An access list on a router is an example of which type of firewall?

An access list on a router is best categorized as a stateless firewall. This is because access lists operate by evaluating each packet individually against predetermined rules without maintaining any context or state about the connection. Each packet is assessed based solely on its headers, such as source and destination IP addresses and ports, and this decision is made independently of any previous packets.

In contrast, stateful firewalls track the state of active connections and make decisions based on the context of the traffic within those sessions. This allows stateful firewalls to offer more dynamic and sophisticated control over network traffic compared to stateless methods.

While packet-filtering is sometimes associated with stateless firewalls, it refers more generally to the concept of examining packet headers and making forwarding decisions based on defined rules. Although access lists implement packet filtering, categorizing them strictly as such does not highlight their lack of connection state awareness, which is a critical aspect of being stateless.