IP address parser and CIDR subnet calculator in one place
This IP address parser reads any IPv4 or IPv6 address — with or without a prefix length, a netmask, a zone ID or brackets — and shows everything a network engineer usually works out by hand: the canonical text form, the fully expanded form, integer, hexadecimal and binary values, the reverse DNS name, and which IANA special-purpose block the address belongs to. Add a prefix such as /26 and it doubles as a subnet calculator, with network and broadcast addresses, netmask, wildcard mask, usable host range and host count.
Below the main result are three subnet tools: split a network into equal subnets, summarise a messy list of addresses and ranges into the fewest CIDR blocks, and check whether an address falls inside one or more ranges. Everything is calculated in your browser with exact 128-bit arithmetic — nothing you type is sent anywhere. To see who operates a public address and where it is, use IP Lookup; to find your own, open What Is My IP.
How to use the IP Address Parser & Subnet Calculator
- Type or paste an address into “IP address, CIDR block or integer”, for example
192.168.1.130/26or2001:db8::1. Results update as you type. - Read the canonical form at the top, then the Address card (formats, reverse DNS name, embedded IPv4) and the Subnet card.
- Check the special-purpose table to see whether the address is private, documentation, link-local, multicast or globally reachable.
- Pick a subnet tool — “Split a subnet”, “Summarise a list” or “Is an IP in a range?” — and fill in its fields.
- Use “Copy all details”, “Copy subnet list” or “Copy merged list” to paste the results into a ticket, firewall rule or configuration file.
IP Address Parser & Subnet Calculator features
RFC 5952 normalisation
IPv6 addresses are lower-cased, leading zeros dropped and the longest run of zero groups compressed — the form RFC 5952 recommends — with mixed notation for IPv4-mapped addresses.
IANA special-purpose ranges
Every block in the IPv4 and IPv6 special-purpose registries (updated 9 October 2025), with their Source, Destination, Forwardable, Globally Reachable and Reserved-by-Protocol properties.
Embedded addresses decoded
IPv4-mapped, NAT64, 6to4 and Teredo addresses reveal the IPv4 address inside; modified EUI-64 interface IDs reveal the MAC address they were built from.
Correct edge cases
/31 networks give two usable addresses (RFC 3021), /32 a single host, and IPv6 blocks of any size are counted exactly.
Split, summarise, contains
Divide a block by number of subnets, prefix length or hosts needed; merge overlapping and adjacent ranges; test membership against several ranges at once.
Worked example: 192.168.1.130/26
A /26 keeps 26 network bits, so 6 bits are left for hosts: 26 = 64 addresses per block. The netmask is 255.255.255.192 and the wildcard mask (its inverse, used in Cisco access lists) is 0.0.0.63. The last octet, 130, falls in the block that starts at 128 (blocks begin at 0, 64, 128 and 192), so the network address is 192.168.1.128 and the broadcast address is 192.168.1.191. Hosts can use 192.168.1.129 to 192.168.1.190 — 62 addresses, because the network and broadcast addresses are reserved.
Two exceptions apply: a /31 has no broadcast address, so both of its addresses can be used on a point-to-point link (RFC 3021), and a /32 identifies exactly one host. In IPv6 there is no broadcast at all; the first address of each subnet is the Subnet-Router anycast address.
How RFC 5952 shortens an IPv6 address
IPv6 allows many spellings of the same address, which breaks searches, log matching and string comparisons. RFC 5952 defines one canonical text form:
- Use lower-case hex digits and drop leading zeros in each group:
0db8becomesdb8. - Replace the longest run of two or more all-zero groups with
::; if two runs tie, shorten the first. A single zero group is never shortened. - So
2001:0db8:0000:0000:0001:0000:0000:0001becomes2001:db8::1:0:0:1, and2001:0:0:1:0:0:0:1becomes2001:0:0:1::1. - Write an IPv4-mapped address as
::ffff:192.0.2.128, keeping the familiar dotted IPv4 part.
Common special-purpose ranges
| Range | Meaning |
|---|---|
| 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16 | Private-Use networks (RFC 1918) |
| 100.64.0.0/10 | Shared address space for carrier-grade NAT (RFC 6598) |
| 169.254.0.0/16, fe80::/10 | Link-local — automatic addresses that never leave the local link |
| 192.0.2.0/24, 198.51.100.0/24, 203.0.113.0/24, 2001:db8::/32, 3fff::/20 | Documentation and examples |
| fc00::/7 | IPv6 unique local addresses, the counterpart of private IPv4 (RFC 4193) |
| 2002::/16, 2001::/32, 64:ff9b::/96 | 6to4, Teredo and NAT64 — transition formats with an IPv4 address inside |
IP Address Parser & Subnet Calculator FAQ
How many usable hosts are in a subnet?
For IPv4, 2(32 − prefix) − 2: a /24 has 254, a /26 has 62 and a /30 has 2. The two missing addresses are the network and broadcast addresses. A /31 is the exception with 2 usable addresses (RFC 3021) and a /32 is a single host.
What is the difference between a netmask and a wildcard mask?
A netmask has 1 bits for the network part (255.255.255.0 for a /24); a wildcard mask is its inverse (0.0.0.255) and is used by Cisco ACLs and OSPF network statements. You can type either after a slash and the parser converts it to a prefix length.
Why does my IPv6 address look different after parsing?
The canonical RFC 5952 form drops leading zeros, uses lower case and compresses the longest run of zero groups. It is the same address — only the spelling changes, so logs and configuration files can be compared reliably.
Can this IP address parser tell me where an address is located?
No — it works offline from the address itself. It tells you whether an address is private, reserved or globally reachable. For the owner, ISP and country of a public address, use the IP Lookup tool.
How do I summarise several subnets into one route?
Open “Summarise a list” and paste the blocks. Adjacent blocks merge only when the result is a valid CIDR block — 192.168.0.0/24 and 192.168.1.0/24 become 192.168.0.0/23. The covering supernet shows the single smallest block containing everything and how many extra addresses it would include.
What does the %eth0 at the end of an IPv6 address mean?
It is a zone ID. Link-local addresses such as fe80::1 exist on every interface, so the zone tells the operating system which interface to use. In URLs the % is written as %25, for example [fe80::1%25eth0] (RFC 6874).