GATE CSE 2024 | Set 1 | Question: 21

Question

Which of the following fields is/are modified in the $\text{IP}$ header of a packet going out of a network address translation $\text{(NAT)}$ device from an internal network to an external network?

• A. Source $\text{IP}$
• B. Destination $\text{IP}$
• C. Header Checksum
• D. Total Length 

Answer 1

NAT device takes the outgoing packet and replaces the source IP address from private address pool to a IP address from its public address pool.

Since the source IP address is changed, the header checksum will also be recalculated so that the router does not get error while checking the header checksum.

Answer: A,C

Source: NPTEL lecture , GO classes lecture