Name: 二層交換機 vs 三層交換機！ (Layer 2 vs Layer 3 Switches)
Uploaded: 2025-11-15T00:39:55.000Z
Duration: 6 min 2 s

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In this video, we're going to be talking about the difference between layer two and layer three switches.

在這支影片裡，我們要來聊聊 layer two 和 layer three switch 的差別。

So the first thing we have to determine is, well, what is a switch?

那首先我們要確定的是，嗯，什麼是 switch 呢？

Now, a switch is a device that has multiple ports that accepts Ethernet connections from network devices.

其實 switch 是一種有多個連接埠的設備，可以接受來自網路設備的 Ethernet 連接。

And its function is to create a network by allowing devices to talk to each other and exchange data.

它的功能是透過讓設備互相溝通並交換資料來建立一個網路。

Now, the term layer refers to the different layers in the OSI model.

那這裡的 layer 指的是 OSI 模型中的不同層級。

OSI stands for Open Systems Interconnection.

OSI 是 Open Systems Interconnection 的縮寫。

And this model was created as a standard that describes how information from software in one device moves through a network to reach software in another device.

這個模型被建立成一個標準，用來描述一個設備上的軟體資訊如何透過網路傳送到另一個設備上的軟體。

And it does this by breaking down the huge task of data communication into seven different layers, giving control of a data being sent from one layer to another.

它透過將龐大的資料通訊任務分解成七個不同的層級來達成這點，並控制資料從一個層級傳送到另一個層級。

So a layer two switch, just like its name says, operates at layer two of the OSI model, which is the datalink layer.

所以 layer two switch，就像它的名字一樣，是在 OSI 模型中的第二層運作，也就是資料鏈結層。

a layer two switch uses the Mac address of a device to determine where to send data.

layer two switch 會利用設備的 Mac 位址來決定要將資料送到哪裡。

So when devices connect to a layer two switch, the switch will learn the Mac addresses of those devices and store them in its table.

所以當設備連接到 layer two switch 時，交換器就會學習這些設備的 Mac 位址並儲存在它的表格中。

So when a data packet is sent from a device connected to a layer two switch, the switch will forward the data to the intended destination port.

是以，當資料封包從連接到 layer two switch 的設備發送時，交換器會將資料轉送到目標連接埠。

So, as an example, if computer A wanted to talk to computer B, computer A will put computer B's Mac address in the data packet and then send it to the switch.

所以，舉個例子，如果電腦 A 想跟電腦 B 對話，電腦 A 會把電腦 B 的 Mac 位址放在資料封包裡，然後傳送給交換器。

And then the switch will read the destination's Mac address and then look at its table to determine which port matches the specified Mac address.

然後交換器會讀取目標的 Mac 位址，並查看它的表格，找出哪個連接埠符合指定的 Mac 位址。

And then it'll forward the data to that port where computer B is connected.

然後它會將資料轉送到電腦 B 連接的那個連接埠。

Layer 2 switches are by far the most common type of switches.

Layer 2 switches 是目前最常見的交換器類型。

These are the traditional switches that you'll find in homes and small to medium sized businesses.

這些是你會在家庭和中小型企業中找到的傳統交換器。

Now, a layer three switch, which is also called a multi layer switch, operates at layer three of the OSI model.

現在，layer three switch，也稱為 multi layer switch，是在 OSI 模型第三層運作的。

Layer three is the network layer, and this has to do with routing, which deals with IP addresses.

第三層是網路層，這與路由有關，路由處理的是 IP 位址。

So a layer three switch can route data using IP addresses.

所以 layer three switch 可以使用 IP 位址來路由資料。

But in addition to operating at layer three, it can also operate at layer two.

但除了在第三層運作之外，它也可以在第二層運作。

So it can forward data by using Mac addresses which are layer two, and

所以它可以使用 Mac 位址（這是第二層）來轉送資料，而且

it can also route data using IP addresses which are layer three.

它也可以使用 IP 位址（這是第三層）來路由資料。

So as an example, let's say that in a business, they wanted to separate the network traffic from a couple of different apartments so that the support department doesn't see any traffic from sales and vice versa.

舉個例子，假設在一家公司，他們想把幾個不同部門的網路流量分開，這樣支援部門就不會看到銷售部門的任何流量，反之亦然。

And the best and easiest way to do this is by creating a couple of VLANs VLANs divide a network into separate broadcast domains.

最好的、最簡單的方法就是建立幾個 VLAN。VLAN 會將網路分割成獨立的廣播網域。

So for the support department, we'll create a VLAN, and

所以，對於支援部門，我們會建立一個 VLAN，然後

then we'll give it this IP address group, and then we'll call it VLAN 10.

我們會給它這個 IP 位址群組，然後我們稱它為 VLAN 10。

And then we'll configure a VLAN for the sales department with a different IP address group, and

然後我們會為銷售部門設定一個具有不同 IP 位址群組的 VLAN，

So now, because of the VLANs, each department is on their own subnet, and

所以現在，因為有了 VLAN，每個部門都在自己的子網路上，

the devices in each VLAN can't see or communicate with devices in the other vlan.

而且每個 VLAN 裡的裝置都看不到或無法跟其他 VLAN 的裝置溝通。

But what if, for some reason, the network administrator wanted to allow communication to happen between the two VLANs, but

但如果因為某些原因，網路管理員想讓兩個 VLAN 之間可以溝通，

because the VLANs have different IP address groups, in order for communication to happen, this requires a layer three device.

由於 VLAN 有不同的 IP 位址群組，為了讓溝通發生，這就需要一個 layer three device。

Now, it could use a router to do this, because routers route by IP addresses.

現在，他們可以用路由器來做到這點，因為路由器是根據 IP 位址來路由的。

But a better and easier way to do this is by using a layer 3 switch.

但一個更好、更簡單的方法是使用 layer 3 switch。

By using and configuring a layer 3 switch, it'll allow communication between the VLANs, which is known as inter VLAN routing.

使用並設定 layer 3 switch，就能讓 VLAN 之間進行溝通，這就是所謂的 inter VLAN routing。

And the way it does this is by creating SVIs, or switch virtual interfaces on the layer 3 switch.

它的做法是在 layer 3 switch 上建立 SVI，也就是 switch virtual interfaces。

These virtual interfaces allow data to be routed between VLANs by creating default gateways.

這些虛擬介面透過建立 default gateways，讓資料可以在 VLAN 之間進行路由。

So, for example, when computer A on VLAN 10 wants to communicate with computer D on VLAN 20, computer A will send the data packet to the default gateway, which is the SVI assigned to VLAN 10.

所以，舉例來說，當 VLAN 10 上的電腦 A 想跟 VLAN 20 上的電腦 D 溝通時，電腦 A 會把資料封包送到預設閘道，也就是指派給 VLAN 10 的 SVI。

And then the layer 3 switch will check its routing table just like a router would, and

然後 layer 3 switch 就會像路由器一樣檢查它的路由表，

then will forward the packet to VLAN20's SVI and then to computer D.

接著會把封包轉送到 VLAN 20 的 SVI，然後到電腦 D。

So, in a nutshell, that's how a layer three switch works.

所以，簡單來說，這就是 layer three switch 的運作方式。

Now, there are other devices that operate at layer three, and these are routers.

現在，還有其他在 layer three 運作的設備，那就是路由器。

And routers only operate at layer three, but

路由器只在 layer three 運作，但是

layer three switches operate at both layer three and layer two.

layer three switches 在 layer three 和 layer two 都有運作。

So they basically combine the functionality of a router and a switch.

所以它們基本上結合了路由器和交換器的功能。

However, a layer three switch cannot do everything that a router does.

不過，layer three switch 無法做到路由器所能做的一切。

It doesn't have the complete routing capabilities of a router.

它沒有路由器完整的路由功能。

So, as a review, layer two switches forward data based on Mac addresses, while layer three switches route data based on IP addresses, but

所以，複習一下，layer two switch 是根據 Mac 位址來轉送資料，而 layer three switch 則是根據 IP 位址來路由資料，但是

it can also forward data based on Mac addresses.

它也能夠根據 Mac 位址來轉送資料。

Layer 2 switches cannot route data between VLANs, while layer 3 switches can.

Layer 2 switch 無法在 VLAN 之間路由資料，而 layer 3 switch 則可以。

Layer 2 switches require little to no configuration, while layer 3 switches require a more complex configuration.

Layer 2 switch 的設定非常簡單，幾乎不需要設定，而 layer 3 switch 的設定則比較複雜。

And as far as price, layer 2 switches are relatively inexpensive, and

至於價格方面，layer 2 switch 相當便宜，而

layer 3 switches are significantly more expensive.

And as far as speed, layer two switches are very fast, while layer three switches are slower.

在速度方面，layer two switch 速度非常快，而 layer three switch 則比較慢。

So, guys, I want to thank you for watching this video on the difference between layer two and layer three switches.

所以，各位，感謝大家觀看這部關於 layer two 和 layer three switch 差異的影片。

Please subscribe and I will see you in the next video.