Figure 130 Example: Before Vlan; Figure 131 Example: After Vlan - ZyXEL Communications Unified Security Gateway ZyWALL 1000 User Manual

Figure 130 Example: Before VLAN

In this example, there are two physical networks and three departments A, B, and C. The
physical networks are connected to hubs, and the hubs are connected to the router.
Alternatively, you can divide the physical networks into three VLANs.

Figure 131 Example: After VLAN

Each VLAN is a separate network with separate IP addresses, subnet masks, and gateways.
Each VLAN also has a unique identification number (ID). The ID is a 12-bit value that is
stored in the MAC header. The VLANs are connected to switches, and the switches are
connected to the router. (If one switch has enough connections for the entire network, the
network does not need switches A and B.)
• Traffic inside each VLAN is layer-2 communication (data link layer, MAC addresses). It
is handled by the switches. As a result, the new switch is required to handle traffic inside
VLAN 2. Traffic is only broadcast inside each VLAN, not each physical network.
• Traffic between VLANs (or between a VLAN and another type of network) is layer-3
communication (network layer, IP addresses). It is handled by the router.
This approach provides a few advantages.
• Increased performance - In VLAN 2, the extra switch should route traffic inside the sales
department faster than the router does. In addition, broadcasts are limited to smaller, more
logical groups of users.
• Higher security - If each computer has a separate physical connection to the switch, then
broadcast traffic in each VLAN is never sent to computers in another VLAN.
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