Private IPv4 Range Checker
Check membership in private address blocks.
Private IPv4 Range Checker: inputs and results
Enter an IP address, CIDR prefix, or range. Then check its first and last address below.
Calculated Boundaries & ParametersReady
Key Capabilities
- •100% Client-Side: Zero telemetry or server latency.
- •RFC Compliant: Exact 32-bit and 128-bit integer precision.
- •Quick Copy: Instant access to CIDR, mask, and range bounds.
- •Cross-Platform: Works on desktop, tablet, and mobile browsers.
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How Private IPv4 Range Checker Works?
This tool works by testing an address against the 3 RFC 1918 private blocks: 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16.
Enter an address or prefix
Type
172.31.45.6or a list of addresses.Test the 3 private blocks
The checker masks the address with /8, /12, and /16 and compares the results with each block.
Flag near-miss addresses
Addresses such as
172.32.0.1and100.64.0.1look private but are not RFC 1918.Report the result
The result names the matching private block or marks the address as not private.
Private IPv4 Range Checker Formula
The formula is Private = (IP AND /8 = 10.0.0.0) OR (IP AND /12 = 172.16.0.0) OR (IP AND /16 = 192.168.0.0).
10.0.0.0/8
first octet = 1016,777,216 addresses.
172.16.0.0/12
first octet = 172 AND 16 ≤ second octet ≤ 311,048,576 addresses.
192.168.0.0/16
first 2 octets = 192.16865,536 addresses.
Total private space
17,891,328 addressesAbout 0.42 % of IPv4.
Worked example: 172.31.45.6 and 172.32.0.1
172.31.45.6 → 31 AND 240 = 16 → 172.16.0.0 ✓ private 172.32.0.1 → 32 AND 240 = 32 → 172.32.0.0 ✗ public
Private IPv4 Range Checker Conversion Table
The table checks 12 addresses, including near-miss addresses at the edges of each private block.
| Address | RFC 1918 Private | Matching Block |
|---|---|---|
| 10.0.0.1 | Yes | 10.0.0.0/8 |
| 10.255.255.255 | Yes | 10.0.0.0/8 |
| 11.0.0.1 | No | — |
| 172.15.255.255 | No | — |
| 172.16.0.1 | Yes | 172.16.0.0/12 |
| 172.31.45.6 | Yes | 172.16.0.0/12 |
| 172.32.0.1 | No | — |
| 192.168.1.1 | Yes | 192.168.0.0/16 |
| 192.169.0.1 | No | — |
| 100.64.0.1 | No | Shared 100.64.0.0/10 (RFC 6598) |
| 169.254.1.1 | No | — |
| 8.8.8.8 | No | — |
What is Private IPv4 Range Checker?
The Private IPv4 Range Checker is a tool that tests whether an IPv4 address belongs to the private address space reserved by RFC 1918.
RFC 1918, published in 1996, sets aside 3 blocks for internal networks: 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. Internet routers do not route these blocks, so the same private addresses are reused in millions of networks behind Network Address Translation (NAT).
The /12 block causes the most confusion. The 172.16.0.0/12 block covers 172.16.0.0 to 172.31.255.255 only, so 172.32.0.1 is a public address.
What are the uses of Private IPv4 Range Checker?
There are 4 main uses of the Private IPv4 Range Checker, including SSRF protection, log triage, and NAT troubleshooting.
Blocking SSRF requests
Applications that fetch URLs reject private destinations to stop Server-Side Request Forgery (SSRF).
Triaging log entries
Private source addresses point to internal traffic, not external clients.
Troubleshooting NAT
A public-facing service that sees private client addresses reveals a missing NAT or proxy header.
Validating public IP fields
Forms that ask for a public server address reject private entries.