How do computers
find each other?
Build a connection, send a packet, and watch every decision it meets along the way.
IP addressBuilding address
PortRoom number
RouterPost office
FirewallSecurity guard
One device, three ways to find it.
The right address depends on where you are standing.
Localhost stays at home
127.0.0.1 always means the device you are currently using. Pinging it tests your computer’s network software—not your Wi-Fi or internet connection.
ping 127.0.0.1
Three reserved neighborhoods
If an address begins with one of these ranges, it stays inside a private network.
10.0.0.0 – 10.255.255.255Large networks
172.16.0.0 – 172.31.255.255Organizations & cloud
192.168.0.0 – 192.168.255.255Homes & classrooms
Meet the team behind every connection.
Tap each helper to see the job it performs.
DHCP says, “Welcome—here are your settings.”
When your device joins Wi-Fi, DHCP automatically supplies an IP address, subnet mask, default gateway, and DNS server.
RememberYou usually don’t choose your phone’s IP address. DHCP does.
An IP finds the computer. A port finds the app.
Diagnose the network, one test at a time.
This practice terminal behaves like a real command line, but it is completely simulated.
Packet Path classroom terminal
Type help or choose a mission from the left.
Start hereRun ipconfig to discover Alice’s network settings.
Can you connect the node?
Use what you learned to solve six real networking decisions.
Alice’s laptop is 192.168.1.25. Her router is 192.168.1.1 with public IP 203.0.113.50. Bitcoin Core is running on Alice’s laptop.
You can now explain how computers find each other.
You connected addresses, routes, services, and security—just like a network engineer.