PRIVATE IP
192.168.1.25
Inside your network
Private addresses are used within local networks such as your home, office or lab.
They are not directly routable across the public internet.
Cyber Basics • Lesson 02
Understanding IP addresses.
Every device communicating across a network needs a way to be identified. IP addresses provide that addressing system. Understanding them is one of the foundations of networking and cybersecurity.
Start here
What is an IP address?
An IP address is a numerical address used to identify where network traffic should be sent.
Think of it a little like an address used for delivering a parcel. The network needs to know where information is going and where the response needs to return.
192.168.1.25
An example IPv4 address
Important:
An IP address identifies a network interface at a particular point
in a network. It does not identify a person.
Private vs public
Your device usually has more than one IP context.
At home, your devices normally use private IP addresses to communicate inside your local network. Your router then connects that network to the internet using a public IP address.
PUBLIC IP
203.0.113.42
On the internet
Public addresses are globally routable and allow networks and internet services to communicate.
Your ISP normally provides your internet connection with a public address, although some providers use technologies such as CGNAT.
203.0.113.42 is from an address range reserved for documentation and examples. It is not somebody's real public IP being exposed here.
Private IPv4 ranges
You've probably seen one of these before.
IPv4 reserves several ranges specifically for private networks. Home routers commonly allocate addresses from these ranges.
10.0.0.0 – 10.255.255.255
10.0.0.0/8
172.16.0.0 – 172.31.255.255
172.16.0.0/12
192.168.0.0 – 192.168.255.255
192.168.0.0/16
This is why addresses beginning with 192.168 are so common on home networks.
NAT
How can your whole house share one public IPv4 address?
Your laptop, phone, television and other devices can each have their own private IPv4 address while sharing the internet connection's public IPv4 address.
Laptop
192.168.1.20
Phone
192.168.1.21
TV
192.168.1.22
→
ROUTER
NAT
→
INTERNET
203.0.113.42
Network Address Translation, or NAT, translates connections between the private network and the public side of the router.
NAT changes addressing information as traffic crosses the router.
Your router's stateful firewall is a separate security function, so
NAT itself should not be treated as a replacement for a firewall.
IPv4 and IPv6
Why are there two types of IP address?
IPv4
192.168.1.25
IPv4 uses 32-bit addresses and provides roughly 4.3 billion possible addresses.
The growth of the internet eventually made that address space too small for every device to simply have a unique IPv4 address.
IPv6
2001:db8::1234
IPv6 uses 128-bit addresses, providing an enormously larger address space.
IPv6 is increasingly deployed alongside IPv4 rather than the internet switching from one to the other overnight.
Static & dynamic
IP addresses don't always stay the same.
Dynamic
An address is assigned automatically and may change. DHCP is commonly used to allocate addresses to devices on local networks, while ISPs may also dynamically assign public addresses.
Static
An address is deliberately kept consistent. Servers, network equipment and infrastructure often benefit from predictable addresses.
Privacy & security
What can someone learn from your public IP?
Public IP addresses are visible to internet services you communicate with. They can reveal useful information, but they are often misunderstood.
Network information
The ISP or network provider, ASN and an approximate geographic area can often be determined from public databases.
Your home address
Public IP geolocation is not GPS. A normal IP lookup does not automatically provide someone's exact street address, name or physical location.
However:
A public IP can still be useful information to an attacker. They may
test the address for internet-accessible services or combine it with
information obtained elsewhere.
This is one reason correctly configured routers and firewalls matter.
Why cybersecurity cares
IP addresses appear everywhere in security.
When investigating network activity, analysts regularly work with source and destination IP addresses.
Source IP
198.51.100.24
Destination
203.0.113.42
Destination Port
443
Protocol
TCP
Those details can help answer questions such as: where did a connection originate, which system was contacted, and which network service was involved?
The public addresses in this example come from documentation ranges reserved for examples.