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8.1 | |
VLAN Concepts | |
| 8.1.3 | |
VLAN operation |
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Each switch port could be assigned to a different VLAN. Ports assigned to the same VLAN share broadcasts. Ports that do
not belong to that VLAN do not share these broadcasts. This improves the
overall performance of the network.
Static membership VLANs are called
port-based and port-centric membership VLANs. As a device enters the
network, it automatically assumes the VLAN membership of the port to
which it is attached.
Users attached to the same shared segment, share the bandwidth of that segment. Each additional user attached to the shared medium means less bandwidth and deterioration of network performance. VLANs offer more bandwidth to users than a shared network. The default VLAN for every port in the switch is the management VLAN. The management VLAN is always VLAN 1 and may not be deleted. All other ports on the switch may be reassigned to alternate VLANs. Dynamic membership VLANs are created
through network management software. CiscoWorks 2000 or CiscoWorks for
Switched Internetworks is used to create Dynamic VLANs. Dynamic VLANs allow for
membership based on the MAC address of the device connected to the
switch port. As a device enters the network, it queries a database
within the switch for a VLAN membership.
In port-based or port-centric VLAN
membership, the port is assigned to a specific VLAN membership
independent of the user or system attached to the port. When using this
membership method, all users of the same port must be in the same VLAN.
A single user, or multiple users, can be attached to a port and never
realize that a VLAN exists.
Network administrators are responsible
for configuring VLANs both manually and statically.
Each interface on a switch behaves like a
port on a bridge. Bridges filter traffic that does not
need to go to segments other than the source segment. If a frame needs
to cross the bridge, the bridge forwards the frame to the correct
interface and to no others. If the bridge or switch does not know the
destination, it floods the frame to all ports in the broadcast domain or VLAN, except the source port.
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This
approach is easy to manage because no complex lookup tables are required
for VLAN segmentation. 
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