VLANs are an effective mechanism for
extending firewalls from the routers to the switch fabric and
protecting the network against potentially dangerous broadcast
problems. Additionally, VLANs maintain all of the performance benefits
of switching. These firewalls are accomplished by assigning switch
ports or users to specific VLAN groups both within single switches and
across multiple connected switches. Broadcast traffic within one VLAN
is not transmitted outside the VLAN. Conversely, adjacent ports do not
receive any of the broadcast traffic generated from other VLANs. This
type of configuration substantially reduces the overall broadcast
traffic, frees bandwidth for real user traffic, and lowers the overall
vulnerability of the network to broadcast storms.
You can easily control the size of the
broadcast domain by regulating the overall size of its VLANs,
restricting the number of switch ports within a VLAN and restricting
the number of users residing on these ports. The smaller the VLAN
group, the smaller the number of users affected by broadcast traffic
activity within the VLAN group.
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