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# System prepended metadata

title: 網概hw4

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# 網概hw4
![image](https://hackmd.io/_uploads/rJVOF_eQC.png)

## Question 1: Select the first ICMP Echo Request message sent by your computer, andexpand the Internet Protocol part of the packet in the packet details window. What isthe IP address of your computer?
Ans: 192.168.1.15

## Question 2: Within the IP packet header, what is the value in the upper layer protocolfield?
Ans: ICMP(1)

## Question 3: How many bytes are in the IP header?
header length is 20 bytes

## How many bytes are in the payload of the IP datagram?
payload length = total length - header length = 56 - 20 = 36 bytes

## Question 5: Has this IP datagram been fragmented?
under the flag section, reserved bit is not set, so this datagram is not been fragmented

## Question 6: Which fields in the IP datagram always change from one datagram to the next within this series of ICMP messages sent by your computer? 

![image](https://hackmd.io/_uploads/B1UJA_xQA.png)
![image](https://hackmd.io/_uploads/rJXxC_lQR.png)

according to above, the identification, TTL and header checksum field are always change

![image](https://hackmd.io/_uploads/HkDE0OlXA.png)
## Question 7: What is the value in the Identification field and the TTL field?
Ans: Identification 51646, TTL 64