domain. Each switch would also be connected to a router so that packets could be routed
between broadcast domains. Instead, using VLANs, one switch could be used and the switch
would treat three different sets of ports as three different broadcast domains.
In the first case, three switches are used and no VLANs are required. Each switch treats all ports
as members of one broadcast domain. In Figure 4-22, one switch is used; the switch is
configured so that the ports are considered to be in three different broadcast domains. In both
cases, separate broadcast domains imply separate Layer 3 groupings; a router is needed for
forwarding traffic among the different Layer 3 groups.