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Network Working Group R. Droms Request for Comments: 1534 Bucknell University Category: Standards Track October 1993

               Interoperation Between DHCP and BOOTP

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

 DHCP provides a superset of the functions provided by BOOTP. This
 document describes the interactions between DHCP and BOOTP network
 participants.

1. Introduction

 The Dynamic Host Configuration Protocol (DHCP) provides a mechanism
 for transmitting configuration parameters to hosts using the TCP/IP
 protocol suite.  The format of DHCP messages is based on the format
 of BOOTP messages, so that, in certain circumstances, DHCP and BOOTP
 participants may exchange messages.  This document specifies the ways
 in which DHCP and BOOTP participants may interoperate.

 DHCP introduces a small change in terminology intended to clarify the
 meaning of one of the fields.  What was the "vendor extensions" field
 in BOOTP has been re-named the "options" field in DHCP.  Similarly,
 the tagged data items that were used inside the BOOTP "vendor
 extensions" field, which were formerly referred to as "vendor
 extensions", are now termed simply "options".  This document will
 refer to BOOTP vendor extensions and DHCP options uniformly as
 "options".

 Throughout this document, DHCP messages that include a 'DHCP message
 type' option will be referred to by the type of the message; e.g., a
 DHCP message with 'DHCP message type' option type 1 will be referred
 to as a "DHCPDISCOVER" message.

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2. BOOTP clients and DHCP servers

 The format of DHCP messages is defined to be compatible with the
 format of BOOTP messages, so that existing BOOTP clients can
 interoperate with DHCP servers.  Any message received by a DHCP
 server that includes a 'DHCP message type' (51) option is assumed to
 have been sent by a DHCP client.  Messages without the DHCP Message
 Type option are assumed to have been sent by a BOOTP client.  Support
 of BOOTP clients by a DHCP server is optional at the discretion of
 the local system administrator.  If a DHCP server that is not
 configured to support BOOTP clients receives a BOOTREQUEST message
 from a BOOTP client, that server silently discards the BOOTREQUEST
 message.

 If a DHCP server is configured to support BOOTP clients, it may be
 configured to supply static addresses, automatic addresses or both.
 Static addresses are those that have been previously assigned by a
 system administrator and are stored in a database available to the
 DHCP server.  Automatic addresses are those selected by the DHCP
 server from its pool of unassigned addresses.

 Since BOOTP clients may not be prepared to receive automatic
 addresses, the decision to allow a DHCP server to return automatic
 addresses must be under the control of the system administrator.  If
 a DHCP server supports supplying automatic addresses to BOOTP
 clients, this feature must be configurable, and the feature must
 default off.  Enabling of the feature must be the result of an active
 decision by the system administrator.

 If a DHCP server returns a automatic address, the BOOTP client will
 not be aware of the DHCP lease mechanism for network address
 assignment.  Thus the DHCP server must assign an infinite lease
 duration to for automatic addresses assigned to BOOTP clients.  Such
 network addresses cannot be automatically reassigned by the server.
 The local system administrator may choose to manually release network
 addresses assigned to BOOTP clients.

 A DHCP server that supports BOOTP clients MUST interact with BOOTP
 clients according to the BOOTP protocol.  The server MUST formulate a
 BOOTP BOOTREPLY message rather than a DHCP DHCPOFFER message (i.e.,
 the server MUST NOT include the 'DHCP message type' option and MUST
 NOT exceed the size limit for BOOTREPLY messages).  The server marks
 a binding for a BOOTP client as BOUND after sending the BOOTP
 BOOTREPLY, as a non-DHCP client will not send a DHCPREQUEST message
 nor will that client expect a DHCPACK message.

 DHCP servers MAY send any DHCP Options to a BOOTP client as allowed
 by the "DHCP Options and BOOTP Vendor Extensions" RFC [2].

Droms [Page 2]  RFC 1534 Interoperation Between DHCP and BOOTP October 1993

 In summary, a DHCP server:

    o MAY support BOOTP clients,

    o May return automatic addresses to BOOTP clients,

    o MUST provide a configuration switch if returning automatic
      addresses to BOOTP clients,

    o MUST default this optional configuration to OFF,

    o MUST abide by the BOOTP specification when interacting with
      BOOTP clients, and

    o MAY send DHCP options (those options defined in the DHCP options
      document but not in the BOOTP vendor extensions documents) to
      a BOOTP client.

3. DHCP clients and BOOTP servers

 A DHCP client MAY use a reply from a BOOTP server if the
 configuration returned from the BOOTP server is acceptable to the
 DHCP client.  A DHCP client MUST assume that an IP address returned
 in a message from a BOOTP server has an infinite lease.  A DHCP
 client SHOULD choose to use a reply from a DHCP server in preference
 to a reply from a BOOTP server.

4. References

 [1] Wimer, W., "Clarifications and Extensions for the Bootstrap
     Protocol", RFC 1532, Carnegie Mellon University, October 1993.

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

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

5. Security Considerations

 Security issues are not discussed in this memo.

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6. Author's Address

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

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

Droms [Page 4]