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grouped into VLAN groups consisting of two or more ports. All the
end-stations, multiport repeaters, and router interfaces connected to
the port group are members of the same broadcast domain. Figure
6.12 is an example of a switch configured with two port-based VLAN
devices: ports 1 through 6 are VLAN 1, and 7 through 12 are VLAN 2.
End-stations connected to these ports only see Layer 3 broadcast
traffic that is specific to their VLAN port group. In order for the two
VLANs to exchange traffic, a router is needed.
Figure 6.12. A switched backbone topology utilizing
VLANs for Layer 3 segmentation.
The downside to port-based VLANs is mostly housekeeping chores.
Port configurations must be manually tracked and labeled. There is
also the added hassle of having to change the port allocations when
networks expand and contract, or as end-stations are moved between
VLANs. Special care must also be used when establishing links
between switches. With most implementations, VLANs (by default) do
not span across multiple switches automatically; they need to be
configured on each switch accordingly.