9 Virtual LAN
9.1 Legacy LAN Technology
In packet switching networks, a LAN can be understood as the physical connection
between hosts (equipment that uses the LAN to communicate to each other) and
switching equipment (switches) that will deal with exchanging data from hosts.
If a company with many departments (many types of data traffic) would like to
segregate its LAN, for management purposes and to maintain LAN performance, it
would use different LAN infrastructure for each department. All traffic between them
should be routed. This issue would not be a problem if the hosts were static, which is
not a common behaviour. There are new people joining the LAN, mobile users, and
new changes in organization infrastructure and so on.
As an example, imagine the organization shown in below. Departments A and B are
located in different rooms, and each department’s LAN is physically separated from
each other.
Figure 41: Different LAN from different departments
Now imagine there is a need to increase Department A hosts, but there is no space at
the department’s room, the new host would stay at Department B’s room. With
legacy VLAN-unaware equipment, this increase at Department A’s LAN size would be
done as shown below.
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