Subnet calculator
Enter an address with a prefix or a mask, for example 192.168.10.37/26 or 10.0.0.1 255.255.240.0.
Frequently asked questions
How many hosts fit in a /24?
A /24 has 256 addresses. The first is the network address and the last is the broadcast address, so 254 are usable for hosts.
What is a wildcard mask?
The inverse of the subnet mask (255.255.255.0 becomes 0.0.0.255). Cisco ACLs and OSPF use it to say which bits must match.
Tools
DNS propagation checkerQuery resolvers around the world and the zone's authoritative nameservers in one go, and see on the map where your change has arrived.PingRound-trip time and packet loss from our server. Use TCP mode when a host drops ICMP.TracerouteThe path packets take from our server to the target, hop by hop, with the network (ASN) each router belongs to.SSL / TLS checkCertificate validity, chain, hostname match and which TLS versions the server accepts.Port checkIs a TCP port reachable from the internet? Test a server, or your own connection to confirm port forwarding.HTTP headersFollow the redirect chain, see response headers and timing, and grade the security headers.WHOIS lookupRegistration details for a domain or the owner of an IP range, straight from the registry's WHOIS servers.Mail & blacklistMX, SPF, DMARC and DKIM for a domain, plus a check of its mail servers against public DNS blocklists.What is my IP?This is the address websites see when you connect to them.