Examples of configuration changes that one can do from a managed switch include: enable features such as Spanning Tree Protocol, set port bandwidth, create or modify Virtual LANs ( VLANs ), etc.

** Cisco home page for Virtual LANs / VLAN Trunking Protocol ( VLANs / VTP ) ( discusses DSL, DTP, GVRP, ISL, VTP, 802. 1Q )

IEEE 802. 1Q is the networking standard that supports Virtual LANs ( VLANs ) on an Ethernet network.

Larger LANs are characterized by their use of redundant links with switches using the spanning tree protocol to prevent loops, their ability to manage differing traffic types via quality of service ( QoS ), and to segregate traffic with VLANs.

Developed by IEEE, VLANs allow multiple tagged LANs to share common trunking.

At these lower speeds, ATM provides a useful ability to carry multiple logical circuits on a single physical or virtual medium, although other techniques exist, such as Multi-link PPP and Ethernet VLANs, which are optional in VDSL implementations.

VLANs are layer 2 constructs, compared with IP subnets, which are layer 3 constructs.

In cloud computing VLANs and IP addresses on them are resources which end users can manage.

While VLANs are commonly used in modern Ethernet networks, using them for the original purpose would be rather unusual.

These charts must be manually updated by the technical staff whenever port membership changes are made to the VLANs.

Remote configuration of VLANs presents several opportunities for a technician to cut off communications accidentally and lose connectivity to the devices they are attempting to configure.

Technologies able to implement VLANs are:

In the context of VLANs, the term " trunk " denotes a network link carrying multiple VLANs, which are identified by labels ( or " tags ") inserted into their packets.

These inconsistencies can result in security violations, because VLANs can cross connect when duplicate names are used.

They also could become internally disconnected when they are mapped from one LAN type to another, for example, Ethernet to ATM LANE ELANs or FDDI 802. 10 VLANs.

Static VLANs are also referred to as port-based VLANs.

Dynamic VLANs are created through the use of software.

Some MLS's are also able to route between VLANs and / or ports like a common router.

After the frames are transmitted on their respective VLANs through the corporate network, the VLAN tag is stripped before the frame leaves the VLAN-aware corporate network, and is sent to its destination, which is another computer belonging to the same department.

The two most common forms of network virtualization are protocol-based virtual networks ( such as VLANs, VPNs, and VPLSs ) and virtual networks that are based on virtual devices ( such as the networks connecting virtual machines inside a hypervisor ).

IEEE 802. 1aq ( Shortest Path Bridging SPB ) allows all paths to be active with multiple equal cost paths, provides much larger layer 2 topologies ( up to 16 million compared to the 4096 VLANs limit ), faster convergence times, and improves the use of the mesh topologies through increase bandwidth and redundancy between all devices by allowing traffic to load share across all paths of a mesh network.

Simpler devices only support partitioning on a port level ( if at all ), so sharing VLANs across devices requires running dedicated cabling for each VLAN.

With a VLAN Management Policy Server ( VMPS ), an administrator can assign switch ports to VLANs dynamically based on information such as the source MAC address of the device connected to the port or the username used to log onto that device.

The Cisco Inter-Switch Link ( ISL ) protocol for supporting VLANs on Ethernet and similar LAN technologies was based on IEEE 802. 10 ; in this application 802. 10 has largely been replaced by IEEE 802. 1Q.

Without VLANs, a switch considers all interfaces on the switch to be in the same broadcast domain.

VLANs can also help create multiple layer 3 networks on the same layer 2 switch.

In an environment employing VLANs, a one-to-one relationship often exists between VLANs and IP subnets, although it is possible to have multiple subnets on one VLAN.

Placing cloud-based virtual machines on VLANs may be preferable to directly on the Internet to avoid security issues.

A basic switch not configured for VLANs has VLAN functionality disabled or permanently enabled with a default VLAN that contains all ports on the device as members.

Under IEEE 802. 1Q, the maximum number of VLANs on a given Ethernet network is 4, 096.

VTP uses Layer 2 trunk frames to manage the addition, deletion, and renaming of VLANs on a network-wide basis from a centralized switch in the VTP server mode.

Before creating VLANs on the switch that will propagate via VTP, a VTP domain must first be set up.

In a switch that supports protocol-based VLANs, traffic is handled on the basis of its protocol.

To allow for multiple VLANs on one link, frames from individual VLANs must be identified.

VLANs have to be on a Sub-Interface, It is best practice to match the Sub-Interface # and the VLAN #

VLANs have to be on a Sub-Interface, It is best practice to match the Sub-Interface # and the VLAN #

* Managing VLANs on mission-critical shared Ethernet adapters-IBM

VLANs can logically group networks so that the network location of users is no longer so tightly coupled to their physical location.

Separating VLANs divides broadcast domains as well, but provides no means to network these without layer 3 functionality.

One helpful analogy is that by creating multiple VLANs, the number of broadcast domains increases, but the size of each broadcast domain size decreases.

For example in fibre-to-the-home switches typically offer several Ethernet ports connected to different VLANs.

Different Internet service providers may use the different VLANs.

For a price much lower than a fully managed switch they provide a web interface ( and usually no CLI access ) and allow configuration of basic settings, such as VLANs, port-bandwidth and duplex.

Creating VLANs can serve security and performance goals by reducing the size of the broadcast domain.

The ATM interface became the most popular, as it supported the increasing bandwidth demands and also supported VLANs.

More sophisticated devices can mark packets through tagging, so that a single interconnect ( trunk ) may be used to transport data for various VLANs.

However, unlike physically separate networks, VLANs share bandwidth, so VLAN trunks may require aggregated links and / or quality of service priorization.

Network architects set up VLANs to provide the segmentation services traditionally provided by routers in LAN configurations.

VLANs address issues such as scalability, security, and network management.

By definition, switches may not bridge IP traffic between VLANs as it would violate the integrity of the VLAN broadcast domain.

By using VLANs you can easily split the network up so some hosts won't use that DHCP server and will obtain link-local addresses, or obtain an address from a different DHCP server.

VLANs and IP subnets provide independent Layer 2 and Layer 3 constructs that map to one another and this correspondence is useful during the network design process.