Network Devices: From Hubs to Switches and Routers

Network Devices: From Hubs to Switches and Routers

What you'll learn

• Tell repeaters, hubs, bridges, switches and routers apart by the one decision each makes
• Explain collision domains and broadcast domains — and which device breaks which
• Recognize your home "router" as four or five devices collapsed into one box
• Read a NIC's link, activity and speed lights as diagnostic evidence
• Build hub and switch topologies in Packet Tracer and watch flooding disappear

The evolution arc: repeater → hub → bridge → switch

This lesson builds on Chapters 1, 2 and 4 of Dr. Tahseen Al-Doori's Network Essentials. Chapter 4 tells the device story as an evolution, and it is worth preserving as one, because each generation exists to fix the failure of the one before.

The repeater solved attenuation. Early networks hit the wall you learned two lessons ago: signals fade with distance. The repeater is a two-port box that takes a weakening signal in one side and sends a fresh copy out the other — and crucially it regenerates rather than merely amplifies: it rebuilds the clean square voltage pattern the sender originally produced, instead of boosting a degraded blur (an amplifier would boost the noise too). One repeater doubles your reach; chain several and the network spans a campus. Think of a long-distance courier system with relay stations: no single rider crosses the country — the message is handed to a fresh rider at each post.

The hub is a repeater that learned to multiply. Someone realized the regenerated signal could go out many ports at once, and the multiport repeater — soon just called a hub — became the center of the star topologies you met in Module 1. But notice what a hub does not do: it makes no decision at all. Every bit arriving on any port is blindly repeated to every other port. Every connected computer hears everything, relevant or not; only the addressed machine keeps the frame, while the rest discard it — after wasting the wire's time and, less charmingly, after having had every chance to eavesdrop. A hub is a layer 1 device in the fullest sense: it understands voltage, and nothing else.

The bridge brought the first intelligence. A bridge (originally two ports, like a repeater that went to school) reads each arriving frame's source MAC address and memorizes which side that machine lives on. From then on it forwards a frame across only if the destination actually lies on the other side, and keeps local chatter local. For the first time, a device learned the network instead of merely repeating it. (A history sidebar for completeness: the book also records translational bridges, which converted between frame formats like Ethernet and Token Ring, and source-route bridges for Token Ring networks — with Token Ring withdrawn, both are museum pieces (obsolete), and the transparent, learning kind of bridge is the only branch of the family with descendants.)

The switch is that descendant: a multiport learning bridge, one bridge brain per port. It memorizes which MAC address lives on which port and forwards each frame only to the port where the destination lives. The book gives this private connection a name you will use forever: a micro-segment — a temporary, full-speed circuit between exactly two ports. Modern switches add more (VLAN creation, loop avoidance, port-level security — all previewed in Chapter 4 and given their own lesson at the end of this module), but the learning-and-forwarding core is the whole trick. And it ended the hub's career completely: the book already remarked that nobody manufactures hubs anymore, and two decades later that is simply, literally true. Hubs are extinct (obsolete) — you study them because they make the switch's intelligence visible, and because "how does a switch differ from a hub?" remains an interview classic.

Collision domains and broadcast domains

Two pieces of vocabulary turn the evolution story into engineering. Both describe a kind of "blast radius," and each is broken by a different device.

A collision domain is the set of devices that share one signal path and can therefore interfere with each other by transmitting simultaneously. A classic analogy from Dr. Al-Doori's course sets it in a classroom: when students pair up for lab work, each pair tunes into its own conversation and tunes out the rest of the room. Two partners can still talk over each other — that pair is one collision domain — but they cannot collide with the pair across the room. On a hub, there are no pairs: the entire network is one big shared conversation, one collision domain, and the more machines you add, the more they step on each other. A switch shatters this: every port becomes its own collision domain — its own micro-segment — and since each port is also full duplex (separate transmit and receive paths, from lesson 1), collisions on a modern switched network are effectively extinct. Hold that thought for the Ethernet lesson, where it rewrites some history.

A broadcast domain is the set of devices that receive a broadcast frame — a frame addressed to everyone (destination MAC of all ones; you met one in your Module 2 capture). Here is the crucial asymmetry: a switch does not break broadcast domains. In the classroom, the paired conversations don't stop the instructor's announcement from reaching every ear. Likewise a switch, seeing a broadcast — or any frame whose destination MAC it has not yet learned — forwards it out every port except the one it arrived on. That unknown-destination behavior is called flooding, and it is deliberate: like a manager who, unsure who owns a task, emails the entire team, the switch prefers wasteful delivery to failed delivery. Every port of every switch you connect together remains one single broadcast domain.

So: hubs share everything; switches isolate conversations but still share broadcasts. Which raises the obvious question — what happens when the broadcast domain itself grows too large?

Routers: where one network ends

Broadcasts are useful in small doses (Module 4 shows you ARP and DHCP leaning on them), but they reach every machine, and a network where thousands of hosts broadcast is a network drowning in background noise. Physics is unsympathetic: a wire carries only so much signal. The thought experiment from Chapter 1 makes the point at maximum scale: imagine the entire Internet as one broadcast domain — billions of hosts, every announcement reaching all of them. Nothing would ever get through. The Internet works because it is cut into millions of separate broadcast domains.

The cutting tool is the router — the device that refuses to forward broadcasts, full stop. A router connects networks to each other and moves traffic between them using layer 3 logic: it reads each packet's destination IP address, extracts the network portion (Module 4 teaches you the mask arithmetic behind that), looks the network up in its routing table, and forwards the packet toward the best next hop. Chapter 1 offers the analogy that makes routing intuitive: a road map, where each town stands for a LAN and the roads between towns stand for WAN links. The router is the navigator choosing among alternative routes — by distance, by speed, by congestion — and recalculating when conditions change.

Two behaviors separate a router from everything earlier in this lesson. First, the broadcast refusal: broadcasts stop at the router's port, which is precisely why each router port defines a separate network — a separate broadcast domain. Second, no flooding: where a switch sprays an unknown destination everywhere, a router silently drops a packet whose destination network is not in its table. A switch's job is "deliver somehow"; a router's job is "deliver correctly or not at all." (In the book's era routers bristled with serial and T-1 ports for WAN circuits; those are period pieces now — a modern router's WAN side is Ethernet or fiber like everything else.)

Recap table, from Module 2's map, now with the reasoning attached:

The rest of the cast

The NIC. The network interface card is the host's own doorway to all of this — the one device every machine has. Inside, the interface transmits and receives at the same time — on 10/100 links using one pair in each direction, and on gigabit and faster across all four pairs at once, with the electronics cancelling each end's own echo — buffer memory holds frames coming and going, and a driver connects the hardware to the operating system. In 2026 the "card" is usually invisible — a chip on the motherboard, a USB dongle, or a Wi-Fi radio — but its diagnostic gift is unchanged: the lights. The link light glows when layer 1 sees a live connection (its absence sends you straight back to the previous lesson's cable checks); the activity light blinks with traffic; on many devices a speed light color-codes the negotiated rate. Free evidence, always on, first thing a professional looks at.

The home "router." The box your ISP gave you is the whole lesson in one plastic shell: a small switch (the LAN ports), a router (LAN to internet), a wireless access point, a firewall, and a DHCP server — four or five devices collapsed into one (current reality; the book's multilayer-switch concept, consumer-sized). Knowing what is inside the box is what lets you troubleshoot it as five things rather than one mystery.

Glimpses of later modules. A firewall filters traffic against rules — the modern incarnation is the NGFW (next-generation firewall), and Module 7 is devoted to it. Modems and ONTs adapt your LAN to the access medium (DSL, cable coax, fiber); their 2026 forms live in Module 6. DNS and DHCP are services, not boxes — often running on a router — and get full lessons in Module 5. And the book's heavier appliances — content switches and load balancers spreading work across server farms, bandwidth shapers rationing capacity per application — largely dissolved into software and cloud services (modern replacement); the functions thrive, the dedicated boxes mostly don't. QoS, the shaper's surviving idea, returns in Module 8.

From the textbook to 2026

The arc holds up beautifully: repeaters amplified, hubs multiplied, bridges learned, switches conquered — and the book's own observation that hubs were already unbuyable has hardened into extinction. Standalone bridges are gone too; the switch is the bridge, perfected. Routers shed their serial-port bristles and speak Ethernet on every side. The firewall grew into the NGFW (Module 7). Load balancing and shaping moved into software and cloud. And the home gateway quietly became the era's most common multilayer device. The vocabulary you drilled — collision domain, broadcast domain, flooding, micro-segment — is unchanged and daily-professional; it is the hardware that kept moving.

Watch: Hub, Switch, & Router Explained — What's the Difference?

Why this video earns its place. This short animation from PowerCert Animated Videos — one of the most widely recommended visual channels for networking fundamentals, with millions of views on this video alone and a standing place in Network+ study lists — compresses this lesson's evolution arc into about seven minutes of clean motion graphics. Watching data physically fan out of a hub and then thread through a switch's port table gives your visual memory something the page cannot.

As you watch, notice:

• The hub segment shows every port receiving every message — the single collision domain you just studied. The video treats hubs matter-of-factly; it dates from 2017, so add the 2026 frame yourself: this device is extinct, and the segment is your history lesson.
• The switch's MAC-address table filling up as devices talk — the learning behavior that makes micro-segments possible. The video calls a switch an "intelligent hub," a friendly simplification; you know the truer genealogy — it is a multiport learning bridge.
• The router deciding what leaves the local network — the video's framing of the router as the network's gateway is exactly the default-gateway role you saw frames addressed to in Module 2's capture.
• What the video doesn't say: it stays high-level by design, so collision domains, broadcast domains, VLANs and duplex never appear by name — the sections above carry those, and the next two lessons go deeper still. Where the animation shows what each box does, our prose is your record of why.

The video reinforces visually what you just learned — the lesson is complete without it.

Lab: Packet Tracer #1 — Hub vs Switch

Time to see flooding and micro-segmentation for yourself. Cisco Packet Tracer is a free network simulator: you drag devices onto a canvas, wire them, and — its superpower for learners — run traffic in slow motion, watching each frame travel as an animated envelope. It becomes your workbench for the rest of the course (five labs and the capstone build happen here), so this first lab includes setup.

Objective. Build the same four-PC network twice — once on a hub, once on a switch — and capture the observable difference in how each treats a simple ping.

Setup.

• Download Packet Tracer free of charge via Cisco Networking Academy: enroll in the free self-paced course "Getting Started with Cisco Packet Tracer" at netacad.com (a free account is required), which provides the installer for Windows, macOS and Linux plus a gentle interface tour. Any recent Packet Tracer version works for this course; the instructions below name interface elements generically, so small layout differences between versions won't matter.
• Install, launch, and sign in with the same free account when prompted.
• Start a new blank file.

Steps.

Part 1 — the hub network.

1. In the device palette (bottom of the window), open the network-devices category, find Hubs, and drag one generic hub onto the left half of the canvas.
2. From End Devices, drag four PCs around it in a semicircle. Packet Tracer names them PC0 through PC3.
3. Open Connections (the lightning-bolt category), choose Copper Straight-Through, and cable each PC's FastEthernet port to a port on the hub. Wait for the link indicators at both ends of every cable to turn green — the simulator's link lights.
4. Give each PC an address: click the PC → Desktop tab → IP Configuration, and set PC0 to 192.168.1.10, PC1 to 192.168.1.11, PC2 to 192.168.1.12, PC3 to 192.168.1.13, each with subnet mask 255.255.255.0. (Module 4 demystifies these numbers; today they are just labels that let the machines find each other.)
5. Confirm life signs in Realtime mode: PC0 → Desktop → Command Prompt → ping 192.168.1.13. You should see replies.
6. Now the real experiment. Switch to Simulation mode (the toggle in the bottom-right corner of the canvas area). In the simulation panel, click Edit Filters and clear everything except ICMP — so only ping traffic appears.
7. Repeat ping 192.168.1.13 from PC0. Advance the simulation one step at a time with the capture/forward button and watch the envelope: it travels to the hub, and the hub emits a copy out of every port at once. PC1 and PC2 receive the envelope and mark it with a red X — discarded, not for them. Only PC3 accepts and answers. Watch the reply flood identically on the way back.
8. Click the envelope at any stop and skim the PDU details window: layer 2 shows source and destination MAC addresses; layer 3 the IP addresses — Module 2's encapsulation, animated.

Part 2 — the switch network.

9. On the right half of the same canvas, build the twin: drag a 2960 switch from the switches category, four new PCs (PC4–PC7), cable with Copper Straight-Through, and address them 192.168.1.20 through .23, mask 255.255.255.0. One switch-specific patience note: a 2960's link indicators start amber and turn green after roughly half a minute — that is the switch's loop-protection routine checking the new port (the final lesson of this module explains it). Wait for green.
10. Still in Realtime mode, ping once from PC4 to PC7 — this first exchange lets the switch learn who lives where (and quietly includes a broadcast lookup you will study in Module 4).
11. Switch to Simulation mode (ICMP filter still on) and ping PC7 from PC4 again. Step through: the envelope goes to the switch — and leaves by exactly one port, straight to PC7. PC5 and PC6 never see it. The reply comes back down the same private lane. That is a micro-segment.
12. Save the file as m3-pt1 — labs later in the course reuse these habits, and the file is your evidence.

Expected result. Hub: every ICMP envelope appears at every PC, with red X discards at the bystanders. Switch: after the learning ping, envelopes travel point-to-point only.

Verify. You can answer, from what you watched rather than from the text: which topology delivered copies to machines that didn't want them? On the switch, how many PCs besides the target saw the ping? (Zero.)

Questions.

1. On the hub network, which PCs received PC0's ping request, and what did each do with it?
2. What did the switch have to learn before it could forward without flooding, and where did it learn it from?
3. Suppose PC1 and PC2 on the hub transmitted at the same instant. Using this lesson's vocabulary, what is the risk, and why does the same risk vanish on the switch?
4. Both of your networks are one broadcast domain each. Which device from this lesson would you add to split one, and what would it refuse to forward?

(Answers: 1 — all three others received it; PC1 and PC2 discarded it as not addressed to them, PC3 accepted and replied. 2 — which MAC address lives on which port, learned from the source addresses of frames arriving at each port. 3 — a collision: all hub ports share one collision domain; the switch gives every port its own micro-segment with full duplex, so simultaneous senders never interfere. 4 — a router; it would refuse to forward broadcast frames, ending the shared broadcast domain at its port.)

If it goes wrong.

• Link indicators red or absent. Wrong cable type (use Copper Straight-Through) or the cable was attached to the wrong port — delete the cable (select, then press Delete) and re-cable.
• Amber indicators on the switch that never turn green. Normal for the first half-minute per port (loop protection); use the fast-forward-time button to skip the wait. If amber persists, re-check cabling.
• Ping fails in Realtime mode. Re-open IP Configuration on both PCs: the addresses must differ only in the last number, and the mask must read 255.255.255.0 on every machine.
• Simulation shows nothing. Check Edit Filters — if every protocol is unticked, nothing displays. Tick ICMP.
• The simulation panel floods with other traffic. Filters again: untick everything except ICMP for a clean view.
• Envelope stalls at the first hop. Keep clicking the capture/forward step button; simulation mode only advances when you do (that is the point).

Reset/cleanup. Nothing to undo — the simulation touched no real network. Keep m3-pt1.pkt; the final lesson of this module builds directly on your switch half.

Check yourself

1. Twelve PCs hang off one hub. Count the collision domains and broadcast domains. Move the same twelve PCs to one switch — count both again.
2. A frame arrives at a switch addressed to a MAC the switch has never seen. What does the switch do, what is this behavior called, and why is it a feature rather than a bug?
3. The same situation at layer 3: a packet arrives at a router for a network absent from its routing table. Contrast the router's response with the switch's, and explain the philosophy behind the difference.
4. Name the devices collapsed inside a typical home gateway, and give one troubleshooting benefit of seeing it as several devices instead of one.
5. A user reports "no network." The PC's link light is dark. Which layer are you at, which lesson's checklist applies, and name its first two steps.
6. Your company replaces its last hub with a switch. Give one performance reason and one privacy reason the change matters, using this lesson's vocabulary.

Answers

1. Hub: one collision domain, one broadcast domain. Switch: twelve collision domains (one micro-segment per port), still one broadcast domain — switches don't stop broadcasts.
2. It forwards the frame out every port except the arrival port — flooding. It is a feature because delivery must not fail merely because the address is unlearned; the true owner will answer, the switch will learn its port from that reply's source address, and flooding for that destination stops.
3. The router silently drops the packet (and may send an error message back — Module 2's ICMP). The switch's philosophy is "deliver somehow" inside one network; the router's is "deliver correctly or not at all" between networks — spraying traffic across the Internet's networks would be chaos.
4. Switch (LAN ports), router, wireless access point, firewall, DHCP server. Seeing them separately lets you isolate: wired PCs fine but Wi-Fi down means the access-point function, not "the router," is the suspect.
5. Layer 1 — and the previous lesson's verification checklist: substitute a known-good patch cable, then inspect the RJ-45 contacts for seated pins (then a different port).
6. Performance: per-port collision domains end the interference of a shared medium, and each port runs full duplex at full rate. Privacy: frames travel only to the destination port, so bystander machines no longer receive — and cannot eavesdrop on — traffic that isn't theirs.

Key terms

• Repeater — two-port layer 1 device that regenerates (not merely amplifies) a fading signal to extend reach.
• Hub — multiport repeater; repeats every signal to every port, no decisions; extinct in 2026.
• Bridge — the first learning device: memorizes source MACs and forwards between two sides only when needed.
• Switch — multiport learning bridge; forwards each frame only to the destination's port, creating micro-segments.
• Micro-segment — the private full-speed circuit between two switch ports in conversation.
• Collision domain — devices sharing a signal path who can interfere by transmitting simultaneously; a switch gives every port its own.
• Broadcast domain — devices reached by a broadcast frame; ends only at a router port.
• Flooding — a switch forwarding an unknown-destination frame out all ports except the arrival port.
• Router — layer 3 device forwarding packets between networks by IP and routing table; refuses broadcasts, drops the unroutable.
• Routing table — the router's list of known networks and best next hops.
• NIC — the host's network interface; its link/activity/speed lights are free layer 1 evidence.
• Driver — the software binding a NIC to the operating system.
• NGFW — next-generation firewall, the modern firewall (Module 7).
• Packet Tracer — Cisco's free network simulator; this course's build-and-experiment workbench.

Summary

• The device family evolved by fixing failures: repeaters beat attenuation, hubs multiplied ports, bridges learned addresses, switches perfected learning into per-port micro-segments.
• Collision domains are broken by switches (one per port, full duplex); broadcast domains are broken only by routers.
• A switch floods unknown destinations and broadcasts — deliberate generosity; a router drops what it cannot route — deliberate discipline.
• Each router port is a separate network; without routers cutting the world into broadcast domains, the Internet could not exist.
• Hubs are extinct; standalone bridges are gone; the home gateway packs switch, router, access point, firewall and DHCP into one box.
• NIC lights are the cheapest diagnostic instrument you own.
• In Packet Tracer you watched a hub flood every port and a switch deliver point-to-point — the whole lesson in two animations.

Next lesson

The boxes are sorted — but what are the rules they speak? Next: Ethernet itself and the IEEE standards family — how to decode the name printed on a port or a spec sheet, what bandwidth really promises versus what throughput delivers, and how the speed ladder climbed from 10 megabits to 800 gigabits.

Sources and further study

• Al-Doori, T., Network Essentials, Chapters 1, 2 and 4 — the device evolution arc, the collision/broadcast domain teaching, and the device survey.
• Cisco, "What Is a Network Switch vs. a Router?" — https://www.cisco.com/c/en/us/solutions/small-business/resource-center/networking/network-switch-vs-router.html — the vendor's own beginner framing of this lesson's central contrast.
• Cisco Networking Academy, "Getting Started with Cisco Packet Tracer" — https://www.netacad.com/courses/getting-started-cisco-packet-tracer — the free course that provides the simulator download used in this lab.