D-Link DFL-2500 User Guide - Page 75
Virtual LAN VLAN
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56 Chapter 9. Interfaces 9.2 Virtual LAN (VLAN) Virtual Networking is the ability of network appliances to manage the logical network topologies on top of the actual physical connections, allowing arbitrary segments within a network to be combined into a logical group. Since the flexibility and the ease of network control provided by the logical topologies, virtual networking has become one of the major areas in the internetworking. D-Link firewalls are fully compliant with IEEE 802.1Q specification for Virtual LANs, featured by defining virtual interfaces upon the physical Ethernet interface. Each virtual interface is interpreted as a logical interface by the firewall, with the same security policies control and configuration capabilities as regular interfaces. 9.2.1 VLAN Infrastructure A Local Area Network (LAN) is a broadcast domain, that is, a section of the network within whose boundaries any broadcast traffic is delivered to all end-nodes. When the LAN environment grows bigger, the support of broadcast or multicast applications that flood packets throughout the network costs considerable waste of bandwidth, since packets are often forwarded to nodes that do not require them. Virtual LAN (VLAN) allows a single physical LAN to be partitioned into several smaller logical LANs which are different broadcast domains. It limits the size of the broadcast domain for each logical LAN, saves the broadcast cost of the bandwidth to optimize the performance and resource allocation, and also divides larger LANs into several independent security zones to add security control points. Devices located in the same LAN can communicate without the awareness of the devices in other virtual LANs. This is ideal for separating industrial departments from physical topology to different function segments. A simple infrastructure of VLAN is shown in Figure 9.1. In this case, a D-Link firewall is configured to have 2 VLAN interfaces. Now, although the clients and servers are still sharing the same physical media, Client A can only communicate with Server D and the firewall since they are configured D-Link Firewalls User's Guide