Networking always felt like one of those "black box" topics to me — you know your laptop connects to Wi-Fi and somehow reaches the internet, but the actual mechanics of how devices talk to each other on a local network stay invisible. I decided to fix that by getting hands-on with Cisco Packet Tracer and building the simplest possible network from scratch: a handful of PCs, one switch, and enough IP addresses to make them all understand each other.
This post walks through exactly what I did, why each step matters, and how I verified the whole thing actually worked — not just looked right on screen.
Problem Statement
The goal was straightforward on paper: connect four computers to a single switch, give each one its own IP address, and confirm they can all reach each other over the network. Simple as that sounds, it forces you to actually understand a few core networking concepts:
- Why you need a specific cable type to connect a PC to a switch
- How IP addresses and subnet masks decide which devices can "see" each other
- How to prove connectivity actually works, instead of just assuming it does
Tools Used
- Cisco Packet Tracer
- 1x Switch (2960 series)
- 4x PCs
- Copper Straight-Through cables
Step-by-Step Walkthrough
Step 1: Set Up the Devices
I opened Packet Tracer and dragged a 2960 switch into the middle of the workspace, then placed four PCs around it. Nothing connected yet — just laying out the topology first so I could see the shape of the network before wiring anything up.
Step 2: Cable Everything Together
This is where the "which cable do I use" question comes in. There are two main copper cable types in Packet Tracer: Straight-Through and Crossover. The rule of thumb is:
- Different device types (PC ↔ Switch, PC ↔ Router) → Straight-Through cable
- Same device types (Switch ↔ Switch, PC ↔ PC) → Crossover cable
Since I was connecting PCs to a switch — two different device types — a Straight-Through cable was the correct choice. I connected each PC's FastEthernet0 port to its own port on the switch:
PC0 → Switch Fa0/1
PC1 → Switch Fa0/2
PC2 → Switch Fa0/3
PC3 → Switch Fa0/4
After a few seconds, every link light turned green, which confirmed the physical layer connection was solid on all four links.
Step 3: Assign IP Addresses
With cabling done, the next job was making each PC addressable on the network. I went into each PC's Desktop → IP Configuration, switched to Static, and assigned the following:
| PC | IP Address | Subnet Mask |
|---|---|---|
| PC0 | 192.168.1.1 | 255.255.255.0 |
| PC1 | 192.168.1.2 | 255.255.255.0 |
| PC2 | 192.168.1.3 | 255.255.255.0 |
| PC3 | 192.168.1.4 | 255.255.255.0 |
The subnet mask is the important detail here. Using 255.255.255.0 on every PC keeps them all in the same 192.168.1.0 network, which is what allows them to talk to each other directly without needing a router. If the subnet masks didn't match, or the IPs landed in different subnets, the PCs would technically be cabled together but logically isolated — a good reminder that physical connection and network connection are two very different things.
How to Verify
Configuring IPs is one thing — proving they actually work is another. I opened PC0's Command Prompt and ran:
ping 192.168.1.2
ping 192.168.1.3
ping 192.168.1.4
Every single ping came back with a Reply from... response and 0% packet loss, which confirmed PC0 could reach PC1, PC2, and PC3 without any issues.
Pinging 192.168.1.2 with 32 bytes of data:
Reply from 192.168.1.2: bytes=32 time<1ms TTL=128
Reply from 192.168.1.2: bytes=32 time<1ms TTL=128
Reply from 192.168.1.2: bytes=32 time<1ms TTL=128
Reply from 192.168.1.2: bytes=32 time<1ms TTL=128
Ping statistics for 192.168.1.2:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss)
If a ping had failed, the next things I'd check are: cable type, whether the link light is actually green, whether the subnet masks match across devices, and whether I typo'd an IP address (it happens more often than you'd think).
What I Learned
This was a small setup, but it packed in a surprising number of fundamentals:
- Switches operate at Layer 2 — they don't care about IP addresses to forward traffic within the same network, but the PCs still need valid IPs to communicate meaningfully above that layer.
- Cable type matters more than I expected. Straight-Through vs. Crossover isn't just trivia — plugging in the wrong one (in real hardware, anyway) can mean no link light at all.
- Subnet masks define the "neighborhood." Two devices can be cabled together perfectly and still fail to talk if their masks put them in different logical networks.
- Ping is your best friend for verification. It's a simple command, but it's the fastest way to confirm connectivity actually exists rather than just looking correct visually.
Common Mistakes Table
| Mistake | Why It Happens | Fix |
|---|---|---|
| Using a Crossover cable instead of Straight-Through | Mixing up when each cable type applies | Remember: different device types = Straight-Through |
| Mismatched subnet masks | Copy-pasting config without double-checking | Verify every PC uses the same mask if they should be on one network |
| Typo in IP address | Manual entry across multiple PCs | Double-check each octet before moving to the next PC |
| Assuming green link light = full connectivity | Confusing physical layer with network layer | Always confirm with ping, not just visual cues |
| Forgetting to set Static mode before entering an IP | DHCP is selected by default | Switch to Static first, then fill in the address fields |
Conclusion
Building this tiny four-PC network was a great reminder that networking fundamentals aren't complicated once you actually build them out yourself instead of just reading about them. Cabling, addressing, and verifying — that's really the whole loop, and once it clicks, scaling up to routers, VLANs, and larger topologies feels a lot less intimidating.