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Basic Working Principles of Switches

Basic Working Principles of Switches

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The most common network equipment is switches, so it is very important to learn it. Great oaks grow from little acorns, and a brick by roots. Before study, we should learn it how to work to understand profoundly. So today we’ll talk about basic working principle of switches .So today we’ll talk about switches basic working principle.

Before talking about switch, let’s look at an switches-like network device -hub.

HUB is the physical equipment. Some classmates may ask, its appearance similar to 5-mouth small switches, why it is the physical device, but switches are in date chain?

In fact, a device in which layer is to see which layer in it can resolve in the date package, such as a router as a third-layer device due to resolving the IP header, and according to the source IP to route. Similarly, switches can parse the MAC address  in the data frame and transfer according to the relevant information, so it belongs to the second-layer device.

However, hub does not parse any information, transfer to all people without thinking, leading to all joints in the same collision domain, so it belongs to the physical device.

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We`ve mentioned switches, the second-layer device, transfers according to the MAC address, so how do switches finish transmission?

First, in default, switches, each interface of switches is a collision domain, and all interfaces are in the same broadcast domain. There is a MAC address table in switches. Cisco switches can check it through “show MAC address – table” and Huawei switches can use “display MAC address” to check.

As we can see, the MAC address table has information such as vlan, MAC address, the interface id, ports etc.. If there is a static, it generally specifies the MAC address table by hand, and dynamic is switches gained by study. Nevertheless, what kind of mechanism that switches generate MAC address according to ?

When the switch receives a data frame, it will go to check the source MAC. If the MAC address table don’t have the address, we can connect the address and the interface receiving the data frame, recording to the MAC address table. If the MAC address table has the corresponding relation of the MAC address and the interface, then we should refresh the aging time (default aging time of MAC address table is 300 seconds).

When our MAC address table is set up, the switch will transmit data. But how it do this?

As we can see, the switch will check the destination MAC, If not exist, it will be regarded as an unknown unicast frame and floods towards all ports in a common broadcast domain expect for the receiving port.

To sum up, each interface of the switch is a collision domain, which means the switch isolates the collision domain.The switch is the network device working in the second layer, We can check and transmit mac address table according to the layer 2 header information. If there is no matched mac address, the switch will transmit in flood. However, the mac address table of the switch can be build by spontaneous study.

Basic Working Principles of Switches

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