COMP3331 COMP9331 Computer Networks and Applications Exam
Consider two clients PC and PC1 using the private IP address from a subnet 192.168.5.0/24 inside the
organization. Clients’ port numbers are given randomly from 40000 to 40003. Ignore the green and red triangle in
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the above diagram. The router is separating between the private network and the public network. The router is
connected to the Internet (i.e., public network) through the interface E-th1, and the router is using the E-thO
interface to connect to the private network. Two clients want to get a web service from the server whose IP
address is 200.10.30.40. The router’s external interface (E-th1) IP address is 195.12.15.20. The company has
bought only one public address which is 195.12.15.20. Consider the router is acting as a NAT router. In the NAT
router, clients can be given a port number from 50000 to 50003.
If you want to capture the traffic from the router interface, E-th1 then fill the following table if PC1 wants to send a
request to the server, 200.10.30.40 for getting a web service without security.
What is the source IP address? 195.12.15.20
What is the destination IP address? 200.10.30.40
What is the source port number? 80
What is the destination port number?
Now consider the web response is coming from the web server to the client, PC1 and you capture the packet from
router interface E-th0.
What is the source IP address? 192.168.5.0
What is the destination IP address? 192.168 5.2
What is the source port number? 50000
What is the destination port number?
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