STUDY GUIDE
Understanding the Concepts of Virtual Local Area Network (VLAN)
Objectives
This module covers the following objectives for the “configure, verify and troubleshoot a switch with
VLANs and inter-switch communications” section of the CCNA module exam:
➢ Describe how VLANs create logically separate networks and the need for routing between them.
➢ Configure, verify and troubleshoot VLANs, trunking on CISCO switches and inter-VLAN routing..
➢ Familiarize yourself with the SHOW commands and other troubleshooting commands used in this
protocol.
Study Strategies
➢ Read and patiently understand the discussion presented in this module.
➢ Smartly rewrite in your notebook or make a summary of notes about the information being presented. By
this strategy, you will learn how to visualize the concepts and imagine how a switch fundamentally
operates in a network environment.
➢ Complete the challenge and the exercises at the end of the module. This will solidify the concepts that
you have learned through simulation. Simulation will be done by group and you need to collaborate with
your group members.
Introduction
Recalling that one of the functions of a switch is to distribute traffic within a network going to the end
devices. This traffic may either come from the outside of the network, which can be from the Internet, or may
come within its network itself. Switched networks are very ideal especially if you have several end devices that
you want to connect with and usually, these devices are grouped into different departments or classes depending
on their function on the network. But we have to take note that having a switch with only a default configuration
to group devices will still lead in grouping them as a whole or what we call one big broadcast domain.
ACCOUNTING
DEPARTMENT
fa0/0
fa0/3 HR
fa0/2 DEPARTMENT
fa0/1
PC_A
0000.0000.9999
ADMIN
DEPARTMENT
JCQ.ECE 1
, One of the underlying problems with Layer 2 switches is that excessive broadcast and multicast traffic
can affect other devices in a switched network because bridges and switches flood these types of messages. If you
are a receiver of all this excessive traffic, you have to waste processing utilization and endure wasted bandwidth
even if those devices are not in your department (Ciora et al. 2008). Say for instance for the above illustration,
when PC_A wants to send a message to the HR department, that broadcast message will still be send to and
received by all of the grouped devices connected on the switched network. Even if this traffic is irrelevant with
other group of devices, it will still be sent to and received by them.
Broadcast messages are good and necessary in the process of communication of network devices, but, the
more we add routing and end-user devices into our infrastructure, the more the devices need to process incoming
broadcast messages from all of its members in the network. This will lead to high CPU utilization and will
eventually make the network slower and slower. Another problem in a big broadcast domain is the security issue.
Since every device in the switched network receive the incoming broadcast message, anyone may also see or
receive the information even if it is not intended for these end user devices.
So in order for us to at least minimize this problem, the conventional way is to replace the switch with a
router since router, as we recall with our previous face to face discussion, isolates a network and segment every
broadcast domain per each available port interface. This means that traffic for every port is segregated with each
other and traffic is forwarded by layer 3 capability- routing using the IP address. So when PC_A wants only to
reach to the HR department, traffic will then only be forwarded to the port where HR department is connected to
– efficient traffic forwarding process with greater security than in switch.
ACCOUNTING
DEPARTMENT
fa0/0
fa0/3 HR
fa0/2 DEPARTMENT
fa0/1
PC_A
192.168.4.12
ADMIN
DEPARTMENT
The only drawback of using a router to solely segment traffic of different departments or groups of devices
is that, port interfaces are limited and it is not efficiently wise to dedicate a single port just to forward packets of
one broadcast domain inside a local area network. Consider also that routers are way more expensive than
switches.
With these reasons, we will be introducing a solution where we can virtually segment our LAN into
different groups or departments in a switched environment. This virtual segmentation is what we call Virtual
Local Area Network (VLAN).
What is a Virtual LAN (VLAN)?
According to Cisco, Virtual Local Area Network or VLAN is a group of devices on one or more LANs
that are configured to communicate as if they were attached to the same wire, when in fact they are located on a
JCQ.ECE 2
Understanding the Concepts of Virtual Local Area Network (VLAN)
Objectives
This module covers the following objectives for the “configure, verify and troubleshoot a switch with
VLANs and inter-switch communications” section of the CCNA module exam:
➢ Describe how VLANs create logically separate networks and the need for routing between them.
➢ Configure, verify and troubleshoot VLANs, trunking on CISCO switches and inter-VLAN routing..
➢ Familiarize yourself with the SHOW commands and other troubleshooting commands used in this
protocol.
Study Strategies
➢ Read and patiently understand the discussion presented in this module.
➢ Smartly rewrite in your notebook or make a summary of notes about the information being presented. By
this strategy, you will learn how to visualize the concepts and imagine how a switch fundamentally
operates in a network environment.
➢ Complete the challenge and the exercises at the end of the module. This will solidify the concepts that
you have learned through simulation. Simulation will be done by group and you need to collaborate with
your group members.
Introduction
Recalling that one of the functions of a switch is to distribute traffic within a network going to the end
devices. This traffic may either come from the outside of the network, which can be from the Internet, or may
come within its network itself. Switched networks are very ideal especially if you have several end devices that
you want to connect with and usually, these devices are grouped into different departments or classes depending
on their function on the network. But we have to take note that having a switch with only a default configuration
to group devices will still lead in grouping them as a whole or what we call one big broadcast domain.
ACCOUNTING
DEPARTMENT
fa0/0
fa0/3 HR
fa0/2 DEPARTMENT
fa0/1
PC_A
0000.0000.9999
ADMIN
DEPARTMENT
JCQ.ECE 1
, One of the underlying problems with Layer 2 switches is that excessive broadcast and multicast traffic
can affect other devices in a switched network because bridges and switches flood these types of messages. If you
are a receiver of all this excessive traffic, you have to waste processing utilization and endure wasted bandwidth
even if those devices are not in your department (Ciora et al. 2008). Say for instance for the above illustration,
when PC_A wants to send a message to the HR department, that broadcast message will still be send to and
received by all of the grouped devices connected on the switched network. Even if this traffic is irrelevant with
other group of devices, it will still be sent to and received by them.
Broadcast messages are good and necessary in the process of communication of network devices, but, the
more we add routing and end-user devices into our infrastructure, the more the devices need to process incoming
broadcast messages from all of its members in the network. This will lead to high CPU utilization and will
eventually make the network slower and slower. Another problem in a big broadcast domain is the security issue.
Since every device in the switched network receive the incoming broadcast message, anyone may also see or
receive the information even if it is not intended for these end user devices.
So in order for us to at least minimize this problem, the conventional way is to replace the switch with a
router since router, as we recall with our previous face to face discussion, isolates a network and segment every
broadcast domain per each available port interface. This means that traffic for every port is segregated with each
other and traffic is forwarded by layer 3 capability- routing using the IP address. So when PC_A wants only to
reach to the HR department, traffic will then only be forwarded to the port where HR department is connected to
– efficient traffic forwarding process with greater security than in switch.
ACCOUNTING
DEPARTMENT
fa0/0
fa0/3 HR
fa0/2 DEPARTMENT
fa0/1
PC_A
192.168.4.12
ADMIN
DEPARTMENT
The only drawback of using a router to solely segment traffic of different departments or groups of devices
is that, port interfaces are limited and it is not efficiently wise to dedicate a single port just to forward packets of
one broadcast domain inside a local area network. Consider also that routers are way more expensive than
switches.
With these reasons, we will be introducing a solution where we can virtually segment our LAN into
different groups or departments in a switched environment. This virtual segmentation is what we call Virtual
Local Area Network (VLAN).
What is a Virtual LAN (VLAN)?
According to Cisco, Virtual Local Area Network or VLAN is a group of devices on one or more LANs
that are configured to communicate as if they were attached to the same wire, when in fact they are located on a
JCQ.ECE 2
