RFC1119)

0026 Time Server Protocol. J. Postel. May 1983. (Format: TXT=3024
bytes) (Also RFC0868)

in 'bootp-dhcp-option-100':

To: iana@ISI.EDU
Subject: Re[2]: Information about DHCP Options
Date: Mon, 30 Dec 1996 15:29:34 -0500
From: Harry_Hans_at_PO-SIGNAL@ZEUS.SIGNALCORP.COM (Harry Hans)

Printer Name Option:

This option specifies a list of names for printers on the client's
subnet. The printers may or may not be up and running. Printer
names should be listed in order of preference.

The code for this option is 100, and its minimum length is 1.

code length Printer Name
| | | | | | |
| 100 | n | h1 | h2 | h3 | h4 | ...........
| | | | | | |


Tag Name Data Length Meaning
--- ---- ----------- -------
2 Time Offset 4 Time Offset in Seconds from UTC
4 Time Server N N/4 Timeserver addresses
42 NTP Servers N NTP Server Addresses
88 IEEE 1003.1 POSIX N IEEE 1003.1 POSIX Timezone
100 Printer Name N Printer Name

'ftp://ftp.isi.edu/in-notes/rfc2132.txt' page 6:

3.4. Time Offset

The time offset field specifies the offset of the client's subnet in
seconds from Coordinated Universal Time (UTC). The offset is
expressed as a two's complement 32-bit integer. A positive offset
indicates a location east of the zero meridian and a negative offset
indicates a location west of the zero meridian.

The code for the time offset option is 2, and its length is 4 octets.

Code Len Time Offset
| 2 | 4 | n1 | n2 | n3 | n4 |

'ftp://ftp.isi.edu/in-notes/rfc2132.txt' page 6:

3.6. Time Server Option

The time server option specifies a list of RFC 868 [6] time servers
available to the client. Servers SHOULD be listed in order of

The code for the time server option is 4. The minimum length for
this option is 4 octets, and the length MUST always be a multiple of

Code Len Address 1 Address 2
| 4 | n | a1 | a2 | a3 | a4 | a1 | a2 | ...

'ftp://ftp.isi.edu/in-notes/rfc2132.txt' page 18:

8.3. Network Time Protocol Servers Option

This option specifies a list of IP addresses indicating NTP [18]
servers available to the client. Servers SHOULD be listed in order
of preference.

The code for this option is 42. Its minimum length is 4, and the
length MUST be a multiple of 4.

Code Len Address 1 Address 2
| 42 | n | a1 | a2 | a3 | a4 | a1 | a2 | ...

in 'bootp-dhcp-option-88':

From: mwc@atlantic.sun.com
Date: Wed, 30 Oct 1996 15:17:59 -0500 (EST)
Subject: Request for DHCP option code
To: iana@ISI.EDU

I requesting an option code for the following working doc.

Thank you,
Mike Carney
Sun Microsystems, Inc.

Network Working Group M. W. Carney
INTERNET-DRAFT Sun Microsystems, Inc.
November 1996

DHCP Option for IEEE 1003.1 POSIX Timezone Specifications



The Dynamic Host Configuration Protocol (DHCP) [1] provides a
framework for passing configuration information to hosts on a TCP/IP
network. This document defines a new option to extend the available
option codes [3].


DHCP includes an option for the specification of the Universal
Coordinated Time Offset [2], which is defined as a
two's complement 32-bit integer representing the offset in seconds
from UCT. Unfortunately, the UCT offset option does not provide
enough information for an Internet client to determine such
timezone-related details as the timezone names, daylight savings
time start and end times in addition to the timezone UCT offsets.

This document defines a new option which addresses these
shortcomings by delivering timezone information in the form of a
1003.1 POSIX Timezone specifier [4].

Definition of option 88, IEEE 1003.1 POSIX Timezone specifier

This NVT ASCII string represents the IEEE 1003.1 POSIX Timezone
specification that a client is to use to set its timezone. The
option code number is 88.

Code Len POSIX Timezone string
| 88 | n | a1 | a2 | a3 | a4 | ...

The format of the IEEE 1003.1 POSIX timezone specification is
defined as follows:

stdoffset[dst[offset],[start[/time],end[/time]]], where:

std, dst: three or more bytes for the standard timezone (std) and
daylight savings timezone (dst). If dst is missing, then
daylight savings time does not apply in this locale. Any
characters (or case) except a leading colon, digits,
comma, minus or plus sign are allowed.

offset: Indicates the value one must add to local time to arrive
at UCT, of the form: hh[:mm[:ss]]. offset following std
is required. If no offset follows dst, then dst is
assumed to be one hour ahead of standard time. Digits
always interpreted as decimal number.

hour: 0-23, minutes and seconds: 0-59. If preceded by a '-',
the timezone is east of the Prime Meridian, otherwise
it is west ('+' is optional)

start/time,end/time: Indicate when to change to and back from
daylight savings time. The 'time' field indicates when,
in local time, the change is made.

start, end:

Jn: The julian day n, (1 <= n <= 365). Leap days
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.

time: time has the same format as offset, except that
no leading '-' or '+' is permitted. The default
is 02:00:00.

An Example
Eastern USA time zone, 1986:



[1] Droms, R., "Dynamic Host Configuration Protocol", RFC 1541,
Bucknell University, October 1993.

[2] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
Extensions", RFC 1533, Lachman Associates, October 1993.

[3] Droms, R., "Procedure for Defining New DHCP Options", Work in
progress, February, 1996.

[4] IEEE, "1003.1 POSIX Timezone Specification", 1988.

Security Considerations

Security issues are not discussed in this document.

Author's Address

Mike Carney
Sun Microsystems, Inc.
2 Elizabeth Drive
Chelmsford, MA 01824

Phone: (508) 442-0469
EMail: Mike.Carney@East.Sun.COM

Time Service RFCs

0868 Time Protocol. J. Postel, K. Harrenstien. May-01-1983. (Format:
TXT=3140 bytes) (Also STD0026) (Status: STANDARD)

1119 Network Time Protocol (Version 2) specification and implementation.
D.L. Mills. Sep-01-1989. (Format: TXT=143, PS=518020
bytes) (Obsoletes RFC0958, RFC1059) (Obsoleted by RFC1305) (Also
STD0012) (Status: STANDARD)

1305 Network Time Protocol (Version 3) Specification, Implementation.
David L. Mills. March 1992. (Format: TXT=307085 bytes) (Obsoletes
RFC0958, RFC1059, RFC1119) (Status: DRAFT STANDARD)


0951 Bootstrap Protocol. W.J. Croft, J. Gilmore. Sep-01-1985. (Format:
TXT=28354 bytes) (Updated by RFC1395, RFC1497, RFC1532, RFC1542)
(Status: UNKNOWN)

1542 Clarifications and Extensions for the Bootstrap Protocol. W.
Wimer. October 1993. (Format: TXT=52948 bytes) (Obsoletes RFC1532)
(Updates RFC0951) (Status: DRAFT STANDARD)

2131 Dynamic Host Configuration Protocol. R. Droms. March 1997.
(Format: TXT=113738 bytes) (Obsoletes RFC1541) (Status: DRAFT

2132 DHCP Options and BOOTP Vendor Extensions. S. Alexander, R. Droms.
March 1997. (Format: TXT=63670 bytes) (Obsoletes RFC1533) (Status:

2489 Procedure for Defining New DHCP Options. R. Droms. January 1999.
(Format: TXT=10484 bytes) (Also BCP0029) (Status: BEST CURRENT