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.
But Professor Lasky had hidden a trap. The instructions, step 7: “Verify that PC3 cannot ping PC5.” Alex did. It couldn’t. Good. 3.3.12 packet tracer - vlan configuration.pka
“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. ” Alex said