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I know, that this is an old question, but this is where google led me, so for future reference:

You can limit the range of ephemeral ports (i.e. ports that are assigned to sockets that do not request a certain port number) using

echo 4000-4200,5000-6000 | sudo tee /proc/sys/net/ipv4/ip_local_reserved_ports

here you forbid to use ports in the range 4000 to 4200 or 5000 to 6000. You can check all available ports using

echo /proc/sys/net/ipv4/ip_local_port_range

If you want this changes to take effect on startup, add a line similar to the following to /etc/rc.local:

echo 4000-4200,5000-6000 > /proc/sys/net/ipv4/ip_local_reserved_ports