Security

Security
In a simple internetwork, host connectivity is achieved by connecting hosts to hubs and switches
that are linked together with routers. Security is then maintained at the router, but this causes
three serious security problems:

Anyone connecting to the physical network has access to the network resources on that
physical LAN.

A user can plug a network analyzer into the hub and see all the traffic in that network.

Users can join a workgroup just by plugging their workstation into the existing hub.
By using VLANs and creating multiple broadcast groups, administrators now have control
over each port and user. Users can no longer just plug their workstation into any switch port
and have access to network resources. The administrator controls each port and whatever
resources it is allowed to use.
Because groups can be created according to the network resources a user requires, switches can
be configured to inform a network management station of any unauthorized access to network
resources. If inter-VLAN communication needs to take place, restrictions on a router can also be
implemented. Restrictions can also be placed on hardware addresses, protocols, and applications.