Network Subnet Calculator - CIDR IP Calculator
Calculate subnet masks, network addresses, broadcast addresses, and usable host ranges. Essential tool for network engineers and sysadmins.
Understanding Subnetting
Subnetting divides an IP network into smaller, manageable segments. Each subnet has its own network address, broadcast address, and range of usable host addresses. Proper subnetting improves network performance, enhances security, and optimizes IP address allocation.
What is CIDR Notation?
CIDR (Classless Inter-Domain Routing) notation represents IP addresses with their associated network prefix. For example, 192.168.1.0/24 means the first 24 bits define the network, leaving 8 bits for host addresses (256 total addresses, 254 usable).
Key Subnet Concepts
- Network Address: First address in the subnet (all host bits = 0). Cannot be assigned to hosts.
- Broadcast Address: Last address in the subnet (all host bits = 1). Sends to all hosts in subnet.
- Subnet Mask: Binary mask separating network and host portions (e.g., 255.255.255.0).
- Wildcard Mask: Inverse of subnet mask, used in ACLs and OSPF configuration.
Common Subnet Sizes
- /8: 16,777,214 hosts (Class A default)
- /16: 65,534 hosts (Class B default)
- /24: 254 hosts (Class C default, most common)
- /28: 14 hosts (small office)
- /30: 2 hosts (point-to-point links)
- /32: 1 host (single host route)
Private IP Ranges (RFC 1918)
- 10.0.0.0/8: 16 million addresses
- 172.16.0.0/12: 1 million addresses
- 192.168.0.0/16: 65,536 addresses
Subnetting Use Cases
- VLANs: Separate departments or functions onto different subnets.
- Security: Isolate sensitive systems in their own subnet.
- Performance: Reduce broadcast domain size.
- IP Management: Efficient allocation of limited addresses.