Code Len Text
+-----+-----+-----+-----+---
| 56 | n | c1 | c2 | ...
+-----+-----+-----+-----+---
9.10. Maximum DHCP Message Size
This option specifies the maximum length DHCP message that it is
willing to accept. The length is specified as an unsigned 16-bit
integer. A client may use the maximum DHCP message size option in
DHCPDISCOVER or DHCPREQUEST messages, but should not use the option
in DHCPDECLINE messages.
The code for this option is 57, and its length is 2. The minimum
legal value is 576 octets.
Code Len Length
+-----+-----+-----+-----+
| 57 | 2 | l1 | l2 |
+-----+-----+-----+-----+
9.11. Renewal (T1) Time Value
This option specifies the time interval from address assignment until
the client transitions to the RENEWING state.
The value is in units of seconds, and is specified as a 32-bit
unsigned integer.
The code for this option is 58, and its length is 4.
Code Len T1 Interval
+-----+-----+-----+-----+-----+-----+
| 58 | 4 | t1 | t2 | t3 | t4 |
+-----+-----+-----+-----+-----+-----+
9.12. Rebinding (T2) Time Value
This option specifies the time interval from address assignment until
the client transitions to the REBINDING state.
The value is in units of seconds, and is specified as a 32-bit
unsigned integer.
The code for this option is 59, and its length is 4.
Code Len T2 Interval
+-----+-----+-----+-----+-----+-----+
| 59 | 4 | t1 | t2 | t3 | t4 |
+-----+-----+-----+-----+-----+-----+
9.13. Vendor class identifier
This option is used by DHCP clients to optionally identify the vendor
type and configuration of a DHCP client. The information is a string
of n octets, interpreted by servers. Vendors may choose to define
specific vendor class identifiers to convey particular configuration
or other identification information about a client. For example, the
identifier may encode the client's hardware configuration. Servers
not equipped to interpret the class-specific information sent by a
client MUST ignore it (although it may be reported). Servers that
respond SHOULD only use option 43 to return the vendor-specific
information to the client.
The code for this option is 60, and its minimum length is 1.
Code Len Vendor class Identifier
+-----+-----+-----+-----+---
| 60 | n | i1 | i2 | ...
+-----+-----+-----+-----+---
9.14. Client-identifier
This option is used by DHCP clients to specify their unique
identifier. DHCP servers use this value to index their database of
address bindings. This value is expected to be unique for all
clients in an administrative domain.
Identifiers SHOULD be treated as opaque objects by DHCP servers.
The client identifier MAY consist of type-value pairs similar to the
'htype'/'chaddr' fields defined in [3]. For instance, it MAY consist
of a hardware type and hardware address. In this case the type field
SHOULD be one of the ARP hardware types defined in STD2 [22]. A
hardware type of 0 (zero) should be used when the value field
contains an identifier other than a hardware address (e.g. a fully
qualified domain name).
For correct identification of clients, each client's client-
identifier MUST be unique among the client-identifiers used on the
subnet to which the client is attached. Vendors and system
administrators are responsible for choosing client-identifiers that
meet this requirement for uniqueness.
The code for this option is 61, and its minimum length is 2.
Code Len Type Client-Identifier
+-----+-----+-----+-----+-----+---
| 61 | n | t1 | i1 | i2 | ...
+-----+-----+-----+-----+-----+---
10. Defining new extensions
The author of a new DHCP option will follow these steps to obtain
acceptance of the option as a part of the DHCP Internet Standard:
1. The author devises the new option.
2. The author requests a number for the new option from IANA by
contacting:
Internet Assigned Numbers Authority (IANA)
USC/Information Sciences Institute
4676 Admiralty Way
Marina del Rey, California 90292-6695
or by email as: iana@iana.org
3. The author documents the new option, using the newly obtained
option number, as an Internet Draft.
4. The author submits the Internet Draft for review through the IETF
standards process as defined in "Internet Official Protocol
Standards" (STD 1). The new option will be submitted for eventual
acceptance as an Internet Standard.
5. The new option progresses through the IETF standards process; the
new option will be reviewed by the Dynamic Host Configuration
Working Group (if that group still exists), or as an Internet
Draft not submitted by an IETF working group.
6. If the new option fails to gain acceptance as an Internet
Standard, the assigned option number will be returned to IANA for
reassignment.
This procedure for defining new extensions will ensure that:
* allocation of new option numbers is coordinated from a single
authority,
* new options are reviewed for technical correctness and
appropriateness, and
* documentation for new options is complete and published.
11. Acknowledgements
The author thanks the many (and too numerous to mention!) members of
the DHC WG for their tireless and ongoing efforts in the development
of DHCP and this document.
The efforts of J Allard, Mike Carney, Dave Lapp, Fred Lien and John
Mendonca in organizing DHCP interoperability testing sessions are
gratefully acknowledged.
The development of this document was supported in part by grants from
the Corporation for National Research Initiatives (CNRI), Bucknell
University and Sun Microsystems.
12. References
[1] Droms, R., "Dynamic Host Configuration Protocol", RFC2131,
Bucknell University, March 1997.
[2] Reynolds, J., "BOOTP Vendor Information Extensions", RFC1497,
USC/Information Sciences Institute, August 1993.
[3] Croft, W., and J. Gilmore, "Bootstrap Protocol", RFC951,
Stanford University and Sun Microsystems, September 1985.
[4] Braden, R., Editor, "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC1122, USC/Information Sciences
Institute, October 1989.
[5] Mogul, J., and J. Postel, "Internet Standard Subnetting
Procedure", STD 5, RFC950, USC/Information Sciences Institute,
August 1985.
[6] Postel, J., and K. Harrenstien, "Time Protocol", STD 26, RFC
868, USC/Information Sciences Institute, SRI, May 1983.
[7] Postel, J., "Name Server", IEN 116, USC/Information Sciences
Institute, August 1979.
[8] Mockapetris, P., "Domain Names - Implementation and
Specification", STD 13, RFC1035, USC/Information Sciences
Institute, November 1987.
[9] Postel, J., "Quote of the Day Protocol", STD 23, RFC865,
USC/Information Sciences Institute, May 1983.
[10] McLaughlin, L., "Line Printer Daemon Protocol", RFC1179, The
Wollongong Group, August 1990.
[11] Accetta, M., "Resource Location Protocol", RFC887, CMU,
December 1983.
[12] Mogul, J. and S. Deering, "Path MTU Discovery", RFC1191,
DECWRL, Stanford University, November 1990.
[13] Deering, S., "ICMP Router Discovery Messages", RFC1256,
Xerox PARC, September 1991.
[14] Leffler, S. and M. Karels, "Trailer Encapsulations", RFC893,
U. C. Berkeley, April 1984.
[15] Hornig, C., "Standard for the Transmission of IP Datagrams over
Ethernet Networks", RFC894, Symbolics, April 1984.
[16] Postel, J. and J. Reynolds, "Standard for the Transmission of
IP Datagrams Over IEEE 802 Networks", RFC1042, USC/Information
Sciences Institute, February 1988.
[17] Sun Microsystems, "System and Network Administration", March
1990.
[18] Mills, D., "Internet Time Synchronization: The Network Time
Protocol", RFC1305, UDEL, March 1992.
[19] NetBIOS Working Group, "Protocol Standard for a NetBIOS Service
on a TCP/UDP transport: Concepts and Methods", STD 19, RFC1001,
March 1987.
[20] NetBIOS Working Group, "Protocol Standard for a NetBIOS Service
on a TCP/UDP transport: Detailed Specifications", STD 19, RFC
1002, March 1987.
[21] Scheifler, R., "FYI On the X Window System", FYI 6, RFC1198,
MIT Laboratory for Computer Science, January 1991.
[22] Reynolds, J., and J. Postel, "Assigned Numbers", STD 2, RFC1700,
USC/Information Sciences Institute, July 1992.
13. Security Considerations
Security issues are not discussed in this memo.
14. Authors' Addresses
Steve Alexander
Silicon Graphics, Inc.
2011 N. Shoreline Boulevard
Mailstop 510
Mountain View, CA 94043-1389
Phone: (415) 933-6172
EMail: sca@engr.sgi.com
Ralph Droms
Bucknell University
Lewisburg, PA 17837
Phone: (717) 524-1145
EMail: droms@bucknell.edu