IP Addressing and Subnet Masks: How Networks Work
IP Addressing and Subnet Masks: How Networks Work
Every device on the internet or a local network has an IP address.
But how does it know if another device is on the same network or not?
That’s where the subnet mask comes in.
📌 What is an IP address?
An IPv4 address has 4 numbers separated by dots → e.g. 192.168.1.20
It’s also called a dotted quad because it has 4 octets.
🧩 What does the subnet mask do?
The subnet mask tells you:
- What part of the address is the network
- What part is the host (specific device on that network)
Example:
IP: 192.168.1.20
Mask: 255.255.255.0
→ Network part: 192.168.1
→ Host part: 20
Devices on the same network can communicate directly.
If not, the message goes through a gateway.
🔍 What does “/24” mean?
The CIDR notation (e.g. /24) is a shorthand for the subnet mask.
/24= 24 bits for the network →255.255.255.0/16=255.255.0.0/8=255.0.0.0
Example:
192.168.1.0/24 → 256 total IPs (0 to 255)
→ 254 usable for hosts (excluding network and broadcast)
🎯 Practical Example
Two PCs:
- IP: 192.168.1.10/24
- IP: 192.168.1.50/24
✅ Can talk directly.
But 192.168.2.10/24? ❌ Outside the network → needs a gateway.