How IP Addresses Work

Home network — from your device to the internet

Private IP (local only)
Public IP (internet visible)
💻
PC
192.168.1.10
📱
Phone
192.168.1.11
📺
TV
192.168.1.12
◄
►
private
network
NAT boundary
🌐
Router
192.168.1.1 85.23.41.100
◄
►
public
internet
☁️
Internet
sees only
85.23.41.100
◄
►
request /
response
🖥️
Server
188.210.222.16
Why does the router have two IPs?
LAN side — Private IP
192.168.1.1
Assigned by the router itself. Used only inside your home network so your devices have somewhere to send traffic. Never visible on the internet.
WAN side — Public IP
85.23.41.100
Assigned by your ISP. This is the address the internet sees. All your devices share this one IP when communicating with the outside world.
Why two and not one?
The router sits between two separate networks — your home network and the internet. It needs one address for each side, just like a house has a door number inside a building and a street address outside.
How it works technically — two separate network interfaces
🏢
ISP
assigns public IP
ISP cable
🔌
WAN port
85.23.41.100
routes traffic
⚙️
NAT
🔌
LAN port
192.168.1.1
home network
💻
Your devices
192.168.1.x
Each port is a separate network interface — WAN faces the internet, LAN faces your home.
The router passes traffic between them and translates IPs using NAT.
NAT Translation Table (inside your router)
Device Private IP : Port Public IP : Port Destination
PC 192.168.1.10:54321 85.23.41.100:54321 google.com:80
Phone 192.168.1.11:61200 85.23.41.100:61200 youtube.com:443
TV 192.168.1.12:49800 85.23.41.100:49800 netflix.com:443
How a request travels — step by step
1
Your PC sends a request
FROM: 192.168.1.10:54321 → TO: google.com:80
2
Router rewrites the source IP (NAT)
192.168.1.10:54321 → 85.23.41.100:54321   (saves mapping in table)
3
Google receives the request and responds
FROM: google.com:80 → TO: 85.23.41.100:54321
4
Router checks its table and forwards to your PC
85.23.41.100:54321 → 192.168.1.10:54321   (back to your device)