Interoperation Between DHCP and BOOTP

BOOTP's 'vendor extensions' field and the tagged data items within it have been renamed 'options' in DHCP to clarify meaning; this document treats both uniformly as 'options'.

The decision to allow a DHCP server to return automatic addresses to BOOTP clients must be under administrator control and default to OFF, because BOOTP clients may not be prepared to receive automatic addresses and will not participate in the DHCP lease lifecycle.

DHCP message format is defined to be compatible with BOOTP message format, enabling existing BOOTP clients to interoperate with DHCP servers. A message received by a DHCP server that includes a 'DHCP message type' option (51) is assumed to be from a DHCP client; messages without it are assumed to be from a BOOTP client.

A DHCP client MAY use a reply from a BOOTP server if the configuration returned is acceptable. The 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.

A DHCP server supporting BOOTP clients MUST formulate a BOOTP BOOTREPLY message rather than a DHCP DHCPOFFER; it MUST NOT include the 'DHCP message type' option and MUST NOT exceed the size limit for BOOTREPLY messages.

DHCP servers MAY send any DHCP options to a BOOTP client as allowed by the 'DHCP Options and BOOTP Vendor Extensions' RFC.

If a DHCP server supports supplying automatic addresses to BOOTP clients, this feature MUST be configurable and MUST default to OFF; enabling it must be an active decision by the system administrator.

Support of BOOTP clients by a DHCP server is optional at the discretion of the local system administrator. If a DHCP server not configured to support BOOTP clients receives a BOOTREQUEST, it MUST silently discard the message.

The server marks a binding for a BOOTP client as BOUND after sending the BOOTP BOOTREPLY, because a non-DHCP client will not send a DHCPREQUEST message nor expect a DHCPACK message.

When a DHCP server returns an automatic address to a BOOTP client, it MUST assign an infinite lease duration, since the BOOTP client is unaware of DHCP lease mechanics. Such addresses cannot be automatically reassigned by the server.

The 'DHCP message type' option (option type 51) is the distinguishing marker between DHCP and BOOTP messages. Its presence signals a DHCP client; its absence signals a BOOTP client.

Security issues are not discussed in this memo.

security