Shulou(Shulou.com)06/03 Report--

The switch is based on the logical link layer of the second layer of the OSI model, which takes the frame as the transmission unit, connects multiple terminal devices and divides the conflict domain in the same network, and can realize fast data transmission.

There are several key words marked in red, which are explained separately:

1 OSI model and logical link layer

The OSI model is established by ISO International Standards Organization. It can be said that all network devices are manufactured based on this model and are divided into seven layers.

7 Application layer

Various applications of computers

6 presentation layer

Data conversion and encryption 5 session layer

Connect 4 transport layer

TCP UDP protocol

3 Network layer

Router multilayer switch

2 logical link layer

Switch bridge

1 physical layer

Various port hubs for network cable

It can be seen that switch manufacturing is based on the physical layer and logical link layer.

2 frames of data are transmitted on the network in a very small unit called Frame, and the frame components include frame headers and frame data. It can be roughly expressed as follows:

2-story head

3-story head

4-story head

User data

2-story tail

3 conflict domain within a certain range of the network, two computers will collide when they communicate at the same time, then the CSMA/CD network is a conflict domain (collision domain). For example, in the same classroom, there are 30 students who cannot speak at the same time. At the same time, there will be conflicts and they must speak one by one in order. This classroom can be regarded as a conflict domain, and 30 students can be regarded as the terminal equipment of this conflict domain.

How the switch works:

Core work: MAC address table

Explain the MAC address.

Globally, the only address that represents a network device, commonly referred to as a physical address

For example, look at the following MAC address

00D0,97 19re7A 5A generally uses hexadecimal to indicate that the red part is the manufacturer's code and the blue part is the number given by the manufacturer to this product.

In the network world, both MAC address and IP address must be used to determine.

How it works:

1 tabulated-View the source MAC

The switch receives the data frame at port 1 and extracts the layer 2 header source MAC, which forms an one-to-one correspondence with the inbound port.

For example, the source MAC is A, so the entry formed at this time is Amurl.

2 look up the table the switch will extract the target MAC from the received data frame, and find out whether the corresponding entry exists in the local forwarding table of the switch.

If it exists, the data is sent out the corresponding port

If it does not exist, data is sent out of an exit other than the incoming port, a process called flooding flooding.

Add: in reality, when the switch is powered on, the terminal will send unprovoked ARP on its own, and it will also send senseless ARP regularly to generate the MAC address table.

Explain that ARP:ARP is a protocol. The corresponding MAC address is obtained based on the IP address, in order to realize the fast encapsulation of the layer 2 header of the frame. Principle: when the sender equipment sends the ARP request, it is broadcast; when the target equipment sends the ARP request, it is unicast.

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