Clarifications and Extensions for the Bootstrap Protocol
RFC 1542

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Network Working Group                                           W. Wimer
Request for Comments: 1542                    Carnegie Mellon University
Updates: 951                                                October 1993
Obsoletes: 1532
Category: Standards Track

        Clarifications and Extensions for the Bootstrap Protocol

Status of this Memo

   This RFC specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" for the standardization state and status
   of this protocol.  Distribution of this memo is unlimited.

Abstract

   Some aspects of the BOOTP protocol were rather loosely defined in its
   original specification.  In particular, only a general description
   was provided for the behavior of "BOOTP relay agents" (originally
   called BOOTP forwarding agents").  The client behavior description
   also suffered in certain ways.  This memo attempts to clarify and
   strengthen the specification in these areas.  Due to some errors
   introduced into RFC 1532 in the editorial process, this memo is
   reissued as RFC 1542.

   In addition, new issues have arisen since the original specification
   was written.  This memo also attempts to address some of these.

Table of Contents

   1. Introduction.................................................  2
   1.1 Requirements................................................  3
   1.2 Terminology.................................................  3
   1.3 Data Transmission Order.....................................  4
   2. General Issues...............................................  5
   2.1 General BOOTP Processing....................................  5
   2.2 Definition of the 'flags' Field.............................  5
   2.3 Bit Ordering of Hardware Addresses..........................  7
   2.4 BOOTP Over IEEE 802.5 Token Ring Networks...................  8
   3. BOOTP Client Behavior........................................  9
   3.1 Client use of the 'flags' field.............................  9
   3.1.1 The BROADCAST flag........................................  9
   3.1.2 The remainder of the 'flags' field........................  9
   3.2 Definition of the 'secs' field.............................. 10
   3.3 Use of the 'ciaddr' and 'yiaddr' fields..................... 10

Wimer                                                           [Page 1]
RFC 1542        Clarifications and Extensions for BOOTP     October 1993

   3.4 Interpretation of the 'giaddr' field........................ 11
   3.5 Vendor information "magic cookie"........................... 12
   4. BOOTP Relay Agents........................................... 13
   4.1 General BOOTP Processing for Relay Agents................... 14
   4.1.1 BOOTREQUEST Messages...................................... 14
   4.1.2 BOOTREPLY Messages........................................ 17
   5. BOOTP Server Behavior........................................ 18
   5.1 Reception of BOOTREQUEST Messages........................... 18
   5.2 Use of the 'secs' field..................................... 19
   5.3 Use of the 'ciaddr' field................................... 19
   5.4 Strategy for Delivery of BOOTREPLY Messages................. 20
   Acknowledgements................................................ 21
   References...................................................... 22
   Security Considerations......................................... 23
   Author's Address................................................ 23

1. Introduction

   The Bootstrap Protocol (BOOTP) is a UDP/IP-based protocol which
   allows a booting host to configure itself dynamically and without
   user supervision.  BOOTP provides a means to notify a host of its
   assigned IP address, the IP address of a boot server host, and the
   name of a file to be loaded into memory and executed [1].  Other
   configuration information such as the local subnet mask, the local
   time offset, the addresses of default routers, and the addresses of
   various Internet servers can also be communicated to a host using
   BOOTP [2].

   Unfortunately, the original BOOTP specification [1] left some issues
   of the protocol open to question.  The exact behavior of BOOTP relay
   agents formerly called "BOOTP forwarding agents") was not clearly
   specified.  Some parts of the overall protocol specification actually
   conflict, while other parts have been subject to misinterpretation,
   indicating that clarification is needed.  This memo addresses these
   problems.

   Since the introduction of BOOTP, the IEEE 802.5 Token Ring Network
   has been developed which presents a unique problem for BOOTP's
   particular message-transfer paradigm.  This memo also suggests a
   solution for this problem.

   NOTE: Unless otherwise specified in this document or a later
   document, the information and requirements specified througout this