A structured lesson workspace with readable content, hands-on examples, and a clean path to completion.
Exam drawing: router with 2 cables, each to a switch, 4 PCs left, 3 PCs right. Question: how many collision? How many broadcast? Half the class answers 2 and 2. Answer is 9 and 2. This lesson makes sure you're the other half.
Collision domain = who can collide with you. Today: one switch port = one collision domain, collisions don't happen (full-duplex). Old hubs: all ports = one domain. Broadcast domain = who gets your broadcast (ARP, DHCP). Switches forward broadcasts, routers stop them. VLANs (Module 6) split one switch into many broadcast domains.
| Box | Collisions | Broadcasts |
|---|---|---|
| Hub | All ports together = 1 | Passes through, no change |
| Switch, no VLANs | Each port alone = N domains | All ports together = 1 |
| Switch + VLANs 10,20 | Still each port alone | One per VLAN = 2 (detail Module 6) |
| Router | Each port alone | Each port alone = boundary |
Memory hook: switches divide collisions, routers divide broadcasts. Hubs divide nothing.
Router Gi0/0 -> Switch1 (4 PCs). Router Gi0/1 -> Switch2 (3 PCs). No VLANs. Count: each switch access port = 1 collision (4+3=7), each router-to-switch link = 1 (2). Total collisions = 9. Broadcasts = everything that reaches without crossing router: left side = 1, right side = 1. Total = 2.
Trap: two switches trunked with no VLANs = 1 broadcast, not 2. Trunk forwards broadcasts. Only router ports and VLANs create new broadcast domains. Trunk = 1 wire = 1 collision domain even with many VLAN tags.
Don't count switches as broadcast boundaries. 'Two switches = two broadcasts' is the #1 wrong answer. Switches forward, routers and VLANs stop.
You can now count any drawing in 30 seconds. Next: read any switch port in 5 seconds.
Finish the lesson once you have worked through the material. This awards ★ 25 XP.