Which device protects an internal network from the Internet?

A firewall is specifically designed to protect an internal network from unauthorized access and malicious traffic originating from external networks, like the Internet. It inspects incoming and outgoing network traffic and blocks or permits packets based on a defined set of security rules. A router primarily forwards packets between different networks and can offer some basic security features, but its main role isn't deep packet inspection or comprehensive threat protection. An access point provides wireless connectivity to a network. A Layer 2 switch connects devices within the same local area network (LAN) and operates at the data link layer, without providing internetwork security.