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.

switchport trunk allowed vlan add 30 Ping. Success. All three switches now carried all three VLANs. One last test. PC4 (Accounting, S2) → PC6 (Accounting, S3). Works. PC2 (Engineering, S1) → PC5 (Engineering, S2). Works.

“I need a trunk,” Alex whispered.

“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.

He walked off. The switches hummed.

“This is too friendly,” Alex muttered. “I don’t want Accounting to talk to Engineering. They have nothing in common except coffee.”

enable configure terminal vlan 10 name Accounting vlan 20 name Engineering vlan 30 name Staff end It felt like naming three new pets. But switches don’t wag tails. They just add lines to a file called vlan.dat .

But Professor Lasky had hidden a trap. The instructions, step 7: “Verify that PC3 cannot ping PC5.” Alex did. It couldn’t. Good.

The Switch that Forgot How to Listen

Alex saved the configuration: write memory .

A quick check. PC3 was also in Accounting. It should work.

“Check,” Alex whispered, moving to S2 and S3. Repeat. Repeat. VLAN 10, 20, 30. Accounting. Engineering. Staff.

The scenario: VLAN Configuration . Objective: Slice this single broadcast domain into three separate pieces of virtual reality.