The Comprehensive Guide to IP Address Lookup & Subnet Netmask Calculation
Whether you are asking "what is my IP address?", diagnosing local network connectivity, or planning corporate routing topologies with a subnet calculator and netmask calculator, understanding Internet Protocol addressing is the foundation of modern networking.
1. What Is an IP Address and How Does an IP Lookup Work?
An IP address (Internet Protocol address) is a unique numeric address that identifies any device connected to the Internet or a local area network (LAN). When you use an IP lookup by address tool, the system queries global Regional Internet Registries (RIRs like ARIN, RIPE, APNIC) and geolocation databases (GeoIP) to extract:
- Public IP Address: Your public-facing IPv4 or IPv6 identifier.
- Internet Service Provider (ISP): The telecommunication company routing your bandwidth (e.g., Comcast, AT&T, Vodafone, Jio).
- Autonomous System Number (ASN): The BGP routing identifier controlling network traffic.
- Geographical Location: Country, state/region, city, and approximate latitude/longitude coordinates.
2. Understanding Subnetting, Netmasks & CIDR Notation
A subnet mask (network mask / netmask) divides an IP address into two components: the Network portion (which identifies the subnet) and the Host portion (which identifies specific computers, printers, or servers on that subnet).
In CIDR (Classless Inter-Domain Routing) notation, the netmask is written as a prefix length (e.g. /24). A /24 prefix indicates that the first 24 bits are dedicated to the network, leaving 8 bits for host addresses ($2^8 - 2 = 254$ usable hosts).
IPv4 Subnet Mask & Usable Hosts Quick Reference Table
| CIDR Prefix | Subnet Netmask | Total Usable Hosts | Common Application |
|---|---|---|---|
| /30 | 255.255.255.252 | 2 | Point-to-point router links |
| /29 | 255.255.255.248 | 6 | Small business static IP pools |
| /28 | 255.255.255.240 | 14 | Office department subnets / DMZ |
| /24 | 255.255.255.0 | 254 | Standard Home & Office Wi-Fi LANs |
| /16 | 255.255.0.0 | 65,534 | Enterprise intranets & AWS VPCs |
| /8 | 255.0.0.0 | 16,777,214 | Global Telecoms & ISP Backbones |
3. Public vs Private IP Address Ranges
According to RFC 1918, private IPv4 address blocks are reserved for local private networks and are not routed on the public internet:
- Class A Private:
10.0.0.0to10.255.255.255(/8 prefix) - Class B Private:
172.16.0.0to172.31.255.255(/12 prefix) - Class C Private:
192.168.0.0to192.168.255.255(/16 prefix) - Loopback Address:
127.0.0.1(localhost)