- Client on a private network sends a request to a web server on the public Internet.
- N A T router translates source address and forwards the request to the web server
- T h e web server responds to the client’s translated address
- The N A T router translates the client address ( destination) back to the original private address
Objectives
- Explain the active network connections open on a computer when viewing a particular web page.
- Determine what an internal IP address and port number are translated to using port address.
Background / Preparation
Port address translation (PAT) is a form of network address translation ( N A T ) .With PAT, the router. translates multiple internal ( usually private) addresses to a single public IP address on an interface that is connected to the Internet. Port numbers are used, in combination with IP addresses, to keep track of individual connections. In this lab, you use the ipconfig and netstat commands to view open ports on a computer. You will be able to see the initial IP address and port combination, and determine the translated IP address and port combination The following resources are required:
- Computer running Windows XP Professional.
- Connection to a gateway router or an I S R using P A T.
- Internet connection.
- Access to the PC command prompt.
Step 1: Determine the IP address of the computer
Open a Command Prompt window by clicking Start > Run and typing cmd. Alternatively, you may click Start > All programs > Accessories > Command Prompt. At the prompt, type the ipconfig command to display the IP address of the computer.
a. What is the IP address of the computer?
Jawab:192.168.194.175
b. Is there a port number shown, and why or why not?
Jawab:Ya, ada port number yang muncul, hal ini karena access point telah dikelompokkan atau dibagi dalam beberapa titik akses, sehingga memiliki default gateway yaitu 192.168.194.129
Step 2 : Determine the IP addresses of the gateway router or ISR
Check with your instruct or to get the IP addresses for the ISR NAT router gateway.
Internal Ethernet Address : 192.168.10.1
External Internet Address : 192.168.20.1
Step 3 : Display base line netstat results.
a. At the command prompt, type the netstat –n command.
b. What type of information does the netstat –n command return?
Jawab:Protocol, IP address, Foreign address.
c. Where does the IP address found in Step 1 appear? Is there a port number associated with it? Why or why not?
Jawab:Ya ditemukan, karena menggunakan port gateway.
Step 4 : Display active network connections
c. Go back to the Command Prompt Window. Type the netstat –n command again, and then type the command without the – n option. The output looks similar to the following figure, depending on what other network applications and connections are open when you issued the command.
d. What is the difference in the output between the netstat and netstat – n commands?
Jawab:Perbedaannya ialah pada netstat –n hanya menampilakan informasi dari address local ke foreign address. Sedangkan netstat tampa –n akan menapilakn informasi secara details mulai dari ip address, alamat protocol yang digunakan, lokasi isp. Dan user.
e. Write down the connection entries for the client IP address and the IP address of the www.cisco.com web server.
| Local client IP address and port number : | Foreign IP address and port number : |
| 127.0.0.1 :1227 | 127.0.0.1 :1228 |
| 127.0.0.1 :1228 | 127.0.0.1 :1227 |
| 127.0.0.1 :1229 | 127.0.0.1 :1230 |
| 192.168.194.175:2233 | 64.233.181.136 :80 |
| 192.168.194.175:52103 | 192.168.194.129 :53 |
| 192.168.194.175:54674 | 192.168.194.129:53 |
| 192.168.194.175:58266 | 192.168.194.129:53 |
| 192.168.194.175:64274 | 192.168.194.129:53 |
| 192.168.194.175:64293 | 192.168.194.129:53 |
| 192.168.194.175:65399 | 192.168.194.129 |
f. Are there more netstat entries the second time?
Jawab:Tidak ada lagi perintah nestat yang berbeda meskipun untuk pengulangan kedua kalinya.
STEP 6 : Reflections
a. Port address translation (PAT) is also called NAT with overload. What does the term “overload” refer to?
Jawab:overload merupakan istilah ditujukan pada IP address karena pada nat overload bukan hanya satu alamat ip public yang terekspos,bisa lebih dari satu jika berupa overload.
b. The NAT terminology used in the lab includes four type of address: Inside-local, inside-global, outside-local, and outside-global. In many connections that pass through NAT routers, two of these address are often the same. Which two of these four addresses normally remain unchanged, and why do you think that is the case?
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