Monday, July 23, 2012

Tutorial of VLAN on Why to Use, What is and How to Configure VLAN?


Why to Use VLAN?
As most of us may know that traditional network designs use routers to create broadcast domains and limit broadcasts between multiple subnets. This prevents broadcast floods in larger networks from consuming resources, or causing unintentional denials of service unnecessarily. Unfortunately, the traditional network design methodology has some flaws in designA switch can have anywhere from 12 ports to 80 or more, and by default all hosts connected to that switch are going to be in the same broadcast domain.
For some network services and protocols, a broadcast received by a host results in that receiving host transmitting a broadcast of its own. Then when all the hosts receive that broadcast, they all end up transmitting even more broadcasts. Pretty soon, all these broadcasts have snowballed into a broadcast storm, which can take up most of a network's bandwidth and make normal network operations almost impossible. Thus, applying VLAN is necessary with the following benefits: 1. VLAN can reduce administration costs associated with moves, adds, and changes; 2. VLAN can control broadcast activity and provide better network security; 3. VLAN have the function of leveraging existing investments with flexible and scalable segmentation

Generally speaking, a VLAN is a logical local area network (or LAN) that extends beyond a single traditional LAN to a group of LAN segments, given specific configurations. Because a VLAN is a logical entity, its creation and configuration is done completely in software.
Therefore, identifiers and configurations for a VLAN must be properly prepared for it to function as expected. Frame coloring is the process used to ensure that VLAN members or groups are properly identified and handled. With frame coloring, packets are given the proper VLAN ID at their origin so that they may be properly processed as they pass through the network. The VLAN ID is then used to enable switching and routing engines to make the appropriate decisions as defined in the VLAN configuration.
VLAN Configuration

How to Configure VLAN?
1. Log in to the Visual Switch Manager for the switch which you would like to enable VTP.
2. Select “VTP Management” from the “VLAN” tab of the menu bar.
3. Select the “VTP Configuration” tab. enter a “Domain Name” and “VTP Password,” and click “OK” to confirm settings. (The domain name and VTP password must be the same for all switches in the same VTP domain.)
4. Select “VTP Management” from the “VLAN” tab. Select the “VLAN Configuration” tab, and click the “New” button that appears at the bottom of the window.
5. Enter a new VLAN ID and descriptive name; click “OK” to confirm settings and exit the new VLAN dialog box. Click the “OK” button a second time to exit the VTP Management page.
6. Select “VLAN Membership” from the “VLAN” tab. Click on the Assign VLANs tab, and select a port or interface. Choose “ISL Trunk” or "802.1Q trunk" from the “Mode” drop-down field to configure the interface as a trunk port to accept traffic for more than one VLAN. (This will also allow this server to receive VTP messages from other servers on the network.)
7. Using "ISL Trunk" or "802.1Q Trunk" will vary based on the model of the switch. Newer switch models typically use "802.1Q Trunk."
8. Enter the VLAN IDs separated by commas in the “Assigned VLANs” column. Click “Apply” to confirm settings.
9. Click the “Trunk Configuration” tab, and then the “Modify” button to change the default settings for the interface or port. (You can limit the VLANs that send traffic over a trunk line and modify the list of VLANs that are pruning-eligible. VTP pruning stops unnecessary traffic for VLANs on trunk ports that are configured as pruning-eligible.)
10. Click "OK" to confirm settings and exit the VLAN Management window. This will return you to the Visual Switch Manager home page.

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