Virtual LAN

A logical network segment configured on a managed network switch.

VLAN membership is configured by assigning a switch port to a VLAN. Switches can have multiple VLANs configured, but switch ports can only be a member of one VLAN at a time. VLANs can be configured across switches, meaning that two switches can have ports that are part of the same VLAN.

Trunk Ports

Trunk ports are used to connect two switches together. They're usually done using ports that support Gigabit Ethernet speeds. Trunk ports are members of all the VLANs defined on the switch, and they carry traffic between the interconnected switches. When traffic is being sent over a trunk port, frames are tagged by the sending switch with the VLAN ID so the destination sitch knows where the frame originated from. This is done using The Trunking Protocol, which is responsible for describing the format that switches use for frame tagging.

Broadcast Domains

Using VLANs, switches can create multiple IP broadcast comains. Each VLAN is in it's own self-contained domain, and broadcasted traffic is only sent to members of the VLAN. In an enterprise setting, this often means that workstations in one VLAN can't communicate with workstations in aother. To enable inter-VLAN communications, employment of a router (or a layer 3 switch 😉) is required.