BOOTP is a TCP/IP protocol.
The BOOTP server listens on the well-known BOOTP server port 67, which Dynamic Host Configuration Protocol (DHCP) also uses. Because of this, BOOTP and DHCP cannot operate at the same time on the same system. (DHCP is the preferred method for supporting BOOTP clients.) When the server receives a client request, it looks up the IP address for the client and returns a reply to that client. This reply contains both the IP address of the client and the name of the load file. The client then initiates a Trivial File Transfer Protocol (TFTP) request to the server for the load file.
A BOOTP relay agent listens to UDP port 68, and forwards BOOTP request packets received on this port to the destinations specified on the command line.