Nirtual local area network

A virtual local Area Network (VLAN) is a communication technology that divides a physical LAN into multiple broadcast domains logically.
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Each VLAN is a broadcast domain. Hosts within a VLAN can directly communicate with each other, but cannot directly communicate with each other. In this way, broadcast packets are restricted to one VLAN..
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Early Ethernet is a data network communication technology based on CSMA/CD (Carrier Sense Multiple Access/Collision Detection) sharing communication media. A large number of hosts can cause serious conflicts, broadcast flooding, performance degradation, and even network unavailability. Although Layer 2 devices can solve serious conflicts, they cannot isolate broadcast packets and improve network quality.
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In this case, VLAN technology appears. In this technology, a LAN can be divided into multiple logical vlans. Each VLAN is a broadcast domain. The communication between hosts in a VLAN is the same as that in a LAN. As shown in the following picture..

Therefore, vlans have the following advantages:

● Restricted broadcast domain: The broadcast domain is restricted to one VLAN, which saves bandwidth and improves network processing capability.
● Enhances LAN security. Packets in different vlans are isolated from each other. That is, users in one VLAN cannot directly communicate with users in other vlans.
● Improves network robustness: faults are restricted to only one VLAN. Faults in this VLAN do not affect the normal operation of other vlans.
● Flexible construction of virtual workgroups: vlans can be used to assign different users to different workgroups. Users in the same workgroup are not limited to a fixed physical range, which makes network construction and maintenance more flexible.

Vlan technology is widely used in switch, ONU, OLT and other device communication.

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