Author: Valter Popeskic

Frame Tagging

It is possible to build VLANs to pair number of connected switches. In the figure below you can see that the hosts from different VLANs are spread throughout number of switches. The biggest advantage to implement VLANs is its flexible and power-packed nature. The drawback is that it can become complicated—also for a switch— so it is important to have a way through which keeping the track of each one is easy i.e. all the users and frames when they travel the VLANs  and switch fabric. (Switch fabric is actually referred to as a group of switches that shares the same information of VLAN.)

Inter-Switch Link (ISL) is specifically used for tagging information of VLAN onto an Ethernet frame. This tagging information permits multiplexing of VLANs over a trunk link and this takes place through an external covering procedure or method, as a result of which the switch can easily determine/identify the membership of VLAN frame over the trunked link. When you run ISL, then it is easy to interconnect number of switches and it is also possible to maintain the information of VLAN while the traffic is passing on trunk links between switches.

The frames are actually switched all over the internetwork, it is important for the switches to keep the record of all the various kinds of frames, and also know how to utilize it on the basis of the hardware address. The management of frames is done in a different manner depending on the kind of link they are passing through.

In the switched environment there are two various kinds of links access and trunk links:

All About VLAN Memberships

The administrator create LANs and also assign switch ports to every VLAN. This type of VLAN is referred to as static VLAN . If the administrator is ready to put little more effort then he can assign hardware addresses to all the host devices in a database, in order to assign VLANs vitally the switches can be configured every time a host is connected/plugged into a switch.  

Scalability and Flexibility of VLAN technology has sent the hubs into oblivion

You must have got some idea that the layer-2 switches have nothing to do with Network layer protocol but it only read frames for filtering. It forwards all the broadcasts, by default. In order to build and execute VLANs, you necessarily need to build smaller broadcast domains at layer-2 switches. In other words, the broadcasts sent in one VLAN from one node won’t be passed on to ports that are configured to be in some other VLAN. So, the users or switch ports can be easily assigned to groups of VLAN (known as a switch fabric ), you can flexibly add into that broadcast domain the users of your choice no matter where they physically exist.