VLAN Topology
Switched LAN technology enables you to organize systems on a local network into VLANs. Before you divide a local network into VLANs, you must obtain switches that support the VLAN technology. You can configure all ports on a switch to serve a single VLAN or multiple VLANs, depending on the VLAN topology. Each switch manufacturer has different procedures for configuring ports on a switch.
The following figure shows a local area network that has been divided into three VLANs.
Figure 3-1 Local Area Network With Three VLANs
In the illustration, the LAN has the subnet address 192.168.84.0.
acctg0 with VLAN ID 789 – Accounting group. This group owns Host D and Host E.
humres0 with VLAN ID 456 – Human Resources group. This group owns Host B and Host F.
infotech0 with VLAN ID 123 – Information Technology group. This group owns Host A and Host C.
This LAN is subdivided into three VLANs to correspond with three workgroups:
A variation of this figure is shown in the following figure, where only one switch is used and multiple hosts belonging to different VLANs connect to that single switch.
Figure 3-2 A Switch Connecting Multiple Hosts of Different VLANs
In the figure, Host A and Host C belong to the Information Technology VLAN with the VLAN ID 123. One of Host A's interface is configured with the VLAN ID 123. This interface connects to Port 1 on Switch 1, which is also configured with the VLAN ID 123. Host B is a member of the Human Resources VLAN with the VLAN ID 456. Host B's interface connects to Port 5 on Switch 1, which is configured with the VLAN ID 456. Finally, the interface of Host C is configured with the VLAN ID 123. The interface connects to Port 9 on Switch 1. Port 9 is also configured with the VLAN ID 123.
The illustration also shows that a single host can belong to multiple VLANs. For example, Host A has two VLANs configured over the interface of the host. The second VLAN is configured with the VLAN ID 456 and is connected to Port 3 that is configured with the VLAN ID 456. Therefore, Host A is a member of both the infotech0 and the humres0 VLANs.