Review ActivitiesChapter Summary VLANs provide the capability to create multiple broadcast domains on a single physical switch. The creation of smaller broadcast domains using VLANs has many advantages, including the reduction of the number of hosts that receive broadcasts, multicasts, and unknown unicast frames; increasing security by providing traffic isolation; and the capability to offer flexible network design. VLAN trunking is used to transport the traffic in multiple VLANs between switches using a single physical connection. IEEE 802.1Q trunking inserts an extra 4-byte tag to the Ethernet header to mark the VLAN to which it belongs. Routing between VLANs requires a Layer 3 device, such as a router configured with an IEEE 802.1Q trunking interface (ROAS), or a Layer 3 switch. There are four different switch port trunking administrative modes: access, trunk (static), dynamic desirable, and dynamic auto. If a switch port is configured with the access administrative mode it will always remain in access operational mode. If a switch port is configured with the trunk administrative mode it will always remain in trunk operational mode. If a switch port is configured with dynamic desirable administrative mode it will attempt to form a trunk with a remote device configured with the trunk, dynamic desirable, or dynamic auto administrative modes. If a switch port is configured with dynamic auto administrative mode it will form a trunk with a remote device configured with the dynamic desirable and trunk administrative modes. When connected to an IP telephony solution a switch port can be configured with a data VLAN and a voice VLAN. The voice VLAN traffic is typically tagged using IEEE 802.1Q. When configuring a switch port for IP telephony, configure it as if it were a normal access port, and then add the additional voice configuration commands to support a voice VLAN.