🌐 Free Online Network Tools
Free networking calculators — IP subnet and CIDR calculators, IPv4 to IPv6 conversion, IP validator, MAC address formatter, port lookup, and download time calculator.
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Subnetting is the kind of task where a small arithmetic slip produces a configuration that looks fine and quietly breaks a network. These networking tools do the bit-level maths for you and show their working, so you can check the result rather than trust it blindly. You can expand an address and prefix into the network address, broadcast address, usable host range and host count, split a block into smaller subnets or summarise a range back into the fewest CIDR blocks, convert an IPv4 address into its IPv6 representations, validate and classify any address, reformat a MAC address between the four notations different vendors use, look up what service normally sits on a port, and work out how long a download will take at a given speed. Every one of them is pure computation or a static reference — there are no lookups against an external service, which means nothing here can go stale or fail because a third-party API changed.
Subnetting and CIDR with the edge cases handled
The subnet calculator converts your address to a 32-bit value, builds the mask from the prefix length, and derives the network and broadcast addresses, the first and last usable host, the host count, the wildcard mask for access control lists, and a binary view with the network boundary visible. It handles the prefixes that break most free calculators: a slash-31 has two addresses and no broadcast address at all, which is exactly how point-to-point links are configured, and a slash-32 is a single host. Calculators that blindly subtract two from the address count report negative hosts for these, which is nonsense. The CIDR tool goes further — splitting a block into equal smaller subnets, summarising an arbitrary start-to-end range into the minimum set of aligned blocks, and checking whether two blocks overlap or contain one another. IPv6 arithmetic is done with big integers, because a 128-bit address cannot be held in a regular number.
Address validation, conversion, and MAC analysis
The validator accepts IPv4 and IPv6, rejects the ambiguous forms such as octets with leading zeros, and then classifies what you gave it: public, private, loopback, link-local, multicast, documentation, or carrier-grade NAT — that last range is frequently mistaken for public space and is worth knowing about. The IPv4-to-IPv6 converter produces the mapped, 6to4 and NAT64 representations, and compresses or expands IPv6 addresses following the canonical rules, which specify lowercase hex and collapsing the leftmost longest run of zeros. The MAC address tool reformats between colon, hyphen, Cisco dot and bare notations, and reads the two meaningful bits in the first octet to tell you whether the address is unicast or multicast and whether it was assigned by a manufacturer or set locally. It does not claim to name the vendor, because the manufacturer registry changes constantly and a bundled copy would eventually be wrong.
Reference data and bandwidth arithmetic
The port reference covers the well-known and registered ports people actually search for, with the protocol, the usual service, and a security note where one is warranted — Telnet on 23 sends everything in the clear, FTP on 21 sends credentials in plaintext, and RDP on 3389 should never face the open internet. It also explains the three port ranges, which is useful when you are choosing a port for your own service. The download time calculator exists because of one persistent confusion: internet speeds are quoted in megabits per second while file sizes are in megabytes, a factor of eight apart. The tool shows that division explicitly, accepts either unit for either input, and lets you choose between decimal and binary interpretations of a megabyte, since your internet provider and your operating system use different ones. There is also a reverse mode for working out the speed you need to move a given amount of data in a given window.