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# System prepended metadata

title: 計網作業一

---

# 計網作業一

## 一
#### 1.
![](https://i.imgur.com/48jiWGj.png)

#### 2.
The service is STUN(Session Traversal Utilities for NAT).

It provides a tool for hosts to discover the presence of a network address translator, and to discover the mapped, usually public, Internet Protocol (IP) address and port number that the NAT has allocated for the application's User Datagram Protocol (UDP) flows to remote hosts.

##### ref:https://en.wikipedia.org/wiki/STUN

#### 3.
port:3478

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## 二
#### 1.
I use ```ssh b09902070@linux6.csie.ntu.edu.tw``` to connect to the NTU CSIE work station.
![](https://i.imgur.com/LpiISFw.png)


#### 2.
which port this SSH server uses:22



#### 3.
It uses public IP, since the IP is 140.112.XX.XX (from the picture it shows that this is a public IP) .

![](https://i.imgur.com/5lWYbsf.png)
###### ref:https://ipwithease.com/public-ip-vs-private-ip/

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## 三
same fields: Source Port, Destination Port, and Checksum

different fields: TCP has other fields like Sequence Number, Acknowledgement Number, and Window that UDP doesn't have.

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## 四
#### 1.
![](https://i.imgur.com/8tbVvs1.png)

#### 2.
台灣首府大學的校務行政資訊系統

#### 3.
若封包資訊被人監聽、攔截，那該密碼就會流出，十分危險。

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## 五
我發現到不僅每種protocol有著各自的底色，就連TCP本身都有不同的顏色（灰色、藍色、黑色等），後來就在view裡面看到一個coloring rule，才知道各自底色所代表的意義，而且這些顏色還可以再自定義。

![](https://i.imgur.com/MpFyU1m.png)
