What is a subnet calculator?

A subnet calculator is a tool that takes an IP address and subnet mask (or CIDR notation) and computes the network address, broadcast address, usable host range, number of hosts, and other network details automatically.

What is VLSM and how does the VLSM calculator work?

VLSM (Variable Length Subnet Masking) allows you to use different subnet sizes within the same network, optimizing IP address usage. Our VLSM calculator takes your network address and a list of required host counts, then automatically allocates the most efficient subnets.

What is CIDR notation?

CIDR (Classless Inter-Domain Routing) notation represents an IP address and its subnet mask as a single expression. For example, 192.168.1.0/24 means the network 192.168.1.0 with a 24-bit subnet mask (255.255.255.0), giving 254 usable hosts.

How do I calculate a wildcard mask?

A wildcard mask is the inverse of a subnet mask, used in Cisco ACLs and OSPF configurations. To calculate it, subtract each octet of the subnet mask from 255. For example, subnet mask 255.255.255.0 becomes wildcard mask 0.0.0.255.

Is this subnet calculator free to use?

Yes, this is a completely free online subnet calculator. No registration, no login, and no API key required. All calculations run in your browser instantly.

Can I check if two networks overlap?

Yes! Use our Network Overlap Checker tab. Enter two or more network ranges in CIDR notation and the tool will instantly detect if they overlap — perfect for cloud VPC planning (AWS, Azure, GCP) and network design.

Free IP Subnet Calculator & Network Planner Tool

IPv4 Subnet Calculator

Enter an IP address with CIDR notation or subnet mask to calculate full network details

IP Address

Subnet Mask

Quick Select:

Examples:

⚡

Results appear instantly as you type

VLSM Network Planner

Variable Length Subnet Masking — Enter your parent network and required host counts per subnet

Parent Network (CIDR)

Network Overlap Checker

Detect conflicting IP ranges — critical for AWS VPC, Azure VNet, and GCP VPC network planning

☁️ Cloud Planning Tip: AWS VPC peering, Azure VNet peering, and GCP VPC peering all require non-overlapping CIDR ranges. Use this tool before provisioning cloud networks to avoid conflicts.

Wildcard Mask Converter

Convert subnet masks to Cisco ACL wildcard masks and vice-versa

Subnet Mask or CIDR

Common masks:

Property	Value	Binary

📋 Complete CIDR ↔ Subnet ↔ Wildcard Reference

CIDR	Subnet Mask	Wildcard Mask	Hosts	Networks

IPv6 Subnet Calculator

Calculate IPv6 network details, expand/compress addresses, and plan IPv6 subnets

IPv6 Address / Prefix

Examples:

IP Geolocation Lookup

Look up location, ISP, ASN and other details for any public IPv4 or IPv6 address

🔒 Privacy Note: Lookups use the public ip-api.com free API. Only public IPs are supported. Private RFC1918 addresses cannot be geolocated.

Network Engineer Cheat Sheet

Essential IP addressing reference — bookmark this page for quick access

📊 IPv4 CIDR Quick Reference

CIDR	Subnet Mask	Hosts	Wildcard
/8	255.0.0.0	16,777,214	0.255.255.255
/16	255.255.0.0	65,534	0.0.255.255
/24	255.255.255.0	254	0.0.0.255
/25	255.255.255.128	126	0.0.0.127
/26	255.255.255.192	62	0.0.0.63
/27	255.255.255.224	30	0.0.0.31
/28	255.255.255.240	14	0.0.0.15
/29	255.255.255.248	6	0.0.0.7
/30	255.255.255.252	2	0.0.0.3
/31	255.255.255.254	2*	0.0.0.1
/32	255.255.255.255	1 (host)	0.0.0.0

* /31 used for point-to-point links per RFC 3021

🏠 Private IP Ranges (RFC 1918)

Range	CIDR	Class	Hosts
10.0.0.0–10.255.255.255	10.0.0.0/8	A	16.7M
172.16.0.0–172.31.255.255	172.16.0.0/12	B	1.04M
192.168.0.0–192.168.255.255	192.168.0.0/16	C	65,534

🔧 Special IP Addresses

Address / Range	Purpose
127.0.0.0/8	Loopback / localhost
169.254.0.0/16	APIPA / Link-local
224.0.0.0/4	Multicast
240.0.0.0/4	Reserved (Class E)
0.0.0.0/8	This network (source only)
255.255.255.255	Limited broadcast

☁️ Cloud Provider IP Ranges

Provider	Common VPC Default	Notes
AWS	172.31.0.0/16	Default VPC, avoid in production
Azure	10.0.0.0/16	Default VNet suggestion
GCP	10.128.0.0/9	Auto-mode VPC
Docker	172.17.0.0/16	Default bridge network
K8s Pods	10.244.0.0/16	Flannel default
K8s Services	10.96.0.0/12	kubeadm default

📡 Common Port Reference

Port	Protocol	Service
22	TCP	SSH
53	TCP/UDP	DNS
80	TCP	HTTP
443	TCP	HTTPS
3389	TCP	RDP
3306	TCP	MySQL
5432	TCP	PostgreSQL
6379	TCP	Redis
8080	TCP	HTTP Alt
179	TCP	BGP
161/162	UDP	SNMP
123	UDP	NTP

Built by Austere Systems · austeresystems.eu

Visual IP & Network Planner