DHCP clients initially have no configured IP address, and must therefore send a broadcast DHCPDiscover request to obtain an IP address from a DHCP server.If the client is on same broadcast domain the client is offered an address when a DHCP server responds with a DHCPOffer message containing an IP address and configuration information for lease to the client.

If the DHCP server is on different broadcast domain.Then it is performed by use of a DHCP Relay Agent.The Cisco implementation of DHCP Relay is provided through interface-level ip helper command . DHCP server responds with a DHCPOffer message containing an IP address and configuration information for lease to the client.