VLAN Trunking Questions 4
Here you will find answers to VLAN Trunking Questions – Part 4
Question 1
When a VLAN port configured as a trunk receives an untagged frame, what will happen?
A. The frame will be dropped
B. The frame will cause an error message to be sent
C. The frame will be processed as a native VLAN frame
D. The frame will first be tagged, then processed as a native VLAN frame
Answer: C
Question 2
Study the diagram below carefully, which three statements are true? (Choose three)
A – DTP packets are sent from Switch SB.
B – DTP is not running on Switch SA.
C – A trunk link will be formed.
D – The native VLAN for Switch SB is VLAN 1.
Answer: A C D
Explanation:
Dynamic Trunking Protocol (DTP) is the Cisco-proprietary that actively attempts to negotiate a trunk link between two switches. If an interface is set to switchport mode dynamic desirable, it will actively attempt to convert the link into trunking mode. If the peer port is configured as switchport mode trunk, dynamic desirable, or dynamic auto mode, trunking is negotiated successfully -> C is correct.
SB is in “dynamic desirable” mode so it will send DTP packets to SA to negotiate a trunk link -> A is correct.
On an 802.1Q trunk, DTP packets are sent on the native VLAN. By default, it is VLAN 1 (notice that SA’s native VLAN is 5) -> D is correct.
(Note: an 802.1Q trunk’s native VLAN is the only VLAN that has untagged frames)
Below is the switchport modes for easy reference:
| Mode | Function |
| Dynamic Auto | Creates the trunk based on the DTP request from the neighboring switch. |
| Dynamic Desirable | Communicates to the neighboring switch via DTP that the interface would like to become a trunk if the neighboring switch interface is able to become a trunk. |
| Trunk | Automatically enables trunking regardless of the state of the neighboring switch and regardless of any DTP requests sent from the neighboring switch. |
| Access | Trunking is not allowed on this port regardless of the state of the neighboring switch interface and regardless of any DTP requests sent from the neighboring switch. |
| Nonegotiate | Prevents the interface from generating DTP frames. This command can be used only when the interface switchport mode is access or trunk. You must manually configure the neighboring interface as a trunk interface to establish a trunk link. |
