DHCP is where a client broadcasts to the network asking for network settings. The DHCP server accepts the request and gives the client the settings. When setting up a DHCP server you must reserve a block of IP addresses for the server to pass out, that is called an address pool. The DHCP process is four steps. It starts by the client sending a DHCPDISCOVER broadcast. The DHCP server then sends back a DHCPOFFER. The client sends back a DHCPREQUEST to the DHCP server that sent the first request. Finaly the DHCP server sends a DHCPACK to the client. DHCP relay is used for network segments that don't have their own DHCP server. The DHCP relay knows the IP address of the DHCP server and forwards the request. The DHCP relay then takes the reply and passes it back to the requesting client.
SNMP helps maintain centralized administration by allowing you to monitor and control remote hosts from one location. SNMP agents receive requests and reports information. SNMP managers manage the SNMP community by accepting SNMP traps and sending GET commands to SNMP agents. SNMP traps are message initiated by the client. The SNMP trap is the only SNMP communication initiated by the SNMP agent. Send authentication traps send a message when it receives a SNMP request from an unauthorized host.