Configuring Junos OS to Extend the Default Port Address Range
By default, the upper range of a port address is 5000. You can increase the range from which the port number can be selected to decrease the probability that someone can determine your port number.
To configure Junos OS to extend the default port address range, include the source-port statement at the [edit system internet-options] hierarchy level:[edit system internet-options]source-port upper-limit upper-limit;
upper-limit upper-limit is the upper limit of a source port address and can be a value from 5000 through 65,355.