A VLAN or a Virtual LAN acts like an ordinary LAN, but connected devices don't have to be physically connected to the same segment. The networks on a vlan will behave as if they are part of the same physical lan. even if you change the location of one such node or host on a vlan, it will not change the structure, as physical positioning does not effect a vlan structure. vlans are configured through software and not hardware, hence if you remove a vlan host from one physical location to another location, it will not affect the vlan, and it will still be a part of it. hence it requires little or no hardware reconfiguration. interconnectivity between vlan computers are maintained by tagging data travelling between them.
The term VLAN was specified by IEEE 802.1Q; it defines a method of differentiating traffic on a LAN by tagging the Ethernet frames. By extension, VLAN is used to mean the traffic separated by Ethernet frame tagging or similar mechanisms.
benefits of vlans:
Increased performance : Switched networks by nature will increase performance over shared media devices in use today, primarily by reducing the size of collision domains. Grouping users into logical networks will also increase performance by limiting broadcast traffic to users performing similar functions or within individual workgroups. Additionally, less traffic will need to be routed, and the latency added by routers will be reduced.
Improved manageability : VLANs provide an easy, flexible, less costly way to modify logical groups in changing environments. VLANs make large networks more manageable by allowing centralized configuration of devices located in physically diverse locations.
Network tuning and simplification of software configurations : VLANs will allow LAN administrators to "fine tune" their networks by logically grouping users. Software configurations can be made uniform across machines with the consolidation of a department’s resources into a single subnet. IP addresses, subnet masks, and local network protocols will be more consistent across the entire VLAN. Fewer implementations of local server resources such as BOOTP and DHCP will be needed in this environment. These services can be more effectively deployed when they can span buildings within a VLAN.
Physical topology independence : VLANs provide independence from the physical topology of the network by allowing physically diverse workgroups to be logically connected within a single broadcast domain. If the physical infrastructure is already in place, it now becomes a simple matter to add ports in new locations to existing VLANs if a department expands or relocates. These assignments can take place in advance of the move, and it is then a simple matter to move devices with their existing configurations from one location to another. The old ports can then be "decommissioned" for future use, or reused by the department for new users on the VLAN
Increased security options : VLANs have the ability to provide additional security not available in a shared media network environment. By nature, a switched network delivers frames only to the intended recipients, and broadcast frames only to other members of the VLAN. This allows the network administrator to segment users requiring access to sensitive information into separate VLANs from the rest of the general user community regardless of physical location. In addition, monitoring of a port with a traffic analyzer will only view the traffic associated with that particular port, making discreet monitoring of network traffic more difficult.
Picking pebbles on the shore of the networking ocean
