3com 2928 Betriebsanweisung

 

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Ethernet is a network technology based on the Carrier Sense Multiple Access/Collision Detect 
(CSMA/CD) mechanism. As the medium is shared, collisions and excessive broadcasts are common 
on an Ethernet. To address the issue, virtual LAN (VLAN) was introduced. The idea is to break a LAN 
down into separate VLANs, that is, Layer 2 broadcast domains whereby frames are switched between 
ports assigned to the same VLAN. VLANs are isolated from each other at Layer 2. A VLAN is a bridging 
domain, and all broadcast traffic is contained within it, as shown in 

A VLAN diagram 

 

 
VLANs are logically divided on an organizational basis rather than on a physical basis. For example, all 
workstations and servers used by a particular workgroup can be connected to the same LAN, 
regardless of their physical locations.  
VLAN technology delivers the following benefits: 

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Confining broadcast traffic within individual VLANs. This reduces bandwidth waste and improves 
network performance.  

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Improving LAN security. By assigning user groups to different VLANs, you can isolate them at 
Layer 2. For hosts in different VLANs to communicate, routers or Layer 3 switches are required.  

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Flexible virtual workgroup creation. As users from the same workgroup can be assigned to the 
same VLAN regardless of their physical locations, network construction and maintenance is much 
easier and more flexible.  

To enable a network device to identify frames of different VLANs, a VLAN tag field is inserted into the 
data link layer encapsulation.