Cisco CCNA VLANs and 802.1Q Trunking 2 — Questions and Answers
Question 1: What is the valid VLAN ID range for extended VLANs on a Cisco switch?
- 1006–4094 (Correct answer)
- 1025–4094
- 1006–4095
- 1024–4096
Correct answer: 1006–4094
Extended VLANs use IDs 1006–4094, while normal-range VLANs span 1–1005.
Question 2: Which command verifies the trunking status and allowed VLANs on interface Gi0/1?
- show interfaces Gi0/1 trunk (Correct answer)
- show vlan brief
- show interfaces Gi0/1 switchport
- show trunk Gi0/1
Correct answer: show interfaces Gi0/1 trunk
`show interfaces Gi0/1 trunk` displays trunking mode, encapsulation, and the allowed VLAN list.
Question 3: A port is configured with `switchport mode dynamic desirable`. What will happen if the neighboring port is set to `switchport mode access`?
- The port becomes an access port (Correct answer)
- The port becomes a trunk
- The link goes down
- The port stays in dynamic desirable mode indefinitely
Correct answer: The port becomes an access port
Dynamic desirable will form a trunk only if the neighbor also negotiates trunking; an access-mode neighbor causes it to become an access port.
Question 4: Which 802.1Q field identifies the VLAN to which a frame belongs?
- VLAN ID (VID) (Correct answer)
- Priority Code Point (PCP)
- Drop Eligible Indicator (DEI)
- EtherType (0x8100)
Correct answer: VLAN ID (VID)
The 12-bit VLAN Identifier (VID) field in the 802.1Q tag specifies the VLAN.
Question 5: What happens to traffic from a VLAN that has been pruned from a trunk link?
- It is not forwarded across that trunk (Correct answer)
- It is forwarded as untagged traffic
- It is dropped and logged
- It is redirected to the native VLAN
Correct answer: It is not forwarded across that trunk
VTP pruning or manual pruning removes a VLAN from a trunk so its traffic is not flooded unnecessarily across that link.
Question 6: A switch receives a tagged frame with VLAN 10 on a port configured as an access port for VLAN 20. What does the switch do?
- Drops the frame (Correct answer)
- Forwards the frame to VLAN 10
- Strips the tag and forwards on VLAN 20
- Adds a second tag and floods the frame
Correct answer: Drops the frame
Cisco switches drop tagged frames received on access ports because access ports expect untagged traffic.
Question 7: What is the purpose of the `switchport trunk native vlan 99` command?
- Sets VLAN 99 as the untagged VLAN on the trunk (Correct answer)
- Allows only VLAN 99 on the trunk
- Makes VLAN 99 the management VLAN
- Removes all other VLANs from the trunk
Correct answer: Sets VLAN 99 as the untagged VLAN on the trunk
This command changes the native VLAN on the trunk to VLAN 99, so untagged frames are associated with VLAN 99.