RFC1534 - Interoperation Between DHCP and BOOTP

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 RFCspecifies 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.

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].

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", RFC1532, Carnegie Mellon University, October 1993.

[2] Alexander, S., and R. Droms, "DHCP Options and BOOTP Vendor

Extensions", RFC1533, Lachman Technology, Inc., Bucknell

University, October 1993.

[3] Droms, R., "Dynamic Host Configuration Protocol", RFC1531,

Bucknell University, October 1993.

5. Security Considerations

Security issues are not discussed in this memo.

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