Free CIDR Subnet Calculator: IP Ranges & Mask Bits
Classless Inter-Domain Routing (CIDR) is the foundation of modern IPv4 network architecture, allowing network architects and cloud engineers to allocate IP address blocks efficiently without the rigid constraints of traditional class-based networking. Planning virtual private clouds (VPCs), subnets, and routing tables requires accurate calculations of broadcast boundaries and usable host capacities.
The Pingzo CIDR Subnet Calculator instantly parses any IPv4 address and subnet prefix from /0 to /32. It calculates the network ID, broadcast address, subnet mask, wildcard mask, and usable host range in real time, displaying both dotted-decimal and binary representations to eliminate manual conversion mistakes.
Designing secure network topologies is vital, but verifying connectivity to external endpoints and cloud services is just as essential. With Pingzo Network & Port Monitoring, you can track the availability and latency of public gateway IPs, load balancers, and custom TCP ports with immediate alerts sent via WhatsApp, SMS, Slack, or email.
Monitor regional endpoints and custom network ports
Need to monitor connection latency to a specific IP, database port, or microservice VPC? Pingzo monitors multi-region targets and custom TCP/HTTP channels, alerting your network team via WhatsApp in real-time.
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Frequently Asked Questions
What is CIDR notation?
CIDR (Classless Inter-Domain Routing) notation is a compact representation of an IP address and its associated routing prefix. It appends a slash followed by the prefix length in bits (e.g., /24 represents a subnet mask with 24 active bits).
Why are the first and last IP addresses excluded?
In a standard IP network, the first address is reserved for the Network ID (identifying the subnet itself), and the last address is reserved for the Broadcast ID (used to send packets to all devices on the subnet). They cannot be assigned to hosts.
What are /31 and /32 subnets used for?
A /31 subnet has only 2 IP addresses and is used for point-to-point links between routers (RFC 3021). A /32 subnet represents a single host IP address (often used for loopback configurations or host routes).
How do subnet masks and wildcard masks differ?
A subnet mask identifies which bits belong to the network versus the host portion (e.g., 255.255.255.0). A wildcard mask is the exact bitwise inverse (0.0.0.255), frequently used in Cisco ACLs, OSPF routing rules, and firewall packet filters.
How does Pingzo help with IP and subnet monitoring?
Once your subnets and VPCs are planned, Pingzo actively monitors your public IP addresses, load balancers, and network ports from multiple global regions. If an IP becomes unreachable or latency spikes, Pingzo sends immediate alerts via WhatsApp, SMS, Slack, or email.