Final answer:
Network Address Translation (NAT), Classless Inter-Domain Routing (CIDR), and Subnetting are three mechanisms used to extend the lifetime and usefulness of IPv4.
Step-by-step explanation:
The three mechanisms used to extend the lifetime and usefulness of IPv4 are Network Address Translation (NAT), Classless Inter-Domain Routing (CIDR), and Subnetting.
Network Address Translation (NAT) is used to translate private IPv4 addresses to public IPv4 addresses, allowing multiple devices to share a single public IP address. This helps conserve IPv4 addresses and allows for more devices to connect to the internet.
Classless Inter-Domain Routing (CIDR) allows for more efficient IP address allocation by using variable-length subnet masking. This enables organizations to use smaller blocks of IP addresses, leading to less wastage and better utilization of the available IP address space.
Subnetting is a process that divides a large IP network into smaller subnetworks or subnets. By doing so, it enables the efficient use of IP addresses and helps in managing network resources.