🌐 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.
7 tools available · 100% free · No signup required
MAC Address Formatter & Analyzer
Format MAC addresses between colon, hyphen, Cisco dot, and bare notations. Analyze I/G and U/L bits, generate EUI-64 interface identifiers for IPv6 SLAAC, and create random locally-administered MACs — all 100% client-side.
IP Subnet Calculator
Calculate network address, broadcast, first and last usable hosts, wildcard mask, and total host count from any IPv4 address and prefix length or subnet mask.
CIDR Calculator
Expand CIDR notation to IP ranges (IPv4 and IPv6), split a block into smaller subnets, check overlap between two CIDRs, and summarize multiple prefixes into the smallest covering supernet.
Port Number Lookup
Look up common TCP/UDP port numbers, their associated protocols, and security notes. Search by port number or service name across a curated reference of approximately 100 commonly queried ports.
Bandwidth & Download Time Calculator
Calculate how long a download takes at a given connection speed, or the speed needed to finish in a set time. Handles the Mbps vs MB/s confusion, decimal vs binary bytes, and TCP overhead — all in your browser.
IPv4 to IPv6 Converter
Encode an IPv4 address into every standard IPv6 form — IPv4-mapped, 6to4, and NAT64 — and compress or expand any IPv6 address to its RFC 5952 canonical form, all in your browser.
IP Address Validator & Classifier
Validate IPv4 and IPv6 addresses and classify each as public, private, loopback, link-local, CGNAT, multicast, or documentation. Includes batch mode, reverse-DNS name, and integer, hex, and binary forms.
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.