Which are valid modes for a switch port used as a VLAN trunk? (Choose three.)
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A. B. C. D. E. F.BCD
A VLAN trunk port is used to carry traffic for multiple VLANs. When a switch port is configured as a VLAN trunk, it can carry traffic for all VLANs that are allowed on the trunk.
There are two protocols that switches use to negotiate the trunking process: Cisco's proprietary Dynamic Trunking Protocol (DTP) and the open standard IEEE 802.1q.
The modes that a switch port can be configured for VLAN trunking depends on the negotiation protocol being used.
Here are the valid modes for a switch port used as a VLAN trunk based on the negotiation protocol:
"trunk" mode - This mode is used when 802.1q is enabled on the switch port. It forces the port to be a trunk port, and it will not send DTP messages. This mode allows traffic from all VLANs to traverse the trunk link.
"dynamic auto" mode - This mode is used when DTP is enabled on the switch port, and the switch port is set to negotiate with the other end of the link. In this mode, the port will become a trunk port if the other end of the link is set to "dynamic desirable" or "trunk" mode.
"dynamic desirable" mode - This mode is used when DTP is enabled on the switch port, and the switch port is set to actively negotiate with the other end of the link. In this mode, the port will become a trunk port if the other end of the link is set to "dynamic auto", "dynamic desirable", or "trunk" mode.
Therefore, the correct answers to the question "Which are valid modes for a switch port used as a VLAN trunk?" are:
A. transparent - this is not a valid mode for a switch port used as a VLAN trunk. B. auto - this is a valid mode when using DTP, but it's not one of the three valid modes listed in the question. C. on - this is not a valid mode for a switch port used as a VLAN trunk. D. desirable - this is a valid mode when using DTP and is one of the three valid modes listed in the question. E. blocking - this is not a valid mode for a switch port used as a VLAN trunk. F. forwarding - this is not a valid mode for a switch port used as a VLAN trunk.
Therefore, the three valid modes for a switch port used as a VLAN trunk are "trunk", "dynamic auto", and "dynamic desirable".