socket programming and port scans

[rbt]

I don't fully understand sockets, I just know enough to be dangerous. 
The below is not detected by nmap, but is affected by iptables or ipsec. 
Can anyone explain why that is?

     s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
     s.bind((ip_param, port_param))
     while 1:
         s.listen(5)

I can connect to the socket server and even transmit data so I know it's 
there.

Thanks,
rbt