APPLICATION EXAMPLES
Making VLAN Connections
VLANs can be based on port groups, or each data frame can be explicitly tagged to identify the VLAN group it belongs to. 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, it is therefore better to use VLAN tagging. This allows you to assign multiple VLAN groups to the “trunk” ports (that is, tagged ports) connecting different switches.
Figure 3-4. Making VLAN Connections
R&D
VLAN 1
Tagged
Ports
Finance
VLAN 2
Testing
VLAN 3
VLAN 4
Untagged Ports | Tagged Port |
VLAN
unaware
switch
Marketing
Finance
VLAN 3
VLAN aware switch
R&D
Testing
VLAN 1
VLAN 2
Note: When connecting to a switch that does not support IEEE 802.1Q VLAN tags, use untagged ports.
February 2003 | © 2003 Foundry Networks, Inc. | 3-5 |
