Home > Articles > Certification > Cisco Certification > CCENT

What Happens in the VLAN Stays in the VLAN

  • Print
  • + Share This
This article discusses the secrets of the VLAN and why it is a critical tool in today's networks.
Like this article? We recommend

What is your favorite use of the word Virtual? Virtual Machine, Virtual Reality, Virtual Assistant? One of my favorites is Virtual Local Area Network, (VLAN). Join me as we discover the secrets of the VLAN and why it is a critical tool in today’s networks.

How well do you deal with interruptions?

Imagine going to a conference where there were four sessions (1 through 4) being presented. A single large ballroom was rented at a nice hotel for the event, and a session was being presented in each corner of the ballroom. Listeners could hear each of the presenters in their respective corner, but there’s a problem. Frequently, over the broadcast system that can be heard by the entire room, announcements are periodically being made. Every time an announcement is made, everyone in all the sessions to stop what they were doing to see if the message being broadcast was important or relevant to them. If the broadcast message wasn’t relevant to an individual, they turn their attention back to their session. If the broadcast was relevant to an individual, such as “Would Bob Jones identify yourself, we have found your wallet.”, then Bob would respond appropriately by raising his hand, (while everyone that wasn’t Bob will never get that time back).

Broadcasts that interrupt every host are a way of life in the Network.

In an Ethernet network running IPv4, broadcasts are necessary interruptions that go to all devices in that same network/broadcast domain. Consider this packet in Figure 1.

This is an example of when a broadcast would be generated, namely, when a device is trying to learn the MAC address of another device on the local network. Because the sender doesn’t know what the Layer 2 MAC address is yet, a broadcast is sent, which all other devices must process to see if the message being carried is relevant to them. Then the device that has the MAC address being looked for (in our example, the host of 10.3.0.2) will respond with a reply, while all the other devices on the network go back to their normal business.

The level of tolerance

A small network with a few dozen hosts won’t normally generate a large amount of broadcasts, so the interruptions to the group are acceptable. But as we add more devices to that same network, such as a thousand new hosts, the quantity of broadcasts (which interrupt all other hosts on that same network) becomes high enough to bog down all the devices on that network. Imagine being interrupted hundreds of times per hour, or even per minute, and you get the picture of what the hosts on that network are going through. We do have some options for reducing the number of broadcasts that each of our hosts has to process. Read on and we will take a look together at a solution.

Reducing the Impact of Broadcasts

A solution to the problem of having too many devices (and as a result too many broadcasts) on a single network (which is a single broadcast domain) is to take a large network of 1000 hosts and carve it up into smaller networks, (for example, four networks of 250 hosts each). Let’s call these smaller networks 1, 2, 3, and 4. Each of these four smaller networks would be a separate broadcast domain. If a broadcast was generated in network 1, it would only have to be processed by devices in that same network. The other networks would only have to process the local broadcasts in their own smaller network. Broadcasts that begin in a broadcast domain/network, stay in that same broadcast domain/network.

Carving out the smaller networks

Let’s visualize a Layer 2 switch that has 1000 ports (and yes, I know, that is a lot!) If we connected computers to most of those ports, by default we would have one large network (one large broadcast domain), and too many broadcasts, as discussed earlier. To create the smaller networks, we could purchase 3 additional switches, and move 250 devices to each of the switches, or we could train the original 1000 port switch to logically create the 4 separate networks. Perhaps we tell the switch that ports 1-250 belong to network 1, ports 251-500 belong to network 2, ports 501-750 belong to network 3, and ports 751-1000 belong to network 4. These would be four separate broadcast domains, disconnected from each other. There is a feature that allows this, called a Virtual Local Area Network, which is really just an individual broadcast domain.

VLANs to the rescue

A Virtual Local Area Network (VLAN) is the function in the switch that can separate one or more ports and put them in their own broadcast domain. VLAN is synonymous with “broadcast domain.” From our example earlier, if we assign ports 1-250 to VLAN 1, ports 251-500 to VLAN 2, ports 501-750 to VLAN 3, and ports 751-1000 to VLAN 4, then any devices we connected to those switch ports would belong to the VLAN that the specific switch port is assigned to. Now a single broadcast sent into any of the networks would be confined to that domain, or in other words be limited to only the other devices in that same VLAN. From our title, “What happens in the VLAN (related to L2 broadcasts) stay in the VLAN.”

Table 1

Ports on the Switch

VLAN assignment of those switch ports

FastEthernet 1-250

VLAN 1

FastEthernet 251-500

VLAN 2

FastEthernet 501-750

VLAN 3

FastEthernet 751-1000

VLAN 3

The role of IP addresses

The VLAN are like streets that are man-made with heavy machinery. Imagine four separate streets that have just been leveled and paved with asphalt. The only problem with these new streets is that they haven’t been named. They will be given names as we place houses on those streets, and each house will have the common street name, as well as a house number. In our networks, each VLAN is simply an un-named (from an IP perspective), separate Level 2 broadcast domain, until we add the first IP device(s) or hosts to that VLAN.

As an example, let’s suppose we connect two PCs to ports 1 and 2 of the switch so that each host is associated with VLAN 1 (due to the configured switch ports the PCs are connected to). The PCs, even though they are in the same broadcast domain (VLAN), must also be configured to be on the same logical IP network, which is configured on each PC. If both PCs were configured to be on the 23.1.2.0/24 network, with a full IP address of 23.1.2.10/24 and 23.1.2.11/24 respectively, they would then be able to communicate with each other using IP. We could add a router that has an interface connected to a switch port that is in the same VLAN, and give the router an IP address of 23.1.2.1/24 and then tell the PC’s to use the router as a default gateway if they ever wanted to communicate with devices on a different network than the local 23.1.2.0/24. The router, to be effective, would need three more interfaces, each connected to the other three VLANs, (for example, switch ports 251, 501 and 751), and would need compatible IP addresses for those other three networks that agreed with the other devices in each of those VLANs. There is usually a correlation of one IP network or sub network with one VLAN.

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020