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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.
Figure 2-4. Making VLAN Connections
Note: When connecting to a switch that does not support IEEE 802.1Q VLAN tags, use
untagged ports.
Finance
Marketing
VLAN 3
Untagged Ports
VLAN
unaware
switch
Tagged Port
VLAN
aware
switch
Tagged
Ports
Finance
VLAN 3
R&D
VLAN 2
Testing
R&D
Testing
VLAN 1
VLAN 2
VLAN 4
VLAN 1
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Console
1357911131517192123
1000=Green 10/100=Yellow
Power
BPS
Diag
2
46810
12
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2224
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Act
FDX
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FDX
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