you can configure your firewall to block or allow both ways

ie:

add allow all from 10.0.0.150 2000 to 10.0.0.151 80
add deny all from any to any

this would only allow a socket connection to port 80 on 10.0.0.151 if 10.0.0.150 would actually bind their socket to port 2000.

Anyway, its a mute discussion. Its more fun to squable about protocols