Figure 2.85 shows a switched LAN in an engineering firm in which 10 stations are grouped into three LANs that are connected by a switch. The first four engineers work together as the first group, the next three engineers work together as the second group, and the last three engineers work together as the third group. The LAN is configured to allow this arrangement.
Vendors use different characteristics such as port numbers, MAC addresses, IP addresses, IP multicast addresses, or a combination of two or more of these.
2. Port Numbers
Some VLAN vendors’ uses switch port numbers as a membership characteristic. For example, the administrator can define that stations connecting to ports 1, 2, 3, and 7 belong to VLAN 1; stations connecting to ports 4, 10, and 12 belong to VLAN 2; and so on.
3. MAC Addresses
Some VLAN vendors use the 48-bit MAC address as a membership characteristic. For example, the administrator can stipulate that stations having MAC addresses E21342A12334 and F2A123BCD341belong to VLAN 1.
4. IP Addresses
Some VLAN vendors use the 32-bit IP address as a membership characteristic. For example, the administrator can stipulate that stations having IP addresses 126.96.36.199, 188.8.131.52, 184.108.40.206, and 220.127.116.11 belong to VLAN 1.
5. Multicast IP Addresses
Some VLAN vendors use the multicast IP address as a membership characteristic. Multicasting at the IP layer is now translated to multicasting at the data link layer.
Recently, the software available from some vendors allows all these characteristics to be combined. The administrator can choose one or more characteristics when installing the software.
Stations are configured in one of three ways: manual, semiautomatic, and automatic.
a. Manual Configuration
In a manual configuration, the network administrator uses the VLAN software to manually assign the stations into different VLANs at setup. Later migration from one VLAN to another is also done manually. Note that this is not a physical configuration; it is a logical configuration.
b. Automatic Configuration
In an automatic configuration, the stations are automatically connected or disconnected from a VLAN using criteria defined by the administrator. When a user changes the project, he or she automatically migrates to a new VLAN.
c. Semiautomatic Configuration
A semiautomatic configuration is somewhere between a manual configuration and an automatic configuration. Usually, the initializing is done manually, with migrations done automatically.
8. Time-Division Multiplexing (TDM)
In this method, the connection (trunk) between switches is divided into timeshared Channels. For example, if the total number of VLANs in a backbone is five, each trunk is divided into five channels. The traffic destined for VLAN 1 travels in channel, the traffic destined for VLAN 2 travels in channel 2, and so on. The receiving switch determines the destination VLAN by checking the channel from which the frame arrived.
There are several advantages to using VLANs.
· Cost and Time Reduction
· Creating Virtual Work Groups