"A VLAN divides a single broadcast domain
into multiple smaller broadcast domains. By doing so, VLANs isolate traffic
within each domain, reducing the overall broadcast traffic on the network and
improving network performance and security."
VLANs is a layer 2 security that divides a single
broadcast domain into multiple broadcast domains. By default, all switch port
is part of a single broadcast domain and VLAN can divide it into multiple
smaller broadcast domains. VLANs range started from 1 to 1005 and we can create
VLANs from 2 to 1001. VLAN 1 is the default VLAN and by default, all switched ports
are members of VLAN 1 also known as Native VLANs. VLAN range 1001 to 1005 is
reserved for Token Ring and FDDI. We can also use VLANs' extended range from
1006-4094.
Advantages of VLANs-
1. It
controls unnecessary broadcasts over the network.
2. It
can enhance network security.
3. It
can improve network performance.
4. It
can logically segment based on a particular department.
5. It can help to manage the network smoothly.
There are two types of VLAN-
Static VLAN-
1. Static
VLANs are based on port numbers.
2. Need
to manually assign a port on a switch to a VLAN.
3. Static
VLAN is also called port-based VLAN.
4. One
port can be a member of only one VLAN
Dynamic VLAN-
1. Dynamic
VLANs are based on the Mac add of a PC.
2. Switch
automatically assigns a port to a VLAN
3. Each
port can be a member of multiple VLANs
4. For
dynamic VLAN configuration a software called VMPS (VLAN membership policy
server) is needed.
Access Ports-
Access
ports are the fundamental building blocks of a managed switch. An access port
is assigned to only one VLAN. It carries traffic from the specified VLAN to the
device connected to it or from the device to other devices on the same VLAN on
that switch. The 802.1Q tags are not included in packets transmitted or
received on access ports.
Trunk links-
Trunks
can carry multiple VLAN traffic. A trunk link is a 100 or 1000mbps
point-to-point link between two switches between a switch and router or between
a switch and server. These carry the traffic of multiple LANs from 1 to 1005 at
a time. Trunking allows you to make a single port part of multiple VLANs at the
same time.
VLAN identification method (Frame Tagging)-
1. Single
VLAN can span over multiple switches.
2. To
make sure that the same VLAN users on different switches communicate with each
other there is a method of tagging that happens on trunk links.
3. Tag
is added before a frame is sent and removed once it is received on the trunk
link.
4. Frame
tagging happens only on trunk links
5. Vlan
identification is what switches use to keep track of all those frames moving
through the trunk links.
Trunking method for frame tagging process-
Inter-Switch link (ISL)
1. It
is a Cisco proprietary version.
2. It
works with Ethernet standards.
3. It
adds 30 bytes of tagging information.
4. All
VLAN traffic is tagged.
5. Frame
is not modified.
IEEE802.1Q
1. It
is an open standard and we can use it on different vendor switches.
2. It
works only on Ethernet standards.
3. Only
4 bytes tag will be added to the original frame.
4. Unlike
ISL, 802.1Q does not encapsulate the frame. It modifies the existing Ethernet
frame to include the VLAN ID.
How to Configure VLANs-
Access switches 1 configuration-
Create
VLANs-
Switch#conf t
Switch(config)#vlan
10
Switch(config-vlan)#name
sales
Switch(config-vlan)#vlan
20
Switch(config-vlan)#name
Account
Switch(config-vlan)#vlan
30
Switch(config-vlan)#name
IT
Switch(config-vlan)#do
wr
Building
configuration...
[OK]
See
VLANs Status-
Switch(config-vlan)#do
sh vlan brief
Switch(config-vlan)#do
sh interface trunk
Switch#show
vlan id 10
Switch#show
vlan name IT
Assign port to specific VLANs-
Switch(config)#int range fa 0/1-2
Switch(config-if-range)#switchport
mode access
Switch(config-if-range)#switchport
access vlan 10
Switch(config-if-range)#int
range fa 0/3-4
Switch(config-if-range)#switchport
mode trunk
Access switches2
configurations-
Create
VLANs-
Switch#conf t
Switch(config)#vlan
10
Switch(config-vlan)#name
sales
Switch(config-vlan)#vlan
20
Switch(config-vlan)#name
Account
Switch(config-vlan)#vlan
30
Switch(config-vlan)#name
IT
Switch(config-vlan)#do
wr
Building
configuration...
[OK]
See
VLANs Status-
Switch(config-vlan)#do
sh vlan brief
Switch(config-vlan)#do
sh interface trunk
Switch#show
vlan id 10
Switch#show
vlan name IT
Assign port to specific VLANs-
Switch(config)#int range fa 0/1-2
Switch(config-if-range)#switchport
mode access
Switch(config-if-range)#switchport
access vlan 20
Switch(config-if-range)#int
range fa 0/3-4
Switch(config-if-range)#switchport
mode trunk
Access switches3
configurations-
Create
VLANs-
Switch#conf t
Switch(config)#vlan
10
Switch(config-vlan)#name
sales
Switch(config-vlan)#vlan
20
Switch(config-vlan)#name
Account
Switch(config-vlan)#vlan
30
Switch(config-vlan)#name
IT
Switch(config-vlan)#do
wr
Building
configuration...
[OK]
See
VLANs Status-
Switch(config-vlan)#do
sh vlan brief
Switch(config-vlan)#do
sh interface trunk
Switch#show
vlan id 10
Switch#show
vlan name IT
Assign port to specific VLANs-
Switch(config)#int range fa 0/1-2
Switch(config-if-range)#switchport
mode access
Switch(config-if-range)#switchport
access vlan 30
Switch(config-if-range)#int
range fa 0/3-4
Switch(config-if-range)#switchport
mode trunk
Access switches
4 configurations-
Create
VLANs-
Switch#conf t
Switch(config)#vlan
10
Switch(config-vlan)#name
sales
Switch(config-vlan)#vlan
20
Switch(config-vlan)#name
Account
Switch(config-vlan)#vlan
30
Switch(config-vlan)#name
IT
Switch(config-vlan)#do
wr
Building
configuration...
[OK]
See
VLANs Status-
Switch(config-vlan)#do
sh vlan brief
Switch(config-vlan)#do
sh interface trunk
Switch#show
vlan id 10
Switch#show
vlan name IT
Assign port to specific VLANs-
Switch(config)#int range fa 0/1-2
Switch(config-if-range)#switchport
mode access
Switch(config-if-range)#switchport
access vlan 10
Switch(config-if-range)#int
range fa 0/3-4
Switch(config-if-range)#switchport
mode trunk
Distribution
Switch 1 configuration
Switch#conf
t
Switch(config)#int range fa 0/1-5
Switch(config-if-range)#switchport
mode trunk
Switch(config-if-range)#do wr
Building configuration...
[OK]
Switch(config-if-range)#vlan 10
Switch(config-vlan)#name sales
Switch(config-vlan)#vlan 20
Switch(config-vlan)#name Account
Switch(config-vlan)#vlan 30
Switch(config-vlan)#name IT
Switch(config-vlan)#do wr
Building configuration...
Distribution Switch 2 configuration
Switch#conf
t
Switch(config)#int range fa 0/1-5
Switch(config-if-range)#switchport
mode trunk
Switch(config-if-range)#do wr
Building configuration...
[OK]
Switch(config-if-range)#vlan 10
Switch(config-vlan)#name sales
Switch(config-vlan)#vlan 20
Switch(config-vlan)#name Account
Switch(config-vlan)#vlan 30
Switch(config-vlan)#name IT
Switch(config-vlan)#do wr
Building configuration...
Core Switch configuration
Switch#conf
t
Switch(config)#int range fa 0/1-2
Switch(config-if-range)#switchport
mode trunk
Switch(config-if-range)#do wr
Building configuration...
[OK]
Switch(config-if-range)#vlan 10
Switch(config-vlan)#name sales
Switch(config-vlan)#vlan 20
Switch(config-vlan)#name Account
Switch(config-vlan)#vlan 30
Switch(config-vlan)#name IT
Switch(config-vlan)#do wr
Building configuration...
What Is Inter-VLAN Routing?
VLANs
are used to segment switched Layer 2 networks and two different VLANs cannot
communicate with each other. It means hosts in one VLAN cannot communicate with
hosts in another VLAN unless there is a router or a Layer 3 switch to provide
routing services.
Inter-VLAN routing is the process of forwarding network
traffic from one VLAN to another VLAN.
There
are three inter-VLAN routing options:
- Legacy
Inter-VLAN routing: This is a legacy solution. It does not scale
well.
- Router-on-a-Stick: This
is an acceptable solution for a small- to medium-sized network.
- Layer 3 switch using switched
virtual interfaces (SVIs): This
is the most scalable solution for medium to large organizations.
InterVLAN Routing by Layer 3 Switch
CoreSwitch(config-if)#int vlan 10
CoreSwitch(config-if)#ip add
10.0.0.1 255.0.0.0
CoreSwitch(config-if)#no shut
CoreSwitch(config-if)#int vlan 20
CoreSwitch(config-if)#ip add
20.0.0.1 255.0.0.0
CoreSwitch(config-if)#no shut
CoreSwitch(config-if)#int vlan 30
CoreSwitch(config-if)#ip add
30.0.0.1 255.0.0.0
CoreSwitch(config-if)#no shut
CoreSwitch(config-if)#do wr
Building configuration...
[OK]
CoreSwitch(config-if)#exit
CoreSwitch(config)#ip routing
CoreSwitch(config)#do wr
Building configuration...
[OK]
InterVLAN Routing by Router
If you are going to configure
Inter-VLAN routing by Router then you need to configure Encapsulation on router
Fast Ethernet Interface by creating Sub-Interface for multiple VLANs- for
example
#Conf t
#int fa 0/0.10
#encapsulation dot1.Q VLAN 10
#IP address 10.0.0.1 255.255.255.0
#int fa 0/0.20
#encapsulation dot1.Q VLAN 20
#IP address 20.0.0.1 255.255.255.0
#int fa 0/0.30
#encapsulation dot1.Q VLAN 30
#IP address 30.0.0.1 255.255.255.0
#int fa 0/0
#no shut
#do wr
