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Stateful Inspection vs Packet Filtering and Firewall Rules This lesson covers stateful inspection versus packet filtering. Packet filtering is just based on the header. However, the stateful firewall inspects traffic and only allows initiated traffic in. This lesson also discusses firewall rules, specifically inbound versus outbound. An inbound firewall rule is one that dictates what is allowed from the public network into the private network. Outbound traffic is what is travelling from the private network to the public network. Outbound rules are more trustworthy than inbound rules. Inbound rules also have an implicit deny, which allows a packet to be denied if a rule is not known. Finally, Access Control Lists (ACL) can permit or deny traffic and are specified based on IP/Port/MAC source or destination.