Subnet Calculator
The ultimate utility for network engineers and architects. Analyze CIDR ranges, subnet masks, and network boundaries with professional precision.
10.0.0.0/8 - Large Enterprise
172.16.0.0/12 - Medium Org
192.168.1.0/24 - Home/Small Office
127.0.0.1/32 - Local Host
Beyond the IP: The Architectural Power of Subnetting
In the digital age, IP addresses are the coordinates of the internet. However, an unmanaged pool of IP addresses is like a city without streets. **Subnetting** is the process of creating that urban planning—dividing a large network into smaller, logically efficient neighborhoods.
The "Usable Host" Dilemma
A common point of confusion for network students is why a /24 network has 256 total addresses but only **254 usable hosts**. This is because the first address (binary ending in all 0s) is reserved as the **Network ID**, and the last address (all 1s) is reserved as the **Broadcast ID**. Our calculator automatically deducts these for you, ensuring your VLSM planning is always accurate.
Security & Isolation
Subnetting allows you to isolate sensitive departments. By placing HR and Finance on different subnets, you can implement router-based access control lists (ACLs) to prevent unauthorized internal traffic.
Traffic Management
Large networks suffer from "broadcast storms." Subnetting breaks up these broadcast domains, significantly reducing congestion and improving overall packet delivery speeds.
CIDR: The Language of Modern Routing
Before 1993, we used "Classful" networking, which was incredibly wasteful. CIDR (Classless Inter-Domain Routing) introduced the slash notation (e.g., /22) we use today. It allows for "Supernetting"—combining multiple contiguous /24 networks into a single route—standard practice for ISPs to keep global routing tables lean.
CIDR Quick Reference
Protocol FAQ
What is a Wildcard Mask?
It is the inverse of a subnet mask (e.g., 0.0.0.255 for a /24). It is primarily used in OSPF routing and Cisco Access Control Lists to specify which bits of an IP should be ignored.
Can a subnet have 0 usable hosts?
Yes. In a /31 or /32 network, there are no addresses left for both Network/Broadcast and Usable hosts. However, RFC 3021 allows /31 for point-to-point links by treating both as usable.
How do I choose the right subnet size?
Calculate the current number of devices, multiply by 1.5 for 2-year growth, and find the smallest CIDR that fits. For 20 devices, you need 30 IPs, so a /27 is perfect.