Yes you could do it via firewall rules, but...
Look under IP Services, you can control access to services to speciffic addresses, networks etc.
Read the manual and understan what you are doing, or you can lock yourself out of the router and may need to use telnet, serial cable etc to get access to the device.
I dont climb towers, but if you misconfigure the services section, you may be finding out just how well your climbing harness still fits...
Craig