802.1X authentication provides a method for network devices to authenticate users or devices before allowing them access to the network, which can be effective against unauthorized devices but doesn't address address flooding attacks. Switch port security is indeed the right feature for limiting access to a switch port to a specific number of known devices, thereby preventing both unauthorized network access and mitigating address flooding attacks, which occur when a network device is overwhelmed with data from multiple unknown devices. While a captive portal can restrict access through a web page, it does not inherently prevent device-level access attacks, and DHCP snooping is a security feature that monitors and filters DHCP traffic, which is unrelated to direct switch port security measures.