RFC 1533 (rfc1533) - Page 2 of 30

DHCP Options and BOOTP Vendor Extensions

RFC 1533        DHCP Options and BOOTP Vendor Extensions    October 1993


    9.  DHCP Extensions ........................................... 23
   10.  Extensions ................................................ 27
   11.  Acknowledgements .......................................... 28
   12.  References ................................................ 28
   13.  Security Considerations ................................... 19
   14.  Authors' Addresses ........................................ 30

1. Introduction

   This document specifies options for use with both the Dynamic Host
   Configuration Protocol and the Bootstrap Protocol.

   The full description of DHCP packet formats may be found in the DHCP
   specification document [1], and the full description of BOOTP packet
   formats may be found in the BOOTP specification document [3].  This
   document defines the format of information in the last field of DHCP
   packets ('options') and of BOOTP packets ('vend').  The remainder of
   this section defines a generalized use of this area for giving
   information useful to a wide class of machines, operating systems and
   configurations. Sites with a single DHCP or BOOTP server that is
   shared among heterogeneous clients may choose to define other, site-
   specific formats for the use of the 'options' field.

   Section 2 of this memo describes the formats of DHCP options and
   BOOTP vendor extensions.  Section 3 describes options defined in
   previous documents for use with BOOTP (all may also be used with
   DHCP).  Sections 4-8 define new options intended for use with both
   DHCP and BOOTP. Section 9 defines options used only in DHCP.

   References further describing most of the options defined in sections
   2-6 can be found in section 12.  The use of the options defined in
   section 9 is described in the DHCP specification [1].

   Information on registering new options is contained in section 10.

2. BOOTP Extension/DHCP Option Field Format

   DHCP options have the same format as the BOOTP "vendor extensions"
   defined in RFC 1497 [2].  Options may be fixed length or variable
   length.  All options begin with a tag octet, which uniquely
   identifies the option.  Fixed-length options without data consist of
   only a tag octet.  Only options 0 and 255 are fixed length.  All
   other options are variable-length with a length octet following the
   tag octet.  The value of the length octet does not include the two
   octets specifying the tag and length.  The length octet is followed
   by "length" octets of data.  In the case of some variable-length
   options the length field is a constant but must still be specified.




Alexander & Droms