NetTool1

IP Subnetting Guide: CIDR, Subnet Masks & Network Ranges

Master IP subnetting, CIDR notation, subnet masks, and network ranges with practical examples and a free calculator.

Table of Contents

  1. IP Address Basics
  2. CIDR Notation
  3. Subnet Masks
  4. Calculating Subnets
  5. IPv6 Subnetting
  6. FAQ

IP Address Basics

An IPv4 address is a 32-bit number written as four octets: 192.168.1.100. Each octet ranges 0-255. The address has two parts: network (identifies the network) and host (identifies the device).

RangeCIDRAddressesUse
10.0.0.0 – 10.255.255.25510.0.0.0/816.7MLarge networks
172.16.0.0 – 172.31.255.255172.16.0.0/121.05MMedium networks
192.168.0.0 – 192.168.255.255192.168.0.0/1665,536Home/office

CIDR Notation

CIDR (Classless Inter-Domain Routing) notation specifies the IP and prefix length: 192.168.1.0/24. The prefix length tells how many bits are the network part.

CIDRSubnet MaskUsable HostsTypical Use
/8255.0.0.016,777,214Large ISPs
/16255.255.0.065,534Large orgs
/24255.255.255.0254Small offices
/28255.255.255.24014Small subnets
/30255.255.255.2522Point-to-point
/32255.255.255.2551Single host

Subnet Masks

A subnet mask uses 1s for network bits and 0s for host bits. ANDing an IP with its mask gives the network address:

IP:   192.168.1.100 = 11000000.10101000.00000001.01100100
Mask: 255.255.255.0 = 11111111.11111111.11111111.00000000
AND:  192.168.1.0   = 11000000.10101000.00000001.00000000

Calculating Subnets

For 192.168.10.0/24:

Use NetTool1 Subnet Calculator to get network, broadcast, host range, and wildcard mask instantly.

IPv6 Subnetting

IPv6 uses 128-bit addresses: 2001:0db8:85a3::8a2e:0370:7334. Standard allocation uses /48 for organizations and /64 for individual subnets.

PrefixUseSubnets
/32ISP allocation65,536 /48s
/48Organization65,536 /64s
/64Single LAN segment18 quintillion hosts

FAQ

What is the difference between /24 and /16?
/24 provides 254 usable hosts. /16 provides 65,534 usable hosts. The smaller the prefix, the larger the network.
Why subtract 2 from total addresses?
The first address is the network identifier and the last is the broadcast address. Neither can be assigned to hosts.
What is a /30 subnet used for?
/30 gives exactly 2 usable hosts, perfect for point-to-point links between two routers.