Final answer:
Andy should use private IP addressing for the internal network of the company, as these addresses are not routable on the Internet and fit the requirement of keeping internal hosts non-accessible from the Internet while still allowing them to reach remote networks using NAT.
Step-by-step explanation:
Andy is a network technician preparing to configure a company's network with segments including an internal network, a DMZ, and an external network. The IP addressing solution that would work for Andy's network configuration, where no hosts on the internal network should be directly accessible by their IP address from the Internet, but should be able to reach remote networks if they have been assigned an IP address within the network, is private addressing.
Private addresses are reserved for use within a private network and are not routable on the Internet, which means they are ideal for internal hosts that should not be directly accessible from the Internet. Devices on the internal network can communicate with external networks using a method called Network Address Translation (NAT), typically implemented on the firewall.
Teredo tunneling is used to facilitate communication between IPv6 and IPv4 networks, which is not specifically relevant to this network's requirements. APIPA (Automatic Private IP Addressing) assigns a unique IP address from a predefined range when a DHCP server is not available, but it is not suitable for a defined corporate network. Classless refers to a method of IP address allocation that allows for a flexible division of the IP address space and is also not specifically required to meet the criteria given for Andy's network configuration.