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IP Subnet Calculator

Calculate subnet masks, network addresses, broadcast addresses, host ranges, and CIDR notation for network planning and administration.

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Network
Not Set
Total Hosts
0
Usable IPs
0
Subnet Mask
0.0.0.0

โš™๏ธ Network Configuration

Invalid IP address or CIDR notation

Common Network Examples

Explore different subnet configurations commonly used in network administration and planning.

๐Ÿ  Home Network

Typical home router configuration with 254 usable IP addresses for devices.

Network: 192.168.1.0/24 | Hosts: 254

๐Ÿข Large Enterprise

Class A private network providing over 16 million IP addresses for large organizations.

Network: 10.0.0.0/8 | Hosts: 16,777,214

๐Ÿช Medium Business

Class B private network suitable for medium-sized businesses with multiple departments.

Network: 172.16.0.0/12 | Hosts: 1,048,574

๐Ÿ”— Small Subnet

Small subnet perfect for point-to-point links or small device groups.

Network: 192.168.10.0/28 | Hosts: 14

Understanding IP Subnetting

IP subnetting is the practice of dividing a network into smaller, more manageable sub-networks. This process helps optimize network performance, improve security, and efficiently utilize IP address space. Our calculator simplifies complex subnet calculations for network administrators and developers.

Private vs Public IP Addresses

Understanding the difference between private and public IP addresses is crucial for network planning and security:

  • Private IP Addresses: Reserved for internal networks and not routed on the internet
  • Public IP Addresses: Globally unique addresses that can be reached from anywhere on the internet
  • NAT Translation: Private addresses use Network Address Translation to access the internet
  • Address Conservation: Private addressing helps conserve limited IPv4 address space

Private IP Address Ranges (RFC 1918)

These IP ranges are reserved for private networks and not routed on the internet:

  • Class A Private: 10.0.0.0/8 (10.0.0.0 to 10.255.255.255) - 16,777,216 addresses
  • Class B Private: 172.16.0.0/12 (172.16.0.0 to 172.31.255.255) - 1,048,576 addresses
  • Class C Private: 192.168.0.0/16 (192.168.0.0 to 192.168.255.255) - 65,536 addresses

Special-Use IP Address Ranges

Beyond private and public addresses, several ranges serve special purposes:

  • Loopback: 127.0.0.0/8 - Local host communication (localhost)
  • Link-Local: 169.254.0.0/16 - Automatic Private IP Addressing (APIPA)
  • Multicast: 224.0.0.0/4 - One-to-many communication
  • Reserved: 240.0.0.0/4 - Experimental and future use
  • Broadcast: 255.255.255.255/32 - Limited broadcast address
  • This Network: 0.0.0.0/8 - Current network (RFC 1122)

Key Networking Concepts

Understanding these fundamental concepts is essential for effective network design and management:

  • Network Address: The first IP address in a subnet, identifying the network itself
  • Broadcast Address: The last IP address in a subnet, used for network-wide communications
  • Subnet Mask: Defines which portion of an IP address represents the network and host parts
  • CIDR Notation: Compact representation of subnet masks using slash notation (e.g., /24)
  • Host Range: Usable IP addresses between network and broadcast addresses
  • Wildcard Mask: Inverse of subnet mask, commonly used in routing protocols

CIDR Notation Explained

Classless Inter-Domain Routing (CIDR) notation simplifies subnet mask representation:

  • /8: 255.0.0.0 - Class A networks (16,777,214 hosts)
  • /16: 255.255.0.0 - Class B networks (65,534 hosts)
  • /24: 255.255.255.0 - Class C networks (254 hosts)
  • /28: 255.255.255.240 - Small subnets (14 hosts)
  • /30: 255.255.255.252 - Point-to-point links (2 hosts)

Private IP Address Ranges

These IP ranges are reserved for private networks and not routed on the internet:

  • Class A: 10.0.0.0 to 10.255.255.255 (10.0.0.0/8)
  • Class B: 172.16.0.0 to 172.31.255.255 (172.16.0.0/12)
  • Class C: 192.168.0.0 to 192.168.255.255 (192.168.0.0/16)

Network Security Considerations

Proper subnetting enhances network security through segmentation:

  • Isolate sensitive systems on separate subnets with strict access controls
  • Implement VLANs to create logical separation within physical networks
  • Use firewall rules to control traffic between different subnets
  • Monitor inter-subnet traffic for security anomalies
  • Apply different security policies based on subnet purpose
  • Consider DMZ subnets for public-facing services

IPv4 Address Exhaustion & Solutions

With IPv4 addresses becoming scarce, efficient planning is essential:

  • CIDR: Classless routing allows more flexible address allocation
  • VLSM: Variable Length Subnet Masking optimizes address usage
  • NAT/PAT: Network Address Translation extends private network capabilities
  • IPv6 Migration: Plan for eventual transition to IPv6
  • Address Reclamation: Regularly audit and reclaim unused addresses

Common Networking Troubleshooting

Use subnet calculations to diagnose network connectivity issues:

  • Verify devices are in the correct subnet for communication
  • Check subnet mask configuration consistency across devices
  • Ensure default gateways are properly configured for inter-subnet routing
  • Validate DHCP scope ranges match subnet boundaries
  • Confirm routing table entries for proper subnet reachability

Follow these guidelines for effective subnet design:

  • Plan for future growth by allocating more addresses than currently needed
  • Use consistent subnet sizes within the same network tier
  • Document your subnet allocation scheme for maintenance
  • Consider VLAN integration for logical network segmentation
  • Reserve specific subnets for management and infrastructure devices
  • Implement proper access controls between different subnets

Frequently Asked Questions

Get answers to common questions about IP subnetting, CIDR notation, and network calculations.

What is IP subnetting and why is it important? +
IP subnetting divides a large network into smaller, manageable sub-networks. It's important for efficient IP address utilization, improved network performance, enhanced security through network segmentation, reduced broadcast traffic, and simplified network management. Subnetting also enables better organization of network resources and helps implement security policies.
How does CIDR notation work? +
CIDR (Classless Inter-Domain Routing) notation uses a slash followed by a number to indicate how many bits of the IP address represent the network portion. For example, /24 means the first 24 bits are the network portion, leaving 8 bits for hosts (256 total addresses, 254 usable). The higher the CIDR number, the smaller the subnet and fewer available host addresses.
What's the difference between network and broadcast addresses? +
The network address is the first IP address in a subnet and identifies the network itself - it cannot be assigned to devices. The broadcast address is the last IP address in a subnet and is used to send messages to all devices on that network simultaneously. Both addresses are reserved and not available for host assignment, which is why usable hosts = total addresses - 2.
How do I calculate the number of hosts in a subnet? +
To calculate hosts in a subnet, use the formula: 2^(32-CIDR) for total addresses. For example, a /24 subnet has 2^(32-24) = 2^8 = 256 total addresses. Subtract 2 for the network and broadcast addresses to get 254 usable host addresses. The host bits are determined by subtracting the CIDR value from 32 (total bits in IPv4).
What are private IP address ranges? +
Private IP addresses are reserved for internal networks and include: 10.0.0.0/8 (10.0.0.0 to 10.255.255.255) for large networks, 172.16.0.0/12 (172.16.0.0 to 172.31.255.255) for medium networks, and 192.168.0.0/16 (192.168.0.0 to 192.168.255.255) for small networks. These addresses are not routed on the internet and must use NAT for internet access.
What is a subnet mask and how does it work? +
A subnet mask is a 32-bit number that separates an IP address into network and host portions. It uses binary 1s for the network portion and 0s for the host portion. For example, 255.255.255.0 (/24) has 24 ones followed by 8 zeros, meaning the first three octets identify the network and the last octet identifies the host within that network.
How do I choose the right subnet size for my network? +
Choose subnet size based on current needs plus future growth. Count the number of devices you need to support, add 30-50% for growth, then select the next larger subnet size. For example, if you need 100 addresses, choose /25 (126 usable hosts) rather than /26 (62 hosts). Consider organizational structure, security requirements, and broadcast domain optimization.
What is Variable Length Subnet Masking (VLSM)? +
VLSM allows using different subnet mask lengths within the same network, enabling more efficient IP address allocation. Instead of using the same subnet size everywhere, you can create smaller subnets for point-to-point links (/30) and larger subnets for user networks (/24). This optimizes address space utilization and reduces waste in network design.
How does subnetting improve network security? +
Subnetting improves security by creating logical network segments that can be controlled with firewalls, access control lists (ACLs), and routing policies. You can isolate different departments, separate guest networks from corporate resources, implement different security policies per subnet, and limit broadcast storms. This segmentation contains security breaches and allows granular access control.
What tools do network administrators use for subnet planning? +
Network administrators use subnet calculators, IP address management (IPAM) tools, network documentation software, and spreadsheet templates for subnet planning. Professional tools include SolarWinds IPAM, Infoblox, phpIPAM, and Cisco Prime. These tools help track IP allocations, plan subnet hierarchies, manage DHCP scopes, and maintain accurate network documentation.
Can I subnet an already subnetted network? +
Yes, you can create sub-subnets by further dividing an existing subnet. This is called hierarchical subnetting. For example, you can divide a /24 network into four /26 subnets or eight /27 subnets. Each level of subnetting reduces the available host addresses but provides more granular network control and organization. Plan carefully to avoid overlapping address ranges.
What common mistakes should I avoid when subnetting? +
Common subnetting mistakes include: overlapping subnet ranges, not planning for growth, inconsistent subnet sizing, poor documentation, forgetting to reserve addresses for infrastructure, not considering VLAN integration, and creating too many small subnets that waste addresses. Always validate your subnet plan, document thoroughly, and test configurations before deployment.

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