Which NAT-related technique would commonly help maintain TCP connectivity across NATs?

• A. Disable NAT
• B. Use UDP only
• C. NAT traversal techniques and keep-alives help maintain connectivity
• D. Port mappings are irrelevant

Answer: (C)

Maintaining a TCP session across NATs centers on keeping the NAT mappings alive. NAT devices create a translation entry for a connection and usually drop that entry after a period of inactivity. If nothing keeps the binding active, return traffic can’t be routed correctly and the TCP connection will appear to drop. NAT traversal techniques address this by establishing or refreshing bindings, and keep-alives provide the necessary periodic traffic—often small, regular packets—that prevents the NAT from timing out. With these heartbeats, TCP data can continue flowing through the NATs as long as both sides remain reachable, even when they sit behind different NATs.

Disabling NAT isn’t practical in real networks, relying on UDP alone doesn’t guarantee the reliability TCP requires, and NATs depend on port mappings to direct traffic—saying they’re irrelevant isn’t accurate.