Wireshark Lab IP

Wire Shark Lab: IP

1. Capturing packets from an execution of traceroute

Do the following:

•   Start up Wireshark and begin packet capture (Capture->Start) and then press OK on the Wireshark Packet Capture Options screen (we’ll not need to select any options here).

Atur Value Packet size menjadi 56 bytes. Edit > option > engine

 

Mulai Capture , misal alamat riowenda.blogspot.com

Tampilan Packet Size 56

 

 

2. A look at the captured trace

In your trace, you should be able to see the series of ICMP Echo Request (in the case of

windows machine) or the UDP segment (in the case of Unix) sent by your computer and

the ICMP TTL-exceeded messages returned to your computer by the intermediate routers. In

the questions below, we’ll assume you are using a Windows machine; the corresponding

questions for the case of a Unix machine should be clear. Whenever possible, when answering a

question below you should hand in a printout of the packet(s) within the trace that you used to

answer the question asked. When you hand in your assignment, annotate the output so that it’s

clear where in the output you’re getting the information for your answer (e.g., for our classes,

we ask that students markup paper copies with a pen, or annotate electronic copies with text

in a colored font).To print a packet, use File->Print, choose Selected packet only, choose Packet

summary line, and select the minimum amount of packet detail that you need to answer the

question.

1.  Select the first ICMP Echo Request message sent by your computer, and expand the Internet Protocol part of the packet in the packet details window. What is the IP address of your computer?

Jawab : alamat ip computer saya 192.168.1.17

2. Within the IP packet header, what is the value in the upper layer protocol field?

Jawab :

Protocol: ICMP (1)

3.    How many bytes are in the IP header? How many bytes are in the payload of the IP datagram? Explain how you determined the number of payload bytes.

Jawab:

  

20 bytes are in the IP header

Ip header = 20 bytes

Payload = total length - header

56 – 20 = 36

Payload = 36

4.  Has this IP datagram been fragmented? Explain how you determined whether or not the datagram has been fragmented.

Jawab

Tidak , fragment offset

Next, sort the traced packets according to IP source address by clicking on the Source column header; a small downward pointing arrow should appear next to the word Source. If the arrow points up, click on the Source column header again. Select the first ICMP Echo Request message sent by your computer, and expand the Internet Protocol portion in the “details of selected packet header” window. In the “listing of captured packets” window, you should see all of the subsequent ICMP messages (perhaps with additional interspersed packets sent by other protocols running on your computer) below this first ICMP. Use the down arrow to move through the ICMP messages sent by your computer.

5.  Which fields in the IP datagram always change from on datagram to the next within this series of ICMP messages sent by your computer?

Jawab: Frame, Identification dan TTL

6.  Which fields says constant? Which of the fields must stay constant? Which fields must change? Why?

Jawab:

Field yg konstan: Header length, Protocol, Source dan Destination( jika pada alamat ip yg sama)

Field yg harus berubah : TTL karena waktu untuk terus atau menggunakan paket atau data berbeda- beda

7. Describe the pattern you see in the values in the Identification of the IP datagram.

Jawab:

TTL dan identification naik satu tiap paket selanjutnya.

Next (with the packets still sorted by source address) find the series of ICMP TTL exceeded replies sent to your computer by the nearest (first hop) router.

8.  What is the value in the Identification field and the TTL field?

Jawab:

 Identification:  0xe632 (58930)

TTL : 254

9.  Do these values remain unchanged for all of the ICMP TTL-exceeded replies sent to your computer by the nearest (first hop) router? Why?

Jawab: Identifikasi dan TTL berubah. Setelah ping kembali, TTL memberikan default 254 hop pertama dan hop berikutnya mengubah nilai TTL

3. Fragmentation

Pada Tahap soal berikut gunakan pingplotter , ganti value packet size menjadi 2000bytes, Kemudian 

Capture wireshark terlebih dahulu , lalu di ikuti dengan trace pingplotter.

10.  Find the first ICMP Echo Request message that was sent by your computer after you changed the Packet Size in pingplotter to be 2000. Has that message been fragmented across more than one IP datagram?

Jawab: memiliki lebih dari satu datagram IP

  

  

11.  Print out the first fragment of the fragmented IP datagram. What information in the IP header indicates that the datagram been fragmented? What information in the IP header indicates whether this is the first fragment versus a latter fragment? How long is this IP datagram?

Jawab: jumlah Fragment: 2, Total 1980 bytes

Frame: 1, payload: 0-1479 (1480 bytes)

Frame: 2, payload: 1480-1979 (500 bytes)

12. Print out the second fragment of the fragmented IP datagram. What information in the IP header indicates that this is not the first datagram fragment?  Are the more fragments?  How can you tell?

Jawab : Kita bisa tahu bahwa ini bukan fragmen pertama, karena offset fragmennya 1480. Ini adalah fragmen terakhir, karena lebih banyak fragmen bendera tidak ditentukan.

13. What fields change in the IP header between the first and second fragment?

Jawab :

 Field header IP yang berubah antar fragmen adalah : total length, Flags, Fragment offset, dan checksum 

4.    Now find the first ICMP Echo Request message that was sent by your computer after you changed the Packet Size in pingplotter to be 3500.

Pada tahap soal ini ganti value packet size menjadi 3500 

14.  How many fragments were created from the original datagram? Jawab:

Jumlah Fragment : 3, Total 3480 bytes

1) Frame: 1, payload: 0-1479 (1480 bytes)

2) Frame: 2, payload: 1480-1979 (1480 bytes)

3) Frame: 3, payload: 2960-3479 (520 bytes)

 

15. What fields change in the IP header among the fragments?

Jawab: Identification and fragment offset changed

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