Valid Modes for a VLAN Trunk

Explanation

Switches use VLAN trunking to carry traffic between different VLANs. When a switch port is configured as a trunk port, it is able to carry traffic for multiple VLANs. There are several modes in which a switch port can be configured as a VLAN trunk. The valid modes for a switch port used as a VLAN trunk are:

A. Transparent B. Auto C. On D. Desirable

Here's a detailed explanation of each mode:

A. Transparent Mode: In this mode, the switch port does not add or remove any VLAN tags. It simply forwards the traffic from one VLAN to another. This mode is typically used when the switch is connected to another switch, and the traffic needs to traverse multiple switches.

B. Auto Mode: In this mode, the switch port negotiates with the remote device to determine whether to use trunking. If the remote device is also configured for trunking, the port will become a trunk port. If the remote device is not configured for trunking, the port will become an access port.

C. On Mode: In this mode, the switch port is configured to always be a trunk port, regardless of whether the remote device is configured for trunking or not. If the remote device is also configured for trunking, the two devices will form a trunk link.

D. Desirable Mode: In this mode, the switch port actively tries to form a trunk link with the remote device. If the remote device is also configured for trunking, the two devices will form a trunk link. If the remote device is not configured for trunking, the port will become an access port.

E. Blocking Mode: This mode is not a valid mode for a switch port used as a VLAN trunk. Blocking mode is used in Spanning Tree Protocol (STP) to prevent loops in the network.

F. Forwarding Mode: This mode is not a valid mode for a switch port used as a VLAN trunk. Forwarding mode is used when a port is configured as an access port and is forwarding traffic for a single VLAN.

In summary, the valid modes for a switch port used as a VLAN trunk are Transparent, Auto, On, and Desirable.