3. Common Technology Courses
• After learning, Tom mastered the communication process between two PCs and showed greater interest in
network technologies. The customer raised new requirements in this project: There are offices of both the
technical department and financial department on the fifth and sixth floors, mutual communication is required
inside departments, but communication of the technical department and that of the financial department need to
be isolated from each other.
Layer-2 switch
Layer-2 switch
Layer-3 switch
Technical
department
Technical
department
Financial
department
Financial
department
1 2
3 1
2
3
24 24
2
1
4. Common Technology Courses
• At a glance of this topology, Tom thought of implementing isolation between the technical department and the
financial department on the same switch first.
• Tom recalled the IPv4 address knowledge and remembered that only hosts in the same network segment could
communicate with each other directly. So, Tom thought that IP addresses in different network segments could be
allocated to PCs to implement isolation.
Layer-2 switch
Technical
department
Financial
department
1 2
3
Technical department: 192.168.1.0/24
Financial department: 192.168.2.0/24
5. Common Technology Courses
• Tom told the manager his idea. The manager praised his idea but also reminded Tom that ARP Request packets
would be broadcast in PC communication and the switch flooded the broadcast packets, which could cause junk
traffic. In addition, the idea may put security in risks. If a staff in the technical department changes his/her IP
address to be in the same network segment as IP addresses of the Financial department, he could access PCs of
the Financial department.
• Tom thought that the manager's consideration was right and comprehensive. The manager told Tom that VLANs
and trunks were important features on the layer-2 switch and they could be a good solution.
Layer-2 switch
Technical
department
Financial
department
ARP Request
ARP Request
6. VLAN Principle and Configuration
• Virtual Local Area Network (VLAN)
• A VLAN is a logical network configured on a physical network. Each VLAN is identified by a numeral ID ranging from 1 to
4094. Different VLANs configured on a layer-2 switch are physically isolated and cannot communicate with each other.
• On the switch, each port can be added to a VLAN. Physical ports with the same VLAN ID belong to the same VLAN and hosts
connected to such ports are in the same network. Physical ports with different VLAN IDs belong to different networks. Hosts
connected to such ports cannot communicate with each other even if their IP addresses are in the same network segment.
Each VLAN is equivalent to an independent switch.
• All ports on a switch belong to VLAN 1 by default.
VLAN 10 VLAN 20
Layer-2 switch
Technical
department
Financial
department
1 2
3
7. VLAN Principle and Configuration
• Configuring VLANs
• Step 1: Create VLANs.
• Step 2: Add ports to VLANs on the switch.
RG-S2652G(config)#vlan 10 //Creating a VLAN.
RG-S2652G(config-vlan)# name Technical //Naming the VLAN for VLAN description.
RG-S2652G(config)#vlan 20
RG-S2652G(config-vlan)# name Financial
RG-S2652G(config)#interface range f0/1-2
RG-S2652G(config-if-range)#switchport access vlan 10 //Adding this port to VLAN 10.
RG-S2652G(config)#interface f0/3
RG-S2652G(config-if)#switchport access vlan 20
VLAN 10 VLAN 20
Layer-2 switch
Technical
department
Financial
department
1 2
3
8. VLAN Principle and Configuration
• Displaying VLAN Configuration Results
• Run the show vlan command to display VLAN information and ports contained in
each VLAN.
Ruijie#show vlan
VLAN Name Status Ports
---- -------------------------------- --------- -----------------------------------
1 VLAN0001 STATIC Fa0/4, Fa0/5, Fa0/6, Fa0/7
Fa0/8, Fa0/9, Fa0/10, Fa0/11
Fa0/12, Fa0/13, Fa0/14, Fa0/15
Fa0/16, Fa0/17, Fa0/18, Fa0/19
Fa0/20, Fa0/21, Fa0/22, Fa0/23
Fa0/24, Gi0/25, Gi0/26
10 VLAN0010 STATIC Fa0/1, Fa0/2
20 VLAN0020 STATIC Fa0/3
VLAN 10 VLAN 20
Layer-2 switch
Technical department Financial department
1 2
3
9. VLAN Principle and Configuration
• Displaying the MAC Address Table of the Switch
• The MAC address table contains VLAN information. The switch forwards data only
between ports belonging to the same VLAN.
VLAN 10 VLAN 20
Layer-2 switch
Technicaldepartment Financial department
1 2
3
Ruijie#sh mac-address-table
Vlan MAC Address Type Interface
---------- -------------------- -------- -------------------
10 001a.a919.414d DYNAMIC FastEthernet 0/1
10 000d.9dd2.6587 DYNAMIC FastEthernet 0/2
20 0016.d32c.2070 DYNAMIC FastEthernet 0/3
…
10. VLAN Principle and Configuration
• Summary
• After study, Tom mastered the functions of VLANs and how to configure and display VLANs. It
is an optimal way to isolate communication of the two departments via VLANs.
• Tom added ports to different VLANs by department on the switch. The PCs of different
departments could not communicate with each other even if their IP addresses are in the
same network segment. Therefore, VLANs are really useful.
• Exercises
• What is the function of VLANs? Can physical ports in different VLANs on a layer-2 switch
communicate with each other?
• What are the steps for configuring VLANs?
• How to display the mappings between VLANs and ports? Which VLAN is the default one of
ports on the switch?
