Any message that is received by a DHCP server that includes a DHCP message option type 51 is assumed to have been sent by a DHCP client. Messages that do not have the DHCP Message Type option are assumed to have been sent by a BOOTP client.
- The DHCP DISCOVER\REQUEST that is sent by the BitLocker Network Unlock client in its first two requests has the Message Type option. This means that the requests are DHCP protocol based.
- The DHCP request (that is, the third request) that is sent by client does not have the Message Type option. This means that the request is BOOTP protocol based.
The server marks a binding for a BOOTP client as BOUND after the server sends the BOOTP BOOTREPLY message. 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.
This means that as long as a DHCP server supports BOOTP clients, the DHCP server will reply to BOOTP requests.
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.