Westermo MRD-3x0 - Manual (Page 179)

179 6623-3201
Master address and port
Packets transmitted over network will always be sent to the
address specified in the Master address and Master port fields.
Address and port of last request
Packets transmitted over network will be sent to the source
address of the most recently received packet. If no packets
have been received, packets will be transmitted to the address
specified in the Master address and Master port fields.
For information on setting the Port Configuration, see section
7.2.1.