What are the private IPv4 address ranges?

10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 (RFC 1918). They are used inside offices and homes and are not routed on the public internet. 100.64.0.0/10 is shared address space used for carrier-grade NAT.

What is a wildcard mask?

The inverse of the subnet mask, for example 0.0.0.255 for a /24. Cisco access lists and OSPF use wildcard masks to say which bits of an address must match.

Free IP, Subnet, DNS & Email Tools

Q: What does an IP subnet calculator do?

It takes an IP address and a prefix length (CIDR, for example /24) or subnet mask and works out the network address, broadcast address, first and last usable host, how many hosts fit, the wildcard mask and every other subnet of that size in the block.

Q: How many usable hosts are in a /24?

A /24 (subnet mask 255.255.255.0) has 256 addresses. Two are reserved for the network and broadcast address, leaving 254 usable hosts. A /31 is the exception: point-to-point links use both addresses (RFC 3021).

Find your public IP address and work out any network with the IPv4 and IPv6 subnet calculator, side by side. Then check DNS, MX, SPF, DMARC, DKIM, blacklists, SSL certificates, HTTP headers and WHOIS. Free, no sign-up, and nothing you enter is stored.

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🌐 What's my IPSee the public IP address your connection is using right now, its reverse DNS and country. 🧮 IP subnet calculatorNetwork and broadcast address, usable host range, masks and every subnet in the block, for IPv4 and IPv6. 🔍 DNS lookupQuery any record type (A, AAAA, CNAME, MX, NS, TXT, SOA, SRV, CAA) for a domain. 📧 MX lookupWhich mail servers accept email for a domain, in priority order, with the provider identified. 🛡 SPF checkValidate the SPF record: mechanisms, the 10-lookup limit and the all qualifier. 🔒 DMARC checkIs the domain protected against spoofing? Policy, reporting addresses and alignment. 🔑 DKIM checkFind and validate DKIM signing keys, by selector or by scanning the common ones. ⛔ Blacklist checkIs a mail server IP or domain listed on the major spam blocklists (18 DNSBLs)? 🔐 SSL certificate checkExpiry, issuer, covered names, chain and protocol for any HTTPS host. 📄 HTTP headersResponse headers for a URL with a security-header scorecard (HSTS, CSP, X-Frame-Options...). ↩ Reverse DNSPTR record for an IP and whether it forward-confirms (FCrDNS), a common mail deliverability check. 🔐 Has my password been pwned?Check a password against 900+ million leaked passwords without it ever leaving your browser (k-anonymity: only 5 characters of its hash are sent). 📋 WHOIS lookupRegistrar, key dates, name servers and status for a domain, or the network owner of an IP.

About the IP and subnet tools

What does an IP subnet calculator do?

Enter an IP address and a prefix length (CIDR, for example /24) or a subnet mask such as 255.255.255.0. The calculator works out the network address, broadcast address, first and last usable host, the number of hosts, the wildcard mask and every other subnet of that size in the block. It runs entirely in your browser.

How many usable hosts are in a /24?

A /24 has 256 addresses. The network and broadcast addresses are reserved, leaving 254 usable hosts. Each extra prefix bit halves the block: a /25 gives 126 hosts, a /26 gives 62, a /30 gives 2. A /31 is the exception: point-to-point links use both addresses (RFC 3021).

Private IP address ranges

10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 are private (RFC 1918) and are not routed on the internet, which is why your device address differs from the public IP shown by What's my IP. 100.64.0.0/10 is shared space used for carrier-grade NAT, and 169.254.0.0/16 means a device failed to get a DHCP address.

IPv6 subnets

IPv6 addresses are 128 bits. A single LAN is normally a /64, a site is usually given a /48 or /56, and fe80::/10 addresses are link-local only. Paste any IPv6 address, full or compressed, and choose a prefix to see the network range and how many addresses it holds.

Free tools from Total Group, IT support, cyber security and compliance for regulated businesses. Lookups run on our own servers; nothing you enter is stored or shared. Need help fixing what a check found? Talk to us.