IP Address Validator (IPv4 + IPv6) with Subnet Helper
Validate v4 or v6. Add a CIDR for subnet math. Pure client-side.
What this tool does
Accepts an IPv4 dotted-quad or IPv6 hex-colon address, optionally followed by a slash and a CIDR prefix length. Validates the address, normalizes the format, and (if a prefix is provided) computes the network address, the broadcast address (IPv4 only), the usable host range, and the total number of addresses in the subnet. Everything is calculated locally; no DNS lookups, no external calls.
How to use it
Paste an address into the input. With no slash, you get just validation and the
normalized form. Add /24 or /64 or any valid prefix length to
get subnet info. Examples: 192.168.1.10/24 shows network
192.168.1.0, broadcast 192.168.1.255, 254 usable hosts.
2001:db8::1/64 shows the network address and the address count.
Common use cases
- Confirming an address you typed is syntactically valid before pasting it into a config file.
- Computing the broadcast address of a subnet without doing the binary math by hand.
- Counting how many usable hosts a /23 has compared to a /24 (for capacity planning).
- Normalizing a sloppy IPv6 string with redundant leading zeros into the canonical form.
- Spotting that
192.168.1.0/24network address differs from a typical host like192.168.1.1.
Common pitfalls
- IPv6 abbreviation rules. A run of all-zero groups can be replaced with
::at most once per address.2001::1::1is invalid (two compressions). - Broadcast and IPv6. IPv6 has no broadcast address; it uses multicast instead. This tool shows broadcast for IPv4 only.
- Network address vs host. The first address in a CIDR block (e.g.,
192.168.1.0for /24) is reserved as the network address, not a usable host. IPv6 conventions vary by use case.
Frequently asked questions
- What is CIDR notation and what does the slash number mean?
- CIDR notation appends /N to an IP address where N is the prefix length: how many bits identify the network. /24 means the first 24 bits are network and the last 8 are host. A /16 has twice as many host addresses as /17. IPv4 prefix lengths run /0 to /32; IPv6 runs /0 to /128.
- What is the difference between network address and broadcast address?
- For IPv4, the first address in a CIDR block (host bits all zero) is the network address used as the network identifier. The last address (host bits all one) is the broadcast address used to reach every host on the network at once. Neither is usable as a regular host address. So a /24 has 256 addresses but only 254 usable for hosts.
- Does IPv6 have a broadcast address?
- No. IPv6 abandoned broadcast in favor of multicast for one-to-many delivery. The first and last addresses in an IPv6 prefix are typically usable as host addresses. The :: address (all zeros) is reserved as the unspecified address, and some prefixes have other special meanings, but the network/broadcast distinction from IPv4 does not apply.
- How do I shorten an IPv6 address?
- IPv6 addresses can be compressed by replacing the longest run of consecutive all-zero groups with :: (only once per address). Leading zeros within a group can be omitted. For example 2001:0db8:0000:0000:0000:0000:0000:0001 becomes 2001:db8::1. The tool prints addresses in this canonical compressed form automatically.
- What does /32 (or /128 for IPv6) mean?
- A /32 (IPv4) or /128 (IPv6) prefix describes a single host: the prefix length covers the entire address, leaving no host bits. Useful for firewall rules that target one specific machine. The opposite extreme, /0, matches all addresses (the entire internet) and is useful for default routes.
- Is 192.168.1.1/24 valid? It is a host, not a network.
- Syntactically yes. CIDR notation can describe either a network or a specific host within a network. 192.168.1.1/24 means "host 192.168.1.1 on the 192.168.1.0/24 network." Tools and configs interpret this depending on context. The tool here treats it as a host address and computes the surrounding network info from it.
Cite this tool
For academic, journalistic, or technical references. Pick a format:
Citations use 2026 as the publication year. Access date is left as a fillable placeholder where the citation style expects one.