The pedagogical objectives of this lesson are:
– Differentiate level 2 and 3 broadcasts.
– Why the Vlans were invented
– What are the benefits that Vlans bring
– Understand Vlan numbering
– Set up a Vlan on a CISCO Switch.
Recall on broadcasts
The goal of the Vlans is to reduce the broadcasting field! That's it!
Before understanding the purpose of the Vlans, it is essential to understand how broadcasts can pollute a network!
There are two types of broadcasts:
– Level 3 Broadcast (Example: IP Address – X.X.X.255 /24 )
– Level 2 Broadcast (in all cases: FF:FF:FF:FF:FF:FF:FF)
The Vlans will decrease the level 2 broadcast ingfield.
Question: What will a switch do when it receives a Level 2 broadcast?
Answer: It will broadcast it on all these ports except on the receiving port, regardless of IP addresses !!! normal!! A switch does not look at layer 3 of the Model OSI!!
In a world without Vlan
You can see below a standard corporate network. This network includes:
– 10 Boss (IP address range: 192.168.10.0 /24 )
– 50 Secretaries / Accountant (IP address range: 192.168.20.0 /24 )
– 200 Sellers (IP address range: 192.168.30.0 /24 )
If one of our computers broadcasts ANP, it will be broadcast on ALL the ports of our network!
All our posts will broadcast to operate, our network will soon be polluted!
How can we reduce the number of broadcasts on the network?
– Removing jobs? impossible
– Create a network per working group? yes
– The Boss network (10 users) – Decrease in the number of broadcasts received by 96.2%
– The Secretary Network (50 users) – Decrease in the number of broadcasts received by 80.8%
– The Sellers network (200 users) – Decrease in the number of broadcasts received by 23.1%
– It's very expensive this method!!!!!!!
How do I do that?
Find a solution to create this type of architecture with little hardware!!
The solution found:
– Virtual LAN (VLAN)
Reduce the broadcast domain.
– Improve network management.
– Optimize bandwidth.
– Separate the streams.
So how does it actually work?
Before you know how Vlans work, it's important to understand how a Switch works !!! If you haven't read the article on CAM Tables. I'll give you an appointment in 5 minutes…..
Are you back? Perfect 🙂
You just saw that a Switch works thanks to the CAM table !!! This CAM Table allows you to create a relationship between a MAC address and a physical port! To limit broadcast domains and thereby stop broadcasting it on all ports of the switch, our equipment will create a CAM table by VLAN !!!!
These CAM Tables are completely independent! So a port in the Vlan 10 can only chat with the Vlan 20!
Let's go into the switch and see what's going on:
Switch show vlan
Come on it starts, numbers from everywhere …
On the left you can see numbers (1, 1002, 1003…). Here's how the switch will create the groups, it will apply them a VLAN number:
– The Vlans Standard
– Reserved Vlans (impossible to remove, because they serve for FDDI and Token, old topologies using a principle of detection and correction by token)
– Extended Vlans
The order you just made provides you with the vlan Database.
The Vlan Database is the database containing all existing vlans (except for scope).
This database is present in The Flash memory and is called a "vlan.dat" file.
This database can be completed online or via the VTP protocol.
Location of the VLAN database
The Vlan database is located in the flash memory of our equipment:
To view the content of your Flash:
Switch flash show:
By default, all ports are in the Vlan 1.
To put the port and therefore a customer position in a different Vlan, you will have to:
– Create the Vlan in the Vlan Database.
– Assign a port in this Vlan.
Switch (config) vlan Number-du-vlan Switch (config-vlan) name Name-du-vlan Switch (config) interface that you want to set up Switch (config-if) - switchport mode access Switch (config-if) - switchport access vlanNumber de vlan
Switch (config) vlan 10 Switch (config-vlan) - name SECRETARY Switch (config) vlan 20 Switch (config-vlan) - name BOSS Switch (config) vlan 30 Switch (config-vlan) - name VENDEUR Switch (config) - FastEthernet interface 0/1 Switch (config-if) - switchport mode access Switch (config-if) - switchport access vlan 10 Switch (config) - FastEthernet interface 0/4 Switch (config-if) - switchport mode access Switch (config-if) - switchport access vlan 20 Switch (config) - FastEthernet interface 0/7 Switch (config-if) - switchport mode access Switch (config-if) - switchport access vlan 30
Switch show vlan Switch show vlan brief Switch show vlan id Number-du-vlan
Use the command:
Switch show interface switchport
Compare an interface where you implanted a vlan with a "nude."
How do I get two switches to communicate?
We have two Switches
The answer to the question can be found in the following article:
Hoping this article has been helpful to you! Post your com'!!