What Is an IP Address?
An IP address is the number the internet uses to find your device. IPv4 vs IPv6, public vs private ranges, the old address classes and who hands them out.
What an IP Address Does
An IP address (Internet Protocol address) is the number every device on a network gets so other devices know where to send data. A postal address for a computer: no address, no delivery. Every page you open, email you send or video you stream starts with your device handing its IP to a server.
IPv4 vs IPv6 Format
IPv4 is four numbers from 0 to 255 with dots between them, like 192.168.1.1. Each number is one octet (8 bits), so the address is 32 bits. IPv6 is eight groups of four hex digits separated by colons, like 2001:0db8:85a3:0000:0000:8a2e:0370:7334. That is 128 bits, which is where the extra room comes from.
| Feature | IPv4 | IPv6 |
|---|---|---|
| Address Length | 32 bits | 128 bits |
| Format | Dotted decimal (192.0.2.1) | Hexadecimal colon (2001:db8::1) |
| Total Addresses | ~4.3 billion | ~340 undecillion |
| Example | 203.0.113.50 | 2001:db8::8a2e:370:7334 |
Public vs Private IP Addresses
Your public IP is the one the internet sees: globally unique, routable, assigned by your ISP. A private IP only works inside your home or office network. Every device on your Wi-Fi has one, and they all share the single public IP through NAT (Network Address Translation) on the router.
| Type | Range | Use |
|---|---|---|
| Private (Class A) | 10.0.0.0 - 10.255.255.255 | Large enterprise networks |
| Private (Class B) | 172.16.0.0 - 172.31.255.255 | Medium-sized networks |
| Private (Class C) | 192.168.0.0 - 192.168.255.255 | Home and small office networks |
| Loopback | 127.0.0.0 - 127.255.255.255 | Testing on your own machine |
IP Address Classes
The original IPv4 scheme sorted addresses into five classes by the first octet:
- Class A (1 to 126): large networks, 16 million hosts each
- Class B (128 to 191): medium networks, 65,534 hosts each
- Class C (192 to 223): small networks, 254 hosts each
- Class D (224 to 239): multicast
- Class E (240 to 255): experimental
Nobody allocates by class any more. CIDR (Classless Inter-Domain Routing) replaced it, and a block is now written with a prefix length like /24 or /16.
Who Assigns IP Addresses?
- IANA (Internet Assigned Numbers Authority) holds the global pool and hands big blocks to the regional registries.
- The five RIRs (Regional Internet Registries) split them up by region: ARIN for North America, RIPE NCC for Europe, the Middle East and Central Asia, APNIC for Asia-Pacific, LACNIC for Latin America and the Caribbean, AFRINIC for Africa.
- ISPs get blocks from their RIR and give single addresses to customers, fixed (static) or on the fly through DHCP (dynamic).
A static IP is the same every time you connect, which servers need. A dynamic IP comes from the ISP's DHCP and can change now and then. Most home connections are dynamic.
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