Before you do something, you must understand what you are doing. Therefore, in the beginning – a little theory. What is VLAN ?! Vlan is an abbreviation for Virtual Local Area Network, which means “virtual local computer network”. This is a logically united group of hosts having a common set of specific requirements and interacting in such a way that, regardless of their physical location, the hosts see each other as if they were connected to a broadcast domain. At the same time, traffic is tagged in accordance with the rules of the IEEE 802.1Q standard, i.e. inside the frame is a tag containing information about traffic belonging to a specific Vlan. In fact, using “vlan” or “vilan” (as anyone calls it) one can divide a network into logical segments and even more – the technology allows you to group workstations into workstations into one logical network, even if they are physically located in different networks. At the same time, any traffic quietly goes between them – Unicast, Broadcast or Multicast, but only within this logical network.
Cisco switches use the special VTP protocol to manage Vlan. It allows you to create, rename, or delete a vlan on a server device – you automatically do the same on all switches connected to the VTP domain. In a small network this can be convenient, but in large networks where there are already dozens and hundreds of VTP switches in the Transparent state.
Each virtual network has its own Vlan ID or VID, which is used in the 802.1Q standard. The standard range of Vlan ID values for network devices is from 0 to 4095. In this case, as a rule, VIDs 0 and 4095 cannot be used, since they are reserved for other tasks and numbers 1 to 4094 remain available. By the way, whatever there was a limit on the number of supported vlans (10, 100 or 1000), their identifiers, however, can be taken from the entire range. On the Cisco equipment, there are two Vlan groups – normal-range and extended-range. In Russian – normal and extended ranges, respectively. The standard range includes Vlan – from 1 to 1005, and the extended range – from 1006 to 4094. It should be borne in mind that VID 1002 – 1005 are reserved for Token Ring and FDDI Vlan and cannot be taken.
Now let’s look at the Cisco Catalyst switch. In my example, I will consider 2960 with IOS version 12.2 (35) SE5). We go to the switch in the Enable mode. We type the command:
switch # show vlan
The result will be a list of all vlan created on the device:
As you can see, the first in the list is Vlan 1 with the name “Defaut”. In the default configuration, all ports are included in it.