Virtual LAN(IEEE 802.1Q):

✔  VLANs allow network administrators to group hosts together even if the hosts are not on the same network switch.

✔  Routers in VLAN topologies filter broadcast traffic, enhance network security, perform address summarization, and mitigate network congestion. Switches may not bridge network traffic between VLANs, as doing so would violate the integrity of the VLAN broadcast domain.

✔  VLANs can help reduce network traffic by forming multiple broadcast domains, to break up a large network into smaller independent segments with fewer broadcasts being sent to every device on the overall network.

✔  VLANs can also help create multiple layer 3 networks on a single physical infrastructure. For example, if a Dynamic Host Configuration Protocol (DHCP) server is plugged into a switch it will serve any host on that switch that is configured for DHCP. By using VLANs, the network can be easily split up so some hosts will not use that DHCP server and will obtain link-local addresses, or obtain an address from a different DHCP server.

✔  VLANs are data link layer (OSI layer 2) constructs, analogous to IP subnets, which are network layer (OSI layer 3) constructs. 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

✔  VLANs can be used to partition a local network into several distinctive segments, for example:

✔  Production

✔  Voice over IP

✔  Network management

✔  Storage area network (SAN)

✔  Guest network

✔  Demilitarized zone (DMZ)

✔  Client separation (ISP, in a large facility, or in a datacenter)

✔  In cloud computing VLANs, IP addresses, and MAC addresses on them are resources which end users can manage. Placing cloud-based virtual machines on VLANs may be preferable to placing them directly on the Internet to avoid security issues.

✔  VLANs operate at Layer 2 (the data link layer) of the OSI model. Administrators often configure a VLAN to map directly to an IP network, or subnet, which gives the appearance of involving Layer 3 (the network layer)

✔  a network of computers that behave as if they are connected to the same wire even though they may actually be physically located on different segments of a LAN. VLANs are configured through software rather than hardware, which makes them extremely flexible. One of the biggest advantages of VLANs is that when a computer is physically moved to another location, it can stay on the same VLAN without any hardware reconfiguration.

Establishing VLAN memberships:

The two common approaches to assigning VLAN membership are as follows:

• Static VLANs

• Dynamic VLANs

✔  Static VLANs are also referred to as port-based VLANs. Static VLAN assignments are created by assigning ports to a VLAN. As a device enters the network, the device automatically assumes the VLAN of the port. If the user changes ports and needs access to the same VLAN, the network administrator must manually make a port-to-VLAN assignment for the new connection.

✔  Dynamic VLANs are created using software. 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. As a device enters the network, the switch queries a database for the VLAN membership of the port that device is connected to.