Name: 默认网关（Default Gateway Explained）
Uploaded: 2022-12-13T16:37:47.000Z
Duration: 6 min 35 s

What is a default gateway?  So that is the topic of this video.

什麼是默認網關？所以這就是這個視頻的主題。

Now as a demonstration on a Windows computer, let's  check the network configuration.  So if you open up  

現在作為在 Windows 計算機上的演示，讓我們檢查網絡配置。因此，如果您打開

a command prompt and then you type in ipconfig  and in the output you'll see the IP address,  

命令提示符，然後輸入 ipconfig，在輸出中您將看到 IP 地址、

subnet mask, and the default gateway that's  been assigned to this computer.  So you might  

子網掩碼和分配給這台計算機的默認網關。所以你可能

be asking yourself, well what is a default gateway? And simply put, a default gateway is a device that  

會問自己，什麼是默認網關？簡單地說，默認網關是一種

forwards data from one network to another.  And the  majority of the time, this is going to be a router.  

將數據從一個網絡轉發到另一個網絡 的設備 。大多數時候，這將是一個路由器。

So for example here we have a local area network.  So here is the router, switch, and the computers.  

例如，這裡我們有一個局域網。所以這裡是路由器、交換機和計算機。

And on the other side of the router we have the  internet, which is another network.  So in order for  

在路由器的另一端，我們有互聯網，這是另一個網絡。因此，為了讓

these computers to access another network, such  as a web page out on the internet, the data has  

這些計算機訪問另一個網絡，例如 Internet 上的網頁，數據必須

to exit its own local network by going through the  default gateway, which is the router.  And then the  

通過默認網關（即路由器）退出其本地網絡。然後

router will forward the data to the internet.  Now  this also works both ways.  So if a device on the  

路由器將數據轉發到互聯網。現在這也適用於兩種方式。因此，如果 Internet

internet wanted to communicate with a computer on  this network, it has to go through this network's  

上的設備 想要與該網絡上的計算機通信，它必須通過該網絡的

default gateway and then to the computer.  So  in a nutshell, that's what a default gateway is.  

默認網關，然後到達該計算機。簡而言之，這就是默認網關。

It lets devices from one network communicate with  devices on another network.  And as I said before,  

它允許來自一個網絡的設備與另一個網絡上的設備進行通信。正如我之前所說，

this is typically going to be a router.  A router  is the gateway or doorway to every network.  And 

這通常是一個路由器。路由器是每個網絡的網關或入口。

the term default means that the designated  device is the first option that's looked upon  

而 默認一詞意指指定設備 ， 這 時候數據需要退出網絡

when data needs to exit the network.  Now if these  computers here wanted to communicate with each  

看低第一個選項 。現在，如果這裡的這些計算機想要相互通信

other, they can just talk directly to each other  through the switch.  And this is because all these  

，它們可以通過交換機直接相互 通信 。這是因為所有這些

computers are on the same network.  Their data  doesn't have to exit the network and go through  

計算機都在同一個網絡上。他們的數據不必退出網絡並通過

the default gateway.  So this brings us to our next  question.  And that is, if these computers wanted to  

默認網關。所以這就引出了我們的下一個問題。也就是說，如果這些計算機想要

communicate with another computer, how do they know whether that computer is on their own network  

與另一台計算機通信，它們如何知道該計算機是在自己的網絡上

or if it's on a different network.  Because as I stated  before, if this computer wants to communicate with  

還是在不同的網絡上。因為正如我之前所說的，如果這台計算機想要與

a computer on the same network, it can just talk  directly to it.  But if it wants to communicate  

同一網絡上的計算機 通信 ，它可以直接與之對話。但是如果它想

with a computer on a different network, it has  to go through the default gateway.  So again how  

與不同網絡上的計算機 通信 ，它必須通過默認網關。那麼 它又是

does it know?  And this is where the IP address and  subnet mask come in.  An IP address consists of two  

怎麼 知道的呢？這就是 IP 地址和子網掩碼的用武之地。 IP 地址由兩

parts.  The first part is the network address and  the second part is the host address.  So the way to  

部分組成。第一部分是網絡地址，第二部分是主機地址。因此，

tell which portion belongs to either the network  or the host, is where the subnet mask comes in.  

判斷哪個部分屬於網絡或主機的方法是使用子網掩碼的地方。

A subnet mask is a number that resembles an IP  address.  And it reveals how many bits in the IP  

子網掩碼是一個類似於 IP 地址的數字。它 通過屏蔽 IP 地址的網絡部分來

address are used for the network by masking the  network portion of the IP address.  So here we have  

揭示 IP 地址中有 多少位 用於網絡。所以這裡我們有

the IP address and subnet mask in binary form.  So the way to tell which portion of this IP address  

二進制形式的IP地址和子網掩碼。因此，判斷此 IP 地址的哪一部分

is the network portion, is when the subnet mask  binary digit is a 1 it will indicate the position  

是網絡部分的方法是，當子網掩碼二進制數字為 1 時，它將指示

of the IP address that defines the network.  So   we'll cross out all the digits in the IP address  

定義網絡的 IP 地址 的位置 。因此，我們將刪除 IP 地址

that line up with the 1s in the subnet mask.  And  when you do this, it will reveal that the first  

中與子網掩碼中的 1 對齊的 所有數字

three octets or sets are the network portion  and the remaining is the host portion.  So any  

。當你這樣做時，它會顯示前 三個八位字節或組是網絡部分，其餘是主機部分。因此

computer or device on a network where the first  three numbers of the IP address are 192.168.0  

，網絡中 IP 地址的前三個數字為 192.168.0 的 任何 計算機或設備都

means that those computers are on the same network.   Which means that the computers can talk directly  

意味著這些計算機位於同一網絡上。這意味著計算機可以直接

to each other without exiting through the default  gateway.  And then the host portion is what's  

相互 交談 ，而無需通過默認網關退出。然後主機部分是

uniquely assigned to devices, such as computers.  So here we have a private network that has  

唯一分配給設備的部分，例如計算機。所以這裡我們有一個私有網絡，它

been divided into two sub networks or subnets.  The  subnet on the left is on the 192.168.0 network and the  

被分成了兩個子網或子網。左側的子網位於 192.168.0 網絡 上，右側 的

subnet on the right is on the 192.168.1 network.  And each subnet has their own default gateway.  

子網位於 192.168.1 網絡上。每個子網都有自己的默認網關。

Now let's say that computer A wanted to  communicate with computer B on this subnet.  

現在假設計算機 A 想要與此子網上的計算機 B 通信。

So computer A is going to check computer B's IP  address to see if it's on the same network or not. 

所以計算機 A 將檢查計算機 B 的 IP 地址，看看它是否在同一網絡上。

And as you can tell, the two computers are on the  same network because the network portion of the IP  

正如您所看到的，這兩台計算機位於同一網絡上，因為 IP 地址

addresses, which are the first three octets, are the  same.  So computer A now knows that computer B is on  

的網絡部分（ 前三個八位字節）是相同的。所以計算機 A 現在知道計算機 B 在

the same network.  So now in order for communication to take place, computer A needs computer B's MAC 

同一網絡上。所以現在為了進行通信，計算機 A 需要計算機 B 的 MAC

address.  And it finds this by sending out an ARP  broadcast out on the network asking computer B  

地址。它通過在網絡上發出 ARP 廣播詢問計算機 B 的 MAC 地址 來發現這一點

for its MAC address.  Then once it has the MAC  address, communication can finally take place.

。然後一旦它有了 MAC 地址，就可以最終進行通信。

So in another scenario let's say that computer  A on this subnet here wanted to communicate with  

因此，在另一種情況下，假設此子網上的計算機 A 想要與 此子網上的計算機 D

computer D on this subnet.  So again computer  A is going to check computer D's IP address  

通信 。因此，計算機 A 將再次檢查計算機 D 的 IP 地址，

to see if it's on the same network or not.  And  as you can tell this time, the two computers  

以查看它是否在同一網絡上。正如您這次所看到的，兩台計算機

are on different networks because the network  portion of the IP addresses, which are the first  

位於不同的網絡上，因為 IP 地址的網絡部分（前

three octets, are different.  And the difference  is the third number.  Computer A is using a 0 

三個八位字節）不同。不同的是第三個數字。計算機 A 使用的是 0

and computer D is using a 1.  So computer A now  knows that computer D is on a different network.  

，計算機 D 使用的是 1。因此計算機 A 現在知道計算機 D 位於不同的網絡上。

So it can't directly communicate with it, it has  to use the default gateway.  So computer A will  

所以它不能直接與之通信，它必須使用默認網關。所以計算機 A 將

send out an ARP broadcast and this time it'll ask  for the MAC address of the default gateway and not  

發出一個 ARP 廣播，這次它會詢問默認網關的 MAC 地址而不是

the computer, because computer D is on a different  network and it won't receive the broadcast because  

計算機，因為計算機 D 在不同的網絡上，它不會收到廣播，因為

ARP broadcasts cannot go past a router.  Then once  it has the MAC address, it'll send the data to the  

ARP 廣播不能去經過路由器。然後一旦它有了 MAC 地址，它就會將數據發送到

default gateway and then it'll be forwarded to the  destination.  So everyone that concludes this video  

默認網關，然後將其轉發到目的地。所以 在默認網關上

on default gateways.  Thank you for watching, please  subscribe, and I'll see you in the next video.

結束此視頻的每個人 。感謝收看，請訂閱，我們下期視頻再見。