Network Engineering
IPv4 Subnet
Calculator
The most complete IPv4 subnet tool. Calculate network ranges, split subnets, visualise binary maps, detect IP classes, and instantly convert between CIDR and dotted-decimal notation.
Network, broadcast, first & last host addresses
Subnet mask, wildcard mask, CIDR conversion
Visual binary bit-map with network/host highlighting
Split any network into N equal subnets
IP class, type & special range detection
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IP Address Input
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Network Details
Binary Visualisation
IP Class
Address Type & Properties
Subnet Splitter
Split into equal subnets
| # | Network | First Host | Last Host | Broadcast | Hosts | Mask |
|---|
All Subnet Masks Reference
| CIDR | Dotted Decimal | Wildcard | Hosts |
|---|
Special IP Ranges
| Range | Type | Purpose |
|---|---|---|
| 10.0.0.0/8 | Private | Class A private |
| 172.16.0.0/12 | Private | Class B private |
| 192.168.0.0/16 | Private | Class C private |
| 127.0.0.0/8 | Loopback | Localhost |
| 169.254.0.0/16 | APIPA | Link-local / DHCP fail |
| 224.0.0.0/4 | Multicast | Class D multicast |
| 240.0.0.0/4 | Reserved | Class E reserved |
| 0.0.0.0/8 | Reserved | This network |
| 100.64.0.0/10 | Shared | Carrier-grade NAT |
| 192.0.2.0/24 | Docs | TEST-NET-1 (RFC 5737) |
| 198.51.100.0/24 | Docs | TEST-NET-2 (RFC 5737) |
| 203.0.113.0/24 | Docs | TEST-NET-3 (RFC 5737) |
| 255.255.255.255/32 | Broadcast | Limited broadcast |
IPv4 Subnetting Reference Guide
Subnetting is the process of dividing a network into smaller sub-networks. It helps conserve IP addresses, improve network performance, and enhance security by limiting broadcast domains. Every network engineer needs to understand CIDR notation, subnet masks, network addresses, and host ranges.
What is CIDR notation and how does it work?
CIDR (Classless Inter-Domain Routing) notation represents an IP address and its subnet mask as IP/prefix-length. For example, 192.168.1.0/24 means the first 24 bits are the network portion and the remaining 8 bits are host bits. /24 equals subnet mask 255.255.255.0, giving 254 usable hosts.
How do I calculate the number of usable hosts in a subnet?
Usable hosts = 2^(host bits) - 2. Subtract 2 because the network address (all host bits = 0) and broadcast address (all host bits = 1) cannot be assigned to devices. For /24: 2^8 - 2 = 254. For /30: 2^2 - 2 = 2. Exception: /31 networks (point-to-point links per RFC 3021) allow 2 usable hosts, and /32 is a single host route.
What is a wildcard mask and how is it different from a subnet mask?
A wildcard mask is the inverse of a subnet mask. Where a subnet mask has 1s for network bits, a wildcard mask has 0s — and vice versa. Wildcard masks are used in Cisco ACLs and OSPF area definitions. For subnet 255.255.255.0, the wildcard is 0.0.0.255. Calculate by subtracting each octet from 255.
What are the private IP address ranges?
RFC 1918 defines three private ranges: 10.0.0.0/8 (16,777,216 addresses, Class A), 172.16.0.0/12 (1,048,576 addresses, Class B, covers 172.16.0.0–172.31.255.255), and 192.168.0.0/16 (65,536 addresses, Class C). These are not routed on the public internet and require NAT to access external networks.
What is subnetting and why is it important?
Subnetting divides a large network into smaller, more manageable sub-networks. Benefits include: reduced broadcast traffic (each subnet is its own broadcast domain), improved security (isolate departments or services), better IP address management, and simplified routing. For example, /24 can be split into two /25 subnets, each with 126 usable hosts instead of 254.
What is the difference between network address and broadcast address?
The network address (all host bits = 0) identifies the subnet itself and cannot be assigned to a host. The broadcast address (all host bits = 1) is used to send packets to all hosts in the subnet simultaneously. For 192.168.1.0/24: network = 192.168.1.0, broadcast = 192.168.1.255, usable hosts = 192.168.1.1 to 192.168.1.254.