# When unsolicited traffic comes to the router (a regular occurrence on the Internet), a NAT system alone will attempt to remap this traffic based on the port number is used. If no such port number is in use, it will either drop the packet (ignore it), or reply with an error code stating that the requested device could not be found. However most networks, including most of those behind cheap consumer routers, typically have a [[firewall]] which blocks this kind of traffic, when an internal device did not first contact that external device. | # When unsolicited traffic comes to the router (a regular occurrence on the Internet), a NAT system alone will attempt to remap this traffic based on the port number is used. If no such port number is in use, it will either drop the packet (ignore it), or reply with an error code stating that the requested device could not be found. However most networks, including most of those behind cheap consumer routers, typically have a [[firewall]] which blocks this kind of traffic, when an internal device did not first contact that external device. |