Virtual Local Area Network (VLAN)
VLAN is a
virtual Local Area Network that is a layer two concept that is used to break a
big collision domain into several small broadcast domains. This logical
division of a switch introduces many benefits which have been listed below.
·
VLAN Configuration solves the broadcasting
problem by dividing the network.
·
VLAN breaks the big broadcast domains into
smaller ones.
·
It enhances the security of the network.
·
Grouping of devices based on function not based
on physical locations.
Below are the things that have
been discussed by the experts on the provided YouTube links.
We normally configure the VLANs
on layer -II & Layer -III switches but when we create a link between two
devices, we remove the VLAN tag, and the link is called “Trunk Link”. The
concept of the trunk has been borrowed from public switched telephone networks,
PSTN where multiple calls are sent through a single media. In a switching environment, we configure a
trunk link between switches to send the traffic from multiple VLANs to another
switch. A trunk link is a critical component to carry the traffic from multiple
VLANs. In the below diagram switches is the second row collects data from the
concerned VLAN devices and forwards it to the central switch through a trunk
link between the switches.
802.1q Trunking Technology
Cisco has introduced trunking a
protocol for carrying the traffic of multiple VLANs, called ISL or inter-switch
link. This protocol’s original ether frame was encapsulated with a new header
and footer and inside the header in the VLAN ID.
In this approach, the frame is
not re encapsulated the frame, but the VLAN ID is inserted in the frame and a
frame check sequence is attached at the end of the frame.
This VLAN “Tag “is used for the
identification of data coming from different VLANs. The only VLAN which doesn’t
have this tag is VLAN 1 which carries all the traffic on the trunk links. But
for security reasons, we always change the native VLAN to any other VLAN on the
Trunks.
VTP Protocol: VLAN Trunking
Protocol
In a production network, the
configuration of VLANS on many switches becomes a very hectic task as we need
to configure the VLANs one by one on all switches. To reduce these efforts and the
chances of mismatched configurations, cisco has introduced a protocol called
VLAN Trunking Protocol. This is the
protocol that works on the trunk links between the switches only.
The VLAN Configuration, addition,
deletion, and modification is not centrally controlled by the VTP server. The
VTP server is the central device that propagates the VLAN information to the
VTP clients. Anything that changes at the VTP server related to VLAN
automatically got updated on the VTP clients. In production networks, we have
more than two switches acting as VTP servers for redundancy purposes.
VTP Modes:
·
VTP Server Mode: The modes which propagate
VLAN information
·
VTP Client Mode: The mode that receives
VLAN information from the server
·
VTP Transparent Mode: This mode passes
VLAN information, the switch doesn’t update its VLAN database
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