Network Security IP Addresses
An IP address is a unique label assigned to every device on a network. It works exactly like a home address — without it, the network would have no way to deliver data to the right device. Every security rule, firewall policy, and access control list uses IP addresses to decide who can send data to whom.
IPv4 — The Address You See Most Often
IPv4 addresses look like four numbers separated by dots: 192.168.1.100. Each number ranges from 0 to 255. The address has 32 bits in total, which allows about 4.3 billion unique addresses.
192 . 168 . 1 . 100 | | | | 8 bits 8 bits 8 bits 8 bits = 32 bits total
The world ran out of IPv4 addresses in 2011 because billions of phones, computers, and smart devices all needed unique addresses. That shortage drove the creation of IPv6 and the wide use of NAT (explained below).
IPv6 — The Modern Address Format
IPv6 uses 128 bits and writes addresses in eight groups of four hexadecimal digits separated by colons: 2001:0db8:85a3:0000:0000:8a2e:0370:7334. IPv6 provides 340 undecillion unique addresses — enough for every grain of sand on Earth to have billions of addresses.
IPv4: 192.168.1.1 (32 bits, ~4.3 billion addresses) IPv6: 2001:db8::1 (128 bits, 340 undecillion addresses)
Public vs Private IP Addresses
Not all IP addresses are visible on the internet. Some are reserved for use inside private networks and never appear on the public internet.
Private Address Ranges (not routable on the internet): 10.0.0.0 – 10.255.255.255 (Class A, large companies) 172.16.0.0 – 172.31.255.255 (Class B, medium networks) 192.168.0.0 – 192.168.255.255 (Class C, homes and small offices) Public Address (visible on the internet): 203.0.113.45 (example — your ISP assigns this to your router)
Your home router gets one public IP from your internet provider. Every device in your house gets a private IP. When any of those devices accesses the internet, the router swaps the private IP for the public IP — a process called NAT.
NAT — Network Address Translation
NAT lets many devices share one public IP address. Think of it like an apartment building: the building has one street address, and the mailman delivers to the building entrance. The front desk (NAT router) then sorts mail to the right apartment (device).
Inside your home (private IPs): Phone: 192.168.1.10 ─┐ Laptop: 192.168.1.11 ─┤──[ Router NAT ]──[ Public: 203.0.113.45 ]── Internet Tablet: 192.168.1.12 ─┘ Websites see only 203.0.113.45 — they cannot see your private addresses.
NAT provides a layer of security by hiding internal device addresses from the internet. An outside attacker cannot directly target 192.168.1.10 because that address is invisible outside your network.
Static vs Dynamic IP Addresses
A static IP never changes. Servers use static IPs because other machines need to find them at the same address every time. A web server that changes its IP address every day would be unreachable.
A dynamic IP changes each time a device connects to the network. DHCP (Dynamic Host Configuration Protocol) assigns dynamic IPs automatically. Home devices and office workstations typically use dynamic IPs because their addresses do not need to be permanent.
Static IP Use: [ Web Server: 203.0.113.10 ] ← always the same, DNS points here Dynamic IP Use: Monday: Your laptop gets 192.168.1.50 Tuesday: Your laptop gets 192.168.1.63 (DHCP reassigned)
Subnetting — Dividing a Network into Segments
A subnet mask tells devices which part of an IP address identifies the network and which part identifies the individual device. This allows one large address range to be split into smaller, isolated segments.
IP Address: 192.168.1.100 Subnet Mask: 255.255.255.0 (written as /24) Network Part: 192.168.1 (the neighborhood) Host Part: .100 (the house number) Devices on 192.168.1.x can talk to each other directly. Devices on 192.168.2.x need a router to communicate.
Subnetting is a critical security tool. Separating the accounts department onto a different subnet from the factory floor means an infected factory machine cannot directly reach financial data without crossing a router — giving security teams a checkpoint to monitor and filter.
How IP Addresses Relate to Security Policies
Scenario | IP-Based Security Action --------------------------|----------------------------------- Known attacker IP | Block on firewall by IP Admin access only | Allow only specific IP range Office printer access | Restrict to internal subnet only Remote staff | VPN assigns trusted IP before access Geo-blocking | Block IP ranges from certain countries
Every firewall rule, every access control list, and every VPN policy references IP addresses. Mastering IP addressing is not optional for network security work — it is the language security tools use to make decisions.