IP & Subnet

These tools cover investigations around IP addresses and network ranges. You can derive the network address and host count from a subnet mask, consult IPv4 and IPv6 CIDR tables, convert between an IP range and CIDR notation, and test whether two CIDR blocks overlap — as well as check your own global IP, validate an address and tell whether it is private, run a WHOIS lookup, and see whether an address is listed on a DNS blacklist.

Subnet Calculator & Quick-Reference Table — Free, /1–/32 CIDR

Instantly calculate the network address, broadcast address, and usable host count from an IPv4 address and subnet mask. Includes a full /1–/32 subnet mask quick-reference table for network design and troubleshooting — fr...

CIDR / Subnet Mask Reference Table

A reference table of subnet masks, wildcard masks, and usable host counts for every prefix length from /0 to /32. Enter how many hosts you need and the smallest CIDR block that fits is highlighted automatically.

What Is My IP Address? Free IP Checker

Instantly check your current global IP address for free. Also shows HTTP connection details and browser environment info — handy for verifying your VPN exit node or device settings.

IP WHOIS Lookup

Look up WHOIS information for any IP address using the RDAP protocol. View the owning organization, network range, country, registration dates, and abuse contact.

IP Address / Domain Blacklist (DNSBL) Checker

Enter an IP address or domain to check it against major DNSBLs (blacklists) such as Spamhaus, SORBS, Barracuda, and SpamCop all at once to see if it's been flagged as a spam source.

IP Range ⇔ CIDR Converter

Enter a start and end IP to split that range into the smallest possible set of CIDR blocks, or enter CIDR notation (e.g. 192.168.1.0/24) to get the block's first/last IP and total address count. Useful for firewall and A...

IP Address Validator — Check IPv4/IPv6 Format & Detect Private Ranges (Free)

Instantly check whether a string is a valid IPv4 or IPv6 address and automatically classify it as private, loopback, link-local, multicast, or public. Runs entirely in your browser — no external lookups, pure format vali...

IPv6 CIDR Reference Table — Address Counts by Prefix Length (Free)

A reference table showing the number of addresses and equivalent /64 subnets for every IPv6 prefix length from /0 to /128. Enter how many /64 subnets you need and the best-fitting prefix length is highlighted automatical...

Subnet Overlap Checker — Detect Whether Two CIDR Blocks Overlap (Free)

Enter two IPv4 CIDR blocks (e.g. 192.168.1.0/24) and instantly find out whether they are identical, one contains the other, or they don't overlap at all. Useful for catching conflicts when designing firewall rules or VPC...