how do i release the ip address of comcast xfinity SMCD3GNV gateway?

When you release that is the point where you do a ipconfig. At that point it will return with a 169 or some other address which would tell the user the connections and their statuses. At the point that you renew it's reset. You could also go into start/control panel/Network and connections and manually disable the connection there as well. You could go to admin tools/ services and stop necessary services that will disable the connection and prevent it from restarting. There are some jusst for the Ethernet/internet controller/ Network Connection devices such as usb receivers. You could disable the USB and many other devices in your device manager. You can disable your ethernet/wireless controllers thus preventing them from even working. There is flood control available in many of today's routers. No fooling. There is actually an option or 6 that will help guard against sniffing and flooding. It's probably in the security section. Most manuals for today's routers are usually available in PDF format requiring the Acrobat Reader.