Dynamic Host Configuration Protocol
The Dynamic Host Configuration Protocol is used to dynamically provide IP address configuration to clients.When a client is configured to use a dynamic IP address the following process is performed at startup:
1.The client sends an DHCPDiscover broadcast which all available DHCP servers can respond.
2.The DHCP servers then sends a DHCP offer packet containing IP address information that the client can use.
3.The client sends a DHCP Request indicating that it accept the offer, the first offer received is then used.
4.The server responds with a DHCP Ack that identifies that the DHCP server knows that the offer was that was accepted.
Because most routers block broadcast packets from passing between networks means that DHCP Discover packet are not able to cross networks ,so to allow a DHCP server to service multiple networks you need to implement a DHCP relay.