Subnets, addresses and MAC lookups
Network maths is exact and unforgiving: one bit off in a netmask and the host range is wrong. These tools do the arithmetic for CIDR blocks, address formats, range-to-CIDR aggregation and IPv6 ULA prefixes, and show the binary so you can check the working.
The MAC vendor lookup uses a bundled OUI list, so it works with no network connection at all.
7 Network tools
Compute network, broadcast, netmask, host range and host count from a CIDR, locally.
Convert an IPv4 address between dotted-decimal, integer, hex, octal, binary and IPv6-mapped, locally.
Find the smallest CIDR block that fully contains a start and end IPv4 address, locally.
Generate a random RFC 4193 Unique Local Address prefix (fd00::/8) with subnet, locally.
Generate random MAC addresses with a chosen separator, case and optional OUI prefix, locally.
Find the vendor of a MAC address from a bundled set of common OUI prefixes, locally.
Pick random, unused-range TCP/UDP port numbers for local services, locally.