vlan in network

vlan in network.

VLAN in Network:

What is VLAN (Virtual LAN)?

Its stands for Virtual Local Area Network. It is a group of devices on one or more LANs that are configured to communicate as if they are attached to the same network.

Characteristics of VLAN:

• A Virtual Local Area Network (VLAN) is a grouping of network nodes like computers, servers and network devices are connected in a logical form.
• It increases the broadcast domains.
• It is providing layer 2 security.
• It will happen in Data Link layer of OSI model.
• VLAN 1 is the default VLAN.
• It can be configured only manageable switch.
• It is divided a larger broadcast domain into multiple smaller broadcast domains.
• It allows the network administrator to grouping by hosts even if the hosts are not directly connected to the same network switch.
• It is easy to change and manage users on a VLAN.

Advantages of VLAN:

• It provides solution of broadcast problem.
• It is reduced the size of broadcast domains.
• It provides additional layer of security.
• It is easily managed and add users.
• Its infrastructure is much cheaper because it’s not required hardware and cable.

Disadvantages of VLAN:

• It cannot provide the data to the other VLANs.
• If attacking a one system, it effected the whole logical network.

Benefit of VLAN:

• Broadcast Control:

When VLAN is created in Switch the number is broadcast domain increases but the size of broadcast domain decreases.

• Security:

VLAN increases layer – 3 security. Only the member of a broadcast domain can have access to the network resources in that particular group. Using VLAN we can restrict hardware address protocol and application.

• Flexibility & Scalability:

Using VLAN devices can be added or remove very easily. A group of users that need a different group for security purpose can be added to a different VLAN, so that other users cannot access them.

Types of VLAN:

There are 5 types of VLANs depending their network traffic –

1. Default VLAN:

When switch start all switch, port become a member of the default VLAN. It makes them a member of a particular broadcast domain. So that they can communicate. In Cisco switches default VLAN is VLAN 1.

2. Data VLAN: –

This VLAN is used to carry only user traffic. It will not carry any management and control related information.

3. Native VLAN: –

A Native VLAN is assigned to an 802.1Q Trunk port. It supports traffic coming many VLAN as well as other Trunk port.

4. Management VLAN: –

This type of VLAN is configure to access the management capability of a Switch.

5. Voice VLAN: –

This VLAN is configure to carry voice traffic. This traffic has the greater priority than data.

VLAN Membership:

There are 2 types of VLAN Membership –

Static VLAN:

• Static VLANs are typically method of creating VLANs by Administrator.
• It is based on Port number.
• It is manually assigning by the administrator on a switch to particular port for the particular VLAN.
• It is also called a Port-based VLAN Membership.
• Here single port can be member of single VLAN.

Dynamic VLAN:

• Dynamic VLAN are created using software or based on the MAC address.
• Here, Switch automatically assigning the port to a VLAN.
• Each port can be member of Multiple VLAN.
• For Dynamic VLAN configuration required VMPS (VLAN Membership Policy Server).

Types of VLAN Port:

1. Access Port:

• It is a member of particular a VLAN.
• It carries traffic of only one VLAN.
• Traffic is both sent & received in native format with no VLAN information.
• Any traffic received in a part is consider that it belongs to the same VLAN.
• Any device that is attached to an access port don’t know which VLAN it is connected to.
• When data is sent through an access port the VLAN information is remove.

2. Trunk Port:

• This name is taken from Telephone system Trunk which carry multiple telephone conversion at a time.
• Trunk port can carry traffic of multiple VLAN.
• A Trunk port must have 100 Mbps, 1 Gbps, 10 Gbps speed.
• It is a point-to-point connection between two switches, a switch and a router, a switch and a server.

VLAN Trunking Protocols:

There are 2 protocols are commonly used in VLAN –

ISL (Inter-Switch Link):

It is a Cisco proprietary protocol.
It is used to interconnect switches and it maintain VLAN information.
It uses an internal process tagging that does not modify ethernet frame.


It is also known as Dot1q.
It is an IEEE standard protocol.
It is an open standard protocol.
It is uses frame-internal process for tagging that modify the ethernet frame.
It is supported upto 4094 VLANs.

VLAN Interview Questions

Q #. What is VLAN?
Ans: –
A VLAN or Virtual Local Area Network is a group of devices that are used to be a single broadcast domain divided into multiple broadcast domains in layer 2 switch network.

Q #. How to create VLAN?
Ans: –

Switch(config)# vlan 50
Switch(config-vlan)# name networkhelp
Switch(config-vlan)# exit

Q #. How to add an interface to a VLAN?
Ans: –

Switch(config)# interface fastethernet 0/0
Switch(config-vlan)# switchport mode access
Switch(config-vlan)# switchport access vlan 30
Switch(config-vlan)# exit

Q #. How to add multiple interface in VLAN at a time?
Ans: –

Switch(config)# interface range fastethernet 0/1 – 2
Switch(config-vlan)# switchport mode access
Switch(config-vlan)# switchport access vlan 200
Switch(config-vlan)# exit

Q #. How to change native VLAN?
Ans: –

Switch(config)# interface fastethernet 0/0
Switch(config-if)# switchport trunk native vlan 100

Q #. Which command is used to see trunk interfaces?
Ans: –

Switch# show interface trunk

Q #. Which command is used to see all VLAN information?
Ans: –

Switch# show vlan

Q #. What is the comment of delete vlan information from Switch?
Ans: –
Delete flash:vlan.dat

Q #. What is the difference between VLAN Access and Trunk Mode?
Ans: –
Access Mode is used to connect end device (host) to switch while Trunk Mode is used to connect between switches.

Q #. What is mean by “Router on Stick”?
Ans: –
The process of connecting one physical (ethernet) link with the trunk logical interface and their configuration as 802.1q link, is called as “Router-on-Stick”. Here, switch is connected within multiple VLAN and router works routing in every VLAN.

Q #. Name of the Trunking Protocols?
Ans: –

• ISL (Inter Switch Link) – This is a Cisco proprietary protocol.
• 802.1q – This is an IEEE standard protocol.

Q #. What is the maximum number of vlans allowed in ISL and 802.1Q?
Ans: –

• ISL maximum permitted in vlan – 1000.
• 802.1Q maximum permitted in vlan – 4094.

Q #. What is the name of VLAN that not tagged by 802.1Q?
Ans: –
Native VLAN.

VLAN Range

VLAN Range.

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