Why use this calculator?
Calculate the network, mask, broadcast and usable address range of an IPv4 address in one click.
Use cases:
- ACLs and firewalls: Get network and wildcard for your rules
- VLAN planning: Size subnets based on host count
- Config verification: Check a configuration provided by an operator
- Documentation: Properly document an addressing plan
What the tool calculates
Key addresses
| Element | Description | Example (/24) |
|---|---|---|
| Network | First address of the block | 192.168.1.0 |
| Broadcast | Last address (broadcast) | 192.168.1.255 |
| First usable | Network + 1 | 192.168.1.1 |
| Last usable | Broadcast - 1 | 192.168.1.254 |
Two ranges, two purposes. The usable range (first usable · last usable) is what you assign to hosts. The complete range (reserved included) reports first, last and total addresses including the network and broadcast addresses - the range you actually need for firewall rules and ACLs, where every address in the block counts.
| Range | First | Last | Total | Use |
|---|---|---|---|---|
| Usable | 192.168.1.1 | 192.168.1.254 | 254 | Host assignment |
| Complete (reserved included) | 192.168.1.0 | 192.168.1.255 | 256 | Firewall / ACL |
Masks
- CIDR: /24
- Decimal: 255.255.255.0
- Wildcard: 0.0.0.255
Classification
The tool tags the address with a badge showing which of 11 categories it belongs to: public, private (RFC 1918), CGNAT (RFC 6598), loopback, link-local (APIPA), multicast, documentation, benchmarking, broadcast, reserved or this-network.
Common prefix table
| CIDR | Mask | Addresses | Hosts | Typical use |
|---|---|---|---|---|
| /32 | 255.255.255.255 | 1 | 1 | Single host |
| /31 | 255.255.255.254 | 2 | 2 | Point-to-point link |
| /30 | 255.255.255.252 | 4 | 2 | Router link |
| /29 | 255.255.255.248 | 8 | 6 | Small network |
| /28 | 255.255.255.240 | 16 | 14 | Small office |
| /27 | 255.255.255.224 | 32 | 30 | SMB |
| /26 | 255.255.255.192 | 64 | 62 | Department |
| /25 | 255.255.255.128 | 128 | 126 | Floor |
| /24 | 255.255.255.0 | 256 | 254 | Standard network |
| /16 | 255.255.0.0 | 65,536 | 65,534 | Large network |
Special address ranges
Private addresses (RFC 1918)
10.0.0.0/8 → 16 million addresses
172.16.0.0/12 → 1 million addresses
192.168.0.0/16 → 65,000 addresses
Other reserved ranges
| Range | Usage |
|---|---|
| 127.0.0.0/8 | Loopback (localhost) |
| 169.254.0.0/16 | Link-local (APIPA) |
| 100.64.0.0/10 | CGNAT operators |
| 224.0.0.0/4 | Multicast |
FAQ - Frequently asked questions
Q: What's the difference between mask and CIDR?
A: The decimal mask (255.255.255.0) and CIDR prefix (/24) represent the same thing: the network bits. CIDR is more compact. A /24 = 255.255.255.0 = 256 addresses.
Q: What is the wildcard mask?
A: The wildcard is the inverse of the mask. For 255.255.255.0, the wildcard is 0.0.0.255. It's used in Cisco ACLs to define which bits must match (0) or can vary (1).
Q: Why can't I use the network and broadcast addresses?
A: The network address (first in the block) identifies the network itself. The broadcast address (last) sends to all hosts. They cannot be assigned to machines.
Q: How many hosts in a /24?
A: A /24 contains 256 addresses (2^8). Minus the network and broadcast, 254 usable addresses remain for hosts.
Q: What is a /31 and when to use it?
A: A /31 (2 addresses, no broadcast) is used for point-to-point links between routers per RFC 3021. Verify your equipment supports it.
Q: Can I use private addresses on the Internet?
A: No. The ranges 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 are reserved for internal networks. They require NAT to access the Internet.
Complementary tools
| Tool | Purpose |
|---|---|
| IPv6 Subnet Calculator | Calculate IPv6 subnets, prefixes and reverse DNS |
| Whois IP | Identify the owner of an IP |
| Reverse DNS | Find the hostname of an IP |
| Check if an IP is blacklisted | See whether an IP is listed on DNS blacklists |