Tomi Holger Engdahl wrote:

> When the PC boots up and is set to
> use DHCP, then it sends a request packet "please give me my IP address"
> as a broadcast message. The ISP DHCP server receives that
> requequest and send back the answer telling that IP address and
> other network settings to use.

Actually, there's a bit more to it, then that. The computer initially
broadcasts a DHCPDISCOVER. Any DHCP server receiving that broadcast, can
then send a response called a DHCPOFFER. The client then chooses which
server to use and sends a DHCPREQUEST, and then receives the DHCPACK,
containing the configuration info, from the server.