1. Network Address Translation Consider the scenario below in which three hosts,
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Question
1. Network Address Translation Consider the scenario below in which three hosts, with private IP addresses 10.0.1.10, 10.0.1.17, 10.0.1.20 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 10.0.1.26, while the router's address on the Internet side has IP address 135.122.192.209 Before doing this problem, you might want to reread the section on the NAT protocol in chapter 4 and view this well-made youtube video https://www.youtube.com/watch?v QBqPzHEDzVo NAT translation table WAN side addr LAN side addr 10.0.1.10 10.0.1.26 S: D. 0.0.1.17 3135.122.192.209 10.0.1.20 Suppose that the host with IP address 10.0.1.20 sends an IP datagram destined to host 128.119.177.190 Assume the source port is 3475, and the destination port is 80. Also, assume that the NAT router will generate a new source port number 5555 when it receives the IP datagram from 10.0.1.20 A. Consider the datagram at step 1, after it has been sent by the host but before it has reached the NATted router. What are the source and destination IP addresses for this datagram? What are the source and destination port numbers for the TCP segment in this IP datagram? Step 1IP address Source Dest Port number B. Now consider the datagram at step 2, after it has been transmitted by the NATted router. What are the source and destination IP addresses for this datagram? What are the source and destination port numbers for the TCP segment in this IP datagram? Step 2IP address Source Dest Port numberExplanation / Answer
Network Address Translation:
Refer figure shown in the question itself.
When a host (connected to a home router) sends a packet to a host in the internet, the home router will convert the private IP address of host(source address) with its own public address and transmit the packet to destined host in internet.
When the reply packet came to home router , it will convert the destination address back to local hosts private address and transmit the packet to that destined host.
This process of address translation is called Network Address Translation.
Now lets look at the answers.
A)
Our private host with source IP address 10.0.1.20 and Port Number 3475 send a packet to a host in the internet with IP Address 128.119.177.190 and Port Number 80.
B)
Address TRanslation, ie the source ip address is replaced by the router with its public ipaddress and port number. Destination port and addres remains same.
C)
NAT updates its Public and Privare address
D)
Host in the internet reply back to the same adress from which router since the initial packet came from routers public address.
E)
Address Translation again. ie, Router forwards the packet to the original owner of the Packet after changing the destination address with owners address.
Step 1 IP Address Port Number Souce Address 10.0.1.20 3475 Destination Address 128.119.177.190 80Related Questions
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