SPI
The term firewall is a blanket term describing security measures that protect a network. Because the router or gateway is your network's connection to the Internet, a built-in firewall helps protect your entire local network, like an alarm system for your house. SPI (Stateful Packet Inspection) is a type of firewall that inspects incoming data packets to make sure they correspond to an outgoing request. Unsolicited and potentially harmful packets are rejected.
SPI firewall is considered to be more advanced than NAT because it is able to examine the information that is coming through to your network from the Internet. You can configure the settings to prevent security threats to your network containing sensitive information.
