Configuring allowed VLANs

By default, all VLANs are allowed across a trunk link on a Cisco switch. We can verify that using the show interfaces trunk command: SW1#show interfaces trunk Port Mode Encapsulation Status Native vlan Fa0/1 on 802.1q trunking 1 Port Vlans Read More …

Configuring voice VLANs

Most corporate networks today use IP telephony. This means that the phones are connect to the same network and use the same cabling as other network devices, such as workstations or routers. Since offices usually have only a single UTP Read More …

Inter-Switch Link (ISL)

Another VLAN tagging protocol is Inter-Switch Link (ISL). This protocol is Cisco proprietary, which means that, unlike 802.1Q, it can be used only between Cisco switches. It is considered to be deprecated, and newer Cisco switches don’t even support it. Read More …

IEEE 802.1Q

IEEE 802.1Q is one of the VLAN tagging protocols supported by Cisco switches. This standard was created by the Institute of Electrical and Electronics Engineers (IEEE), so it an open standard and can be used on non-Cisco switches. To identify Read More …

Frame tagging

To identify the VLAN a packet is belonging to, switches use tagging to assign a numerical value to each frame in a network with multiple VLANs. This is done to ensure that switches know out which ports to forward frames. Read More …

What is a VLAN?

VLANs (Virtual LANs) are logical grouping of devices in the same broadcast domain. VLANs are usually configured on switches by placing some interfaces into one broadcast domain and some interfaces into another. Each VLAN acts as a subgroup of the Read More …