Benefits of Vlan

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Benefits of VLAN
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Introduction
In a switched network there is always a single
broadcast domain which means every device that is
attached to the switch will see the broadcast.  A
VLAN or virtual local area network removes the
physical barrier and treats the host as if
they were all part of the same subnet while
logically separating networks within networks
creating smaller broadcast domains. VLANS offer a
number of advantages over traditional LANS. 
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Simplified Administration

• When a computer is physically moved to another
  location it can stay on the same VLAN without
  any hardware reconfiguration. 
• Performance Using VLANS it reduces the size of
  that broadcast domain therefore improving
  efficiency. For example, if we take three
  computers and we'll say that they are part of
  the manufacturing group. We want to prevent
  manufacturing employees from viewing YouTube
  videos. We can create a VLAN and isolate
  them from the internet. The VLAN does not allow
  internet access but then is trunked to the main
  network.

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• VLAN Security
• Can be used to restrict access. Security also
  provides setup authentication for VLAN Trunking
  Protocol and we can implement wireless
  constraints by ensuring a user assigned to a
  specific VLAN will always connect to that
  VLAN regardless of their location. This isolation
  gives the bonus of additional security. VLAN tags
  can also be maintained between switches. Special
  ports called trunks are configured on
  interfaces, carrying VLAN-tagged frames between
  switches. This allows administrators to segregate
  traffic, not just within a single switch, but
  also amongst the entire enterprise. VLANs also
  enable a practice called Router on a stick. A
  single physical router interface connects to a
  switch. The router port is configured with
  many virtual subinterfaces that run on different
  VLANs.

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• LAN Segmentation
• Virtual local area networks are used to logically
  separate Layer 2 switch networks. Users on
  different VLANs can't communicate directly, just
  as they would if they were on physically
  separate networks. It's a great way to segment a
  network, and improve security. 
• Cost
• Segmenting a large VLAN against a relatively
  smaller VLANs is economical against creating a
  routed network with routers because normally
  routers costlier than switches.
• Physical Layer Transparency
• VLANs are transparent on the physical topology
  and medium over which the network is connected.
• This is an efficient way to connect a low port
  count router to multiple subnets. VLANs are an
  integral part of every enterprise network, giving
  flexibility and security.

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• Establishing VLAN memberships
• Most frequent used approaches are discussed
  below
• Static VLANs or port-based VLANs.
• Static VLAN assignments can be created by
  allocating ports to a VLAN. As a device enters
  the network, the device automatically assumes the
  VLAN of the port. If one changes ports and seeks
  access to the same VLAN, the network
  administrator must manually make a port-to-VLAN
  assignment for the new connection.

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• Dynamic VLANs
• Dynamic VLANs are created using software. With a
  VLAN Management Policy Server (VMPS), an
  administrator can allocate switch ports to VLANs
  dynamically based on information such as the
  source MAC address of the device connected to the
  port or the username used to log onto that
  device. As a device enters the network, the
  switch queries a database for the VLAN membership
  of the port that device is connected to.

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• Protocol-based VLANs For switch which supports
  protocol-based VLANs, traffic will be managed on
  the basis of its protocol. This will segregate
  the traffic from a port based on the particular
  protocol of defined traffic.
• For example,
• If a host generated traffic type ARP on a port A
• A network with IPX traffic to port B
• A router forwarding IP traffic to port C
• If a protocol-based VLAN is created that supports
  IP and contains all three ports, this prevents
  IPX traffic from being forwarded to ports A and
  C, and ARP traffic from being forwarded to ports
  B and C, while still allowing IP traffic to be
  forwarded on all three ports.