Networking
Subnets, prefixes and address maths for IPv4 and IPv6.
Subnet calculatorIPv4 CIDR: network, broadcast, usable range, mask in binary, subnet splitting192.168.1.0/24 → 254 hostsIPv6 calculatorExpand or compress an address, get the prefix range, type and reverse DNS2001:db8::1/64IP address ⇄ integerDotted IPv4 to decimal, hex, binary and octal, and back192.168.1.1 = 3232235777MAC address lookup & formatterVendor (OUI), address type, every notation, EUI-64 and link-local address00:0C:29:… → VMwareDNS lookup & mail checkerLive records from Cloudflare and Google resolvers, propagation diff, SPF include chain, DMARC and DKIMexample.com → A, MX, TXT… SPF 4 of 10 lookupsPort number referenceWhat listens on which port: well-known and commonly seen TCP/UDP ports, searchable5432 → PostgreSQLDNS record explainerPaste dig output or zone lines: every record decoded, SPF, DKIM and DMARC checkedv=spf1 include:… -all → explainedPacket decoderPaste tcpdump/Wireshark hex or drop a pcap: Ethernet, VLAN, ARP, IPv4/6, TCP, UDP, ICMP, DNS, DHCP, TLS decoded field by field4500 003c … → IPv4 › TCP [SYN] seq 1000 ✓ checksumsCIDR aggregator & splitterMerge a list of IPs and ranges into the fewest prefixes, subtract exclusions, or split blocks10.0.0.0/25 + 10.0.0.128/25 → 10.0.0.0/24Reverse DNS generatorPTR names, in-addr.arpa / ip6.arpa zones and bulk PTR records for a block192.168.1.0/24 → 1.168.192.in-addr.arpaUser-agent parserBrowser, engine, OS, device and bot detection for any User-Agent stringMozilla/5.0 (…) Chrome/129 → Chrome 129, Windows