You can configure the device or an interface to act as a DHCP relay agent. Doing so enables the device to respond to DHCP or BOOTP requests broadcast by request as a broadcast message. If the device or an interface detects a broadcast message, it relays the message to a specified DHCP or BOOTP server.
We recommend you to configure the device or an interface to be a DHCP/BOOTP relay agent if you have locally attached hosts and a distant DHCP or BOOTP server. For more information, see JUNOS Policy Framework Configuration Guide