Explain NAT vs PAT and provide a scenario for each.

• A. NAT uses port multiplexing; PAT uses fixed mapping
• B. NAT translates private addresses to a public address one-to-one; PAT translates many private addresses to a single public address using port numbers.
• C. NAT and PAT are synonyms; Both map private to public addresses
• D. NAT is used to connect LANs; PAT translates MAC addresses

Answer: (B)

NAT and PAT address how private devices reach the Internet by mapping private addresses to public ones, but they differ in how many internal hosts share a public address and how that mapping is done.

With NAT in its typical one-to-one form, each private IP is paired with a unique public IP. External hosts see distinct public addresses for each internal device, and inbound traffic can be directed straight to the specific internal host. A common scenario is a business that has multiple public IPs and assigns a dedicated public address to each server. For example, a file server with private 10.0.0.10 maps to public 198.51.100.10, and an application server with private 10.0.0.20 maps to public 198.51.100.20. This provides direct access to each internal server from the Internet without port sharing.

PAT, or many-to-one NAT using port numbers, lets many private addresses share a single public IP. The router keeps track of which internal device a given connection belongs to by using different port numbers. This is common in home or small-office networks where all devices appear to the Internet from one public address. Outgoing connections from different internal hosts use different source ports on the same public IP, so replies are routed back to the correct internal device. For instance, multiple devices behind a single router with public IP 203.0.113.5 can browse the Web simultaneously; the router assigns unique source ports (like 12345, 12346, etc.) so responses come back to the right internal host. If inbound access is needed, port forwarding can direct specific public ports to a chosen internal host.