Network tools
Diagnose DNS, connectivity, certificates and mail delivery from one place. Every check runs live from our server, and every result gets a link you can share.
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.Subnet calculatorEnter an address with a prefix or a mask, for example 192.168.10.37/26 or 10.0.0.1 255.255.240.0.What is my IP?This is the address websites see when you connect to them.
Guides
What Is an IP Address?Learn what an IP address is, how IPv4 and IPv6 differ, which ranges are private (RFC 1918, CGNAT), how NAT works and how to find your own IP address.Subnet Mask and CIDR ExplainedLearn how subnet masks and CIDR notation work, with a worked /26 example, a full /8 to /32 cheat sheet, wildcard masks and IPv6 /48, /56 and /64 rules.The OSI Model: 7 Layers ExplainedThe OSI model has seven layers, from physical to application. Learn each layer, how it maps to TCP/IP, and which layer ping, DNS, TLS and port checks test.Well-Known Ports and What They MeanWhat network ports are, TCP vs UDP, port ranges, how to test if a port is open, closed or filtered, and which ports you should never expose to the internet.How DNS WorksDNS turns domain names into IP addresses. See the resolution path, record types, caching and TTL, what DNS propagation is, and how to spread changes fast.