Subnet Calculator

Subnetting is the fundamental architectural technique used in IPv4 networking to partition a master network into smaller, efficient, and secure broadc

Networking

IPv4 Address

Subnet Mask / Prefix

Formula & Methodology

ext{Subnet Mask} = (2^{32} - 1) ll (32 - ext{Prefix}) pmod{2^{32}} ext{Wildcard Mask} = sim ext{Subnet Mask} pmod{2^{32}} ext{Network IP} = ext{Host IP} & ext{Subnet Mask} ext{Broadcast IP} = ext{Network IP} | ext{Wildcard Mask} ext{Usable Hosts} = 2^{32 - ext{Prefix}} - 2 quad ( ext{for } /0 le ext{Prefix} le /30)

Bitwise AND-ing the 32-bit host IP with the subnet mask clears the host bits, yielding the base network address. Bitwise OR-ing the network address with the inverted wildcard mask sets all host bits to 1, producing the broadcast address. The usable host range spans from one above the network address to one below the broadcast address. For /31 prefixes (RFC 3021), both addresses are usable without dedicated network or broadcast reservations.

Network Identifier & CIDR Block

192.168.1.0/24

Overview

Subnetting is the fundamental architectural technique used in IPv4 networking to partition a master network into smaller, efficient, and secure broadcast domains. The Subnet Calculator analyzes any IPv4 host address and subnet mask prefix (/0 through /32), computing the exact network address, broadcast address, usable client host range, wildcard mask, and total IP capacity.

Whether you are configuring VLAN routing on enterprise switches, defining AWS Virtual Private Cloud (VPC) subnets, setting up firewall access control lists (ACLs), or studying for Cisco CCNA certification, this tool provides instant bitwise accuracy. It incorporates full support for RFC 3021 point-to-point links (/31) and RFC 1918 private scopes.

Worked Examples

Example 1: Standard Class C Local Subnet (192.168.1.10/24)

Host IP = 192.168.1.10, Subnet Mask = /24 (255.255.255.0)

Convert IP to 32-bit binary: 11000000.10101000.00000001.00001010.
Apply /24 mask (first 24 bits 1s, last 8 bits 0s): 255.255.255.0.
Bitwise AND yields network address: 192.168.1.0.
Wildcard mask (bitwise NOT): 0.0.0.255.
Broadcast address: 192.168.1.255.
Usable host range: 192.168.1.1 to 192.168.1.254 (254 usable hosts).

Final Answer: 192.168.1.0/24 (Mask: 255.255.255.0, Usable: 192.168.1.1 - 192.168.1.254)

Example 2: Router Point-to-Point Link (10.0.0.5/31 under RFC 3021)

Host IP = 10.0.0.5, Subnet Mask = /31 (255.255.255.254)

Mask has 31 network bits and 1 host bit (2 total addresses).
Network ID: 10.0.0.4, Broadcast: 10.0.0.5.
Under RFC 3021 point-to-point links, both addresses are usable.
Usable hosts: 10.0.0.4 and 10.0.0.5 (2 usable hosts).

Final Answer: 10.0.0.4/31 (2 usable hosts: 10.0.0.4 - 10.0.0.5)

Example 3: Enterprise Cloud Subnet (172.16.100.50/20)

Host IP = 172.16.100.50, Subnet Mask = /20 (255.255.240.0)

Prefix /20 reserves 12 host bits (2¹² = 4,096 total addresses).
Subnet mask: 255.255.240.0, Wildcard mask: 0.0.15.255.
Network address: 172.16.96.0.
Broadcast address: 172.16.111.255.
Usable host range: 172.16.96.1 to 172.16.111.254 (4,094 usable hosts).

Final Answer: 172.16.96.0/20 (4,094 usable hosts)

Reference Table

Prefix	Subnet Mask	Total IPs	Usable Hosts	Common Usage
/32	255.255.255.255	1	1	Single host route / Loopback
/31	255.255.255.254	2	2	RFC 3021 Point-to-point link
/30	255.255.255.252	4	2	Legacy point-to-point link
/29	255.255.255.248	8	6	Small office / ISP public IP block
/28	255.255.255.240	16	14	Small department / DMZ
/27	255.255.255.224	32	30	Medium department subnet
/26	255.255.255.192	64	62	Corporate branch office
/25	255.255.255.128	128	126	Large department VLAN
/24	255.255.255.0	256	254	Standard Class C LAN
/23	255.255.254.0	512	510	Medium enterprise office
/22	255.255.252.0	1,024	1,022	Enterprise campus / 4x Class C
/21	255.255.248.0	2,048	2,046	Corporate building network
/20	255.255.240.0	4,096	4,094	Cloud VPC application tier
/16	255.255.0.0	65,536	65,534	Class B network / Cloud VPC
/8	255.0.0.0	16,777,216	16,777,214	Class A network (e.g. 10.0.0.0/8)

Frequently Asked Questions

Why are there two fewer usable hosts than total IP addresses?

In standard IPv4 subnets (/0 to /30), the first address is reserved as the Network Identifier and the last address is reserved as the Broadcast Address for all hosts on the subnet. Subtracting these two produces the usable host count.

Can /31 subnets be used for router-to-router point-to-point links?

Yes. RFC 3021 standardizes /31 subnets for point-to-point links. Because there are only two endpoints on a point-to-point link, broadcast and network addresses are unnecessary, allowing both addresses to be assigned to router interfaces.

What is a wildcard mask and where is it used?

A wildcard mask is the bitwise inverse of a subnet mask (255.255.255.255 minus the subnet mask). It is used primarily in Cisco IOS router configurations, Access Control Lists (ACLs), and OSPF network statements.

What are the RFC 1918 private IP address ranges?

RFC 1918 defines three non-routable private address blocks: 10.0.0.0/8 (10.0.0.0 - 10.255.255.255), 172.16.0.0/12 (172.16.0.0 - 172.31.255.255), and 192.168.0.0/16 (192.168.0.0 - 192.168.255.255).

Does this calculator support IPv6?

This calculator is strictly dedicated to 32-bit IPv4 addressing. IPv6 uses 128-bit hexadecimal addressing and follows separate allocation and subnetting conventions.