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IP Subnet Calculator

Calculate comprehensive subnet information for IPv4 and IPv6 networks including network addresses, usable host ranges, subnet masks, and CIDR notation for network planning and administration.

IPv4 Subnet Calculator

Calculate network parameters and host ranges for IPv4 addresses with CIDR notation.

Network Class:

AnyABC

Subnet Mask:

IP Address:

IPv6 Subnet Calculator

Advanced IPv6 subnet calculations with prefix length support and address expansion.

Prefix Length:

IPv6 Address:

Network Security & Best Practices

Subnet Security Guidelines

• Use proper VLAN segmentation to isolate network traffic
• Implement firewall rules between subnets
• Monitor inter-subnet communication patterns
• Use private IP ranges for internal networks
• Document network topology and IP allocations

VLSM Planning Tips

• Start with the largest subnet requirements first
• Leave room for future network growth
• Use consistent addressing schemes
• Consider geographic or departmental groupings
• Plan for management and guest networks

Understanding IP Subnetting

Subnetting is a fundamental networking concept that involves dividing a larger network into smaller, more manageable subnetworks for efficient IP address management, network security, and performance optimization.

Key Concepts:

Network Address: The first address in a subnet, used to identify the network itself
Broadcast Address: The last address in a subnet, used for broadcast communications
Host Range: The usable IP addresses between network and broadcast addresses
Subnet Mask: Defines which portion of an IP address represents the network vs. host

CIDR Notation Explained

Classless Inter-Domain Routing (CIDR) notation is the modern standard for expressing subnet masks using a slash followed by the number of network bits (e.g., /24 instead of 255.255.255.0).

Common CIDR Examples:

/8 = 255.0.0.0 (Class A) - 16,777,214 hosts

/16 = 255.255.0.0 (Class B) - 65,534 hosts

/24 = 255.255.255.0 (Class C) - 254 hosts

/30 = 255.255.255.252 (Point-to-point) - 2 hosts

Pro Tip: Always plan subnets with future growth in mind. It's easier to allocate larger subnets initially than to renumber later.

IPv4 vs IPv6 Addressing

IPv4 Characteristics

• 32-bit address space (4.3 billion addresses)
• Dotted decimal notation (192.168.1.1)
• Class-based addressing (A, B, C, D, E)
• NAT required for private networks
• Mature protocol with universal support
• Address exhaustion is a concern

IPv6 Advantages

• 128-bit address space (340 undecillion addresses)
• Hexadecimal notation (2001:db8::1)
• Hierarchical addressing structure
• Built-in security features (IPSec)
• Simplified header format for faster routing
• No address exhaustion concerns

Migration Considerations:

While IPv6 adoption continues to grow, dual-stack implementations remain common. Network administrators should plan for IPv6 transition while maintaining IPv4 compatibility during the migration period.

IPv4 Subnet Reference Table

Complete CIDR notation reference with host calculations

CIDR	Subnet Mask	Usable Hosts	Network Class
/8	255.0.0.0	16,777,214	Class A
/16	255.255.0.0	65,534	Class B
/24	255.255.255.0	254	Class C
/25	255.255.255.128	126
/26	255.255.255.192	62
/27	255.255.255.224	30
/28	255.255.255.240	14
/29	255.255.255.248	6
/30	255.255.255.252	2
/31	255.255.255.254	0
/32	255.255.255.255	0

Private IP Address Ranges

Private IP addresses are reserved for use within private networks and are not routable on the public Internet. These ranges are defined by RFC 1918 and are commonly used for internal networks.

Class A Private Range

10.0.0.0/8

Range: 10.0.0.0 - 10.255.255.255

Hosts: 16,777,216

Class B Private Range

172.16.0.0/12

Range: 172.16.0.0 - 172.31.255.255

Hosts: 1,048,576

Class C Private Range

192.168.0.0/16

Range: 192.168.0.0 - 192.168.255.255

Hosts: 65,536

Common Private Network Uses:

• Home Networks: Typically use 192.168.x.x range
• Small Businesses: Often use 192.168.x.x or 10.x.x.x ranges
• Large Enterprises: Commonly use 10.x.x.x for scalability
• Service Providers: May use 172.16.x.x for customer networks

Common Subnetting Scenarios

Point-to-Point Links (/30)

Used for router-to-router connections where only 2 hosts are needed.

Network: 192.168.1.0/30
Usable IPs: 192.168.1.1 - 192.168.1.2
Total Hosts: 2

Small Office Network (/28)

Suitable for small departments or branch offices with up to 14 devices.

Network: 192.168.1.0/28
Usable IPs: 192.168.1.1 - 192.168.1.14
Total Hosts: 14

Standard LAN (/24)

Traditional Class C network, perfect for most office environments.

Network: 192.168.1.0/24
Usable IPs: 192.168.1.1 - 192.168.1.254
Total Hosts: 254