Virtual LAN (VLAN) refers to a group of logically network devices on one or more LANs that are configured so that they can communicate as if they were attached to the same cable. VLANs are defined by the standards IEEE 802.1D, 802.1p, 802.1Q and 802.10.
Advantage of VLAN
- More flexibility in administration and changes to the network because all the structure can be changed by simple parameter of the switches.
- Reduction in the broadcasting of traffic on the network.
- Increase in security because information is encapsulated in an additional level and possibly analyzed.
Types of VLAN
- A Port Based VLAN defines a virtual network according to the connection ports on the switch.
A MAC Address-Based VLAN comprises of defining a virtual network according to the MAC addresses of the stations; This type of VLAN is much more flexible than the port based VLAN because the network is independent from the location of the station;
Network Address Based VLAN links subnets according to the source IP address of the datagram. This type of solution provides great flexibility insofar as the configuration of the switches changes automatically when a station is moved. On the other hand there may be slight degradation in performance since the information contained in the packets must be analyzed more closely.
Protocol Based VLAN makes it possible to create a virtual network by protocol type (for example TCP/IP, IPX, AppleTalk, etc.), therefore grouping together all the machines using the same protocol on the same network.
By default VLAN details in CISCO switch, to view the details give “show vlan” in CISCO switch
CCNA Overveiw Page