[CentOS] Port Closing Question..

Is there a software avail or a process that will monitor two ports and 
if there is no traffic close them so the program that is using them can 
reuse them?  I talked to the vendor and they told me I needed to do this 
on the NAT/Firewall , but I dont see anything like that on my router. So 
any suggestions ideas?

thanks,
Ryan Nichols