Which three are valid modes for a switch port used as a VLAN trunk? (choose three)
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A. B. C. D. E. F.ABC
VLAN trunking is a technique used to carry traffic for multiple VLANs over a single physical link between switches. This is accomplished by adding VLAN information to the Ethernet frame as it is transmitted between switches.
In Cisco switches, there are three valid modes for a switch port used as a VLAN trunk:
Trunk: This is the most commonly used mode for VLAN trunking. In this mode, the switch port is explicitly configured to operate as a VLAN trunk. The trunk port can carry traffic for multiple VLANs, and VLAN information is added to the Ethernet frames as they are transmitted between switches.
Dynamic auto: In this mode, the switch port is configured to negotiate with the remote switch to determine whether or not to operate as a trunk. If the remote switch is configured as a trunk or dynamic desirable, then the local switch will also operate as a trunk. If the remote switch is not configured as a trunk or dynamic desirable, then the local switch will operate as an access port.
Dynamic desirable: In this mode, the switch port is configured to actively attempt to negotiate with the remote switch to determine whether or not to operate as a trunk. If the remote switch is configured as a trunk, dynamic auto, or dynamic desirable, then the local switch will also operate as a trunk. If the remote switch is not configured as a trunk, dynamic auto, or dynamic desirable, then the local switch will operate as an access port.
In addition to these three modes, there are also two invalid modes listed in the question:
Blocking: This is not a valid mode for a VLAN trunk. Blocking is a state that a switch port can be in when it is part of a spanning tree protocol (STP) topology. A blocking port does not forward traffic but still listens to incoming traffic to maintain the STP topology.
Transparent: This is not a valid mode for a VLAN trunk. Transparent mode is a feature of Cisco switches that allows them to pass VLAN information between switches without actually participating in the VLAN. In other words, a transparent switch does not add or remove VLAN information from Ethernet frames as they pass through the switch.
Finally, the mode forwarding is not a valid mode for configuring a VLAN trunk. It is a state of a switch port when it is operational and forwarding traffic.