How IP Geolocation & ASN Routing Work
Every public IP address routed over the internet is registered with one of five global Regional Internet Registries (RIRs): ARIN (North America), RIPE NCC (Europe & Central Asia), APNIC (Asia-Pacific), LACNIC (Latin America), and AFRINIC (Africa). These registries publish WHOIS databases detailing which telecommunication company or cloud enterprise owns each CIDR (Classless Inter-Domain Routing) block.
Autonomous System (ASN)
An ASN (e.g., AS13335 for Cloudflare, AS15169 for Google) is a group of IP networks managed under a single unified routing policy using Border Gateway Protocol (BGP).
Reverse DNS (rDNS / PTR)
Reverse DNS resolves an IP address back to its fully qualified domain name (FQDN) via special .in-addr.arpa (IPv4) or .ip6.arpa (IPv6) pointer records.
Geolocation Databases
Services like MaxMind GeoIP2 and IP2Location periodically crawl ISP network topology, latency triangulation, and registry submissions to estimate physical city coordinates.
Common Use Cases for IP Intelligence Lookups
- Email Delivery Troubleshooting: Verify if your mail server's outbound IP is correctly assigned a Reverse DNS (PTR) record that matches your SMTP hostname, preventing spam filter rejections.
- Server Migration & DNS Cutover: Confirm whether your newly deployed VPS or cloud instance has propagated its public IP before switching live production DNS records.
- Cybersecurity & Log Auditing: Investigate suspicious authentication logs, brute-force attempts, or web crawler User-Agents by uncovering the origin ASN, ISP, and host country.
- BGP Route Leak Diagnostics: Identify transit providers and upstream peers handling specific network blocks.
Frequently Asked Questions (FAQ)
Can I look up private or local IP addresses?
No. Addresses in the RFC 1918 range (such as 192.168.x.x, 10.x.x.x, or 172.16.x.x) and loopback addresses (127.0.0.1) exist only inside your local LAN and cannot be looked up on public registries.
Why does IP geolocation sometimes show a different city?
ISPs often pool dynamic addresses across regional hubs. If your ISP routes traffic through a central data center in a neighboring city, geolocation databases will detect that routing facility rather than your local municipality.