What is the primary purpose of NAT in IPv4 networks?

• A. To encrypt traffic across the internet
• B. To translate private addresses to public addresses, allowing multiple internal hosts to access external networks and conserve public IPv4 addresses.
• C. To route packets based on destination MAC
• D. To assign unique addresses to all devices globally

Answer: (B)

NAT is used to let many devices inside a private IPv4 network share public Internet access by translating private addresses to public ones. This address translation, often with port numbers (PAT), lets outbound traffic from multiple internal hosts appear as coming from a single public IP (or a small set of public IPs) and then routes the responses back to the correct internal device. The big idea is address conservation: IPv4 has a limited number of public addresses, so NAT enables internal networks to use private addresses (like 192.168.x.x, 10.x.x.x, or 172.16.x.x) while still reaching external networks.

NAT sits at the network edge (often the router) and keeps a mapping table to track which internal host and port correspond to which external source port, so responses can be rewritten back to the right internal host. This concept isn’t about encrypting traffic, nor about routing based on MAC addresses, nor about assigning globally unique addresses to every device—those are different functions.