Question

a nat router has two ip addresses: 192.128.61.1 and 73.165.43.86. to assign ports to the datagrams going toward the internet from inside the network, the formula (x 39042) mod 65536 is used, where x is the original port number. a tcp segment with the source ip 192.128.61.44, destination ip 21.83.63.189, source port 28285 and destination port 52624 is received and forwarded by the router. when the acknowledgement segment arrives at the router, what will be its source ip, destination ip, source port and destination port?

Answer 1

In the scenario of a NAT router receiving an acknowledgement segment, the source IP is the IP of the external server, and the source port is the same as the original destination port. The destination IP will be the router's external IP, and the destination port is determined using a specified formula to map to the correct internal device.

Step-by-step explanation:

The student has asked about how network address translation (NAT) works in the context of a router handling TCP/IP packets, specifically regarding the assignment of ports and the handling of an acknowledgement segment.

When the acknowledgement (ACK) segment arrives at the router, it will carry the reverse information of the original outgoing TCP segment. The source IP will now be the IP address of the external server, which is 21.83.63.189, and the source port will be the same as the original destination port, which is 52624. The destination IP will be the router's external IP address, which is 73.165.43.86. To determine the destination port, we use the provided formula (x * 39042) mod 65536, where x is the original port number 28285. Calculating this yields a new port number that the NAT table uses to forward the segment to the correct device on the internal network.