What is an IP Address?

An IP address (Internet Protocol address) is a numeric identifier assigned to every device connected to a network. It serves two distinct purposes: identification (which device is this?) and location (how do we route traffic to it?). Without IP addresses, the internet has no way to know where to send a packet.

IPv4 Addresses

The most familiar form is the IPv4 address — four decimal numbers separated by dots, each ranging from 0 to 255. 8.8.8.8 is Google's public DNS server. 1.1.1.1 is Cloudflare's. IPv4 addresses are 32 bits long, encoded as four 8-bit octets.

The 32-bit space provides 2³² = 4,294,967,296 unique addresses. This was more than sufficient in the early 1980s when the internet connected a few hundred research computers. Today, with billions of smartphones, smart TVs, IoT sensors, and servers, 4.3 billion addresses is nowhere near enough — the global IPv4 pool has been exhausted since 2011.

IPv6 Addresses

To solve the exhaustion problem, IPv6 (RFC 2460, 1998) uses 128-bit addresses. These are written as eight groups of four hexadecimal digits separated by colons. Leading zeros in any group can be omitted, and a single longest run of consecutive all-zero groups can be replaced with :::

• Full form: 2606:4700:0000:0000:0000:0000:0000:1111
• Compressed: 2606:4700::1111

IPv6 provides 2¹²⁸ ≈ 3.4 × 10³⁸ addresses — enough that every device ever manufactured could have billions of unique addresses and the pool would not be meaningfully depleted.

How Addresses Are Structured

An IP address is not just a flat number — it encodes hierarchy. Every address is divided into a network portion (identifying which network or subnet the address belongs to) and a host portion (identifying the specific device on that network). The prefix length in CIDR notation defines the split point.

For 8.8.8.8/24: the first 24 bits (8.8.8) identify the network; the last 8 bits (.8) identify the host within that network. This means 8.8.8.8 and 8.8.8.4 are on the same /24 subnet; 8.8.4.4 is on a different subnet within Google's broader address space.

Public vs Private Addresses

Not all IP addresses are reachable from the open internet:

• Public (globally routable) — Unique worldwide, announced in the global BGP table, reachable from anywhere. When you look up an IP in this tool, you are querying public addresses.
• Private (RFC 1918) — Reserved for use inside organizations and homes, not routed on the public internet:
  • 10.0.0.0/8 — 16.7 million addresses, commonly used inside large enterprise networks
  • 172.16.0.0/12 — 1,048,576 addresses (172.16.0.0 through 172.31.255.255)
  • 192.168.0.0/16 — 65,536 addresses, the default range for home routers
• Shared address space (RFC 6598) — 100.64.0.0/10 is used by ISPs for Carrier-Grade NAT (CGNAT) — a second layer of NAT when even public IPv4 addresses are scarce.
• Link-local (RFC 3927) — 169.254.0.0/16 is auto-assigned when DHCP fails (Windows calls this APIPA). Not routed.

How Addresses Are Allocated

IP addresses are not simply handed out to whoever asks. The allocation hierarchy is:

1. IANA — The Internet Assigned Numbers Authority (a function of ICANN) manages the global pool and allocates large blocks to the five Regional Internet Registries (RIRs).
2. RIRs — ARIN (Americas), RIPE NCC (Europe/Middle East), APNIC (Asia-Pacific), LACNIC (Latin America), AFRINIC (Africa) allocate blocks to ISPs and organizations.
3. ISPs/LIRs — Local Internet Registries (usually ISPs) sub-allocate to their customers.
4. End users — Receive assignments from their ISP or directly from an RIR if large enough.

Every legitimate public IP address traces back through this hierarchy to IANA. This chain of custody is what RPKI cryptographically verifies — confirming that the AS announcing a prefix in BGP is actually authorized by the address holder.

IP Addresses and BGP

Public IP addresses are organized into prefixes and announced via BGP. Each prefix is originated by exactly one autonomous system. When you look up an IP address in this tool, the looking glass finds the most-specific BGP prefix covering that address and shows the origin AS, the AS path from the collector, and other routing attributes.

The global BGP routing table contains roughly one million IPv4 prefixes and over 200,000 IPv6 prefixes, representing the entire reachable address space of the public internet.

Geolocation and IP Addresses

IP addresses carry no geographic metadata in the protocol itself. Geographic location is inferred from registration data (where the address block was allocated) and from active measurements (which networks announce the address from which locations). This inference is imprecise: an address registered in the US might be used by a server physically located in Europe via anycast or a VPN. Treating IP geolocation as authoritative is a frequent source of errors in fraud detection and content localization systems.

Look Up IP Addresses

• 8.8.8.8 — Google DNS (IPv4)
• 1.1.1.1 — Cloudflare DNS (IPv4 anycast)
• 2606:4700::1111 — Cloudflare DNS (IPv6)