An IP address is a unique identifier assigned to each device connected to a network. Understanding how IP ranges are structured helps with network design, security, and troubleshooting.
🔢 IP Address Basics
IPv4 addresses are written in dotted-decimal format: 192.168.1.1
They consist of 4 octets (each 8 bits), totaling 32 bits
Range: 0.0.0.0 to 255.255.255.255
📦 Public vs Private IP Ranges
IP Range
Type
Use Case
10.0.0.0/8
Private
Internal networks (enterprise)
172.16.0.0/12
Private
Mid-size private networks
192.168.0.0/16
Private
Home and small office networks
100.64.0.0/10
Carrier-grade NAT
ISPs using NAT for customers
127.0.0.1
Loopback
Localhost testing
169.254.0.0/16
APIPA
Automatic IP when no DHCP
📌 Private IPs are non-routable over the public internet—they’re meant for internal use behind NAT (e.g. routers, firewalls).
🔍 Public IPs
Assigned by regional internet registries (ARIN, RIPE, APNIC)
Routable over the internet
Examples:
Google DNS: 8.8.8.8
Cloudflare DNS: 1.1.1.1
BBC: 151.101.0.81
🧠 CIDR Notation (Classless Inter-Domain Routing)
CIDR
Subnet Mask
Hosts Available
Example Network
/8
255.0.0.0
~16 million
10.0.0.0/8
/16
255.255.0.0
~65,000
192.168.0.0/16
/24
255.255.255.0
254
192.168.1.0/24
/30
255.255.255.252
2 (point-to-point)
192.168.1.4/30
🚫 Reserved and Special-Purpose Ranges
IP Range
Purpose
127.0.0.0/8
Loopback testing (localhost)
169.254.0.0/16
Link-local (no DHCP)
224.0.0.0/4
Multicast addresses
240.0.0.0/4
Reserved for future use
255.255.255.255
Broadcast address (local network)
🛡️ Security & Firewall Tips
🔒 Block inbound access to private IP ranges from the internet
🔍 Monitor outbound traffic—private addresses in DNS or HTTP headers can indicate misconfig or malware
🌐 Use NAT to connect private IPs to the internet safely
🚫 Avoid exposing public services on IPs like 0.0.0.0 unless necessary
✅ Summary
Category
Example Range
Notes
Private
192.168.1.0/24
Internal only
Public
8.8.8.8
Routable, unique
Loopback
127.0.0.1
Localhost testing
APIPA
169.254.x.x
No DHCP fallback
Multicast
224.0.0.0/4
Group-based messaging
💡 Understanding IP ranges is the foundation of secure network design and defence.