When you use a hub, all the ports on it are part of the same network. If you have multiple hubs daisy chained together, you may have a rather large network or broadcast domain. Switches won’t segment your broadcast domains by default because all ports are initially configured to VLAN1. You can use virtual local area networks (VLANs) to break up your large broadcast domains into much smaller ones. You can set up ports connecting switches called trunks to transport traffic from all the VLANs assigned to ports in your network. This allows you to assign individual ports on one switch to a VLAN and assign ports on another switch to use the same VLAN. VLANs can be created by location, function, department even by the application or protocol used regardless of where the resources or users are located.
Critical Information
You can assign VLANs manually (static VLAN) or let the switch assign the VLAN (dynamic VLAN). With a static VLAN, you assign the VLAN number to a port, and then the switch maintains that VLAN assignment until it is manually changed. This type of VLAN configuration is easy to set up and monitor. This also controls the movement of users within the network. Using network management software to configure the ports can be helpful but is not mandatory.
Note: VLAN Membership Policy Server (VMPS) is implemented in order to maintain a database of MAC addresses associated with an identified VLAN for use with dynamic VLAN assignments.
Necessary Procedures
1. Configure the VLANs.
2. Assign switch ports to VLANs.
3. Identify the VLANs.
4. Verify the configuration.
Configuring VLANs
Configuring VLANs is the easy part of the job. Actually, it understands which users you want in each VLAN that is time consuming. Once you have decided the number of VLANs you want to create and the users who will be members of each, you can create your VLAN.
Assigning Switch Ports to VLANs
You can configure each port to be in a VLAN by using the vlan membership command. You can configure VLANs only one port at a time. There is no command to assign more than one port at a time to a VLAN with the 1900 switch.
Identifying VLANs
There are two different types of links in a switched environment:
Access Link
A link that is part of only one VLAN and is referred to as the native VLAN of the port. Any device attached to an access link is unaware of a VLAN membership. This device just assumes it is part of a broadcast domain, with no understanding of the physical network. Switches remove any VLAN information. Access link devices cannot communicate with devices outside their VLAN. The only way to make communication is through router.
Trunk Link
A link that can carry multiple VLANs. Originally named after the trunks of the telephone system, which carry multiple telephone conversations, trunk links are used to connect switches to other switches, to routers, or even to servers. Trunked links are supported on Fast Ethernet or Gigabit Ethernet only. To identify the VLAN that a frame belongs to with Ethernet technology, Cisco switches support two different identification techniques: Inter-Switch Link (ISL) and 802.1Q. Trunk links are used to transport VLANs between devices. The number if VLANs can be from one to few depending on the settings.
Verifying the Configuration
An internetwork switch needs a way to keep track of users and frames as they travel the switch block. A switch block is a group of switches sharing the same VLAN information. As the frame traverses through each switch from the port of entry to the port of exit, the highway of wires, processors, and ASICs between the ports is referred to as the switch fabric.
VLAN frame identification, or frame tagging, is a relatively new approach that was specifically developed for switched communications. In this approach, a unique user-defined identifier is placed in the header of each frame as it’s forwarded throughout the switch fabric. (This identifier is sometimes referred to as a VLAN ID or VLAN color.) The identifier is understood and examined by each switch prior to any broadcasts or transmissions. When the frame exits the switch fabric, the switch removes the identifier before the frame is transmitted to the target end-station.
All this means is that the switch tags a frame with a VLAN identifier that is used only within the switch fabric itself. Before that frame leaves the switch, it removes the VLAN ID, because nothing outside the switch would be able to understand that ID. There is one exception: When you run ISL, the VLAN ID is preserved as it passes over the ISL link.
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- Network Congestion Problem in Ethernet Networks
- Spanning Tree Protocol Exams Questions
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