Guided buildstarter5 steps~10 min5 devices

Sketch your home network

Start from two PCs on a switch, add a home router and the internet, cable them up, then sort every device into endpoints and intermediate nodes.

What you'll be able to do: A five-device sketch of a home network — two PCs, a switch, a router and the internet — where you can point at each device and say whether it is an endpoint or an intermediate node, and which cable is the media between them.

Start this build in the lab

Topics: Network components · Switching · Interfaces

What you'll build

SW-LAN — a switch, the home switch both PCs plug into
PC-A — a pc, the first computer, on Fa0/1
PC-B — a pc, the second computer, on Fa0/2
Home-Router — a router, the home router between the LAN and the internet
Internet — a cloud, the internet — a network of networks run by other people

Step by step

1. Look at the network you were handed
The lab opens on a small network that already works: PC-A and PC-B are each cabled to the switch, SW-LAN, and addressed on 192.168.1.0/24. Ping PC-B from PC-A, then list the switch's ports: Fa0/1 and Fa0/2 read `connected` — those are the two cables — and every other port reads `notconnect`.
On PC-A — Send traffic from one computer to the other
```
ping 192.168.1.20
```
On SW-LAN — See which switch ports have a cable in them
```
enable
show interfaces status
```
Check: run show interfaces status on SW-LAN and look for Fa0/2 connected 1 auto 100 fastethernet.
Why: Even this small network has the ingredients the chapter lists: two endpoints (the PCs, where traffic starts and ends), media (the two copper cables that carry the bits) and an intermediate device (the switch, which passes frames between the PCs but never starts a conversation of its own). Both PCs sit on one subnet, so they need nothing else to talk — and, with no router, nothing on this network can reach anything beyond it.
2. Drag in a router and a cloud
From the palette, drag one router and one cloud onto the canvas: your home router, and the internet behind it. That makes five devices, the most the Free canvas holds. Open the router's console and name it so its prompt says which box you are in. The cloud has no console at all — it stands for the internet, which nobody configures from home — so it keeps the name the canvas gives it, such as CLOUD1.
On Home-Router — Name the router
```
enable
configure terminal
hostname Home-Router
end
```
Check: run show ip interface brief on Home-Router and look for Gi0/0 unassigned YES manual administratively down down.
Why: A router is an intermediate device like the switch, but it works one level up: a switch joins devices into one network, and a router joins whole networks to each other — here, your home network and your internet provider's. `show ip interface brief` also shows something real routers do: every port leaves the factory switched off (`administratively down`) until someone turns it on.
3. Cable the switch to the router
Draw a copper cable from SW-LAN's Gi0/1 to Home-Router's Gi0/0. On its own the cable stays dark, because the router's end is switched off. Give that port the network's gateway address, 192.168.1.1, switch it on with `no shutdown`, then ping it from PC-A: a reply proves the cable, the switch and the port all carry traffic.
- Cable SW-LAN Gi0/1 ↔ Home-Router Gi0/0
On Home-Router — Address the port facing the home network and switch it on
```
enable
configure terminal
interface Gi0/0
ip address 192.168.1.1 255.255.255.0
no shutdown
end
```
On PC-A — Reach the router through the switch
```
ping 192.168.1.1
```
Check: run show ip interface brief on Home-Router and look for Gi0/0 192.168.1.1 YES manual up up.
Why: A cable is media: it carries bits and nothing else, and it carries none while either end is switched off. The address makes the router a member of the home network — 192.168.1.1 shares the first three numbers and the mask with both PCs — so the PCs reach it directly, through the switch. In a real home, this is the address every device sends its internet traffic to.
4. Cable the router to the cloud
Draw a second copper cable, from Home-Router's Gi0/1 to the cloud's Inet0 port. This is the router's internet side, so it needs an address on the provider's network. At home the provider hands one out automatically; here you type it — 203.0.113.2, from a block set aside for examples — and switch the port on. `show ip route` then lists both networks the router belongs to.
- Cable Home-Router Gi0/1 ↔ Internet Inet0
On Home-Router — Address the port facing the internet and switch it on
```
enable
configure terminal
interface Gi0/1
ip address 203.0.113.2 255.255.255.0
no shutdown
end
show ip route
```
Check: run show ip route on Home-Router and look for C 203.0.113.0/24 is directly connected, Gi0/1.
Why: A router holds one address on each network it joins. When a port has an address and is up, the router records that network as directly connected — the C lines in `show ip route`. A port with an address but no cable stays down and adds nothing, which is why this step only turns green once the cable is in. The cloud itself is not one device: it stands for the internet, a network of networks run by thousands of providers, full of intermediate devices you never see.
5. Sort the devices: endpoints or intermediate nodes?
Click each device in turn and decide what job it does. PC-A and PC-B are endpoints: traffic starts and ends on them, and each has one address of its own. SW-LAN and Home-Router are intermediate nodes: they carry other devices' traffic. The switch does it without any address — its MAC address table shows which endpoint sits behind which port — while the router holds one address on each network it joins. The cloud is more intermediate nodes, run by someone else.
On PC-A — An endpoint: one adapter, one address
```
ipconfig
```
On SW-LAN — An intermediate node with no address: it knows where each endpoint is
```
enable
show mac address-table
```
On Home-Router — An intermediate node with an address on each network
```
enable
show ip interface brief
```
Check: run show mac address-table on SW-LAN and look for DYNAMIC Fa0/1.
Why: Every device on this canvas is a node, because each takes part in moving data, but only the endpoints are hosts. The chapter's four ingredients are all here: endpoints (the PCs), media (the four cables), network devices (the switch and the router) and the software and protocols running on all of them. A router can be the busiest box on a network without ever opening a web page itself — it moves everyone else's traffic.

The theory behind it

What is a network?

One router, one PC, one ping — Build the smallest network that works: address a router and a PC on the same subnet and get a reply back.
Three hosts, one switch — Put three PCs on a single subnet through an unconfigured switch and watch it learn who lives where.
ARP and MAC learning, side by side — Watch a host's ARP cache and a switch's MAC table fill from the very first frame — and see why a host never ARPs for anything beyond its gateway.
Two LANs, one router — Put a PC on each of two different subnets and make them talk through a router.
Subnetting drill on the canvas — Subnet 192.168.1.0/24 into four /26s on four router ports, put a PC in each, and prove every /26 is its own broadcast domain.
VLSM for two sites — Carve one /24 into a /26, a /27 and a /30 sized to what each site needs, then route between them with masks that match the plan.

Build it for real

The lab walks you through these steps and ticks each one off as your network starts working.

Open in the lab

What you'll build

Step by step

1. Look at the network you were handed

2. Drag in a router and a cloud

3. Cable the switch to the router

4. Cable the router to the cloud

5. Sort the devices: endpoints or intermediate nodes?

The theory behind it

More in Foundations

Build it for real