GATE-2024-CS1(Forenoon)

When a packet passes through a Network Address Translation (NAT) device from an internal network to an external network, the NAT device modifies the following fields in the IP header:

Source IP: The NAT device replaces the source IP address in the IP header with its own external IP address. This allows devices on the external network to send responses back to the NAT device, which can then forward them to the appropriate internal device.

Header Checksum: The header checksum is typically recalculated by the NAT device to ensure that it reflects any changes made to the IP header, such as the modification of the source IP address.