A network technician provisions an IEEE 802.1Q trunk link on switch `SW-Floor2` interface `GigabitEthernet0/48` to connect to `SW-Core1`. Workstations on VLAN 10 (Finance) immediately lose connectivity to remote resources on the same VLAN, while devices on VLAN 20 (IT) continue communicating normally. The running configuration for interface `GigabitEthernet0/48` displays the following output:
text
interface GigabitEthernet0/48
switchport mode trunk
switchport trunk native vlan 1
switchport trunk allowed vlan 20,30
Which of the following statements accurately identify the cause of the connectivity loss and specify the correct corrective action? (Select TWO.)
- VLAN 10 frames are dropped at the trunk port because VLAN 10 is omitted from the allowed VLAN pruning list on interface GigabitEthernet0/48.Answer
- BVLAN 10 traffic is automatically forwarded untagged over the trunk link because unlisted VLANs default to native VLAN handling.
- The administrator must execute `switchport trunk allowed vlan add 10` on interface GigabitEthernet0/48 to permit VLAN 10 traffic across the link.Answer
- DA Layer 3 router must be installed between SW-Floor2 and SW-Core1 to route VLAN 10 frames across the switchport trunk interface.
Answer
The outage is caused by VLAN 10 being excluded from the trunk port's explicit allowed list. The issue is resolved by running `switchport trunk allowed vlan add 10` on the trunk interface.
On an 802.1Q trunk, configuring `switchport trunk allowed vlan` creates an explicit permit list. Because VLAN 10 was not listed, its frames were filtered at the trunk boundary. Executing `switchport trunk allowed vlan add 10` appends VLAN 10 to the allowed list, enabling frame transmission across switches for that broadcast domain.
Step-by-Step Solution
Key Concept
802.1Q Trunk Allowed VLAN Filtering