What is NAT traversal of VPN and why is it used?

• A. NAT-T encapsulates VPN traffic to pass through NAT devices without breaking the VPN tunnel
• B. NAT traversal allocates IP addresses to VPN clients
• C. NAT traversal compresses VPN data for faster transmission
• D. NAT traversal blocks VPN traffic from traversing NAT devices

Answer: (A)

NAT traversal for VPN is a technique that lets a VPN tunnel work when NAT devices sit between you and the VPN gateway. It does this by encapsulating the VPN’s ESP packets inside UDP, so the NAT can translate the UDP header without breaking the tunnel. This is essential because NAT devices alter IP addresses and ports, which would normally disrupt IPsec communications; wrapping the traffic in UDP lets the NAT maintain proper mappings and keep the tunnel intact (often using UDP port 4500). NAT-T is negotiated during the VPN setup so the endpoints know to use this UDP encapsulation.

The other ideas don’t fit because NAT traversal isn’t about assigning IP addresses to VPN clients, compressing VPN data, or blocking VPN traffic. It’s specifically about making VPN traffic pass through NAT devices reliably.