The problem slapped Alex in the face: .
no vlan 20 Suddenly, PC2 (Engineering, S1) went dark. Not just isolated—gone. The port was still there, but the VLAN didn’t exist. The switch didn’t drop the packets; it just shrugged.
Professor Lasky walked by, glanced at the screen, and said only: “Three VLANs today. Three hundred in the real world. The logic doesn’t change.”
The default port between S1 and S2 (Gig0/1) was just a regular port. It saw a ping from PC1 (VLAN 10, S1) and dropped it before it reached S2. 3.3.12 packet tracer - vlan configuration.pka
Then step 8: “Delete VLAN 20 from S1.”
Alex saved the configuration: write memory .
On S1, G0/1:
interface gigabitEthernet 0/1 switchport mode trunk switchport trunk allowed vlan 10,20,30 Same on S2’s G0/1 and S3’s G0/2.
The scenario: VLAN Configuration . Objective: Slice this single broadcast domain into three separate pieces of virtual reality.
The Switch that Forgot How to Listen
He walked off. The switches hummed.
“Walls built,” Alex said, leaning back. But Professor Lasky’s note glowed again: “VLANs are islands. How do islands talk?” Alex realized: S1 knows VLAN 10 exists on its own ports. S2 knows VLAN 10 exists on its own ports. But between switches? Silence.
interface fastEthernet 0/1 switchport mode access switchport access vlan 10 exit interface fastEthernet 0/2 switchport mode access switchport access vlan 20 F0/3 → VLAN 30. F0/4 → VLAN 10. And so on. The problem slapped Alex in the face: