When the DHCP relay receives a DHCP request message in which the giaddr (gateway IP address) field is 0, how does the DHCP relay process the DHCP request message? 

The DHCP relay fills its IP address in the giaddr field and transmits the DHCP request message to the DHCP server in unicast mode. 

The DHCP relay fills its IP address in the giaddr field and transmits the DHCP request message in broadcast mode. 

The DHCP relay retains the value of the giaddr field and transmits the DHCP request message to the DHCP server in unicast mode. 

The DHCP relay retains the value of the giaddr field and transmits the DHCP request message in broadcast mode.