The correct answer is Captive portals, which provide a convenient method for managing guest networks by requiring users to authenticate or accept terms of service before accessing the network. This isolates the guest users from the internal network, ensuring security. MAC filtering only restricts access based on hardware addresses, which does not provide an isolated network environment for guests. WPA3 provides a secure way to encrypt wireless communications but does not inherently separate guests from internal network resources. Subnetting is a method to divide networks but does not manage or securely isolate guest users.