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Making VLAN Connections
VLANs can be based on port groups, or each data frame can be explicitly
tagged to identify the VLAN group to which it belongs. When using
port-based VLANs, ports can either be assigned to one specific group or
to all groups. Port-based VLANs are suitable for small networks. A single
switch can be easily configured to support several VLAN groups for
various organizational entities (such as Finance and Marketing).
When you expand port-based VLANs across several switches, you need to
make a separate connection for each VLAN group. This approach is,
however, inconsistent with the Spanning Tree Protocol, which can easily
segregate ports that belong to the same VLAN. When VLANs cross
separate switches, you need to use VLAN tagging. This allows you to
assign multiple VLAN groups to the "trunk" ports (that is, tagged ports)
connecting different switches.
R&D
VLAN 1
VLAN 2
Testing
Note: When connecting to a switch that does not support IEEE 802.1Q
VLAN tags, use untagged ports.
Tagged
Ports
Untagged Ports
Finance
Marketing
VLAN 3
VLAN 4
Figure 2-4. Making VLAN Connections
Tagged Port
VLAN
unaware
switch
Finance
VLAN 3
A
E
PPLICATION
R&D
VLAN 1
VLAN 2
XAMPLES
VLAN
aware
switch
Testing
2-5
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