Network Address Translation: Consider the scenario below in which three hosts, w
ID: 3598187 • Letter: N
Question
Network Address Translation:
Consider the scenario below in which three hosts, with private IP addresses 10.0.1.12, 10.0.1.16, 10.0.1.24 are in a local network behind a NATted router that sits between these three hosts and the larger Internet. IP datagrams being sent from, or destined to, these three hosts must pass through this NAT router. The router’s interface on the LAN side has IP address 10.0.1.27, while the router’s address on the Internet side has IP address 135.122.199.211.
Before doing this problem, you might want to reread the section on the NAT protocol in section 4.4.2 in the text.
Suppose that the host with IP address 10.0.1.12 sends an IP datagram destined to host 128.119.164.183. The source port is 3437, and the destination port is 80. Now, please answer all four questions.
Consider the datagram at step 4, after it has been transmitted by the NATted router but before it has been received by the host. What are the source and destination IP address for this datagram? What are the source and destination port numbers for the TCP segment in this IP datagram? Identify the differences in datagram's IP addresses and port numbers between step 3 and step 4. Has a new entry been made in the router's NAT table, or removed from the NAT table? Explain your answer.
NAT translation table WAN side addr LAN side addr 10.0.1.12 S: 10.0.1.27 network 2 S: 10.0.1.16 S: 4 3135.122.199.211 10.0.1.24Explanation / Answer
The NAT router replaces the source addres for all outgoing packets while it relaces the destination address for all incoming packets. With PAT, the original port address is used along with the public IP.
Answer to Question 1:
At step 4, source address is 128.119.164.183 and destination address is 10.0.1.12
Answer to Question 2:
At step 4, source address and port is 128.119.164.183:80 and destination address and port is 10.0.1.12:3437
Answer to Question 3:
At Step 3, source address and port is 128.119.164.183:80 and destination address and port is 135.122.199.211:3437
Thus the difference is only the destination address which is the public IP(135.122.199.211)
Answer to Question 4:
An entry has been made with the following tupples:
Private Address: 10.0.1.12, Private Port: 3437, External Address: 128.119.164.183, External Port: 80, Transport Protocol: TCP
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