network calculator
A precise IPv4/IPv6 subnet tool for engineers, admins, and learners. Enter an address in CIDR notation to get network/broadcast, first & last usable, subnet/wildcard masks (IPv4), reverse DNS pointers, and private/public classification.
Network calculator inputs
Choose IPv4 (32-bit) or IPv6 (128-bit).
Results
General
- IP Version
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- Input Address
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- CIDR Prefix
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- Type
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- Private/Reserved
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Mask / Size
- Subnet Mask (v4)
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- Wildcard Mask (v4)
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- Block Size
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- # of Addresses
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- Usable Hosts (v4)
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Range
- Network
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- First Usable
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- Last Usable
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- Broadcast (v4)
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Representations
- Reverse DNS
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- IPv6 (Compressed)
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- IPv6 (Expanded)
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Data Source & Methodology
Primary references:
- IETF RFC 4632 — Classless Inter-Domain Routing (CIDR): IPv4 Addressing Architecture (August 2006).
- IETF RFC 791 — Internet Protocol (IPv4) (September 1981).
- IETF RFC 4291 — IPv6 Addressing Architecture (February 2006).
- IETF RFC 1035 — DNS: in-addr.arpa / ip6.arpa reverse mapping (November 1987).
Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte.
The Formula Explained
Number of addresses for prefix \( p \):
IPv4: \( N = 2^{(32 - p)} \), IPv6: \( N = 2^{(128 - p)} \)
Network address (integer form):
\( \text{network} = \left\lfloor \dfrac{\text{address}}{2^{(W - p)}} \right\rfloor \times 2^{(W - p)} \) where \( W=32 \) (IPv4) or \( W=128 \) (IPv6).
Broadcast (IPv4): \( \text{broadcast} = \text{network} + N - 1 \)
First/Last usable (IPv4, \(p \le 30\)):
\( \text{first} = \text{network} + 1,\quad \text{last} = \text{broadcast} - 1 \)
Glossary of Variables
- Address: The input IP (IPv4 dotted quad or IPv6 hex) with CIDR prefix.
- Prefix (p): Bits that identify the network portion (0–32 for IPv4, 0–128 for IPv6).
- Subnet Mask: IPv4 mask derived from the prefix (e.g., /24 → 255.255.255.0).
- Wildcard Mask: IPv4 complement mask (e.g., 0.0.0.255 for /24).
- Network/Broadcast: First and last addresses in the block (broadcast only for IPv4).
- Usable Hosts: Number of assignable addresses (IPv4 excludes network & broadcast for /0–/30; special cases noted).
How It Works: A Step-by-Step Example
Example: 192.168.10.42/26
- Prefix \(p=26\) ⇒ \(N = 2^{(32-26)} = 64\) addresses.
- Mask = 255.255.255.192; Wildcard = 0.0.0.63.
- Network = 192.168.10.
0+ multiples of 64 ⇒ 192.168.10.0, 64, 128, 192 … The host (42) lies in the 0–63 block ⇒ Network =192.168.10.0. - Broadcast = Network + 63 =
192.168.10.63. - Usable = 62 addresses:
192.168.10.1to192.168.10.62.
FAQ
What prefixes are valid?
IPv4 allows /0 to /32; IPv6 allows /0 to /128. Subnetting typically uses /8–/30 (IPv4) and /32–/64 (IPv6) for routing practicality.
Why are /31 and /32 special in IPv4?
/31 (RFC 3021) can be used for point-to-point without broadcast; /32 denotes a single host route. Usable host count differs from classic “minus 2” rule.
How do private ranges get detected?
The tool checks RFC-defined ranges (e.g., 10/8, 172.16/12, 192.168/16 for IPv4; fc00::/7 for IPv6 unique local).
Why show reverse DNS?
Operations teams use in-addr.arpa/ip6.arpa to verify PTR (reverse) records. We assemble the canonical pointer for the network address.
What if I only enter a mask?
For IPv4 you can paste a mask (e.g., 255.255.255.0) in the helper. The calculator will map it to the nearest valid prefix.
Does the tool validate non-canonical IPv6?
Yes—addresses are normalized to compressed and expanded forms. Invalid compressions or hextet sizes trigger accessible error messages.
Tool developed by Ugo Candido. Content verified by CalcDomain Editorial Board.
Last accuracy review: