VLANs are usually created by the network administrator, assigning each port of every switch to a VLAN. Depending on the network infrastructure and security policies, the assignment of VLANs can be implemented using two different methods: Static or Dynamic memberships - these two methods are also known as VLAN memberships.
Each of these methods have their advantages and disadvantages and we will be analysing them in great depth to help you decide which would best suite your network.
Depending on the method used to assign the VLAN membership, the switch may require further configuration, but in most cases it's a pretty straight forward process. This page deals with Static VLANs while Dynamic VLANs are covered next.
Static VLANs
Static VLAN membership is perhaps the most widely used method because of the relatively small administration overhead and security it provides. With Static VLANs, the administrator will assign each port of the switch to one VLAN. Once this is complete, they can simply connect each device or workstation to the appropriate port.
The picture below depicts an illustration of the above, where 4 ports have been configured for 4 different VLANs:
The screenshot above shows a Cisco switch (well, half of it :>) where ports 1, 2, 7 and 10 have been configured and assigned to VLANs 1, 5, 2 and 3 respectively.
At this point, we should remind you that these 4 VLANs are not able to communicate between each other without the use of a router as they are treated as 4 separate physical networks, regardless of the network addressing scheme used on each of them. However, we won't provide further detail on VLAN routing since it's covered later on.
Static VLANs are certainly more secure than traditional switches while also considerably easy to configure and monitor. As one would expect, all nodes belonging to a VLAN must also be part of the same logical network in order to communicate with one another. For example, on our switch above, if we assigned network 192.168.1.0/24 to VLAN 1, then all nodes connecting to ports assigned to VLAN 1 must use the same network address for them to communicate between each other, just as if this was an ordinary switch.
In addition, Static VLANs have another strong point - you are able to control where your users move within a large network. By assigning specific ports on your switches throughout your network, you are able to control access and limit the network resources to which your users are able to use.
A good example would be a large network with multiple departments where any network administrator would want to control where the users can physically connect their workstation or laptop and which servers they are able to access.
The following diagram shows a VLAN powered network where the switches have been configured with Static VLAN support.
The network diagram might look slightly complicated at first, but if you pay close attention to each switch, you will notice that it's quite simple - six switches with 6 VLANs configured- one VLAN per department, as shown. While each VLAN has one logical network assigned to it, the IT department has, in addition, placed one workstation in the following departments for support purposes: Management, R&D, and HR department.
The network administrator has assigned Port 1 (P1) on each department switch to VLAN 5 for the workstation belonging to the IT department, while the rest of the ports are assigned to the appropriate VLAN as shown in the diagram.
This setup allows the administrator to place any employee in the IT department, anywhere on the network, without worrying if the user will be able to connect and access the IT department's resources.
In addition, if a user in any of the above departments e.g the Management department, decided to get smart by attempting to gain access to the IT department's network and resources by plugging his workstation to Port 1 of his department's switch. He surely wouldn't get far because his workstation would be configured for the 192.168.1.0 network (VLAN 1), while Port 1 requires him to use a 192.168.5.0 network address (VLAN 5). Logically, he would have to change his IP address to match the network he is trying to gain access to, and in this case this would be network 192.168.5.0.
Summary
To sum up, with Static VLANs, we assign each individual switch port to a VLAN. The network addresses are totally up to us to decide. In our example, the switches do not care what network address is used for each VLAN as they totally ignore this information unless routing is performed (this is covered in the InterVLAN routing page). As far as the switches are concerned, if you have two ports assigned to the same VLAN, then these two ports are able to communicate between each other as it would happen on any normal layer 2 switch.
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