Subnet Mask & IPv4 CIDR Range Calculator

Classless Inter-Domain Routing (CIDR) is the foundational addressing architecture of the global Internet, codified in RFC 4632 to eliminate the rigid inefficiencies of historical Class A, B, and C networks. By utilizing variable-length subnet masks (VLSM), systems architects, cloud engineers, and network administrators can partition address spaces with precision down to the exact bit, conserving scarce IPv4 allocations and structuring secure, isolated virtual private clouds (VPCs).

Refer to the authoritative table below to quickly correlate prefix lengths, dotted quad masks, wildcard inverses, and usable host allowances across standard subnets:

The Internet Assigned Numbers Authority (IANA) reserved three blocks of IPv4 space exclusively for internal enterprise operations under RFC 1918. Routers on the public Internet are explicitly configured to drop traffic originating from or addressed to these ranges without NAT translation.

Integrate programmatic CIDR subnet calculations into CI/CD pipelines and infrastructure-as-code deployments to prevent IP collision errors before provisioning cloud infrastructure:

import ipaddress

# Initialize IPv4 network object
net = ipaddress.ip_network('192.168.1.0/24', strict=False)

print("Network Address:", net.network_address)
print("Broadcast Address:", net.broadcast_address)
print("Subnet Mask:", net.netmask)
print("Wildcard Mask:", net.hostmask)
print("Usable Host Range:", f"{net[1]} - {net[-2]}")
print("Total Usable Hosts:", net.num_addresses - 2)

# Subdivide into smaller /26 micro-subnets
subnets = list(net.subnets(new_prefix=26))
for idx, sub in enumerate(subnets, 1):
    print(f"Subnet {idx}: {sub.with_prefixlen}")

variable "vpc_cidr" {
  default = "10.0.0.0/16"
}

# Automatically carve /24 subnets from /16 VPC root
resource "aws_subnet" "public_subnets" {
  count             = 3
  vpc_id            = aws_vpc.main.id
  # cidrsubnet(prefix, newbits, netnum)
  # adds 8 bits to /16 -> yields /24
  cidr_block        = cidrsubnet(var.vpc_cidr, 8, count.index)
  availability_zone = data.aws_availability_zones.available.names[count.index]

  tags = {
    Name = "Public-Subnet-${count.index + 1}"
  }
}