PLANET SG-1000 - Manual (Page 75)

Under general circumstances, the range of port number of client is 1024-65535. Change
the client range in Custom of is not suggested.
If the port numbers that enter in the two spaces are different port number, then enable the
port number under the range between the two different port numbers (for example:
15328:15333). And if the port number that enter in the two space are the same port number,
then enable the port number as one (for example: 1720:1720).