DHCP Options and BOOTP Vendor Extensions
RFC 1533

quot;
   fields are being overloaded by using them to carry DHCP options. A
   DHCP server inserts this option if the returned parameters will
   exceed the usual space allotted for options.

   If this option is present, the client interprets the specified
   additional fields after it concludes interpretation of the standard
   option fields.

   The code for this option is 52, and its length is 1.  Legal values
   for this option are:

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RFC 1533        DHCP Options and BOOTP Vendor Extensions    October 1993

           Value   Meaning
           -----   --------
             1     the "file" field is used to hold options
             2     the "sname" field is used to hold options
             3     both fields are used to hold options

    Code   Len  Value
   +-----+-----+-----+
   |  52 |  1  |1/2/3|
   +-----+-----+-----+

9.4. DHCP Message Type

   This option is used to convey the type of the DHCP message.  The code
   for this option is 53, and its length is 1.  Legal values for this
   option are:

           Value   Message Type
           -----   ------------
             1     DHCPDISCOVER
             2     DHCPOFFER
             3     DHCPREQUEST
             4     DHCPDECLINE
             5     DHCPACK
             6     DHCPNAK
             7     DHCPRELEASE

    Code   Len  Type
   +-----+-----+-----+
   |  53 |  1  | 1-7 |
   +-----+-----+-----+

9.5. Server Identifier

   This option is used in DHCPOFFER and DHCPREQUEST messages, and may
   optionally be included in the DHCPACK and DHCPNAK messages.  DHCP
   servers include this option in the DHCPOFFER in order to allow the
   client to distinguish between lease offers.  DHCP clients indicate
   which of several lease offers is being accepted by including this
   option in a DHCPREQUEST message.

   The identifier is the IP address of the selected server.

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RFC 1533        DHCP Options and BOOTP Vendor Extensions    October 1993

   The code for this option is 54, and its length is 4.

    Code   Len            Address
   +-----+-----+-----+-----+-----+-----+
   |  54 |  4  |  a1 |  a2 |  a3 |  a4 |
   +-----+-----+-----+-----+-----+-----+

9.6. Parameter Request List

   This option is used by a DHCP client to request values for specified
   configuration parameters.  The list of requested parameters is
   specified as n octets, where each octet is a valid DHCP option code
   as defined in this document.

   The client MAY list the options in order of preference.  The DHCP
   server is not required to return the options in the requested order,
   but MUST try to insert the requested options in the order requested
   by the client.

   The code for this option is 55.  Its minimum length is 1.

    Code   Len   Option Codes
   +-----+-----+-----+-----+---
   |  55 |  n  |  c1 |  c2 | ...
   +-----+-----+-----+-----+---

9.7. Message

   This option is used by a DHCP server to provide an error message to a
   DHCP client in a DHCPNAK message in the event of a failure. A client
   may use this option in a DHCPDECLINE message to indicate the why the
   client declined the offered parameters.  The message consists of n
   octets of NVT ASCII text, which the client may display on an
   available output device.

   The code for this option is 56 and its minimum length is 1.

    Code   Len     Text
   +-----+-----+-----+-----+---
   |  56 |  n  |  c1 |  c2 | ...
   +-----+-----+-----+-----+---

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RFC 1533        DHCP Options and BOOTP Vendor Extensions    October 1993

9.8. 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 |
   +-----+-----+-----+-----+

9.9. 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 |
   +-----+-----+-----+-----+-----+-----+

9.10. 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 |
   +-----+-----+-----+-----+-----+-----+

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RFC 1533        DHCP Options and BOOTP Vendor Extensions    October 1993

9.11. Class-identifier

   This option is used by DHCP clients to optionally identify the type
   and configuration of a DHCP client.  The information is a string of n
   octets, interpreted by servers.  Vendors and sites may choose to
   define specific 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).

   The code for this option is 60, and its minimum length is 1.

   Code   Len   Class-Identifier
   +-----+-----+-----+-----+---
   |  60 |  n  |  i1 |  i2 | ...
   +-----+-----+-----+-----+---

9.12. 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 consist of a type-value pair, similar to the

   It is expected that this field will typically contain a hardware type
   and hardware address, but this is not required.  Current legal values
   for hardware types are defined in [22].

   The code for this option is 61, and its minimum length is 2.

   Code   Len   Type  Client-Identifier
   +-----+-----+-----+-----+-----+---
   |  61 |  n  |  t1 |  i1 |  i2 | ...
   +-----+-----+-----+-----+-----+---

10. Extensions

   Additional generic data fields may be registered 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@isi.edu

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RFC 1533        DHCP Options and BOOTP Vendor Extensions    October 1993

   Implementation specific use of undefined generic types (those in the
   range 61-127) may conflict with other implementations, and
   registration is required.

11. Acknowledgements

   The authors would like to thank Philip Almquist for his feedback on
   this document.  The comments of the DHCP Working Group are also
   gratefully acknowledged.  In particular, Mike Carney and Jon Dreyer
   from SunSelect suggested the current format of the Vendor-specific
   Information option.

   RFC 1497 is based on earlier work by Philip Prindeville, with help
   from Drew Perkins, Bill Croft, and Steve Deering.

12. References

   [1] Droms, R., "Dynamic Host Configuration Protocol", RFC 1531,
       Bucknell University, October 1993.

   [2] Reynolds, J., "BOOTP Vendor Information Extensions", RFC 1497,
       USC/Information Sciences Institute, August 1993.

   [3] Croft, W., and J. Gilmore, "Bootstrap Protocol", RFC 951,
       Stanford University and Sun Microsystems, September 1985.

   [4] Braden, R., Editor, "Requirements for Internet Hosts -
       Communication Layers", STD 3, RFC 1122, USC/Information Sciences
       Institute, October 1989.

   [5] Mogul, J., and J. Postel, "Internet Standard Subnetting
       Procedure", STD 5, RFC 950, 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, RFC 1035, USC/Information Sciences
       Institute, November 1987.

   [9] Postel, J., "Quote of the Day Protocol", STD 23, RFC 865,
       USC/Information Sciences Institute, May 1983.

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RFC 1533        DHCP Options and BOOTP Vendor Extensions    October 1993

   [10] McLaughlin, L., "Line Printer Daemon Protocol", RFC 1179, The
        Wollongong Group, August 1990.

   [11] Accetta, M., "Resource Location Protocol", RFC 887, CMU,
        December 1983.

   [12] Mogul, J. and S. Deering, "Path MTU Discovery", RFC 1191,
        DECWRL,  Stanford University, November 1990.

   [13] Deering, S., "ICMP Router Discovery Messages", RFC 1256,
        Xerox PARC, September 1991.

   [14] Leffler, S. and M. Karels, "Trailer Encapsulations", RFC 893,
        U. C. Berkeley, April 1984.

   [15] Hornig, C., "Standard for the Transmission of IP Datagrams over
        Ethernet Networks", RFC 894, Symbolics, April 1984.

   [16] Postel, J. and J. Reynolds, "Standard for the Transmission of
        IP Datagrams Over IEEE 802 Networks", RFC 1042,  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", RFC 1305, UDEL, March 1992.

   [19] NetBIOS Working Group, "Protocol Standard for a NetBIOS Service
        on a TCP/UDP transport: Concepts and Methods", STD 19, RFC 1001,
        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, RFC 1198,
        MIT Laboratory for Computer Science, January 1991.

   [22] Reynolds, J., and J. Postel, "Assigned Numbers", STD 2, RFC 1340,
        USC/Information Sciences Institute, July 1992.

13. Security Considerations

   Security issues are not discussed in this memo.

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RFC 1533        DHCP Options and BOOTP Vendor Extensions    October 1993

14. Authors' Addresses

   Steve Alexander
   Lachman Technology, Inc.
   1901 North Naper Boulevard
   Naperville, IL 60563-8895

   Phone: (708) 505-9555 x256
   EMail: stevea@lachman.com

   Ralph Droms
   Computer Science Department
   323 Dana Engineering
   Bucknell University
   Lewisburg, PA 17837

   Phone: (717) 524-1145
   EMail: droms@bucknell.edu

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